Bioelectrical phenomena

Abstract In my previous papers on the ‘Electric Organ of the Skate,’ I considered the develop­ment of the organ in Raia batis the structure of the organ in R. circularis, and the structure and development of the organ in R. radiata. I propose now to consider the relations, structure, and progressive growth of the organ in R. batis, to contrast the organ of R. batis with that of Torpedo, and to refer to the various modi­fications of the electric organ I have found in the Skate genus.

@article{doi101098rstb18920010,
    author = "Ewart, J. C.",
    title = "X. The electric organ of the skate.–Observations on the structure, relations, progressive development, and growth, of the electric organ of the skate",
    year = "1892",
    journal = "Philosophical Transactions of the Royal Society of London (B )",
    abstract = "Abstract In my previous papers on the ‘Electric Organ of the Skate,’ I considered the develop­ment of the organ in Raia batis the structure of the organ in R. circularis, and the structure and development of the organ in R. radiata. I propose now to consider the relations, structure, and progressive growth of the organ in R. batis, to contrast the organ of R. batis with that of Torpedo, and to refer to the various modi­fications of the electric organ I have found in the Skate genus.",
    url = "https://doi.org/10.1098/rstb.1892.0010",
    doi = "10.1098/rstb.1892.0010",
    openalex = "W4253036167"
}

@article{doi101002cne910110302,
    author = "Herrick, C. Judson",
    title = "The cranial nerves and cutaneous sense organs of the north american siluroid fishes",
    year = "1901",
    journal = "Journal of Comparative Neurology",
    url = "https://doi.org/10.1002/cne.910110302",
    doi = "10.1002/cne.910110302",
    openalex = "W2097899867",
    references = "doi101002cne910050302, doi101002cne910100302, doi101002cne910110202, doi101002jmor1050020303, doi101002jmor1050100103, doi101002jmor1050120302, doi101002jmor1050150203, doi1023073221399, doi105962bhltitle13244, openalexw605388346"
}

It is pointed out that there are great advantages in using single cells instead of tissues in the study of bioelectrical phenomena. Certain bioelectrical phenomena are discussed in relation to the structure of protoplasm. Under certain circumstances measurements of potential differences may enable us to determine what ions enter the protoplasm. Under suitable conditions we are able to ascertain the potential differences across the protoplasm at single points, instead of being obliged merely to measure the differences between two points.

@article{osterhout1927some,
    author = "Osterhout, W. J. V.",
    title = "SOME ASPECTS OF BIOELECTRICAL PHENOMENA",
    year = "1927",
    journal = "Journal of General Physiology",
    abstract = "It is pointed out that there are great advantages in using single cells instead of tissues in the study of bioelectrical phenomena. Certain bioelectrical phenomena are discussed in relation to the structure of protoplasm. Under certain circumstances measurements of potential differences may enable us to determine what ions enter the protoplasm. Under suitable conditions we are able to ascertain the potential differences across the protoplasm at single points, instead of being obliged merely to measure the differences between two points.",
    url = "https://doi.org/10.1085/jgp.11.1.83",
    doi = "10.1085/jgp.11.1.83",
    number = "1",
    pages = "83-99",
    volume = "11"
}

@article{crossref1928some,
    title = "Some aspects of bioelectrical phenomena",
    year = "1928",
    journal = "Protoplasma",
    url = "https://doi.org/10.1007/bf01607978",
    doi = "10.1007/bf01607978",
    number = "1",
    openalex = "W4251530131",
    pages = "172-172",
    volume = "4"
}

In recent years attention has been given to the influence of electrical currents as fish deflectors or screens, and experiments have been made to determine the magnitude of the currents which are sufficient to paralyse or act as deterrents to fish which may enter the electrical field, but in such strong fields the perception of the mechanism by which fish respond to electric currents is masked by the paralysis produced. It seemed possible that experiments with very weak currents might give fuller information concerning the mechanism by which fish respond to electrical stimulus than those made in strong fields. There is also the possibility that weak electric currents may occur in nature to which fish respond, but before exploring that field of phenomena it is necessary to observe the behaviour of fish under the influence of very weak fields. McMillan found that the field (volts per inch) required to paralyse young salmon varied with the resistivity of the water; thus when the latter was 10,000 ohms per inch cube the paralysing voltage was about 1·5, so that a current density of ampere per square inch was sufficient to cause paralysis, whereas when the resistivity was twelve ohms per inch cube the current required was ·03 ampere. In the former case the conductivity of the fish was greater than that of the water, in the latter case less.

@article{doi101017s0025315400050931,
    author = "Regnart, H. C.",
    title = "The Lower Limits of Perception of Electrical Currents by Fish",
    year = "1931",
    journal = "Journal of the Marine Biological Association of the United Kingdom",
    abstract = "In recent years attention has been given to the influence of electrical currents as fish deflectors or screens, and experiments have been made to determine the magnitude of the currents which are sufficient to paralyse or act as deterrents to fish which may enter the electrical field, but in such strong fields the perception of the mechanism by which fish respond to electric currents is masked by the paralysis produced. It seemed possible that experiments with very weak currents might give fuller information concerning the mechanism by which fish respond to electrical stimulus than those made in strong fields. There is also the possibility that weak electric currents may occur in nature to which fish respond, but before exploring that field of phenomena it is necessary to observe the behaviour of fish under the influence of very weak fields. McMillan found that the field (volts per inch) required to paralyse young salmon varied with the resistivity of the water; thus when the latter was 10,000 ohms per inch cube the paralysing voltage was about 1·5, so that a current density of ampere per square inch was sufficient to cause paralysis, whereas when the resistivity was twelve ohms per inch cube the current required was ·03 ampere. In the former case the conductivity of the fish was greater than that of the water, in the latter case less.",
    url = "https://doi.org/10.1017/s0025315400050931",
    doi = "10.1017/s0025315400050931",
    openalex = "W2116926391"
}

@article{doi101113jphysiol1942sp003975,
    author = "Feldberg, W. and Fessard, Alfred",
    title = "The cholinergic nature of the nerves to the electric organ of the Torpedo (Torpedo marmorata)",
    year = "1942",
    journal = "The Journal of Physiology",
    url = "https://doi.org/10.1113/jphysiol.1942.sp003975",
    doi = "10.1113/jphysiol.1942.sp003975",
    openalex = "W2059293860"
}

The purpose of this paper is to present a hypothesis on the nature of the schooling behaviour of fish based on an ethological investigation of schooling. Recognizing the disadvantages of a limited amount of data and of the use of different species for different parts of the study, the following tentative picture is suggested. Schooling may be considered an instinct as defined by TINBERGEN and is at a relatively low level in the hierarchical organization of behaviour. It has typical appetitive behaviour and a consummatory situation. A single fish separated from its school searches until perceiving a group of fish. It then approaches the group. In most cases vision is the only sense involved in this approach. If more detailed specific stimuli are then perceived (possibly through any of the sense organs) the fish ceases searching and remains with the school; if not, it soon leaves, and appetitive behaviour continues until the appropriate consummatory situation (being in a school of the same species) is attained. This hypothesis is based on the following points: 1. A school of fish is an aggregation formed when one fish reacts to others by remaining near them. 2. Typical features of Gasterosleits ticuleatus and Scardinius erythrophthalmus schools are: performance of the same activity at the same time by all fish, lack of aggressivcness between members and equality of rank of all members. 3. Blinded Scardinius fail to show typical schooling but remain in an area where odours from other Scardinius can be detected. This response may keep schools of this species from scattering widely at night. 4. Visual perception of a school of fish releases approach in single Scardinius and Pristella riddlei. 5. When presented with two different-sized schools of their own species single Gasterosteus, Scardinius and Leuciscus ntlilus prefer the larger to the smaller group. 6. A small Gasterosteus prefers six large to six small Gasterosteus. 7. A single Gasterosteus prefers a school of its own species to a school of Rhodeus amarus but shows no consistent preference when either Pygosteus pungitius or Leuciscus are presented together with Gasterosteus. 8. A single Pristella prefers a school of unoperated Pristella to a school with amputated dorsal fins. The dorsal fin with its conspicuous black patch is jerked more rapidly after alarm. This structure and its special movement may be considered a social releaser. 9. Increased feeding motivation leads to limited dispersal of a school of Gasterosteus. The head-down feeding posture is a signal attracting others in a school to a source of food. 10. Alarm causes an increase in density of a school of Gasterosteus. 11. With increasing reproductive motivation male Gasterosteus cease schooling and try to hold territories. Females disperse to a limited extent.

@article{doi101163156853955x00229,
    author = "Keenleyside, Miles H. A.",
    title = "Some Aspects of the Schooling Behaviour of Fish",
    year = "1955",
    journal = "Behaviour",
    abstract = "The purpose of this paper is to present a hypothesis on the nature of the schooling behaviour of fish based on an ethological investigation of schooling. Recognizing the disadvantages of a limited amount of data and of the use of different species for different parts of the study, the following tentative picture is suggested. Schooling may be considered an instinct as defined by TINBERGEN and is at a relatively low level in the hierarchical organization of behaviour. It has typical appetitive behaviour and a consummatory situation. A single fish separated from its school searches until perceiving a group of fish. It then approaches the group. In most cases vision is the only sense involved in this approach. If more detailed specific stimuli are then perceived (possibly through any of the sense organs) the fish ceases searching and remains with the school; if not, it soon leaves, and appetitive behaviour continues until the appropriate consummatory situation (being in a school of the same species) is attained. This hypothesis is based on the following points: 1. A school of fish is an aggregation formed when one fish reacts to others by remaining near them. 2. Typical features of Gasterosleits ticuleatus and Scardinius erythrophthalmus schools are: performance of the same activity at the same time by all fish, lack of aggressivcness between members and equality of rank of all members. 3. Blinded Scardinius fail to show typical schooling but remain in an area where odours from other Scardinius can be detected. This response may keep schools of this species from scattering widely at night. 4. Visual perception of a school of fish releases approach in single Scardinius and Pristella riddlei. 5. When presented with two different-sized schools of their own species single Gasterosteus, Scardinius and Leuciscus ntlilus prefer the larger to the smaller group. 6. A small Gasterosteus prefers six large to six small Gasterosteus. 7. A single Gasterosteus prefers a school of its own species to a school of Rhodeus amarus but shows no consistent preference when either Pygosteus pungitius or Leuciscus are presented together with Gasterosteus. 8. A single Pristella prefers a school of unoperated Pristella to a school with amputated dorsal fins. The dorsal fin with its conspicuous black patch is jerked more rapidly after alarm. This structure and its special movement may be considered a social releaser. 9. Increased feeding motivation leads to limited dispersal of a school of Gasterosteus. The head-down feeding posture is a signal attracting others in a school to a source of food. 10. Alarm causes an increase in density of a school of Gasterosteus. 11. With increasing reproductive motivation male Gasterosteus cease schooling and try to hold territories. Females disperse to a limited extent.",
    url = "https://doi.org/10.1163/156853955x00229",
    doi = "10.1163/156853955x00229",
    openalex = "W2103188737"
}

ABSTRACT The present study was made on two small specimens of Malapterurus electricus, of standard lengths n.4 and 12.7 mm. As is well known, the postembryonic growth of electric organs in Malapterurus and other electric fishes takes place by an enlargement of the electric units and not by an increase in the number of the electric plates. In the present material, however, there is a multiplication of electric tissue elements in the rostral portion of the electric organ. The structure of this multiplication zone is described. In the anterior region the connective tissue membranes which surround the two halves of the electric organ form structures similar to tendons which are fixed to the ventral surface of the shoulder girdle on each side of the median line. A small deficiency on each side in the muscular wall in the same region was observed in adult specimens by Maurer. This deficiency is more evident in the young specimens studied in the present paper and it is covered from the outside by the multiplication zone of the electric organ. In this place the electric nerve joins the electric organ. The giant electric cell, the surface of which is penetrated by intracellular capillaries, is situated in the anterior part of the spinal cord and its axon emerges with the third ventral spinal root. In the multiplication zone the connective tissue membranes are completely independent of the dermal connective tissue and the space between the electric organ and the skin is of a conventional subdermal type. These circumstances strongly indicate that the electric organ is of myoblastic origin in Malapterurus as in all other electric fishes known in this respect. Nothing has been observed which supports the idea of an adenoid origin of the electric organ in Malapterurus.

@article{doi101242jcss39739455,
    author = "Johnels, Alf G.",
    title = "On the Origin of the Electric Organ in Malapterurus electricus",
    year = "1956",
    journal = "Journal of Cell Science",
    abstract = "ABSTRACT The present study was made on two small specimens of Malapterurus electricus, of standard lengths n.4 and 12.7 mm. As is well known, the postembryonic growth of electric organs in Malapterurus and other electric fishes takes place by an enlargement of the electric units and not by an increase in the number of the electric plates. In the present material, however, there is a multiplication of electric tissue elements in the rostral portion of the electric organ. The structure of this multiplication zone is described. In the anterior region the connective tissue membranes which surround the two halves of the electric organ form structures similar to tendons which are fixed to the ventral surface of the shoulder girdle on each side of the median line. A small deficiency on each side in the muscular wall in the same region was observed in adult specimens by Maurer. This deficiency is more evident in the young specimens studied in the present paper and it is covered from the outside by the multiplication zone of the electric organ. In this place the electric nerve joins the electric organ. The giant electric cell, the surface of which is penetrated by intracellular capillaries, is situated in the anterior part of the spinal cord and its axon emerges with the third ventral spinal root. In the multiplication zone the connective tissue membranes are completely independent of the dermal connective tissue and the space between the electric organ and the skin is of a conventional subdermal type. These circumstances strongly indicate that the electric organ is of myoblastic origin in Malapterurus as in all other electric fishes known in this respect. Nothing has been observed which supports the idea of an adenoid origin of the electric organ in Malapterurus.",
    url = "https://doi.org/10.1242/jcs.s3-97.39.455",
    doi = "10.1242/jcs.s3-97.39.455",
    openalex = "W1961335606"
}

@misc{kleerekoper1956spike4,
    author = "Kleerekoper, H. and Sibakin, K",
    title = "Spike potentials produced by the sea lamprey ( Petromyzon marinus) in the water surrounding the head region",
    year = "1956",
    howpublished = "Nature, v. 178, p. 490-491",
    note = "talkorigins\_source = {true}; raw\_reference = {Kleerekoper, H., and Sibakin, K., 1956, Spike potentials produced by the sea lamprey ( Petromyzon marinus) in the water surrounding the head region: Nature, v. 178, p. 490-491.}"
}

@article{suzuki1956apparatuses,
    author = "Suzuki, Shigetaka",
    title = "Apparatuses for Recording Bioelectrical Phenomena",
    year = "1956",
    journal = "JAPANES JOURNAL OF MEDICAL INSTRUMENTATION",
    url = "https://doi.org/10.4286/ikakikaigakuzassi.26.10\_4",
    doi = "10.4286/ikakikaigakuzassi.26.10\_4",
    number = "10",
    pages = "4-5,10-12,17",
    volume = "26"
}

@article{doi101016s0096417418301239,
    author = "Grundfest, Harry",
    title = "The Mechanisms of Discharge of the Electric Organs in Relation to General and Comparative Electrophysiology",
    year = "1957",
    journal = "Progress in Biophysics and Biophysical Chemistry",
    url = "https://doi.org/10.1016/s0096-4174(18)30123-9",
    doi = "10.1016/s0096-4174(18)30123-9",
    openalex = "W2401721200"
}

ABSTRACT Experiments with moving electrostatic and magnetic fields show that Gymnarchus niloticus is sensitive to a potential gradient of about 0 · 03 µ V./cm. Alternative explanations of some previous experiments are given in terms of this high d.c. sensitivity. An explanation in similar terms is given of experiments in which Gymnotus carapo is trained to detect a stationary magnet. The mechanisms available for the location of objects by electric fish are reviewed. It is concluded from the results of a critical experiment (described in a succeeding section) that Gymnarchus niloticus can detect objects by the disturbance of its own electric field in the water. The approximate theory of this method of object location is derived. The effect on the receptors of the perturbing field due to an object depends on the electrical properties of the receptors: in the extreme cases the stimulation of the receptors is proportional either to the potential or to its second derivative. Graphs are given showing the effect of an object on the potential and on its second derivative around the surface of the fish. Experiments are described using Gymnarchus niloticus which (a) confirm that the mechanism of object location employs electric field distortion; (i) indicate the limits of the sensitivity of the fish. The second derivative mode appears to be the most probable one operating in Gymnarchus. The experimentally determined limits of detection are discussed in relation to the random noise in the receptor circuit: it is concluded that both spatial and temporal integration are likely to be employed. The thresholds for object location and for response to direct currents are compared: it is concluded that the same receptors are probably operating in both cases.

@article{doi101242jeb352451,
    author = "Lissmann, H. W. and Machin, K. E.",
    title = "The Mechanism of Object Location in Gymnarchus Niloticus and Similar Fish",
    year = "1958",
    journal = "Journal of Experimental Biology",
    abstract = "ABSTRACT Experiments with moving electrostatic and magnetic fields show that Gymnarchus niloticus is sensitive to a potential gradient of about 0 · 03 µ V./cm. Alternative explanations of some previous experiments are given in terms of this high d.c. sensitivity. An explanation in similar terms is given of experiments in which Gymnotus carapo is trained to detect a stationary magnet. The mechanisms available for the location of objects by electric fish are reviewed. It is concluded from the results of a critical experiment (described in a succeeding section) that Gymnarchus niloticus can detect objects by the disturbance of its own electric field in the water. The approximate theory of this method of object location is derived. The effect on the receptors of the perturbing field due to an object depends on the electrical properties of the receptors: in the extreme cases the stimulation of the receptors is proportional either to the potential or to its second derivative. Graphs are given showing the effect of an object on the potential and on its second derivative around the surface of the fish. Experiments are described using Gymnarchus niloticus which (a) confirm that the mechanism of object location employs electric field distortion; (i) indicate the limits of the sensitivity of the fish. The second derivative mode appears to be the most probable one operating in Gymnarchus. The experimentally determined limits of detection are discussed in relation to the random noise in the receptor circuit: it is concluded that both spatial and temporal integration are likely to be employed. The thresholds for object location and for response to direct currents are compared: it is concluded that the same receptors are probably operating in both cases.",
    url = "https://doi.org/10.1242/jeb.35.2.451",
    doi = "10.1242/jeb.35.2.451",
    openalex = "W1957563271",
    references = "doi101007bf00340757, doi101016s0096417418301082, doi101016s0096417418301239, doi101038143960c0, doi101038167201a0, doi101152ajplegacy1917443405, lissmann1958on, openalexw3038515387"
}

The electric discharges of Gymnarchus niloticus and of representative species of seven genera of the Mormyridae have been examined in their natural habitat in Africa and in the laboratory. Comparable investigations of the South American Gymnotidae have shown the existence of two discharge types in both these unrelated fish families. The first type of electric discharge consists of very regular sequences of continuously emitted, monophasic pulses, varying from species to species in frequency, and within narrower limits from individual to individual. Fish emitting this first type of pulses include Gymnarchus, Hypopomus and Eigenmannia. The frequency range for these fish lies between 60 and 400 discharges/sec. The frequency does not alter with the state of excitation of the fish. The duration of individual pulses is relatively long, i.e. 2–10 msec. The second type of discharge is less regular in frequency, the pulse duration much shorter and the pulse shape more complex. The individual discharge from the whole electric organ lasts about 0.2 msec, in Petrocephalus. This type of discharge is found in all the examined species of the Mormyridae and in such forms as Gymnotus carapo and Staetogenes elegans. The basic discharge rate of a resting mormyrid is somewhat variable and not strictly rhythmical. It usually lies between 1 and 6 pulses/sec. Stimuli which excite the mormyrids cause an increase in the discharge frequency. The recorded maximum is about 130 pulses/sec. Suitable stimuli can inhibit the discharges of the Mormyridae for prolonged periods. In Gymnotus carapo and Staetogenes elegans the basic discharge rate is higher and of regular rhythmicity. Depending on temperature the frequencies lie between 30 and 87 pulses/sec. When these fish are excited the frequencies are increased up to 200 pulses/sec, for a short time. The shape of the electric field, which is set up with each pulse around the fish, has been examined. A theory has been proposed which suggests that these fish, by means of their electric pulses, can locate objects if their electrical conductivity differs from that of water. These fish have shown themselves extremely sensitive to influences affecting the electric field. This has been studied by applying artificial electric stimuli, by studying the effects of conductors and non-conductors introduced into the field, and the reactions towards magnetic fields and electrostatic charges. Conditioned reflex experiments with Gymnarchus niloticus and Gymnotus carapo have shown that these fish can detect the presence of a stationary magnet, and that they can discriminate between conductors and non-conductors. The prey of these fish does not appear to be affected by the discharges. Inter alia, the electric pulses have a social significance. This locating mechanism may be considered as an adaptation to life in turbid water. Gymnotidae and Mormyridae (taken to include Gymnarchus) show striking features of convergent evolution. Unusual locomotory adaptations such as swimming by means of the dorsal fin (Gymnarchus), the anal fin (Gymnotidae) and ‘Gemminger‘s bones’ (Mormyridae) may be considered as a means which tends to make the axis of symmetry of the fish and of its electric field coincide during active movements. A new theory for the evolution of electric organs has been suggested. A major prerequisite appears to be a receptor sensitive to electrical stimulation. It is suggested that special sensory and nervous differentiations of the lateralis system (‘mormyromasts’, valvulae cerebelli) are concerned with the perception and integration of electric stimuli. Muscular action potentials have been recorded in the water at some distance from non-electric fish. The easiest explanation for the evolution of strong electric organs would appear to start from such muscular action potentials, and proceed via weak electric organs used for orientation, to the powerful offensive and defensive electric organs."

@article{lissmann1958on,
    author = "Lissmann, H. W.",
    title = "On the Function and Evolution of Electric Organs in Fish",
    year = "1958",
    journal = "Journal of Experimental Biology",
    abstract = {The electric discharges of Gymnarchus niloticus and of representative species of seven genera of the Mormyridae have been examined in their natural habitat in Africa and in the laboratory. Comparable investigations of the South American Gymnotidae have shown the existence of two discharge types in both these unrelated fish families. The first type of electric discharge consists of very regular sequences of continuously emitted, monophasic pulses, varying from species to species in frequency, and within narrower limits from individual to individual. Fish emitting this first type of pulses include Gymnarchus, Hypopomus and Eigenmannia. The frequency range for these fish lies between 60 and 400 discharges/sec. The frequency does not alter with the state of excitation of the fish. The duration of individual pulses is relatively long, i.e. 2–10 msec. The second type of discharge is less regular in frequency, the pulse duration much shorter and the pulse shape more complex. The individual discharge from the whole electric organ lasts about 0.2 msec, in Petrocephalus. This type of discharge is found in all the examined species of the Mormyridae and in such forms as Gymnotus carapo and Staetogenes elegans. The basic discharge rate of a resting mormyrid is somewhat variable and not strictly rhythmical. It usually lies between 1 and 6 pulses/sec. Stimuli which excite the mormyrids cause an increase in the discharge frequency. The recorded maximum is about 130 pulses/sec. Suitable stimuli can inhibit the discharges of the Mormyridae for prolonged periods. In Gymnotus carapo and Staetogenes elegans the basic discharge rate is higher and of regular rhythmicity. Depending on temperature the frequencies lie between 30 and 87 pulses/sec. When these fish are excited the frequencies are increased up to 200 pulses/sec, for a short time. The shape of the electric field, which is set up with each pulse around the fish, has been examined. A theory has been proposed which suggests that these fish, by means of their electric pulses, can locate objects if their electrical conductivity differs from that of water. These fish have shown themselves extremely sensitive to influences affecting the electric field. This has been studied by applying artificial electric stimuli, by studying the effects of conductors and non-conductors introduced into the field, and the reactions towards magnetic fields and electrostatic charges. Conditioned reflex experiments with Gymnarchus niloticus and Gymnotus carapo have shown that these fish can detect the presence of a stationary magnet, and that they can discriminate between conductors and non-conductors. The prey of these fish does not appear to be affected by the discharges. Inter alia, the electric pulses have a social significance. This locating mechanism may be considered as an adaptation to life in turbid water. Gymnotidae and Mormyridae (taken to include Gymnarchus) show striking features of convergent evolution. Unusual locomotory adaptations such as swimming by means of the dorsal fin (Gymnarchus), the anal fin (Gymnotidae) and ‘Gemminger‘s bones’ (Mormyridae) may be considered as a means which tends to make the axis of symmetry of the fish and of its electric field coincide during active movements. A new theory for the evolution of electric organs has been suggested. A major prerequisite appears to be a receptor sensitive to electrical stimulation. It is suggested that special sensory and nervous differentiations of the lateralis system (‘mormyromasts’, valvulae cerebelli) are concerned with the perception and integration of electric stimuli. Muscular action potentials have been recorded in the water at some distance from non-electric fish. The easiest explanation for the evolution of strong electric organs would appear to start from such muscular action potentials, and proceed via weak electric organs used for orientation, to the powerful offensive and defensive electric organs."},
    url = "https://doi.org/10.1242/jeb.35.1.156",
    doi = "10.1242/jeb.35.1.156",
    number = "1",
    openalex = "W2287496592",
    pages = "156-191",
    volume = "35",
    references = "doi101002cne910110302, doi101017cbo9780511693281002, doi101038167201a0, doi10108000222931108692993, doi101098rspb19380041, doi101113jphysiol1952sp004695, doi101113jphysiol1953sp004849, doi1023071416035, doi1023072485224, doi105962bhltitle53990"
}

@article{doi101038188760b0,
    author = "Szabó, T",
    title = "Development of the Electric Organ of Mormyridae",
    year = "1960",
    journal = "Nature",
    url = "https://doi.org/10.1038/188760b0",
    doi = "10.1038/188760b0",
    openalex = "W2087313637"
}

@article{doi101111j174966321961tb35555x,
    author = "Bennett, Michael V. L.",
    title = "MODES OF OPERATION OF ELECTRIC ORGANS*",
    year = "1961",
    journal = "Annals of the New York Academy of Sciences",
    url = "https://doi.org/10.1111/j.1749-6632.1961.tb35555.x",
    doi = "10.1111/j.1749-6632.1961.tb35555.x",
    openalex = "W2049570893"
}

The lateral-line organ of killifish is shown to be sensitive to a linear function of water displacements associated with the near-field of sound sources, with the displacement probably being the most important factor rather than velocity or acceleration. The near-field effect is discussed and is shown to be important not only for the lateral-line organs but also for the acoustical and vestibular organs. It is emphasized that the near-field effect introduces considerable complications into the study of the acoustico-lateralis system, and is of conceptual importance for the theory of hearing and the study of schooling fish.

@article{doi10112111909138,
    author = "Harris, Gerard G. and van Bergeijk, Willem A.",
    title = "Evidence that the Lateral-Line Organ Responds to Near-Field Displacements of Sound Sources in Water",
    year = "1962",
    journal = "The Journal of the Acoustical Society of America",
    abstract = "The lateral-line organ of killifish is shown to be sensitive to a linear function of water displacements associated with the near-field of sound sources, with the displacement probably being the most important factor rather than velocity or acceleration. The near-field effect is discussed and is shown to be important not only for the lateral-line organs but also for the acoustical and vestibular organs. It is emphasized that the near-field effect introduces considerable complications into the study of the acoustico-lateralis system, and is of conceptual importance for the theory of hearing and the study of schooling fish.",
    url = "https://doi.org/10.1121/1.1909138",
    doi = "10.1121/1.1909138",
    openalex = "W2068731943"
}

@incollection{majkowski1965bioelectrical,
    author = "MAJKOWSKI, J.",
    title = "BIOELECTRICAL PHENOMENA EVOKED BY RHYTHMICAL STIMULI DURING CONDITIONING AND DIFFERENTIATION. A PHYSIOLOGICAL AND PHARMACOLOGICAL STUDY",
    year = "1965",
    booktitle = "Pharmacology of Conditioning, Learning and Retention",
    url = "https://doi.org/10.1016/b978-1-4831-9847-7.50034-5",
    doi = "10.1016/b978-1-4831-9847-7.50034-5",
    pages = "339-349"
}

Abstract The electric organs (main, Sachs' and Hunter's) of a 23 cm and a 38 cm long Electrophorus electricus were studied by histological methods. The results were compared with 12 cm (Keynes, '61) and 140 cm (Couceiro and Ackermann, '48) specimens. All three electric organs originate from striated muscle fiber as indicated by the presence of a striated structure in the undeveloped electroplates. The three organs do not develop simultaneously but in succession: first Sachs' organ, then the main organ and finally Hunter's organ, with considerable overlap in time. In all three cases, the anterior extremity of the organ develops last. The classical notion that the main organ originates from the lateralis imus muscle is not supported by the present findings.

@article{doi101002ar1091550112,
    author = "Szabo, Thomas L.",
    title = "The origin of electric organs of Electrophorus electricus",
    year = "1966",
    journal = "The Anatomical Record",
    abstract = "Abstract The electric organs (main, Sachs' and Hunter's) of a 23 cm and a 38 cm long Electrophorus electricus were studied by histological methods. The results were compared with 12 cm (Keynes, '61) and 140 cm (Couceiro and Ackermann, '48) specimens. All three electric organs originate from striated muscle fiber as indicated by the presence of a striated structure in the undeveloped electroplates. The three organs do not develop simultaneously but in succession: first Sachs' organ, then the main organ and finally Hunter's organ, with considerable overlap in time. In all three cases, the anterior extremity of the organ develops last. The classical notion that the main organ originates from the lateralis imus muscle is not supported by the present findings.",
    url = "https://doi.org/10.1002/ar.1091550112",
    doi = "10.1002/ar.1091550112",
    openalex = "W2100749683"
}

@book{bennett1968neural2,
    author = "Bennett, M. V. L",
    title = "Neural Control of Electric Organs, in Ingle, D., ed., The Central Nervous System and Fish Behavior",
    year = "1968",
    publisher = "Chicago, University of Chicago Press, p. 147-169",
    note = "talkorigins\_source = {true}; raw\_reference = {Bennett, M. V. L., 1968, Neural Control of Electric Organs, in Ingle, D., ed., The Central Nervous System and Fish Behavior: Chicago, University of Chicago Press, p. 147-169.}"
}

@article{doi101159000125815,
    author = "Bullock, Theodore H.",
    title = "Species Differences in Effect of Electroreceptor Input on Electric Organ Pacemakers and Other Aspects of Behavior in Electric Fish; pp. 85–101",
    year = "1969",
    journal = "Brain Behavior and Evolution",
    url = "https://doi.org/10.1159/000125815",
    doi = "10.1159/000125815",
    openalex = "W1966353278"
}

Macrophage polarization refers to how macrophages have been activated at a given point in space and time. Polarization is not fixed, as macrophages are sufficiently plastic to integrate multiple signals, such as those from microbes, damaged tissues, and...Read More

@article{doi101146annurevph32030170002351,
    author = "Bennett, Michael V. L.",
    title = "Comparative Physiology: Electric Organs",
    year = "1970",
    journal = "Annual Review of Physiology",
    abstract = "Macrophage polarization refers to how macrophages have been activated at a given point in space and time. Polarization is not fixed, as macrophages are sufficiently plastic to integrate multiple signals, such as those from microbes, damaged tissues, and...Read More",
    url = "https://doi.org/10.1146/annurev.ph.32.030170.002351",
    doi = "10.1146/annurev.ph.32.030170.002351",
    openalex = "W2112622162"
}

@book{bennett1971electric3,
    author = "Bennett, M. V. L",
    title = "Electric Organs, in Hoar, W. S., and Randall, D. J., eds., Fish Physiology",
    year = "1971",
    publisher = "New York, Academic Press, v. V, p. 347-491",
    note = "talkorigins\_source = {true}; raw\_reference = {Bennett, M. V. L., 1971, Electric Organs, in Hoar, W. S., and Randall, D. J., eds., Fish Physiology: New York, Academic Press, v. V, p. 347-491.}"
}

@incollection{doi101016s1546509808600515,
    author = "Bennett, Michael V. L.",
    title = "Electric Organs",
    year = "1971",
    booktitle = "Fish physiology",
    url = "https://doi.org/10.1016/s1546-5098(08)60051-5",
    doi = "10.1016/s1546-5098(08)60051-5",
    openalex = "W4211213555",
    references = "doi1010160013469471902690, doi101038167201a0, doi101083jcb172375, doi101083jcb333c7, doi101083jcb403648, doi101098rspb19650016, doi101113jphysiol1952sp004764, doi101113jphysiol1953sp004849, doi101113jphysiol1964sp007378, doi101126science16639131641, doi101146annurevbi36070167003455, doi1023071442263, doi1023072010953, lissmann1958on"
}

@incollection{doi10100797836426592635,
    author = "Kalmijn, Ad. J.",
    title = "The Detection of Electric Fields from Inanimate and Animate Sources Other Than Electric Organs",
    year = "1974",
    booktitle = "Handbook of sensory physiology",
    url = "https://doi.org/10.1007/978-3-642-65926-3\_5",
    doi = "10.1007/978-3-642-65926-3\_5",
    openalex = "W1582039328",
    references = "doi101098rspb19380041, doi101098rsta19680031, mccleave1971weak"
}

Summary (1) The fluid properties of air and water enable animals to orientate to flow and this behaviour in water is termed rheotaxis. Fish, however, have a wide range of responses to currents, extending beyond simple orientation, and the term rheotropism is therefore used as a ‘portmanteau’ word to describe all such reactions. (2) Fish detect currents directly by flow over the body surface or indirectly by other stimuli. Indirect responses are more common and occur in response to visual, tactile and inertial stimuli resulting from displacement of the fish by the current. Reactions to displacement of visual images are called optomotor reactions. The lateral line is not involved except in the detection of small localized jets of water. It has not been demonstrated that any fish can detect the current by electrical stimuli, although it is theoretically possible for some to do so. (3) In the basic form of rhotaxis the fish heads upstream and maintains station by stemming the current. Current detection thresholds fall within the range 0.4 to 10 cm/s for tactile stimuli but may be as low as 0.03 cm/s for visual stimuli. (4) Visual responses have been studied by simulating displacement by the current in optomotor apparatus. Fish respond to a rotating black‐and‐white‐striped background by compensatory movements of the head and eyes ‐ optokinetic nystagmus ‐ or by the optomotor reaction, in which the fish swims with the background. (5) Fish show an orthokinesis in optomotor apparatus, their mean swimming speed increasing with the speed of rotation of the background. The precise form of the relationship varies between species and there is also considerable individual variation in performance. Fish accelerate and decelerate relative to the background, fixating on a particular stripe for short periods. (6) Factors limiting the appearance of the optomotor response are contrast, illuminance, acuity, critical flicker fusion frequency and spectral sensitivity. (7) Fish tolerate retinal image movements equivalent to those received when they are carried forwards by the current but not to those received when they are carried backwards. There are ganglion cells in the optic tectum which are sensitive to the direction of movement of targets across the visual field. In the goldfish there are significantly more units sensitive to movements in the temporo‐nasal than in the opposite direction. (8) There are close parallels between the behaviour of fish in schools and in an optomotor apparatus. The optomotor response is apparently innate, occurring in newly hatched fry. (9) Physical and chemical factors can modify rheotaxis. Temperature and olfactory stimuli affect both the sign of the taxis and the kinetic component of the behaviour. (10) Thyroid hormones which are involved in the control of migration have been shown to affect the kinetic component of rheotaxis. (11) Fish show a number of hydrodynamic adaptations to life in currents. Morphological modifications are greatest in fish from torrential streams, which show extreme dorsoventral flattening and have specialized adhesive organs. Other fish select areas of low velocity or decrease their buoyancy with increasing current speed. (12) Rheotropic behaviour plays an important role in the distribution of fish within stream systems, in the maintenance of territory and station and in feeding behaviour. Territory, station and spawning sites in salmonids are all selected in relation to water velocity. (13) Water currents are thought to provide either a transport system or directional clues for fish on migration. The fish either does not respond to the current and is carried passively downstream, or it makes an orientated movement, swimming up‐ or downstream. (14) Eggs and larvae are known to drift passively downstream from their spawning grounds and some adult fish may also drift passively. In the sea both adult and juvenile fish use a form of modulated drift associated with vertical migration. Fish move up into midwater either by direct tidal selection or in relation to the diel cycle of illuminance. In fresh water the downstream migrations of salmonid fry, and smolts under some conditions, occur by modulated drift. (15) There is no evidence that fish migrating in the sea orientate to the current, but in fresh water the upstream migrations of diadromous fish are clearly orientated movements. (16) Water velocity is a major factor for salmonids migrating upstream. For fry it limits the occurrence of upstream migrations and for adults it can also prevent upstream movement. But migrations are often initiated by freshets, and changing water velocity is thought to be the most important factor associated with a freshet. (17) Both environmental and genetic factors affect the direction of migration in relation to the current. In some sockeye salmon fry direction is determined by temperature, but in others the overall direction of movement is genetically determined and environmental factors only modify the behaviour. (18) Rheotropic behaviour has a number of important practical applications in the capture of fish and in guiding them past dams and power stations. (19) The optomotor response plays a basic role in the capture of roundfish by trawls under conditions when the fish can see the gear. Many fish are caught because they become fatigued after a prolonged period of swimming at the same speed as the trawl. (20) Most success in guiding fish away from hazardous areas and bypassing them round dams has been achieved with mechanical barriers which depend on rheotropic reactions of the fish. (21) Louvre screens are very successful in deflecting juvenile salmonids migrating downstream past small dams but are impracticable at large dams. Instead, the turbine intakes are commonly sited at a considerable depth and fish are bypassed by mechanical screens either at the surface of the forebay or into the gatewells immediately upstream of the turbine intakes. (22) With upstream migrants the basic problem is to attract fish to the lower end of the fishways. An adequate ‘attraction velocity’ is an important feature of fishways, which must be sited so that the fish avoid the high velocity discharges from spillways and turbines.

@article{doi101111j1469185x1974tb01173x,
    author = "Arnold, G. P.",
    title = "RHEOTROPISM IN FISHES",
    year = "1974",
    journal = "Biological reviews/Biological reviews of the Cambridge Philosophical Society",
    abstract = "Summary (1) The fluid properties of air and water enable animals to orientate to flow and this behaviour in water is termed rheotaxis. Fish, however, have a wide range of responses to currents, extending beyond simple orientation, and the term rheotropism is therefore used as a ‘portmanteau’ word to describe all such reactions. (2) Fish detect currents directly by flow over the body surface or indirectly by other stimuli. Indirect responses are more common and occur in response to visual, tactile and inertial stimuli resulting from displacement of the fish by the current. Reactions to displacement of visual images are called optomotor reactions. The lateral line is not involved except in the detection of small localized jets of water. It has not been demonstrated that any fish can detect the current by electrical stimuli, although it is theoretically possible for some to do so. (3) In the basic form of rhotaxis the fish heads upstream and maintains station by stemming the current. Current detection thresholds fall within the range 0.4 to 10 cm/s for tactile stimuli but may be as low as 0.03 cm/s for visual stimuli. (4) Visual responses have been studied by simulating displacement by the current in optomotor apparatus. Fish respond to a rotating black‐and‐white‐striped background by compensatory movements of the head and eyes ‐ optokinetic nystagmus ‐ or by the optomotor reaction, in which the fish swims with the background. (5) Fish show an orthokinesis in optomotor apparatus, their mean swimming speed increasing with the speed of rotation of the background. The precise form of the relationship varies between species and there is also considerable individual variation in performance. Fish accelerate and decelerate relative to the background, fixating on a particular stripe for short periods. (6) Factors limiting the appearance of the optomotor response are contrast, illuminance, acuity, critical flicker fusion frequency and spectral sensitivity. (7) Fish tolerate retinal image movements equivalent to those received when they are carried forwards by the current but not to those received when they are carried backwards. There are ganglion cells in the optic tectum which are sensitive to the direction of movement of targets across the visual field. In the goldfish there are significantly more units sensitive to movements in the temporo‐nasal than in the opposite direction. (8) There are close parallels between the behaviour of fish in schools and in an optomotor apparatus. The optomotor response is apparently innate, occurring in newly hatched fry. (9) Physical and chemical factors can modify rheotaxis. Temperature and olfactory stimuli affect both the sign of the taxis and the kinetic component of the behaviour. (10) Thyroid hormones which are involved in the control of migration have been shown to affect the kinetic component of rheotaxis. (11) Fish show a number of hydrodynamic adaptations to life in currents. Morphological modifications are greatest in fish from torrential streams, which show extreme dorsoventral flattening and have specialized adhesive organs. Other fish select areas of low velocity or decrease their buoyancy with increasing current speed. (12) Rheotropic behaviour plays an important role in the distribution of fish within stream systems, in the maintenance of territory and station and in feeding behaviour. Territory, station and spawning sites in salmonids are all selected in relation to water velocity. (13) Water currents are thought to provide either a transport system or directional clues for fish on migration. The fish either does not respond to the current and is carried passively downstream, or it makes an orientated movement, swimming up‐ or downstream. (14) Eggs and larvae are known to drift passively downstream from their spawning grounds and some adult fish may also drift passively. In the sea both adult and juvenile fish use a form of modulated drift associated with vertical migration. Fish move up into midwater either by direct tidal selection or in relation to the diel cycle of illuminance. In fresh water the downstream migrations of salmonid fry, and smolts under some conditions, occur by modulated drift. (15) There is no evidence that fish migrating in the sea orientate to the current, but in fresh water the upstream migrations of diadromous fish are clearly orientated movements. (16) Water velocity is a major factor for salmonids migrating upstream. For fry it limits the occurrence of upstream migrations and for adults it can also prevent upstream movement. But migrations are often initiated by freshets, and changing water velocity is thought to be the most important factor associated with a freshet. (17) Both environmental and genetic factors affect the direction of migration in relation to the current. In some sockeye salmon fry direction is determined by temperature, but in others the overall direction of movement is genetically determined and environmental factors only modify the behaviour. (18) Rheotropic behaviour has a number of important practical applications in the capture of fish and in guiding them past dams and power stations. (19) The optomotor response plays a basic role in the capture of roundfish by trawls under conditions when the fish can see the gear. Many fish are caught because they become fatigued after a prolonged period of swimming at the same speed as the trawl. (20) Most success in guiding fish away from hazardous areas and bypassing them round dams has been achieved with mechanical barriers which depend on rheotropic reactions of the fish. (21) Louvre screens are very successful in deflecting juvenile salmonids migrating downstream past small dams but are impracticable at large dams. Instead, the turbine intakes are commonly sited at a considerable depth and fish are bypassed by mechanical screens either at the surface of the forebay or into the gatewells immediately upstream of the turbine intakes. (22) With upstream migrants the basic problem is to attract fish to the lower end of the fishways. An adequate ‘attraction velocity’ is an important feature of fishways, which must be sited so that the fish avoid the high velocity discharges from spillways and turbines.",
    url = "https://doi.org/10.1111/j.1469-185x.1974.tb01173.x",
    doi = "10.1111/j.1469-185x.1974.tb01173.x",
    openalex = "W2134130682",
    references = "doi101007bf00622503, doi1010160016003257902983, doi101016s095056015480044x, doi101017cbo9781139103848007, doi101111j1469185x1959tb01289x, doi101111j1469185x1963tb00654x, doi1012019781315141046, doi101242jeb552371, doi1023072644, doi105694j132653771960tb62641x, lissmann1958on"
}

Eigenmannia virescens was observed in aquaria in Guyana, South America, during the non-breeding and breeding seasons. Agonistic behavior was described and correlated with electrical activity. Variations in the electric discharges play important roles in agonistic behavior as displays given during attack and retreat. Although descriptions of sexual behavior are not complete, certain electrical signals also appear to be used in courtship. The role of electrical signals in agonistic behavior of Eigemnannia were studied by (1) an analysis of the behavior of fish in dominant and subordinate roles, (2) an analysis of the simultaneous occurrence of electrical displays and motor actions, (3) an analysis of preceding actions of one fish and following actions of the other fish, and (4) analysis of responses to artificial electrical stimuli. These studies indicate that at least three classes of electric signals are important in communication among Eigenmannia: the normal discharge, Interruptions, and Rises. The normal discharge. The normal discharge of Eigenmannia virescens is species-distinctive in the area where this study was conducted. Playback of recorded signals and presentation of sinusoidal electrical stimuli, indicates that the normal discharge particularly the fundamental frequency of the normal discharge (240 to 600 Hz)- is used in species recognition. Males and females overlap extensively in their discharge frequency, and males do not appear to distinguish the electric discharges of males from those of females. Interruptions. Interruptions are brief cessations of the electric discharge. They are most often 20 to 40 msec in duration during agonistic interactions whereas they are often 60 to 80 msec when given by males during interactions with females during the breeding season. Interruptions are usually given in bouts where a bout is any group of Interruptions separated by less than 1.5 seconds. Interruptions are given almost exclusively by dominant fish. They are given at the same time as Attacks, Threats, and No Action, but rarely during Retreat. Bouts with many Interruptions are more likely to be associated with Attacks, and less likely with No Action, than are bouts containing only a few Interruptions. Interruptions correlate with motivation to Attack, and the number of Interruptions in a bout correlates with the probability of attack. Interruptions in one fish are followed by Retreat and No Action in the other fish, thus they appear to be an effective threat display. Interruptions with long durations are given at high repetition rates by male Eigenmannia in the presence of females during the breeding season, thus they may play a role in courtship. Rises. A Rise is an increase in discharge frequency followed by a decrease to the resting frequency. Rises lasting less than two seconds (Short Rises) are often given by dominant fish in agonistic interactions, most often at the same time as Attacks or Threats. They are given rarely. Long Rises (longer than two seconds) are given predominantly by subordinate fish in agonistic interactions. They are given simultaneous with Retreat and No Action and are thus an indicator of submissive behavior. Long Rises in one fish are followed by Attacks, Threats, Approaches, and by No Action in the other. During the breeding season, females, in the presence of males, often give long series of frequency modulations of unknown significance.

@article{doi101163156853974x00499,
    author = "Hopkins, Carl D.",
    title = "Electric Communication: Functions in the Social Behavior of Eigenmannia Virescens",
    year = "1974",
    journal = "Behaviour",
    abstract = "Eigenmannia virescens was observed in aquaria in Guyana, South America, during the non-breeding and breeding seasons. Agonistic behavior was described and correlated with electrical activity. Variations in the electric discharges play important roles in agonistic behavior as displays given during attack and retreat. Although descriptions of sexual behavior are not complete, certain electrical signals also appear to be used in courtship. The role of electrical signals in agonistic behavior of Eigemnannia were studied by (1) an analysis of the behavior of fish in dominant and subordinate roles, (2) an analysis of the simultaneous occurrence of electrical displays and motor actions, (3) an analysis of preceding actions of one fish and following actions of the other fish, and (4) analysis of responses to artificial electrical stimuli. These studies indicate that at least three classes of electric signals are important in communication among Eigenmannia: the normal discharge, Interruptions, and Rises. The normal discharge. The normal discharge of Eigenmannia virescens is species-distinctive in the area where this study was conducted. Playback of recorded signals and presentation of sinusoidal electrical stimuli, indicates that the normal discharge particularly the fundamental frequency of the normal discharge (240 to 600 Hz)- is used in species recognition. Males and females overlap extensively in their discharge frequency, and males do not appear to distinguish the electric discharges of males from those of females. Interruptions. Interruptions are brief cessations of the electric discharge. They are most often 20 to 40 msec in duration during agonistic interactions whereas they are often 60 to 80 msec when given by males during interactions with females during the breeding season. Interruptions are usually given in bouts where a bout is any group of Interruptions separated by less than 1.5 seconds. Interruptions are given almost exclusively by dominant fish. They are given at the same time as Attacks, Threats, and No Action, but rarely during Retreat. Bouts with many Interruptions are more likely to be associated with Attacks, and less likely with No Action, than are bouts containing only a few Interruptions. Interruptions correlate with motivation to Attack, and the number of Interruptions in a bout correlates with the probability of attack. Interruptions in one fish are followed by Retreat and No Action in the other fish, thus they appear to be an effective threat display. Interruptions with long durations are given at high repetition rates by male Eigenmannia in the presence of females during the breeding season, thus they may play a role in courtship. Rises. A Rise is an increase in discharge frequency followed by a decrease to the resting frequency. Rises lasting less than two seconds (Short Rises) are often given by dominant fish in agonistic interactions, most often at the same time as Attacks or Threats. They are given rarely. Long Rises (longer than two seconds) are given predominantly by subordinate fish in agonistic interactions. They are given simultaneous with Retreat and No Action and are thus an indicator of submissive behavior. Long Rises in one fish are followed by Attacks, Threats, Approaches, and by No Action in the other. During the breeding season, females, in the presence of males, often give long series of frequency modulations of unknown significance.",
    url = "https://doi.org/10.1163/156853974x00499",
    doi = "10.1163/156853974x00499",
    openalex = "W2045271307"
}

@article{doi101007bf01945786,
    author = "Kirschbaum, Frank and Westby, G. W. Max",
    title = "Development of the electric discharge in mormyrid and gymnotid fish (Marcusenius sp. andEigenmannia virescens)",
    year = "1975",
    journal = "Cellular and Molecular Life Sciences",
    url = "https://doi.org/10.1007/bf01945786",
    doi = "10.1007/bf01945786",
    openalex = "W2061204331"
}

@article{doi101007bf02326767,
    author = "Kirschbaum, Frank",
    title = "Environmental factors control the periodical reproduction of tropical electric fish",
    year = "1975",
    journal = "Cellular and Molecular Life Sciences",
    url = "https://doi.org/10.1007/bf02326767",
    doi = "10.1007/bf02326767",
    openalex = "W2051869114"
}

@techreport{adey1977brain1,
    author = "Adey, W. R. and Bawin, S. M",
    title = "Brain interactions with weak electric and magnetic fields",
    year = "1977",
    howpublished = "Neurosciences Research Program Bulletin, v. 15; 129 pp",
    note = "talkorigins\_source = {true}; raw\_reference = {Adey, W. R., and Bawin, S. M., 1977, Brain interactions with weak electric and magnetic fields: Neurosciences Research Program Bulletin, v. 15; 129 pp.}"
}

@book{doi1010079783642811616,
    author = "Heiligenberg, Walter",
    title = "Principles of Electrolocation and Jamming Avoidance in Electric Fish",
    year = "1977",
    booktitle = "Studies of brain function",
    url = "https://doi.org/10.1007/978-3-642-81161-6",
    doi = "10.1007/978-3-642-81161-6",
    openalex = "W2486279222"
}

@article{doi101007bf00368748,
    author = "Kirschbaum, Frank",
    title = "Electric-Organ ontogeny: Distinct Larval organ precedes the Adult organ in weakly electric fish",
    year = "1977",
    journal = "Die Naturwissenschaften",
    url = "https://doi.org/10.1007/bf00368748",
    doi = "10.1007/bf00368748",
    openalex = "W2022907847",
    references = "doi101002ar1091550112, doi101007bf00600512, doi101007bf01662212, doi101007bf01945786, doi101007bf02326767, doi101038188760b0, lissmann1958on"
}

@article{doi101007bf00303241,
    author = "Kirschbaum, Frank",
    title = "Reproduction of the weakly electric fish Eigenmannia virescens (Rhamphichtyidae, Teleostei) in captivity",
    year = "1979",
    journal = "Behavioral Ecology and Sociobiology",
    url = "https://doi.org/10.1007/bf00303241",
    doi = "10.1007/bf00303241",
    openalex = "W2911340723",
    references = "doi10100797814899351442, doi1010079783642811616, doi101007bf00368748, doi101111j109586491972tb05661x, doi101111j143903101974tb00465x, doi101136bjo592111c, doi101139f76123, doi101163156853974x00499, doi1015159783486777031, doi1023071443396, doi105962bhltitle12969"
}

An electric fish in the African family Mormyridae recognizes members of its own species by "listening" to electric organ discharges, which are species-specific signatures. Reactions of fish in the field and of individual electroreceptors to both normal and modified computer-synthesized discharges emphasize the importance of the waveform (time-domain cues) in species recognition.

@article{doi101126science7209524,
    author = "Hopkins, Carl D. and Bass, Andrew H.",
    title = "Temporal Coding of Species Recognition Signals in An Electric Fish",
    year = "1981",
    journal = "Science",
    abstract = {An electric fish in the African family Mormyridae recognizes members of its own species by "listening" to electric organ discharges, which are species-specific signatures. Reactions of fish in the field and of individual electroreceptors to both normal and modified computer-synthesized discharges emphasize the importance of the waveform (time-domain cues) in species recognition.},
    url = "https://doi.org/10.1126/science.7209524",
    doi = "10.1126/science.7209524",
    openalex = "W2030483827",
    references = "doi101016s0066185670800012"
}

Sharks, skates, and rays receive electrical information about the positions of their prey, the drift of ocean currents, and their magnetic compass headings. At sea, dogfish and blue sharks were observed to execute apparent feeding responses to dipole electric fields designed to mimic prey. In training experiments, stingrays showed the ability to orient relative to uniform electric fields similar to those produced by ocean currents. Voltage gradients of only 5 nanovolts per centimeter would elicit either behavior.

@article{doi101126science7134985,
    author = "Kalmijn, Ad. J.",
    title = "Electric and Magnetic Field Detection in Elasmobranch Fishes",
    year = "1982",
    journal = "Science",
    abstract = "Sharks, skates, and rays receive electrical information about the positions of their prey, the drift of ocean currents, and their magnetic compass headings. At sea, dogfish and blue sharks were observed to execute apparent feeding responses to dipole electric fields designed to mimic prey. In training experiments, stingrays showed the ability to orient relative to uniform electric fields similar to those produced by ocean currents. Voltage gradients of only 5 nanovolts per centimeter would elicit either behavior.",
    url = "https://doi.org/10.1126/science.7134985",
    doi = "10.1126/science.7134985",
    openalex = "W1967128502",
    references = "doi101242jeb552371"
}

@article{doi101007bf01047569,
    author = "Kirschbaum, Frank",
    title = "Myogenic electric organ precedes the neurogenic organ in apteronotid fish",
    year = "1983",
    journal = "Die Naturwissenschaften",
    url = "https://doi.org/10.1007/bf01047569",
    doi = "10.1007/bf01047569",
    openalex = "W2031567025",
    references = "doi101007bf00303241, doi101007bf00368748, doi101007bf01945786, doi101016s0140673601565125, doi101098rstb18920010, doi101242jcss39739455"
}

@article{doi101016s0003347285801391,
    author = "Hagedorn, Mary and Heiligenberg, Walter",
    title = "Court and spark: electric signals in the courtship and mating of gymnotoid fish",
    year = "1985",
    journal = "Animal Behaviour",
    url = "https://doi.org/10.1016/s0003-3472(85)80139-1",
    doi = "10.1016/s0003-3472(85)80139-1",
    openalex = "W2074684300",
    references = "doi101007bf00303241, doi101007bf01047569, doi101016s0066185670800012"
}

The organization of electric organs is described for the mormyrid fishes from Africa. The electric organ's spike-generating cells or electrocytes are wafer-shaped cells with a special geometry that relates to the number of phases and polarity of their pulsatile electric organ discharge (EOD) waveform. Six "families" of electrocytes are recognized on the basis of cell geometry. Each family includes species with EODs of similar polarity and phase number. Despite such similarities, there are still dramatic species differences in EOD waveforms for a given family that may further depend on specialized features of the electrocyte's excitable membranes. It is each species' particular electrocyte "profile" that must underlie the development of species-specific and hormone-dependent sex differences in the EOD waveforms.

@article{doi101002cne902440305,
    author = "Bass, Andrew H.",
    title = "Species differences in electric organs of mormyrids: Substrates for species‐typical electric organ discharge waveforms",
    year = "1986",
    journal = "The Journal of Comparative Neurology",
    abstract = {The organization of electric organs is described for the mormyrid fishes from Africa. The electric organ's spike-generating cells or electrocytes are wafer-shaped cells with a special geometry that relates to the number of phases and polarity of their pulsatile electric organ discharge (EOD) waveform. Six "families" of electrocytes are recognized on the basis of cell geometry. Each family includes species with EODs of similar polarity and phase number. Despite such similarities, there are still dramatic species differences in EOD waveforms for a given family that may further depend on specialized features of the electrocyte's excitable membranes. It is each species' particular electrocyte "profile" that must underlie the development of species-specific and hormone-dependent sex differences in the EOD waveforms.},
    url = "https://doi.org/10.1002/cne.902440305",
    doi = "10.1002/cne.902440305",
    openalex = "W2072133929",
    references = "doi101007bf01047569"
}

@article{doi101007bf00603976,
    author = "Crawford, J. Douglas and Hagedorn, Mary and Hopkins, Carl D.",
    title = "Acoustic communication in an electric fish,Pollimyrus isidori (Mormyridae)",
    year = "1986",
    journal = "Journal of Comparative Physiology A",
    url = "https://doi.org/10.1007/bf00603976",
    doi = "10.1007/bf00603976",
    openalex = "W2027878961",
    references = "doi101007bf00303241"
}

@article{doi101007bf00613028,
    author = "Meyer, J. Harlan and Leong, Margaret and Keller, Clifford H.",
    title = "Hormone-induced and maturational changes in electric organ discharges and electroreceptor tuning in the weakly electric fishApteronotus",
    year = "1987",
    journal = "Journal of Comparative Physiology A",
    url = "https://doi.org/10.1007/bf00613028",
    doi = "10.1007/bf00613028",
    openalex = "W2067643778",
    references = "doi101007bf00303241, doi101007bf00368748, doi101007bf01047569"
}

The diencephalic prepacemaker nucleus (PPn) of gymnotiform electric fish projects to the medullary pacemaker nucleus and modulates its regular firing frequency. Each firing of the pacemaker, in turn, drives an electric organ discharge (EOD). Two types of PPn neurons were retrogradely labeled from the pacemaker with HRP in Eigenmannia and Apteronotus. In both species, smaller ovoidal cells were found in the dorsomedial part of the PPn (PPn-G), and larger multipolar cells were found in the ventrolateral part of the PPn (PPn-C). This morphological distinction between the two subnuclei in the PPn was paralleled by a functional dichotomy. Microiontophoresis of L-glutamate in the PPn-G of both species elicited slow and gradual accelerations of EOD frequency characterized by a time constant on the order of seconds. The elicited frequency modulations were similar to those observed during the jamming avoidance response and during courtship. Glutamate stimulation of the PPn-C, in contrast, produced fast and abrupt frequency modulations characterized by a time constant on the order of milliseconds. These abrupt modulations resembled "chirps" observed during courtship and aggression. Similar behavior was produced by intracellular current injection into a PPn-C neuron of Apteronotus, and intracellular labeling of this neuron with Lucifer Yellow revealed a multipolar PPn-C neuron similar to those retrogradely labeled with HRP.

@article{doi101002cne902760108,
    author = "Kawasaki, Masashi and Maler, Leonard and Rose, Gary J. and Heiligenberg, Walter",
    title = "Anatomical and functional organization of the prepacemaker nucleus in gymnotiform electric fish: The accommodation of two behaviors in one nucleus",
    year = "1988",
    journal = "The Journal of Comparative Neurology",
    abstract = {The diencephalic prepacemaker nucleus (PPn) of gymnotiform electric fish projects to the medullary pacemaker nucleus and modulates its regular firing frequency. Each firing of the pacemaker, in turn, drives an electric organ discharge (EOD). Two types of PPn neurons were retrogradely labeled from the pacemaker with HRP in Eigenmannia and Apteronotus. In both species, smaller ovoidal cells were found in the dorsomedial part of the PPn (PPn-G), and larger multipolar cells were found in the ventrolateral part of the PPn (PPn-C). This morphological distinction between the two subnuclei in the PPn was paralleled by a functional dichotomy. Microiontophoresis of L-glutamate in the PPn-G of both species elicited slow and gradual accelerations of EOD frequency characterized by a time constant on the order of seconds. The elicited frequency modulations were similar to those observed during the jamming avoidance response and during courtship. Glutamate stimulation of the PPn-C, in contrast, produced fast and abrupt frequency modulations characterized by a time constant on the order of milliseconds. These abrupt modulations resembled "chirps" observed during courtship and aggression. Similar behavior was produced by intracellular current injection into a PPn-C neuron of Apteronotus, and intracellular labeling of this neuron with Lucifer Yellow revealed a multipolar PPn-C neuron similar to those retrogradely labeled with HRP.},
    url = "https://doi.org/10.1002/cne.902760108",
    doi = "10.1002/cne.902760108",
    openalex = "W2031115633"
}

@article{doi101007bf00295103,
    author = "Westby, G. W. Max",
    title = "The ecology, discharge diversity and predatory behaviour of gymnotiforme electric fish in the coastal streams of French Guiana",
    year = "1988",
    journal = "Behavioral Ecology and Sociobiology",
    url = "https://doi.org/10.1007/bf00295103",
    doi = "10.1007/bf00295103",
    openalex = "W213025685",
    references = "doi101007bf00368748"
}

@article{crossref1990bioelectrical,
    title = "Bioelectrical Phenomena for Medicine",
    year = "1990",
    journal = "Biomedical Safety \& Standards",
    url = "https://doi.org/10.1097/00149078-199009150-00017",
    doi = "10.1097/00149078-199009150-00017",
    number = "16",
    openalex = "W4250101029",
    pages = "127",
    volume = "20"
}

Monoclonal antibody mab-zebrin II was generated against a crude homogenate of cerebellum and electrosensory lateral line lobe from the weakly electric fish Apteronotus leptorhynchus. On Western blots of fish cerebellar proteins, mab-zebrin II recognizes a single polypeptide antigen of apparent molecular weight 36 kD. Immunocytochemistry of apteronotid brains reveals that zebrin II immunoreactivity is confined exclusively to Purkinje cells in the corpus cerebelli, lateral valvula cerebelli, and the eminentia granularis anterior. Other Purkinje cells, in the medial valvula cerebelli and eminentia granularis posterior, are not zebrin II immunoreactive. Immunoreactive Purkinje cells are stained completely, including dendrites, axons, and somata. The antigen seems to be absent only from the nucleus. A similar distribution is seen in catfish, goldfish, and a mormyrid fish. Zebrin II immunoreactivity is also found in the rat cerebellum. Western blotting of rat cerebellar proteins reveals a single immunoreactive polypeptide, with apparent molecular weight 36 kD, as in the fish. Also as in the fish, staining in the adult rat cerebellum is confined to a subset of Purkinje cells. Peroxidase reaction product is deposited throughout the immunoreactive Purkinje cells with the exception of the nucleus. No other cells in the cerebellum express zebrin II. At higher antibody concentrations, a weak glial cross reactivity is seen in most other brain regions: we believe that this is probably nonspecific. Zebrin II+ Purkinje cells are clustered together to form roughly parasagittal bands interposed by similar nonimmunoreactive clusters. In all there are 7 zebrin II+ and 7 zebrin II- compartments in each hemicerebellum. One immunoreactive band is adjacent to the midline; two others are disposed laterally to each side in the vermis; there is a paravermal band; and finally three more bands are identified in each hemisphere. Both in number and position, these compartments correspond precisely to the bands revealed by using another antibody, mabQ113 (anti-zebrin I). In both fish and rat the compartmentation revealed by zebrin II immunocytochemistry is related to the organization of cerebellar afferent and efferent projections and may provide clues as to the fundamental architecture of the vertebrate cerebellum.

@article{doi101002cne902910405,
    author = "Brochu, G. and Maler, Leonard and Hawkes, Richard",
    title = "Zebrin II: A polypeptide antigen expressed selectively by purkinje cells reveals compartments in rat and fish cerebellum",
    year = "1990",
    journal = "The Journal of Comparative Neurology",
    abstract = "Monoclonal antibody mab-zebrin II was generated against a crude homogenate of cerebellum and electrosensory lateral line lobe from the weakly electric fish Apteronotus leptorhynchus. On Western blots of fish cerebellar proteins, mab-zebrin II recognizes a single polypeptide antigen of apparent molecular weight 36 kD. Immunocytochemistry of apteronotid brains reveals that zebrin II immunoreactivity is confined exclusively to Purkinje cells in the corpus cerebelli, lateral valvula cerebelli, and the eminentia granularis anterior. Other Purkinje cells, in the medial valvula cerebelli and eminentia granularis posterior, are not zebrin II immunoreactive. Immunoreactive Purkinje cells are stained completely, including dendrites, axons, and somata. The antigen seems to be absent only from the nucleus. A similar distribution is seen in catfish, goldfish, and a mormyrid fish. Zebrin II immunoreactivity is also found in the rat cerebellum. Western blotting of rat cerebellar proteins reveals a single immunoreactive polypeptide, with apparent molecular weight 36 kD, as in the fish. Also as in the fish, staining in the adult rat cerebellum is confined to a subset of Purkinje cells. Peroxidase reaction product is deposited throughout the immunoreactive Purkinje cells with the exception of the nucleus. No other cells in the cerebellum express zebrin II. At higher antibody concentrations, a weak glial cross reactivity is seen in most other brain regions: we believe that this is probably nonspecific. Zebrin II+ Purkinje cells are clustered together to form roughly parasagittal bands interposed by similar nonimmunoreactive clusters. In all there are 7 zebrin II+ and 7 zebrin II- compartments in each hemicerebellum. One immunoreactive band is adjacent to the midline; two others are disposed laterally to each side in the vermis; there is a paravermal band; and finally three more bands are identified in each hemisphere. Both in number and position, these compartments correspond precisely to the bands revealed by using another antibody, mabQ113 (anti-zebrin I). In both fish and rat the compartmentation revealed by zebrin II immunocytochemistry is related to the organization of cerebellar afferent and efferent projections and may provide clues as to the fundamental architecture of the vertebrate cerebellum.",
    url = "https://doi.org/10.1002/cne.902910405",
    doi = "10.1002/cne.902910405",
    openalex = "W2108206329"
}

@article{doi101016089106189190030g,
    author = "Maler, Leonard and Sas, Emilia and Johnston, S. and Ellis, William G.",
    title = "An atlas of the brain of the electric fish Apteronotus leptorhynchus",
    year = "1991",
    journal = "Journal of Chemical Neuroanatomy",
    url = "https://doi.org/10.1016/0891-0618(91)90030-g",
    doi = "10.1016/0891-0618(91)90030-g",
    openalex = "W1986658120",
    references = "doi101002cne901590106, doi101002cne902030406, doi101002cne902760108, doi101002cne902910405, doi101002cne902920109, doi101016016501738390036x, doi101159000125815, lissmann1958on, openalexw2420592405, openalexw3217656501"
}

Adult males of a new gymnotiform, Hypopomus pinnicaudatus (Hypopomidae), found in the coastal swamps of French Guiana, have long compressed tail filaments, while juvenile males and females have shorter more cylindrical tails. Hypopomus pinnicaudatus generates a simple biphasic pulse-type electric-organ discharge. The discharge is longer in males than in females. The new species can be distinguished from other hypopomids by its color pattern, numbers of abdominal vertebrae, and the shape of the head. It has a widespread distribution in South America.

@article{doi1023071446259,
    author = "Hopkins, Carl D.",
    title = "Hypopomus pinnicaudatus (Hypopomidae), a New Species of Gymnotiform Fish from French Guiana",
    year = "1991",
    journal = "Copeia",
    abstract = "Adult males of a new gymnotiform, Hypopomus pinnicaudatus (Hypopomidae), found in the coastal swamps of French Guiana, have long compressed tail filaments, while juvenile males and females have shorter more cylindrical tails. Hypopomus pinnicaudatus generates a simple biphasic pulse-type electric-organ discharge. The discharge is longer in males than in females. The new species can be distinguished from other hypopomids by its color pattern, numbers of abdominal vertebrae, and the shape of the head. It has a widespread distribution in South America.",
    url = "https://doi.org/10.2307/1446259",
    doi = "10.2307/1446259",
    openalex = "W2315785547"
}

Part 1 Introduction: why study electric fish? experimental strategies. Part 2 The behaviour and ecology of electric fish: types of electric fish and their electric organ discharges evolutionary and ecological considerations noise and signal interference. Part 3 The jamming avoidance response of Eigenmannia: the experimental opening of a loop behavioral rules for the JAR. Part 4 Neuronal implementation of the jamming avoidance response: the coding of amplitude and phase modulations by tuberous electroreceptors the electrosensory lateral line lobe details in the circuitry of the ELL and its modulation by recurrent descending input from the nucleus praeeminentialis the torus semicircularis the gating of amplitude information by phase information - a mechanisms for discriminating the sign of Df projections of the torus semicircularis - the search for the pathway controlling the JAR the diencephalic nucleus electrosensorius, a sensory-motor interface the diencephalic prepacemaker nucleus the medullary pacemaker nucleus - control of the electric organ a summary flow diagram of neuronal structures and functions controlling the JAR. Part 5 General principles in the neuronal organization of the jamming avoidance response: the separation of task-specific sensory channels the central convergence of channels and the conversion of neuronal codes the representation of stimulus variables in ordered maps the emergence of recognition neurons and motor programs the distributed processing of sensory information and the shared use of neuronal circuits the control of motivational states through social signals recurrent descending loops - searchlights and central representations of sensory expectation? developmental and evolutionary considerations.

@book{openalexw1540240802,
    author = "Heiligenberg, Walter and Heiligenberg, Walter",
    title = "Neural Nets in Electric Fish",
    year = "1991",
    abstract = "Part 1 Introduction: why study electric fish? experimental strategies. Part 2 The behaviour and ecology of electric fish: types of electric fish and their electric organ discharges evolutionary and ecological considerations noise and signal interference. Part 3 The jamming avoidance response of Eigenmannia: the experimental opening of a loop behavioral rules for the JAR. Part 4 Neuronal implementation of the jamming avoidance response: the coding of amplitude and phase modulations by tuberous electroreceptors the electrosensory lateral line lobe details in the circuitry of the ELL and its modulation by recurrent descending input from the nucleus praeeminentialis the torus semicircularis the gating of amplitude information by phase information - a mechanisms for discriminating the sign of Df projections of the torus semicircularis - the search for the pathway controlling the JAR the diencephalic nucleus electrosensorius, a sensory-motor interface the diencephalic prepacemaker nucleus the medullary pacemaker nucleus - control of the electric organ a summary flow diagram of neuronal structures and functions controlling the JAR. Part 5 General principles in the neuronal organization of the jamming avoidance response: the separation of task-specific sensory channels the central convergence of channels and the conversion of neuronal codes the representation of stimulus variables in ordered maps the emergence of recognition neurons and motor programs the distributed processing of sensory information and the shared use of neuronal circuits the control of motivational states through social signals recurrent descending loops - searchlights and central representations of sensory expectation? developmental and evolutionary considerations.",
    openalex = "W1540240802"
}

@article{doi101016s0003347206800114,
    author = "McGregor, Peter K. and Westby, G. W. Max",
    title = "Discrimination of individually characteristic electric organ discharges by a weakly electric fish",
    year = "1992",
    journal = "Animal Behaviour",
    url = "https://doi.org/10.1016/s0003-3472(06)80011-4",
    doi = "10.1016/s0003-3472(06)80011-4",
    openalex = "W2087483567"
}

The order Gymnotiformes (South American electric fishes) is a fascinating assemblage of freshwater fishes that share the unusual ability to produce and sense electric fields used for electrolocation and social communication. In the last few decades, the electrogenic and electrosensory systems (EES) of these fish have served as an excellent model to study motor and sensory physiology in vertebrates. In an attempt to the evolution of characters associated with the EES in the group, we applied maximum-parsimony (MP), minimum-evolution (ME), and maximum-likelihood (ML) methods to analyze 302 aligned bases of the mitochondrial 12S rRNA and 416 bases of the mitochondrial 16S rRNA of 19 gymnotiform genera representing all six recognized families. Six catfish genera (order Siluriformes) were also sequenced and used as outgroups. The phylogenetic hypothesis resultant from molecular data analysis differs in some respects from previous hypotheses based on morphological studies. Our results were most informative within the family level, as we were unable to elucidate the relationships among deeper branches in this order with sufficient confidence by using molecular data alone. The phylogenetic information of both mitochondrial DNA segments appears to be affected by functional constraints, and the resultant topologies were sensitive to different weighting schemes and the algorithm used. Nonetheless, we found unanimous support for the following phylogenetic relationships: (1) the family Sternopygidae is an unnatural group, and Sternopygus is the sole representative of a unique lineage within the order; (2) the family Hypopomidae is not monophyletic; and (3) the order Gymnotiformes is composed of at least six natural clades: Sternopygus, family Apteronotidae, a new clade consisting of the remaining sternopygids, families Hypopomidae + Rhamphicthyidae, family Electrophoridae, and family Gymnotidae. By combining molecular, morphological, and physiological information, we propose a new hypothesis for the phylogeny of this group and suggest a new family Eigenmanniidae n. (order Gymnotiformes).

@article{doi101093oxfordjournalsmolbeva040204,
    author = "Alves-Gomes, José and Ortı́, Guillermo and Haygood, Margo G. and Heiligenberg, Walter and Meyer, Axel",
    title = "Phylogenetic analysis of the South American electric fishes (order Gymnotiformes) and the evolution of their electrogenic system: a synthesis based on morphology, electrophysiology, and mitochondrial sequence data.",
    year = "1995",
    journal = "Molecular Biology and Evolution",
    abstract = "The order Gymnotiformes (South American electric fishes) is a fascinating assemblage of freshwater fishes that share the unusual ability to produce and sense electric fields used for electrolocation and social communication. In the last few decades, the electrogenic and electrosensory systems (EES) of these fish have served as an excellent model to study motor and sensory physiology in vertebrates. In an attempt to the evolution of characters associated with the EES in the group, we applied maximum-parsimony (MP), minimum-evolution (ME), and maximum-likelihood (ML) methods to analyze 302 aligned bases of the mitochondrial 12S rRNA and 416 bases of the mitochondrial 16S rRNA of 19 gymnotiform genera representing all six recognized families. Six catfish genera (order Siluriformes) were also sequenced and used as outgroups. The phylogenetic hypothesis resultant from molecular data analysis differs in some respects from previous hypotheses based on morphological studies. Our results were most informative within the family level, as we were unable to elucidate the relationships among deeper branches in this order with sufficient confidence by using molecular data alone. The phylogenetic information of both mitochondrial DNA segments appears to be affected by functional constraints, and the resultant topologies were sensitive to different weighting schemes and the algorithm used. Nonetheless, we found unanimous support for the following phylogenetic relationships: (1) the family Sternopygidae is an unnatural group, and Sternopygus is the sole representative of a unique lineage within the order; (2) the family Hypopomidae is not monophyletic; and (3) the order Gymnotiformes is composed of at least six natural clades: Sternopygus, family Apteronotidae, a new clade consisting of the remaining sternopygids, families Hypopomidae + Rhamphicthyidae, family Electrophoridae, and family Gymnotidae. By combining molecular, morphological, and physiological information, we propose a new hypothesis for the phylogeny of this group and suggest a new family Eigenmanniidae n. (order Gymnotiformes).",
    url = "https://doi.org/10.1093/oxfordjournals.molbev.a040204",
    doi = "10.1093/oxfordjournals.molbev.a040204",
    openalex = "W2149593430",
    references = "doi101007bf01047569, doi101007bf01731581, doi1010160378111988903307, doi101016b9781483232119500097, doi101073pnas74125463, doi101073pnas7641967, doi101073pnas86166196, doi101093oxfordjournalsjhereda111190, doi101093sysbio274401, doi101111j155856461985tb00420x, doi1023072412923"
}

History. Behavior of strongly discharging electric fish. Behavior of weakly discharging electric fish. Some basic principles. Taxonomy, zoogeography, general ecology. Conclusion: future directions and a light finale. Abbreviations. Glossary. References. Appendix. Author index. Species index. Subject index.

@book{openalexw1577734759,
    author = "Möller, Peter",
    title = "Electric fishes: history and behavior",
    year = "1995",
    booktitle = "Chapman \& Hall eBooks",
    abstract = "History. Behavior of strongly discharging electric fish. Behavior of weakly discharging electric fish. Some basic principles. Taxonomy, zoogeography, general ecology. Conclusion: future directions and a light finale. Abbreviations. Glossary. References. Appendix. Author index. Species index. Subject index.",
    openalex = "W1577734759"
}

This concise review focuses on recent advances in the function and mechanism of electroreceptive systems in lower aquatic vertebrates and elucidates the sophisticated principles of communication, prey detection and orientation in these organisms. An introduction into electroreceptors, electric organs and sensory functions is followed by a review of electrocommunication and its behavioral physiology. Throughout each section, one finds a wide range of examples, from sharks, rays and skates to catfishes and stargazers, including also strongly and weakly electric fishes from tropical freshwater bodies.

@book{doi105283epub2108,
    author = "Krämer, Bernd",
    title = "Electroreception and communication in fishes",
    year = "1996",
    booktitle = "University of Regensburg Publication Server (University of Regensburg)",
    abstract = "This concise review focuses on recent advances in the function and mechanism of electroreceptive systems in lower aquatic vertebrates and elucidates the sophisticated principles of communication, prey detection and orientation in these organisms. An introduction into electroreceptors, electric organs and sensory functions is followed by a review of electrocommunication and its behavioral physiology. Throughout each section, one finds a wide range of examples, from sharks, rays and skates to catfishes and stargazers, including also strongly and weakly electric fishes from tropical freshwater bodies.",
    url = "https://doi.org/10.5283/epub.2108",
    doi = "10.5283/epub.2108",
    openalex = "W1573743197",
    references = "doi101007bf01047569"
}

@article{doi101007s003590050098,
    author = "Franchina, Cheryl R.",
    title = "Ontogeny of the electric organ discharge and the electric organ in the weakly electric pulse fish Brachyhypopomus pinnicaudatus (Hypopomidae, Gymnotiformes)",
    year = "1997",
    journal = "Journal of Comparative Physiology A",
    url = "https://doi.org/10.1007/s003590050098",
    doi = "10.1007/s003590050098",
    openalex = "W2039473239",
    references = "doi101007bf00295103, doi101007bf00303241, doi101007bf00613028, doi101007bf01099098, doi101016s0003347206800114, doi101038283249a0, doi101083jcb953763, doi101111j174966321961tb35555x, doi101159000115880, doi1023071446259"
}

@article{doi101007s003590050299,
    author = "Franchina, Cheryl R. and Stoddard, Philip K.",
    title = "Plasticity of the electric organ discharge waveform of the electric fish Brachyhypopomus pinnicaudatus I. Quantification of day-night changes",
    year = "1998",
    journal = "Journal of Comparative Physiology A",
    url = "https://doi.org/10.1007/s003590050299",
    doi = "10.1007/s003590050299",
    openalex = "W2055204402",
    references = "doi101007s003590050098"
}

@article{doi10103827655,
    author = "von der Emde, Gerhard and Schwarz, Stephan and Gomez, Leonel and Budelli, Rubén and Grant, Kirsty",
    title = "Electric fish measure distance in the dark",
    year = "1998",
    journal = "Nature",
    url = "https://doi.org/10.1038/27655",
    doi = "10.1038/27655",
    openalex = "W1651782570",
    references = "doi101242jeb352451"
}

Otophysine fishes have a series of bones, the Weberian ossicles, which acoustically couple the swimbladder to the inner ear. These fishes have evolved a diversity of sound-generating organs and acoustic signals, although some species, such as the goldfish, are not known to be vocal. Utilizing a recently developed auditory brainstem response (ABR)-recording technique, the auditory sensitivities of representatives of seven families from all four otophysine orders were investigated and compared to the spectral content of their vocalizations. All species examined detect tone bursts from 100 Hz to 5 kHz, but ABR-audiograms revealed major differences in auditory sensitivities, especially at higher frequencies (>1 kHz) where thresholds differed by up to 50 dB. These differences showed no apparent correspondence to the ability to produce sounds (vocal versus non-vocal species) or to the spectral content of species-specific sounds. All fishes have maximum sensitivity between 400 Hz and 1,500 Hz, whereas the major portion of the energy of acoustic signals was in the frequency range of 100-400 Hz (swimbladder drumming sounds) and of 1-3 kHz (stridulatory sounds). Species producing stridulatory sounds exhibited better high-frequency hearing sensitivity (pimelodids, doradids), except for callichthyids, which had poorest hearing ability in this range. Furthermore, fishes emitting both low- and high-frequency sounds, such as pimelodid and doradid catfishes, did not possess two corresponding auditory sensitivity maxima. Based on these results it is concluded that selective pressures involved in the evolution of the Weberian apparatus and the design of vocal signals in otophysines were others (primarily predator or prey detection in quiet freshwater habitats) than those serving to optimize acoustical communication.

@article{doi101159000006600,
    author = "Ladich, Friedrich",
    title = "Did Auditory Sensitivity and Vocalization Evolve Independently in Otophysan Fishes?",
    year = "1999",
    journal = "Brain Behavior and Evolution",
    abstract = "Otophysine fishes have a series of bones, the Weberian ossicles, which acoustically couple the swimbladder to the inner ear. These fishes have evolved a diversity of sound-generating organs and acoustic signals, although some species, such as the goldfish, are not known to be vocal. Utilizing a recently developed auditory brainstem response (ABR)-recording technique, the auditory sensitivities of representatives of seven families from all four otophysine orders were investigated and compared to the spectral content of their vocalizations. All species examined detect tone bursts from 100 Hz to 5 kHz, but ABR-audiograms revealed major differences in auditory sensitivities, especially at higher frequencies (>1 kHz) where thresholds differed by up to 50 dB. These differences showed no apparent correspondence to the ability to produce sounds (vocal versus non-vocal species) or to the spectral content of species-specific sounds. All fishes have maximum sensitivity between 400 Hz and 1,500 Hz, whereas the major portion of the energy of acoustic signals was in the frequency range of 100-400 Hz (swimbladder drumming sounds) and of 1-3 kHz (stridulatory sounds). Species producing stridulatory sounds exhibited better high-frequency hearing sensitivity (pimelodids, doradids), except for callichthyids, which had poorest hearing ability in this range. Furthermore, fishes emitting both low- and high-frequency sounds, such as pimelodid and doradid catfishes, did not possess two corresponding auditory sensitivity maxima. Based on these results it is concluded that selective pressures involved in the evolution of the Weberian apparatus and the design of vocal signals in otophysines were others (primarily predator or prey detection in quiet freshwater habitats) than those serving to optimize acoustical communication.",
    url = "https://doi.org/10.1159/000006600",
    doi = "10.1159/000006600",
    openalex = "W2132303623"
}

This paper explores the relationship between psychology and neurobiology in the context of cognitive science. Are the sciences that constitute cognitive science independent and theoretically autonomous, or is there a necessary interaction between them? I explore Fodor's Multiple Realization Thesis (MRT) which starts with the fact of multiple realization and purports to derive the theoretical autonomy of special sciences (such as psychology) from structural sciences (such as neurobiology). After laying out the MRT, it is shown that, on closer inspection, the argument is either circular or self-undermining—the argument either assumes the very autonomy it seeks to demonstrate or the concluded autonomy is contradicted by the theoretical interdependence invoked by the premises of the argument. Next, I explore a concrete example of multiple realization in the explanation of animal behavior: the convergent evolution of jamming avoidance behaviors in three genera of weakly electric fish. Contrary to the image painted by the MRT, the work on these animals involves a high degree of interaction between the various levels of investigation. The fact that our understanding of electric fish behavior involves functional theories and multiple realization without the kind of disunified science that is supposed to follow from such a situation indicates that the mere fact of multiple realization cannot be the basis for an autonomous psychology.

@article{doi101086392790,
    author = "Keeley, Brian",
    title = "Shocking Lessons from Electric Fish: The Theory and Practice of Multiple Realization",
    year = "2000",
    journal = "Philosophy of Science",
    abstract = "This paper explores the relationship between psychology and neurobiology in the context of cognitive science. Are the sciences that constitute cognitive science independent and theoretically autonomous, or is there a necessary interaction between them? I explore Fodor's Multiple Realization Thesis (MRT) which starts with the fact of multiple realization and purports to derive the theoretical autonomy of special sciences (such as psychology) from structural sciences (such as neurobiology). After laying out the MRT, it is shown that, on closer inspection, the argument is either circular or self-undermining—the argument either assumes the very autonomy it seeks to demonstrate or the concluded autonomy is contradicted by the theoretical interdependence invoked by the premises of the argument. Next, I explore a concrete example of multiple realization in the explanation of animal behavior: the convergent evolution of jamming avoidance behaviors in three genera of weakly electric fish. Contrary to the image painted by the MRT, the work on these animals involves a high degree of interaction between the various levels of investigation. The fact that our understanding of electric fish behavior involves functional theories and multiple realization without the kind of disunified science that is supposed to follow from such a situation indicates that the mere fact of multiple realization cannot be the basis for an autonomous psychology.",
    url = "https://doi.org/10.1086/392790",
    doi = "10.1086/392790",
    openalex = "W2069481307",
    references = "doi101093oxfordjournalsmolbeva040204"
}

▪ Abstract Cichlid fishes (Perciformes: Teleostei) found in the lakes of Africa have served as model systems for the study of evolution. The enormous number of species (1000 in Lake Malawi alone), the great diversity of trophic adaptations and behaviors, and the extreme rapidity of their divergence (<50,000 y for some faunas) single out these organisms as examples of evolution in progress. Because these fishes are confined to discrete lacustrine environments and their origination is bounded by geological features, these groups provide models with which to study evolution. We review theoretical studies and empirical research on the cichlid faunas of Africa to provide a synthetic overview of current knowledge of the evolutionary processes at work in this group. This view provides the critical information needed to formulate and test hypotheses that may permit discrimination among the diverse theories and models that have been advanced to explain the evolution of these fishes.

@article{doi101146annurevecolsys311163,
    author = "Kornfield, Irv and Smith, Peter F.",
    title = "African Cichlid Fishes: Model Systems for Evolutionary Biology",
    year = "2000",
    journal = "Annual Review of Ecology and Systematics",
    abstract = "▪ Abstract Cichlid fishes (Perciformes: Teleostei) found in the lakes of Africa have served as model systems for the study of evolution. The enormous number of species (1000 in Lake Malawi alone), the great diversity of trophic adaptations and behaviors, and the extreme rapidity of their divergence (<50,000 y for some faunas) single out these organisms as examples of evolution in progress. Because these fishes are confined to discrete lacustrine environments and their origination is bounded by geological features, these groups provide models with which to study evolution. We review theoretical studies and empirical research on the cichlid faunas of Africa to provide a synthetic overview of current knowledge of the evolutionary processes at work in this group. This view provides the critical information needed to formulate and test hypotheses that may permit discrimination among the diverse theories and models that have been advanced to explain the evolution of these fishes.",
    url = "https://doi.org/10.1146/annurev.ecolsys.31.1.163",
    doi = "10.1146/annurev.ecolsys.31.1.163",
    openalex = "W2112678364",
    references = "doi101111j109586491999tb00848x, doi101111j109636421975tb01893x"
}

According to current phylogenetic theory, both electroreceptors and electric organs evolved multiple times throughout the evolution of teleosts. Two basic types of electroreceptors have been described: ampullary and tuberous electroreceptors. Ampullary‐type electroreceptors appeared once in the common ancestor of the Siluriformes+Gymnotiformes (within the superorder Ostariophysi), and on two other occasions within the superorder Osteoglossomorpha: in the African Mormyriformes and in the African Notopteriformes. Tuberous receptors are assumed to have evolved three times; all within groups that already possessed ampullary receptors. With the exception of a single catfish species, for which studies are still lacking, all fish with tuberous electroreceptors also have an electric organ. Tuberous electroreceptors are found in the two unrelated electrogenic teleost lineages (orders Gymnotiformes and Mormyriformes) and in one non‐electrogenic South American catfish species (order Siluriformes). Electric organs evolved eight times independently among teleosts: five of them among the ostariophysans (once in the gymnotiform ancestor and in four siluriform lineages), once in the common ancestor of Mormyriformes, and in two uranoscopids. With the exception of two uranoscopid genera, for which no electroreceptive capabilities have been discovered so far, all electric organs evolved as an extension of a pre‐existing electroreceptive (ampullary) condition. It is suggested that plesiomorphic electric organ discharges (EODs) possessed a frequency spectrum that fully transgressed the tuning curve of ampullary receptors, i.e. a signal such as a long lasting monophasic pulse. Complex EOD waveforms appeared as a derived condition among electric fish. EODs are under constant evolutionary pressure to develop an ideal compromise between a function that enhances electrolocation and electrocommunication capabilities, and thereby ensures species identity through sexual and behavioural segregation, and minimizes the risk of predation.

@article{doi101111j109586492001tb02307x,
    author = "Alves-Gomes, José",
    title = "The evolution of electroreception and bioelectrogenesis in teleost fish: a phylogenetic perspective",
    year = "2001",
    journal = "Journal of Fish Biology",
    abstract = "According to current phylogenetic theory, both electroreceptors and electric organs evolved multiple times throughout the evolution of teleosts. Two basic types of electroreceptors have been described: ampullary and tuberous electroreceptors. Ampullary‐type electroreceptors appeared once in the common ancestor of the Siluriformes+Gymnotiformes (within the superorder Ostariophysi), and on two other occasions within the superorder Osteoglossomorpha: in the African Mormyriformes and in the African Notopteriformes. Tuberous receptors are assumed to have evolved three times; all within groups that already possessed ampullary receptors. With the exception of a single catfish species, for which studies are still lacking, all fish with tuberous electroreceptors also have an electric organ. Tuberous electroreceptors are found in the two unrelated electrogenic teleost lineages (orders Gymnotiformes and Mormyriformes) and in one non‐electrogenic South American catfish species (order Siluriformes). Electric organs evolved eight times independently among teleosts: five of them among the ostariophysans (once in the gymnotiform ancestor and in four siluriform lineages), once in the common ancestor of Mormyriformes, and in two uranoscopids. With the exception of two uranoscopid genera, for which no electroreceptive capabilities have been discovered so far, all electric organs evolved as an extension of a pre‐existing electroreceptive (ampullary) condition. It is suggested that plesiomorphic electric organ discharges (EODs) possessed a frequency spectrum that fully transgressed the tuning curve of ampullary receptors, i.e. a signal such as a long lasting monophasic pulse. Complex EOD waveforms appeared as a derived condition among electric fish. EODs are under constant evolutionary pressure to develop an ideal compromise between a function that enhances electrolocation and electrocommunication capabilities, and thereby ensures species identity through sexual and behavioural segregation, and minimizes the risk of predation.",
    url = "https://doi.org/10.1111/j.1095-8649.2001.tb02307.x",
    doi = "10.1111/j.1095-8649.2001.tb02307.x",
    openalex = "W2103844962",
    references = "doi101002jmor1051710205, doi101007bf01047569, doi101007s003590050098"
}

Animals can actively influence the content and quality of sensory information they acquire from the environment through the positioning of peripheral sensory surfaces. This study investigated receptor surface positioning during prey-capture behavior in weakly electric gymnotiform fish of the genus Apteronotus. Infrared video techniques and three-dimensional model-based tracking methods were used to provide quantitative information on body position and conformation as black ghost (A. albifrons) and brown ghost (A. leptorhynchus) knifefish hunted for prey (Daphnia magna) in the dark. We found that detection distance depends on the electrical conductivity of the surrounding water. Best performance was observed at low water conductivity (2.8 cm mean detection distance and 2 % miss rate at 35 microS cm(-)(1), A. albifrons) and poorest performance at high conductivity (1.5 cm mean detection distance and 11 % miss rate at 600 microS cm(-)(1), A. albifrons). The observed conductivity-dependence implies that nonvisual prey detection in Apteronotus is likely to be dominated by the electrosense over the range of water conductivities experienced by the animal in its natural environment. This result provides the first evidence for the involvement of electrosensory cues in the prey-capture behavior of gymnotids, but it leaves open the possibility that both the high-frequency (tuberous) and low-frequency (ampullary) electroreceptors may contribute. We describe an electrosensory orienting response to prey, whereby the fish rolls its body following detection to bring the prey above the dorsum. This orienting response and the spatial distribution of prey at the time of detection highlight the importance of the dorsal surface of the trunk for electrosensory signal acquisition. Finally, quantitative analysis of fish motion demonstrates that Apteronotus can adapt its trajectory to account for post-detection motion of the prey, suggesting that it uses a closed-loop adaptive tracking strategy, rather than an open-loop ballistic strike strategy, to intercept the prey.

@article{doi101242jeb2043543,
    author = "MacIver, Malcolm A. and Sharabash, Noura M. and Nelson, Mark",
    title = "Prey-Capture Behavior in Gymnotid Electric Fish: Motion Analysis and Effects of water Conductivity",
    year = "2001",
    journal = "Journal of Experimental Biology",
    abstract = "Animals can actively influence the content and quality of sensory information they acquire from the environment through the positioning of peripheral sensory surfaces. This study investigated receptor surface positioning during prey-capture behavior in weakly electric gymnotiform fish of the genus Apteronotus. Infrared video techniques and three-dimensional model-based tracking methods were used to provide quantitative information on body position and conformation as black ghost (A. albifrons) and brown ghost (A. leptorhynchus) knifefish hunted for prey (Daphnia magna) in the dark. We found that detection distance depends on the electrical conductivity of the surrounding water. Best performance was observed at low water conductivity (2.8 cm mean detection distance and 2 \% miss rate at 35 microS cm(-)(1), A. albifrons) and poorest performance at high conductivity (1.5 cm mean detection distance and 11 \% miss rate at 600 microS cm(-)(1), A. albifrons). The observed conductivity-dependence implies that nonvisual prey detection in Apteronotus is likely to be dominated by the electrosense over the range of water conductivities experienced by the animal in its natural environment. This result provides the first evidence for the involvement of electrosensory cues in the prey-capture behavior of gymnotids, but it leaves open the possibility that both the high-frequency (tuberous) and low-frequency (ampullary) electroreceptors may contribute. We describe an electrosensory orienting response to prey, whereby the fish rolls its body following detection to bring the prey above the dorsum. This orienting response and the spatial distribution of prey at the time of detection highlight the importance of the dorsal surface of the trunk for electrosensory signal acquisition. Finally, quantitative analysis of fish motion demonstrates that Apteronotus can adapt its trajectory to account for post-detection motion of the prey, suggesting that it uses a closed-loop adaptive tracking strategy, rather than an open-loop ballistic strike strategy, to intercept the prey.",
    url = "https://doi.org/10.1242/jeb.204.3.543",
    doi = "10.1242/jeb.204.3.543",
    openalex = "W2103225200",
    references = "doi1010079781461235606, doi10100797894009654236, doi101007bf00303241, doi101007bf00611175, doi101007bf00622503, doi101145129888129892, doi101145166117166134, doi1023072423056, doi1023073798339, doi105962p203769, lissmann1958on, openalexw1577734759, openalexw267370992"
}

Ichthyology & Herpetology (formerly Copeia) publishes work on the biology of fishes, amphibians, and reptiles, or work using those organisms as models for testing hypotheses of broad significance.

@article{doi101643ot04142,
    author = "Burgess, Warren E.",
    title = "CHECK LIST OF THE FRESHWATER FISHES OF SOUTH AND CENTRAL AMERICA",
    year = "2004",
    journal = "Copeia",
    abstract = "Ichthyology \& Herpetology (formerly Copeia) publishes work on the biology of fishes, amphibians, and reptiles, or work using those organisms as models for testing hypotheses of broad significance.",
    url = "https://doi.org/10.1643/ot-04-142",
    doi = "10.1643/ot-04-142",
    openalex = "W2165269240",
    references = "openalexw3001739384"
}

We report here that melanocortin peptides appear to serve as the mechanism by which weakly electric fish couple socially regulated and stress-regulated brain pathways to unique changes in the intrinsic excitability and action potential waveform of excitable membranes in peripheral cells involved in communication. Gymnotiform electric fish modulate their electric organ discharges (EODs) by reshaping the electric discharges of excitable cells in the periphery. These fish show circadian enhancement of the EOD waveform. They also enhance their EOD waveforms within minutes in response to stressors and changes in the social environment, thus altering the communication value of the signal. Changes in the EOD waveform that occur within minutes result from changes in the discharges of individual electrocytes (microEODs) mediated by the cAMP/protein kinase A (PKA) pathway acting on ion channel kinetics. What activates the cAMP/PKA pathway in electrocytes has not been identified. In vivo injections of the melanocortin peptide adrenocorticotropic hormone (ACTH) increase the amplitude and duration of the electric signal waveform of the gymnotiform Brachyhypopomus pinnicaudatus over the course of 1 h. Applied to single electrocytes in vitro, ACTH increases microEOD amplitude and duration within minutes by differentially modulating the action potentials of the two excitable membranes of the electrocyte and changing the timing of these two spikes. Serotonin modulates the EOD in vivo but has no effect on the microEOD in vitro. The cAMP analog 8-bromo-cAMP mimicked the effects of ACTH, whereas inhibition of PKA by protein kinase A inhibitor 14-22 amide blocked the modulatory effects of ACTH, confirming the role of the cAMP/PKA pathway in microEOD modulation by ACTH.

@article{doi101523jneurosci2809052005,
    author = "Markham, Michael R. and Stoddard, Philip K.",
    title = "Adrenocorticotropic Hormone Enhances the Masculinity of an Electric Communication Signal by Modulating the Waveform and Timing of Action Potentials within Individual Cells",
    year = "2005",
    journal = "Journal of Neuroscience",
    abstract = "We report here that melanocortin peptides appear to serve as the mechanism by which weakly electric fish couple socially regulated and stress-regulated brain pathways to unique changes in the intrinsic excitability and action potential waveform of excitable membranes in peripheral cells involved in communication. Gymnotiform electric fish modulate their electric organ discharges (EODs) by reshaping the electric discharges of excitable cells in the periphery. These fish show circadian enhancement of the EOD waveform. They also enhance their EOD waveforms within minutes in response to stressors and changes in the social environment, thus altering the communication value of the signal. Changes in the EOD waveform that occur within minutes result from changes in the discharges of individual electrocytes (microEODs) mediated by the cAMP/protein kinase A (PKA) pathway acting on ion channel kinetics. What activates the cAMP/PKA pathway in electrocytes has not been identified. In vivo injections of the melanocortin peptide adrenocorticotropic hormone (ACTH) increase the amplitude and duration of the electric signal waveform of the gymnotiform Brachyhypopomus pinnicaudatus over the course of 1 h. Applied to single electrocytes in vitro, ACTH increases microEOD amplitude and duration within minutes by differentially modulating the action potentials of the two excitable membranes of the electrocyte and changing the timing of these two spikes. Serotonin modulates the EOD in vivo but has no effect on the microEOD in vitro. The cAMP analog 8-bromo-cAMP mimicked the effects of ACTH, whereas inhibition of PKA by protein kinase A inhibitor 14-22 amide blocked the modulatory effects of ACTH, confirming the role of the cAMP/PKA pathway in microEOD modulation by ACTH.",
    url = "https://doi.org/10.1523/jneurosci.2809-05.2005",
    doi = "10.1523/jneurosci.2809-05.2005",
    openalex = "W2007489643",
    references = "doi101007s003590050098"
}

@incollection{doi101007038728275013,
    author = "Albert, James S. and Crampton, William G. R.",
    title = "Diversity and Phylogeny of Neotropical Electric Fishes (Gymnotiformes)",
    year = "2006",
    booktitle = "Springer handbook of auditory research",
    url = "https://doi.org/10.1007/0-387-28275-0\_13",
    doi = "10.1007/0-387-28275-0\_13",
    openalex = "W2245813655",
    references = "doi101007bf00368748, doi101016s0066185670800012, doi101093oxfordjournalsmolbeva040204, openalexw63312880"
}

@incollection{doi101007038728275014,
    author = "Caputi, Ángel A. and Carlson, Bruce A. and Macadar, O.",
    title = "Electric Organs and Their Control",
    year = "2006",
    booktitle = "Springer handbook of auditory research",
    url = "https://doi.org/10.1007/0-387-28275-0\_14",
    doi = "10.1007/0-387-28275-0\_14",
    openalex = "W2238150397",
    references = "doi101038167201a0, doi101242jeb352451"
}

@article{doi101016jphysbeh200611003,
    author = "Silva, Ana and Perrone, Rossana and Macadar, O.",
    title = "Environmental, seasonal, and social modulations of basal activity in a weakly electric fish",
    year = "2006",
    journal = "Physiology \& Behavior",
    url = "https://doi.org/10.1016/j.physbeh.2006.11.003",
    doi = "10.1016/j.physbeh.2006.11.003",
    openalex = "W2086926782",
    references = "doi101007bf00303241, doi101016s0066185670800012"
}

We investigated whether the evolution of electric organs and electric signal diversity in two independently evolved lineages of electric fishes was accompanied by convergent changes on the molecular level. We found that a sodium channel gene (Na(v)1.4a) that is expressed in muscle in nonelectric fishes has lost its expression in muscle and is expressed instead in the evolutionarily novel electric organ in both lineages of electric fishes. This gene appears to be evolving under positive selection in both lineages, facilitated by its restricted expression in the electric organ. This view is reinforced by the lack of evidence for selection on this gene in one electric species in which expression of this gene is retained in muscle. Amino acid replacements occur convergently in domains that influence channel inactivation, a key trait for shaping electric communication signals. Some amino acid replacements occur at or adjacent to sites at which disease-causing mutations have been mapped in human sodium channel genes, emphasizing that these replacements occur in functionally important domains. Selection appears to have acted on the final step in channel inactivation, but complementarily on the inactivation "ball" in one lineage, and its receptor site in the other lineage. Thus, changes in the expression and sequence of the same gene are associated with the independent evolution of signal complexity.

@article{doi101073pnas0600160103,
    author = "Zakon, Harold H. and Lü, Ying and Zwickl, Derrick J. and Hillis, David M.",
    title = "Sodium channel genes and the evolution of diversity in communication signals of electric fishes: Convergent molecular evolution",
    year = "2006",
    journal = "Proceedings of the National Academy of Sciences",
    abstract = {We investigated whether the evolution of electric organs and electric signal diversity in two independently evolved lineages of electric fishes was accompanied by convergent changes on the molecular level. We found that a sodium channel gene (Na(v)1.4a) that is expressed in muscle in nonelectric fishes has lost its expression in muscle and is expressed instead in the evolutionarily novel electric organ in both lineages of electric fishes. This gene appears to be evolving under positive selection in both lineages, facilitated by its restricted expression in the electric organ. This view is reinforced by the lack of evidence for selection on this gene in one electric species in which expression of this gene is retained in muscle. Amino acid replacements occur convergently in domains that influence channel inactivation, a key trait for shaping electric communication signals. Some amino acid replacements occur at or adjacent to sites at which disease-causing mutations have been mapped in human sodium channel genes, emphasizing that these replacements occur in functionally important domains. Selection appears to have acted on the final step in channel inactivation, but complementarily on the inactivation "ball" in one lineage, and its receptor site in the other lineage. Thus, changes in the expression and sequence of the same gene are associated with the independent evolution of signal complexity.},
    url = "https://doi.org/10.1073/pnas.0600160103",
    doi = "10.1073/pnas.0600160103",
    openalex = "W2107781114",
    references = "doi101007bf00368748"
}

Fishes, the most abundant and diverse group among all vertebrates, exploit the largest number of communication channels. These two volumes explore how fishes use hearing and vision, as well as the vibrational, electric and chemical modalities in their interactions with one another.

@book{doi101213ane0b013e3181c539ce,
    author = "Ladich, Friedrich and Collin, Shaun P. and Mӧller, Peter and Kapoor, B. G.",
    title = "Communication in Fishes",
    year = "2006",
    abstract = "Fishes, the most abundant and diverse group among all vertebrates, exploit the largest number of communication channels. These two volumes explore how fishes use hearing and vision, as well as the vibrational, electric and chemical modalities in their interactions with one another.",
    url = "https://doi.org/10.1213/ane.0b013e3181c539ce",
    doi = "10.1213/ane.0b013e3181c539ce",
    openalex = "W20081146"
}

Fishes suspended in water are subject to the complex nature of three-dimensional flows. Often, these flows are the result of abiotic and biotic sources that alter otherwise uniform flows, which then have the potential to perturb the swimming motions of fishes. The goal of this review is to highlight key studies that have contributed to a mechanistic and behavioural understanding of how perturbing flows affect fish. Most of our understanding of fish behaviour in turbulence comes from observations of natural conditions in the field and laboratory studies employing controlled perturbations, such as vortices generated in the wake behind simple geometric objects. Laboratory studies have employed motion analysis, flow visualization, electromyography, respirometry and sensory deprecation techniques to evaluate the mechanisms and physiological costs of swimming in altered flows. Studies show that flows which display chaotic and wide fluctuations in velocity can repel fishes, while flows that have a component of predictability can attract fishes. The ability to maintain stability in three-dimensional flows, either actively with powered movements or passively using the posture and intrinsic compliance of the body and fins, plays a large role in whether fish seek out or avoid turbulence. Fish in schools or current-swept habitats can benefit from altered flows using two distinct though not mutually exclusive mechanisms: flow refuging (exploiting regions of reduced flow relative to the earth frame of reference) and vortex capture (harnessing the energy of environmental vortices). Integrating how the physical environment affects organismal biomechanics with the more complex issue of behavioural choice requires consideration beyond simple body motions or metabolic costs. A fundamental link between these two ways of thinking about animal behaviour is how organisms sense and process information from the environment, which determines when locomotor behaviour is initiated and modulated. New data are presented here which show that behaviour changes in altered flows when either the lateral line or vision is blocked, showing that fish rely on multi-modal sensory inputs to negotiate complex flow environments. Integrating biomechanics and sensory biology to understand how fish swim in turbulent flow at the organismal level is necessary to better address population-level questions in the fields of fisheries management and ecology.

@article{doi101098rstb20072082,
    author = "Liao, James C.",
    title = "A review of fish swimming mechanics and behaviour in altered flows",
    year = "2007",
    journal = "Philosophical Transactions of the Royal Society B Biological Sciences",
    abstract = "Fishes suspended in water are subject to the complex nature of three-dimensional flows. Often, these flows are the result of abiotic and biotic sources that alter otherwise uniform flows, which then have the potential to perturb the swimming motions of fishes. The goal of this review is to highlight key studies that have contributed to a mechanistic and behavioural understanding of how perturbing flows affect fish. Most of our understanding of fish behaviour in turbulence comes from observations of natural conditions in the field and laboratory studies employing controlled perturbations, such as vortices generated in the wake behind simple geometric objects. Laboratory studies have employed motion analysis, flow visualization, electromyography, respirometry and sensory deprecation techniques to evaluate the mechanisms and physiological costs of swimming in altered flows. Studies show that flows which display chaotic and wide fluctuations in velocity can repel fishes, while flows that have a component of predictability can attract fishes. The ability to maintain stability in three-dimensional flows, either actively with powered movements or passively using the posture and intrinsic compliance of the body and fins, plays a large role in whether fish seek out or avoid turbulence. Fish in schools or current-swept habitats can benefit from altered flows using two distinct though not mutually exclusive mechanisms: flow refuging (exploiting regions of reduced flow relative to the earth frame of reference) and vortex capture (harnessing the energy of environmental vortices). Integrating how the physical environment affects organismal biomechanics with the more complex issue of behavioural choice requires consideration beyond simple body motions or metabolic costs. A fundamental link between these two ways of thinking about animal behaviour is how organisms sense and process information from the environment, which determines when locomotor behaviour is initiated and modulated. New data are presented here which show that behaviour changes in altered flows when either the lateral line or vision is blocked, showing that fish rely on multi-modal sensory inputs to negotiate complex flow environments. Integrating biomechanics and sensory biology to understand how fish swim in turbulent flow at the organismal level is necessary to better address population-level questions in the fields of fisheries management and ecology.",
    url = "https://doi.org/10.1098/rstb.2007.2082",
    doi = "10.1098/rstb.2007.2082",
    openalex = "W2107204370",
    references = "doi101111j1469185x1963tb00654x, doi101126science27553031113, doi101126science28454221954, doi101126science982056, doi1023071445582, openalexw1593581772"
}

The main information on the sounds and sound production in fishes is reviewed. The present systems of sound classification and specialized sound production in fishes with different taxonomic positions and ecology are described. The anatomy of sound generating organs is analyzed, and the mechanisms of production of different types of sounds (stridulation, drumming, cavitation, and percussion, as well as hydrodynamic, pneumatic, stringed, and respiratory sounds) are discussed. A brief characterization of the acoustic parameters of different sound types is given. Recent data on the anatomy and morphology of the sonic muscles (including their innervation, physiology, sexual dimorphism, and seasonal changes) are reviewed. The dynamics of the development of sound generating organs are described, and their capacity for sound production in the ontogeny of fishes is followed.

@article{doi101134s0032945208110039,
    author = "Kasumyan, A. O.",
    title = "Sounds and sound production in fishes",
    year = "2008",
    journal = "Journal of Ichthyology",
    abstract = "The main information on the sounds and sound production in fishes is reviewed. The present systems of sound classification and specialized sound production in fishes with different taxonomic positions and ecology are described. The anatomy of sound generating organs is analyzed, and the mechanisms of production of different types of sounds (stridulation, drumming, cavitation, and percussion, as well as hydrodynamic, pneumatic, stringed, and respiratory sounds) are discussed. A brief characterization of the acoustic parameters of different sound types is given. Recent data on the anatomy and morphology of the sonic muscles (including their innervation, physiology, sexual dimorphism, and seasonal changes) are reviewed. The dynamics of the development of sound generating organs are described, and their capacity for sound production in the ontogeny of fishes is followed.",
    url = "https://doi.org/10.1134/s0032945208110039",
    doi = "10.1134/s0032945208110039",
    openalex = "W2019515841",
    references = "doi1010160010406x67906159, doi101017s0025315400046130, doi101213ane0b013e3181c539ce, doi1023071538923"
}

Hypopomus pinnicaudatus, an electric fish, has a marked sexual dimorphism in its tail filament. Sexually mature males have long, 'feathered' tails as compared with females. The sexual dimorphism emerges when a fish reaches about 110 mm total length. Mature males have larger electrocytes which are more widely spaced and more numerous than those in mature females. The biphasic electric organ discharge (EOD) is longer in males than in females. The peak-to-peak amplitude of the male's EOD is weaker than a female's of the same total length. The weaker discharge is unexpected given the increase in size and number of electrocytes. It is suggested that the reduction in EOD amplitude is a consequence of the increase in EOD duration among males. Further, female choice probably played a role in the evolution of long duration EODs among males, and males may have secondarily grown long tails to compensate for the loss in active space that would otherwise accompany a weaker EOD.

@article{doi101159000115880,
    author = "Hopkins, Carl D. and Comfort, Nathaniel and Bastian, Joseph and Bass, Andrew H.",
    title = "Functional Analysis of Sexual Dimorphism in an Electric Fish, Hypopomus pinnicaudatus, Order Gymnotiformes (Part 1 of 2)",
    year = "2008",
    journal = "Brain Behavior and Evolution",
    abstract = "Hypopomus pinnicaudatus, an electric fish, has a marked sexual dimorphism in its tail filament. Sexually mature males have long, 'feathered' tails as compared with females. The sexual dimorphism emerges when a fish reaches about 110 mm total length. Mature males have larger electrocytes which are more widely spaced and more numerous than those in mature females. The biphasic electric organ discharge (EOD) is longer in males than in females. The peak-to-peak amplitude of the male's EOD is weaker than a female's of the same total length. The weaker discharge is unexpected given the increase in size and number of electrocytes. It is suggested that the reduction in EOD amplitude is a consequence of the increase in EOD duration among males. Further, female choice probably played a role in the evolution of long duration EODs among males, and males may have secondarily grown long tails to compensate for the loss in active space that would otherwise accompany a weaker EOD.",
    url = "https://doi.org/10.1159/000115880",
    doi = "10.1159/000115880",
    openalex = "W2072974606"
}

Electric fish produce weak electric fields to image their world in darkness and to communicate with potential mates and rivals. Eavesdropping by electroreceptive predators exerts selective pressure on electric fish to shift their signals into less-detectable high-frequency spectral ranges. Hypopomid electric fish evolved a signal-cloaking strategy that reduces their detectability by predators in the lab (and thus presumably their risk of predation in the field). These fish produce broad-frequency electric fields close to the body, but the heterogeneous local fields merge over space to cancel the low-frequency spectrum at a distance. Mature males dynamically regulate this cloaking mechanism to enhance or suppress low-frequency energy. The mechanism underlying electric-field cloaking involves electrogenic cells that produce two independent action potentials. In a unique twist, these cells orient sodium and potassium currents in the same direction, potentially boosting their capabilities for current generation. Exploration of such evolutionary inventions could aid the design of biogenerators to power implantable medical devices, an ambition that would benefit from the complete genome sequence of a gymnotiform fish.

@article{doi101641b580508,
    author = "Stoddard, Philip K. and Markham, Michael R.",
    title = "Signal Cloaking by Electric Fish",
    year = "2008",
    journal = "BioScience",
    abstract = "Electric fish produce weak electric fields to image their world in darkness and to communicate with potential mates and rivals. Eavesdropping by electroreceptive predators exerts selective pressure on electric fish to shift their signals into less-detectable high-frequency spectral ranges. Hypopomid electric fish evolved a signal-cloaking strategy that reduces their detectability by predators in the lab (and thus presumably their risk of predation in the field). These fish produce broad-frequency electric fields close to the body, but the heterogeneous local fields merge over space to cancel the low-frequency spectrum at a distance. Mature males dynamically regulate this cloaking mechanism to enhance or suppress low-frequency energy. The mechanism underlying electric-field cloaking involves electrogenic cells that produce two independent action potentials. In a unique twist, these cells orient sodium and potassium currents in the same direction, potentially boosting their capabilities for current generation. Exploration of such evolutionary inventions could aid the design of biogenerators to power implantable medical devices, an ambition that would benefit from the complete genome sequence of a gymnotiform fish.",
    url = "https://doi.org/10.1641/b580508",
    doi = "10.1641/b580508",
    openalex = "W2113711807",
    references = "doi101007s003590050098"
}

@article{kirschbaum2008ontogeny,
    author = "Kirschbaum, F. and Schwassmann, H.O.",
    title = "Ontogeny and evolution of electric organs in gymnotiform fish",
    year = "2008",
    journal = "Journal of Physiology-Paris",
    url = "https://doi.org/10.1016/j.jphysparis.2008.10.008",
    doi = "10.1016/j.jphysparis.2008.10.008",
    number = "4-6",
    openalex = "W2016508187",
    pages = "347-356",
    volume = "102",
    references = "doi101007bf00303241, doi101007bf00368748, doi101007bf01047569, doi101007s003590050098, doi101016s0065345402800092, doi101093oxfordjournalsmolbeva040204, doi101139f75196, doi101213ane0b013e3181c539ce, openalexw3001739384, openalexw63312880"
}

@article{doi101016jbbr200910023,
    author = "Stamper, Sarah A. and Carrera-G, Erika and Tan, Eric W. and Fugère, Vincent and Krahe, Rüdiger and Fortune, Eric S.",
    title = "Species differences in group size and electrosensory interference in weakly electric fishes: Implications for electrosensory processing",
    year = "2009",
    journal = "Behavioural Brain Research",
    url = "https://doi.org/10.1016/j.bbr.2009.10.023",
    doi = "10.1016/j.bbr.2009.10.023",
    openalex = "W2108043271",
    references = "doi101007bf01047569"
}

Natural selection arising from resource competition and environmental heterogeneity can drive adaptive radiation. Ecological opportunity facilitates this process, resulting in rapid divergence of ecological traits in many celebrated radiations. In other cases, sexual selection is thought to fuel divergence in mating signals ahead of ecological divergence. Comparing divergence rates between naturally and sexually selected traits can offer insights into processes underlying species radiations, but to date such comparisons have been largely qualitative. Here, we quantitatively compare divergence rates for four traits in African mormyrid fishes, which use an electrical communication system with few extrinsic constraints on divergence. We demonstrate rapid signal evolution in the Paramormyrops species flock compared to divergence in morphology, size, and trophic ecology. This disparity in the tempo of trait evolution suggests that sexual selection is an important early driver of species radiation in these mormyrids. We also found slight divergence in ecological traits among closely related species, consistent with a supporting role for natural selection in Paramormyrops diversification. Our results highlight the potential for sexual selection to drive explosive signal divergence when innovations in communication open new opportunities in signal space, suggesting that opportunity can catalyze species radiations through sexual selection, as well as natural selection.

@article{doi101086655221,
    author = "Arnegard, Matthew E. and McIntyre, Peter B. and Harmon, Luke J. and Zelditch, Miriam Leah and Crampton, William G. R. and Davis, Justin K. and Sullivan, John P. and Lavoué, Sébastien and Hopkins, Carl D.",
    title = "Sexual Signal Evolution Outpaces Ecological Divergence during Electric Fish Species Radiation",
    year = "2010",
    journal = "The American Naturalist",
    abstract = "Natural selection arising from resource competition and environmental heterogeneity can drive adaptive radiation. Ecological opportunity facilitates this process, resulting in rapid divergence of ecological traits in many celebrated radiations. In other cases, sexual selection is thought to fuel divergence in mating signals ahead of ecological divergence. Comparing divergence rates between naturally and sexually selected traits can offer insights into processes underlying species radiations, but to date such comparisons have been largely qualitative. Here, we quantitatively compare divergence rates for four traits in African mormyrid fishes, which use an electrical communication system with few extrinsic constraints on divergence. We demonstrate rapid signal evolution in the Paramormyrops species flock compared to divergence in morphology, size, and trophic ecology. This disparity in the tempo of trait evolution suggests that sexual selection is an important early driver of species radiation in these mormyrids. We also found slight divergence in ecological traits among closely related species, consistent with a supporting role for natural selection in Paramormyrops diversification. Our results highlight the potential for sexual selection to drive explosive signal divergence when innovations in communication open new opportunities in signal space, suggesting that opportunity can catalyze species radiations through sexual selection, as well as natural selection.",
    url = "https://doi.org/10.1086/655221",
    doi = "10.1086/655221",
    openalex = "W2024050261"
}

Environmental complexity and season both influence brain cell proliferation in adult vertebrates, but their relative importance and interaction have not been directly assessed. We examined brain cell proliferation during both the breeding and non-breeding seasons in adult male electric fish, Brachyhypopomus gauderio, exposed to three environments that differed in complexity: (1) a complex natural habitat in northern Uruguay, (2) an enriched captive environment where fish were housed socially and (3) a simple laboratory setting where fish were isolated. We injected fish with BrdU 2.5 h before sacrifice to label newborn cells. We examined the hindbrain and midbrain and quantified the density of BrdU+ cells in whole transverse sections, proliferative zones and two brain nuclei in the electrocommunication circuitry (the pacemaker nucleus and the electrosensory lateral line lobe). Season had the largest effect on cell proliferation, with fish during the breeding season having three to seven times more BrdU+ cells than those during the non-breeding season. Although the effect was smaller, fish from a natural environment had greater rates of cell proliferation than fish in social or isolated captive environments. For most brain regions, fish in social and isolated captive environments had equivalent levels of cell proliferation. However, for brain regions in the electrocommunication circuitry, group-housed fish had more cell proliferation than isolated fish, but only during the breeding season (season × environment interaction). The regionally and seasonally specific effect of social environment on cell proliferation suggests that addition of new cells to these nuclei may contribute to seasonal changes in electrocommunication behavior.

@article{doi101242jeb051037,
    author = "Dunlap, Kent D. and Silva, Ana and Chung, Michael",
    title = "Environmental complexity, seasonality and brain cell proliferation in a weakly electric fish, Brachyhypopomus gauderio",
    year = "2011",
    journal = "Journal of Experimental Biology",
    abstract = "Environmental complexity and season both influence brain cell proliferation in adult vertebrates, but their relative importance and interaction have not been directly assessed. We examined brain cell proliferation during both the breeding and non-breeding seasons in adult male electric fish, Brachyhypopomus gauderio, exposed to three environments that differed in complexity: (1) a complex natural habitat in northern Uruguay, (2) an enriched captive environment where fish were housed socially and (3) a simple laboratory setting where fish were isolated. We injected fish with BrdU 2.5 h before sacrifice to label newborn cells. We examined the hindbrain and midbrain and quantified the density of BrdU+ cells in whole transverse sections, proliferative zones and two brain nuclei in the electrocommunication circuitry (the pacemaker nucleus and the electrosensory lateral line lobe). Season had the largest effect on cell proliferation, with fish during the breeding season having three to seven times more BrdU+ cells than those during the non-breeding season. Although the effect was smaller, fish from a natural environment had greater rates of cell proliferation than fish in social or isolated captive environments. For most brain regions, fish in social and isolated captive environments had equivalent levels of cell proliferation. However, for brain regions in the electrocommunication circuitry, group-housed fish had more cell proliferation than isolated fish, but only during the breeding season (season × environment interaction). The regionally and seasonally specific effect of social environment on cell proliferation suggests that addition of new cells to these nuclei may contribute to seasonal changes in electrocommunication behavior.",
    url = "https://doi.org/10.1242/jeb.051037",
    doi = "10.1242/jeb.051037",
    openalex = "W2120656715",
    references = "doi101007s003590050098"
}

Gymnotiform weakly electric fishes generate electric organ discharges (EODs) and sense perturbations of the resulting electric field for purposes of orientation, prey detection and communication. Some species produce oscillatory ('wave-type') EODs at very high frequencies (up to 2 kHz) that have been proposed to be energetically expensive. If high-frequency EODs are expensive, then fish may modulate their EOD frequency and/or amplitude in response to low-oxygen (hypoxic) stress and/or compensate for costs of signalling through other adaptations that maximize oxygen uptake efficiency. To test for evidence of an energetic cost of signalling, we recorded EOD in conjunction with metabolic rates, critical oxygen tension and aquatic surface respiration (ASR(90)) thresholds in Apteronotus leptorhynchus, a species found in high-oxygen habitats, and Eigenmannia virescens, a species more typically found in low-oxygen waters. Eigenmannia virescens had a lower mean ASR(90) threshold and critical oxygen tension compared with A. leptorhynchus, consistent with field distributions. Within each species, there was no evidence for a relationship between metabolic rate and either EOD frequency or amplitude under normoxia, suggesting that there is no significant direct metabolic cost associated with producing a higher frequency EOD. However, when exposed to progressive hypoxia, fish generally responded by reducing EOD amplitude, which may reduce energetic costs. The threshold at which fish reduced EOD amplitude tended to be lower in E. virescens, a pattern consistent with higher tolerance to hypoxic stress. The results of this study suggest that wave-type fish reduce their EOD amplitude to reduce direct energetic costs without reducing metabolic rate under hypoxia.

@article{doi101242jeb059444,
    author = "Reardon, Erin E. and Parisi, Alana and Krahe, Rüdiger and Chapman, Lauren J.",
    title = "Energetic constraints on electric signalling in wave-type weakly electric fishes",
    year = "2011",
    journal = "Journal of Experimental Biology",
    abstract = "Gymnotiform weakly electric fishes generate electric organ discharges (EODs) and sense perturbations of the resulting electric field for purposes of orientation, prey detection and communication. Some species produce oscillatory ('wave-type') EODs at very high frequencies (up to 2 kHz) that have been proposed to be energetically expensive. If high-frequency EODs are expensive, then fish may modulate their EOD frequency and/or amplitude in response to low-oxygen (hypoxic) stress and/or compensate for costs of signalling through other adaptations that maximize oxygen uptake efficiency. To test for evidence of an energetic cost of signalling, we recorded EOD in conjunction with metabolic rates, critical oxygen tension and aquatic surface respiration (ASR(90)) thresholds in Apteronotus leptorhynchus, a species found in high-oxygen habitats, and Eigenmannia virescens, a species more typically found in low-oxygen waters. Eigenmannia virescens had a lower mean ASR(90) threshold and critical oxygen tension compared with A. leptorhynchus, consistent with field distributions. Within each species, there was no evidence for a relationship between metabolic rate and either EOD frequency or amplitude under normoxia, suggesting that there is no significant direct metabolic cost associated with producing a higher frequency EOD. However, when exposed to progressive hypoxia, fish generally responded by reducing EOD amplitude, which may reduce energetic costs. The threshold at which fish reduced EOD amplitude tended to be lower in E. virescens, a pattern consistent with higher tolerance to hypoxic stress. The results of this study suggest that wave-type fish reduce their EOD amplitude to reduce direct energetic costs without reducing metabolic rate under hypoxia.",
    url = "https://doi.org/10.1242/jeb.059444",
    doi = "10.1242/jeb.059444",
    openalex = "W2075922811",
    references = "doi1010079789400908291, doi101016s0003347285801391, doi101016s0065345413600017, doi101016s1096495901004080, doi101016s1546509808601636, doi1010970000464720011000000001, doi1023075403, kirschbaum2008ontogeny, openalexw1540240802"
}

One of the most remarkable examples of convergent evolution among vertebrates is illustrated by the independent origins of an active electric sense in South American and African weakly electric fishes, the Gymnotiformes and Mormyroidea, respectively. These groups independently evolved similar complex systems for object localization and communication via the generation and reception of weak electric fields. While good estimates of divergence times are critical to understanding the temporal context for the evolution and diversification of these two groups, their respective ages have been difficult to estimate due to the absence of an informative fossil record, use of strict molecular clock models in previous studies, and/or incomplete taxonomic sampling. Here, we examine the timing of the origins of the Gymnotiformes and the Mormyroidea using complete mitogenome sequences and a parametric bayesian method for divergence time reconstruction. Under two different fossil-based calibration methods, we estimated similar ages for the independent origins of the Mormyroidea and Gymnotiformes. Our absolute estimates for the origins of these groups either slightly postdate, or just predate, the final separation of Africa and South America by continental drift. The most recent common ancestor of the Mormyroidea and Gymnotiformes was found to be a non-electrogenic basal teleost living more than 85 millions years earlier. For both electric fish lineages, we also estimated similar intervals (16-19 or 22-26 million years, depending on calibration method) between the appearance of electroreception and the origin of myogenic electric organs, providing rough upper estimates for the time periods during which these complex electric organs evolved de novo from skeletal muscle precursors. The fact that the Gymnotiformes and Mormyroidea are of similar age enhances the comparative value of the weakly electric fish system for investigating pathways to evolutionary novelty, as well as the influences of key innovations in communication on the process of species radiation.

@article{doi101371journalpone0036287,
    author = "Lavoué, Sébastien and Miya, Masaki and Arnegard, Matthew E. and Sullivan, John P. and Hopkins, Carl D. and Nishida, Mutsumi",
    title = "Comparable Ages for the Independent Origins of Electrogenesis in African and South American Weakly Electric Fishes",
    year = "2012",
    journal = "PLoS ONE",
    abstract = "One of the most remarkable examples of convergent evolution among vertebrates is illustrated by the independent origins of an active electric sense in South American and African weakly electric fishes, the Gymnotiformes and Mormyroidea, respectively. These groups independently evolved similar complex systems for object localization and communication via the generation and reception of weak electric fields. While good estimates of divergence times are critical to understanding the temporal context for the evolution and diversification of these two groups, their respective ages have been difficult to estimate due to the absence of an informative fossil record, use of strict molecular clock models in previous studies, and/or incomplete taxonomic sampling. Here, we examine the timing of the origins of the Gymnotiformes and the Mormyroidea using complete mitogenome sequences and a parametric bayesian method for divergence time reconstruction. Under two different fossil-based calibration methods, we estimated similar ages for the independent origins of the Mormyroidea and Gymnotiformes. Our absolute estimates for the origins of these groups either slightly postdate, or just predate, the final separation of Africa and South America by continental drift. The most recent common ancestor of the Mormyroidea and Gymnotiformes was found to be a non-electrogenic basal teleost living more than 85 millions years earlier. For both electric fish lineages, we also estimated similar intervals (16-19 or 22-26 million years, depending on calibration method) between the appearance of electroreception and the origin of myogenic electric organs, providing rough upper estimates for the time periods during which these complex electric organs evolved de novo from skeletal muscle precursors. The fact that the Gymnotiformes and Mormyroidea are of similar age enhances the comparative value of the weakly electric fish system for investigating pathways to evolutionary novelty, as well as the influences of key innovations in communication on the process of species radiation.",
    url = "https://doi.org/10.1371/journal.pone.0036287",
    doi = "10.1371/journal.pone.0036287",
    openalex = "W2085947098",
    references = "doi1010079783642866593, doi101007bf00160154, doi101007s1312701100560, doi101016jympev200909017, doi101016s0169534703000338, doi101093bioinformaticsbtl446, doi101093molbevmsr121, doi101126science1116412, doi101126science23547931156, doi101186147121487214, doi1012019781003036401, kirschbaum2008ontogeny"
}

PART I: INTRODUCTION 1- The Allure of Electric Fishes: Humboldt's Obsession PART II: ANCIENT CULTURES 2- The Catfish of the Nile 3- Torpedoes in the Greco-Roman World: Pt. 1. Wonders of Nature Between Science and Myth 4- Torpedoes in the Greco-Roman World: Pt. 2. From Therapeutic Shocks to Theories of the Discharge 5- Byzantine and Islamic Writings PART III: MIDDLE AGES TO THE EARLY MODERN PERIOD 6- Torpedoes: From the Scholastics through the Renaissance 7- Rediscovering The Torporific Catfishes 8- The of South America 9- From the Occult to Mechanical Theories of the Discharge PART IV: THE EMERGENCE OF FISH ELECTRICITY 10- The Electrical World of Benjamin Franklin 11- Animal Spirits and Physiology 12- First Steps Toward Fish Electricity 13- The Dutch, the Eel, and Electricity PART V: THE ROYAL SOCIETY AND THE COVETED SPARK 14- Edward Bancroft's Guiana Eels and London Connections 15- John Walsh's Scientific Journey 16- The Royal Society and Interdisciplinary Science 17- Out of the Guianas: The American Philosophical Society and the Eel 18- Alexander Garden: A Linnaean in South Carolina and Captain Banker's Eels 19- Sparks in Darkness and the Eel's Electrical Sense 20- Public Knowledge: Newspapers, Magazines, and Shocking Poetry PART VI: FROM FISH TO NERVE PHYSIOLOGY AND BACK 21- Galvani's Animal Electricity 22- Electric Fishes in Volta's Path to the Battery 23- Galvanism Contra Voltaism: Electric Fishes and the Unsolvable Dilemma 24- Electric Fishes in the Nineteenth Century 25- The Changing Neurohysiological Setting 26- Understanding the Shock Mechanisms: A Twentieth Century Odyssey EPILOGUE APPENDIX I: Names with Birth and Death Dates REFERENCES

@article{doi105860choice493863,
    title = "The shocking history of electric fishes: from ancient epochs to the birth of modern neurophysiology",
    year = "2012",
    journal = "Choice Reviews Online",
    abstract = "PART I: INTRODUCTION 1- The Allure of Electric Fishes: Humboldt's Obsession PART II: ANCIENT CULTURES 2- The Catfish of the Nile 3- Torpedoes in the Greco-Roman World: Pt. 1. Wonders of Nature Between Science and Myth 4- Torpedoes in the Greco-Roman World: Pt. 2. From Therapeutic Shocks to Theories of the Discharge 5- Byzantine and Islamic Writings PART III: MIDDLE AGES TO THE EARLY MODERN PERIOD 6- Torpedoes: From the Scholastics through the Renaissance 7- Rediscovering The Torporific Catfishes 8- The of South America 9- From the Occult to Mechanical Theories of the Discharge PART IV: THE EMERGENCE OF FISH ELECTRICITY 10- The Electrical World of Benjamin Franklin 11- Animal Spirits and Physiology 12- First Steps Toward Fish Electricity 13- The Dutch, the Eel, and Electricity PART V: THE ROYAL SOCIETY AND THE COVETED SPARK 14- Edward Bancroft's Guiana Eels and London Connections 15- John Walsh's Scientific Journey 16- The Royal Society and Interdisciplinary Science 17- Out of the Guianas: The American Philosophical Society and the Eel 18- Alexander Garden: A Linnaean in South Carolina and Captain Banker's Eels 19- Sparks in Darkness and the Eel's Electrical Sense 20- Public Knowledge: Newspapers, Magazines, and Shocking Poetry PART VI: FROM FISH TO NERVE PHYSIOLOGY AND BACK 21- Galvani's Animal Electricity 22- Electric Fishes in Volta's Path to the Battery 23- Galvanism Contra Voltaism: Electric Fishes and the Unsolvable Dilemma 24- Electric Fishes in the Nineteenth Century 25- The Changing Neurohysiological Setting 26- Understanding the Shock Mechanisms: A Twentieth Century Odyssey EPILOGUE APPENDIX I: Names with Birth and Death Dates REFERENCES",
    url = "https://doi.org/10.5860/choice.49-3863",
    doi = "10.5860/choice.49-3863",
    openalex = "W638663349"
}

Animals perform a remarkable diversity of movements through the coordinated mechanical contraction of skeletal muscle. This capacity for a wide range of movements is due to the presence of muscle cells with a very plastic phenotype that display many different biochemical, physiological and morphological properties. What factors influence the maintenance and plasticity of differentiated muscle fibers is a fundamental question in muscle biology. We have exploited the remarkable potential of skeletal muscle cells of the gymnotiform electric fish Sternopygus macrurus to trans-differentiate into electrocytes, the non-contractile electrogenic cells of the electric organ (EO), to investigate the mechanisms that regulate the skeletal muscle phenotype. In S. macrurus, mature electrocytes possess a phenotype that is intermediate between muscle and non-muscle cells. How some genes coding for muscle-specific proteins are downregulated while others are maintained, and novel genes are upregulated, is an intriguing problem in the control of skeletal muscle and EO phenotype. To date, the intracellular and extracellular factors that generate and maintain distinct patterns of gene expression in muscle and EO have not been defined. Expression studies in S. macrurus have started to shed light on the role that transcriptional and post-transcriptional events play in regulating specific muscle protein systems and the muscle phenotype of the EO. In addition, these findings also represent an important step toward identifying mechanisms that affect the maintenance and plasticity of the muscle cell phenotype for the evolution of highly specialized non-contractile tissues.

@article{doi101242jeb082404,
    author = "Güth, Robert and Pinch, Matthew and Unguez, Graciela A.",
    title = "Mechanisms of muscle gene regulation in the electric organ of Sternopygus macrurus",
    year = "2013",
    journal = "Journal of Experimental Biology",
    abstract = "Animals perform a remarkable diversity of movements through the coordinated mechanical contraction of skeletal muscle. This capacity for a wide range of movements is due to the presence of muscle cells with a very plastic phenotype that display many different biochemical, physiological and morphological properties. What factors influence the maintenance and plasticity of differentiated muscle fibers is a fundamental question in muscle biology. We have exploited the remarkable potential of skeletal muscle cells of the gymnotiform electric fish Sternopygus macrurus to trans-differentiate into electrocytes, the non-contractile electrogenic cells of the electric organ (EO), to investigate the mechanisms that regulate the skeletal muscle phenotype. In S. macrurus, mature electrocytes possess a phenotype that is intermediate between muscle and non-muscle cells. How some genes coding for muscle-specific proteins are downregulated while others are maintained, and novel genes are upregulated, is an intriguing problem in the control of skeletal muscle and EO phenotype. To date, the intracellular and extracellular factors that generate and maintain distinct patterns of gene expression in muscle and EO have not been defined. Expression studies in S. macrurus have started to shed light on the role that transcriptional and post-transcriptional events play in regulating specific muscle protein systems and the muscle phenotype of the EO. In addition, these findings also represent an important step toward identifying mechanisms that affect the maintenance and plasticity of the muscle cell phenotype for the evolution of highly specialized non-contractile tissues.",
    url = "https://doi.org/10.1242/jeb.082404",
    doi = "10.1242/jeb.082404",
    openalex = "W1978432174",
    references = "doi101016009286748790585x, doi101016009286749390621v, doi101016s0960982202008096, doi101038nature02871, doi101038ng1725, doi101038nm1582, doi101113jphysiol1973sp010369, doi101126science1139089, doi101126science1846704, doi101186gb200453r13, kirschbaum2008ontogeny"
}

Gymnotiform weakly electric fish produce an electric signal to sense their environment and communicate with conspecifics. Although the generation of such relatively large electric signals over an entire lifetime is expected to be energetically costly, supporting evidence to date is equivocal. In this article, we first provide a theoretical analysis of the energy budget underlying signal production. Our analysis suggests that wave-type and pulse-type species invest a similar fraction of metabolic resources into electric signal generation, supporting previous evidence of a trade-off between signal amplitude and frequency. We then consider a comparative and evolutionary framework in which to interpret and guide future studies. We suggest that species differences in signal generation and plasticity, when considered in an energetics context, will not only help to evaluate the role of energetic constraints in the evolution of signal diversity but also lead to important general insights into the energetics of bioelectric signal generation.

@article{doi101242jeb082735,
    author = "Salazar, Vielka L. and Krahe, Rüdiger and Lewis, John E.",
    title = "The energetics of electric organ discharge generation in gymnotiform weakly electric fish",
    year = "2013",
    journal = "Journal of Experimental Biology",
    abstract = "Gymnotiform weakly electric fish produce an electric signal to sense their environment and communicate with conspecifics. Although the generation of such relatively large electric signals over an entire lifetime is expected to be energetically costly, supporting evidence to date is equivocal. In this article, we first provide a theoretical analysis of the energy budget underlying signal production. Our analysis suggests that wave-type and pulse-type species invest a similar fraction of metabolic resources into electric signal generation, supporting previous evidence of a trade-off between signal amplitude and frequency. We then consider a comparative and evolutionary framework in which to interpret and guide future studies. We suggest that species differences in signal generation and plasticity, when considered in an energetics context, will not only help to evaluate the role of energetic constraints in the evolution of signal diversity but also lead to important general insights into the energetics of bioelectric signal generation.",
    url = "https://doi.org/10.1242/jeb.082735",
    doi = "10.1242/jeb.082735",
    openalex = "W2108783974",
    references = "doi101242jeb059444, doi101242jeb082628"
}

Little is known about the genetic basis of convergent traits that originate repeatedly over broad taxonomic scales. The myogenic electric organ has evolved six times in fishes to produce electric fields used in communication, navigation, predation, or defense. We have examined the genomic basis of the convergent anatomical and physiological origins of these organs by assembling the genome of the electric eel (Electrophorus electricus) and sequencing electric organ and skeletal muscle transcriptomes from three lineages that have independently evolved electric organs. Our results indicate that, despite millions of years of evolution and large differences in the morphology of electric organ cells, independent lineages have leveraged similar transcription factors and developmental and cellular pathways in the evolution of electric organs.

@article{doi101126science1254432,
    author = "Gallant, Jason R. and Traeger, Lindsay L. and Volkening, Jeremy D. and Moffett, Howell and Chen, Po-Hao and Novina, Carl D. and Phillips, George N. and Anand, René and Wells, Gregg B. and Pinch, Matthew and Güth, Robert and Unguez, Graciela A. and Albert, James S. and Zakon, Harold H. and Samanta, Manoj P. and Sussman, Michael R.",
    title = "Genomic basis for the convergent evolution of electric organs",
    year = "2014",
    journal = "Science",
    abstract = "Little is known about the genetic basis of convergent traits that originate repeatedly over broad taxonomic scales. The myogenic electric organ has evolved six times in fishes to produce electric fields used in communication, navigation, predation, or defense. We have examined the genomic basis of the convergent anatomical and physiological origins of these organs by assembling the genome of the electric eel (Electrophorus electricus) and sequencing electric organ and skeletal muscle transcriptomes from three lineages that have independently evolved electric organs. Our results indicate that, despite millions of years of evolution and large differences in the morphology of electric organ cells, independent lineages have leveraged similar transcription factors and developmental and cellular pathways in the evolution of electric organs.",
    url = "https://doi.org/10.1126/science.1254432",
    doi = "10.1126/science.1254432",
    openalex = "W2008761917"
}

Rapid escape swims in fish are initiated by the Mauthner cells, giant reticulospinal neurons with unique specializations for swift responses. The Mauthner cells directly activate motoneurons and facilitate predator detection by integrating acoustic, mechanosensory, and visual stimuli. In addition, larval fish show well-coordinated escape responses when exposed to electric field pulses (EFPs). Sensitization of the Mauthner cell by genetic overexpression of the voltage-gated sodium channel SCN5 increased EFP responsiveness, whereas Mauthner ablation with an engineered variant of nitroreductase with increased activity (epNTR) eliminated the response. The reaction time to EFPs is extremely short, with many responses initiated within 2 ms of the EFP. Large neurons, such as Mauthner cells, show heightened sensitivity to extracellular voltage gradients. We therefore tested whether the rapid response to EFPs was due to direct activation of the Mauthner cells, bypassing delays imposed by stimulus detection and transmission by sensory cells. Consistent with this, calcium imaging indicated that EFPs robustly activated the Mauthner cell but only rarely fired other reticulospinal neurons. Further supporting this idea, pharmacological blockade of synaptic transmission in zebrafish did not affect Mauthner cell activity in response to EFPs. Moreover, Mauthner cells transgenically expressing a tetrodotoxin (TTX)-resistant voltage-gated sodium channel retained responses to EFPs despite TTX suppression of action potentials in the rest of the brain. We propose that EFPs directly activate Mauthner cells because of their large size, thereby driving ultrarapid escape responses in fish.

@article{doi101152jn002282014,
    author = "Tabor, Kathryn M. and Bergeron, Sadie A. and Horstick, Eric J. and Jordan, Diana C. and Aho, Vilma and Porkka‐Heiskanen, Tarja and Haspel, Gal and Burgess, Harold A.",
    title = "Direct activation of the Mauthner cell by electric field pulses drives ultrarapid escape responses",
    year = "2014",
    journal = "Journal of Neurophysiology",
    abstract = "Rapid escape swims in fish are initiated by the Mauthner cells, giant reticulospinal neurons with unique specializations for swift responses. The Mauthner cells directly activate motoneurons and facilitate predator detection by integrating acoustic, mechanosensory, and visual stimuli. In addition, larval fish show well-coordinated escape responses when exposed to electric field pulses (EFPs). Sensitization of the Mauthner cell by genetic overexpression of the voltage-gated sodium channel SCN5 increased EFP responsiveness, whereas Mauthner ablation with an engineered variant of nitroreductase with increased activity (epNTR) eliminated the response. The reaction time to EFPs is extremely short, with many responses initiated within 2 ms of the EFP. Large neurons, such as Mauthner cells, show heightened sensitivity to extracellular voltage gradients. We therefore tested whether the rapid response to EFPs was due to direct activation of the Mauthner cells, bypassing delays imposed by stimulus detection and transmission by sensory cells. Consistent with this, calcium imaging indicated that EFPs robustly activated the Mauthner cell but only rarely fired other reticulospinal neurons. Further supporting this idea, pharmacological blockade of synaptic transmission in zebrafish did not affect Mauthner cell activity in response to EFPs. Moreover, Mauthner cells transgenically expressing a tetrodotoxin (TTX)-resistant voltage-gated sodium channel retained responses to EFPs despite TTX suppression of action potentials in the rest of the brain. We propose that EFPs directly activate Mauthner cells because of their large size, thereby driving ultrarapid escape responses in fish.",
    url = "https://doi.org/10.1152/jn.00228.2014",
    doi = "10.1152/jn.00228.2014",
    openalex = "W2006611223",
    references = "doi101016s1546509808600515"
}

@article{doi101016jphysbeh201506036,
    author = "Dunlap, Kent D. and Ragazzi, Michael",
    title = "Thermal acclimation and thyroxine treatment modify the electric organ discharge frequency in an electric fish, Apteronotus leptorhynchus",
    year = "2015",
    journal = "Physiology \& Behavior",
    url = "https://doi.org/10.1016/j.physbeh.2015.06.036",
    doi = "10.1016/j.physbeh.2015.06.036",
    openalex = "W782284442",
    references = "doi101242jeb059444"
}

BACKGROUND: With its unique ability to produce high-voltage electric discharges in excess of 600 volts, the South American strong voltage electric eel (Electrophorus electricus) has played an important role in the history of science. Remarkably little is understood about the molecular nature of its electric organs. RESULTS: We present an in-depth analysis of the genome of E. electricus, including the transcriptomes of eight mature tissues: brain, spinal cord, kidney, heart, skeletal muscle, Sachs' electric organ, main electric organ, and Hunter's electric organ. A gene set enrichment analysis based on gene ontology reveals enriched functions in all three electric organs related to transmembrane transport, androgen binding, and signaling. This study also represents the first analysis of miRNA in electric fish. It identified a number of miRNAs displaying electric organ-specific expression patterns, including one novel miRNA highly over-expressed in all three electric organs of E. electricus. All three electric organ tissues also express three conserved miRNAs that have been reported to inhibit muscle development in mammals, suggesting that miRNA-dependent regulation of gene expression might play an important role in specifying an electric organ identity from its muscle precursor. These miRNA data were supported using another complete miRNA profile from muscle and electric organ tissues of a second gymnotiform species. CONCLUSIONS: Our work on the E. electricus genome and eight tissue-specific gene expression profiles will greatly facilitate future research on determining the coding and regulatory sequences that specify the function, development, and evolution of electric organs. Moreover, these data and future studies will be informed by the first comprehensive analysis of miRNA expression in an electric fish presented here.

@article{doi101186s1286401512888,
    author = "Traeger, Lindsay L. and Volkening, Jeremy D. and Moffett, Howell and Gallant, Jason R. and Chen, Po-Hao and Novina, Carl D. and Phillips, George N and Anand, René and Wells, Gregg B. and Pinch, Matthew and Güth, Robert and Unguez, Graciela A. and Albert, James S. and Zakon, Harold H. and Sussman, Michael R. and Samanta, Manoj P.",
    title = "Unique patterns of transcript and miRNA expression in the South American strong voltage electric eel (Electrophorus electricus)",
    year = "2015",
    journal = "BMC Genomics",
    abstract = "BACKGROUND: With its unique ability to produce high-voltage electric discharges in excess of 600 volts, the South American strong voltage electric eel (Electrophorus electricus) has played an important role in the history of science. Remarkably little is understood about the molecular nature of its electric organs. RESULTS: We present an in-depth analysis of the genome of E. electricus, including the transcriptomes of eight mature tissues: brain, spinal cord, kidney, heart, skeletal muscle, Sachs' electric organ, main electric organ, and Hunter's electric organ. A gene set enrichment analysis based on gene ontology reveals enriched functions in all three electric organs related to transmembrane transport, androgen binding, and signaling. This study also represents the first analysis of miRNA in electric fish. It identified a number of miRNAs displaying electric organ-specific expression patterns, including one novel miRNA highly over-expressed in all three electric organs of E. electricus. All three electric organ tissues also express three conserved miRNAs that have been reported to inhibit muscle development in mammals, suggesting that miRNA-dependent regulation of gene expression might play an important role in specifying an electric organ identity from its muscle precursor. These miRNA data were supported using another complete miRNA profile from muscle and electric organ tissues of a second gymnotiform species. CONCLUSIONS: Our work on the E. electricus genome and eight tissue-specific gene expression profiles will greatly facilitate future research on determining the coding and regulatory sequences that specify the function, development, and evolution of electric organs. Moreover, these data and future studies will be informed by the first comprehensive analysis of miRNA expression in an electric fish presented here.",
    url = "https://doi.org/10.1186/s12864-015-1288-8",
    doi = "10.1186/s12864-015-1288-8",
    openalex = "W2016184947",
    references = "doi101007bf00818163, doi101016jdevcel200910013, doi101038nature03702, doi101038ng0506500, doi101093bioinformaticsbtl140, doi101093nargkj112, doi101093nargkq1027, doi101126science28253941711, doi1012019781003036401, doi101242jeb082404, doi101242jeb082628, doi101261rna2183803, kirschbaum2008ontogeny"
}

BACKGROUND: African weakly-electric fishes of the family Mormyridae are able to produce and perceive weak electric signals (typically less than one volt in amplitude) owing to the presence of a specialized, muscle-derived electric organ (EO) in their tail region. Such electric signals, also known as Electric Organ Discharges (EODs), are used for objects/prey localization, for the identification of conspecifics, and in social and reproductive behaviour. This feature might have promoted the adaptive radiation of this family by acting as an effective pre-zygotic isolation mechanism. Despite the physiological and evolutionary importance of this trait, the investigation of the genetic basis of its function and modification has so far remained limited. In this study, we aim at: i) identifying constitutive differences in terms of gene expression between electric organ and skeletal muscle (SM) in two mormyrid species of the genus Campylomormyrus: C. compressirostris and C. tshokwe, and ii) exploring cross-specific patterns of gene expression within the two tissues among C. compressirostris, C. tshokwe, and the outgroup species Gnathonemus petersii. RESULTS: Twelve paired-end (100 bp) strand-specific RNA-seq Illumina libraries were sequenced, producing circa 330 M quality-filtered short read pairs. The obtained reads were assembled de novo into four reference transcriptomes. In silico cross-tissue DE-analysis allowed us to identify 271 shared differentially expressed genes between EO and SM in C. compressirostris and C.tshokwe. Many of these genes correspond to myogenic factors, ion channels and pumps, and genes involved in several metabolic pathways. Cross-species analysis has revealed that the electric organ transcriptome is more variable in terms of gene expression levels across species than the skeletal muscle transcriptome. CONCLUSIONS: The data obtained indicate that: i) the loss of contractile activity and the decoupling of the excitation-contraction processes are reflected by the down-regulation of the corresponding genes in the electric organ's transcriptome; ii) the metabolic activity of the EO might be specialized towards the production and turn-over of membrane structures; iii) several ion channels are highly expressed in the EO in order to increase excitability; iv) several myogenic factors might be down-regulated by transcription repressors in the EO.

@article{doi101186s1286401518589,
    author = "Lamanna, Francesco and Kirschbaum, Frank and Waurick, Isabelle and Dieterich, Christoph and Tiedemann, Ralph",
    title = "Cross-tissue and cross-species analysis of gene expression in skeletal muscle and electric organ of African weakly-electric fish (Teleostei; Mormyridae)",
    year = "2015",
    journal = "BMC Genomics",
    abstract = "BACKGROUND: African weakly-electric fishes of the family Mormyridae are able to produce and perceive weak electric signals (typically less than one volt in amplitude) owing to the presence of a specialized, muscle-derived electric organ (EO) in their tail region. Such electric signals, also known as Electric Organ Discharges (EODs), are used for objects/prey localization, for the identification of conspecifics, and in social and reproductive behaviour. This feature might have promoted the adaptive radiation of this family by acting as an effective pre-zygotic isolation mechanism. Despite the physiological and evolutionary importance of this trait, the investigation of the genetic basis of its function and modification has so far remained limited. In this study, we aim at: i) identifying constitutive differences in terms of gene expression between electric organ and skeletal muscle (SM) in two mormyrid species of the genus Campylomormyrus: C. compressirostris and C. tshokwe, and ii) exploring cross-specific patterns of gene expression within the two tissues among C. compressirostris, C. tshokwe, and the outgroup species Gnathonemus petersii. RESULTS: Twelve paired-end (100 bp) strand-specific RNA-seq Illumina libraries were sequenced, producing circa 330 M quality-filtered short read pairs. The obtained reads were assembled de novo into four reference transcriptomes. In silico cross-tissue DE-analysis allowed us to identify 271 shared differentially expressed genes between EO and SM in C. compressirostris and C.tshokwe. Many of these genes correspond to myogenic factors, ion channels and pumps, and genes involved in several metabolic pathways. Cross-species analysis has revealed that the electric organ transcriptome is more variable in terms of gene expression levels across species than the skeletal muscle transcriptome. CONCLUSIONS: The data obtained indicate that: i) the loss of contractile activity and the decoupling of the excitation-contraction processes are reflected by the down-regulation of the corresponding genes in the electric organ's transcriptome; ii) the metabolic activity of the EO might be specialized towards the production and turn-over of membrane structures; iii) several ion channels are highly expressed in the EO in order to increase excitability; iv) several myogenic factors might be down-regulated by transcription repressors in the EO.",
    url = "https://doi.org/10.1186/s12864-015-1858-9",
    doi = "10.1186/s12864-015-1858-9",
    openalex = "W1835895259",
    references = "doi101007bf01047569, doi101186s1286401512888"
}

This review covers two topics: (1) "membrane potential of low magnitude and related electric fields (bioelectricity)" and (2) "cell migration under the guiding cue of electric fields (EF)."Membrane potentials for this "bioelectricity" arise from the segregation of charges by special molecular machines (pumps, transporters, ion channels) situated within the plasma membrane of each cell type (including eukaryotic non-neural animal cells). The arising patterns of ion gradients direct many cell- and molecular biological processes such as embryogenesis, wound healing, regeneration. Furthermore, EF are important as guiding cues for cell migration and are often overriding chemical or topographic cues. In osteoblasts, for instance, the directional information of EF is captured by charged transporters on the cell membrane and transferred into signaling mechanisms that modulate the cytoskeleton and motor proteins. This results in a persistent directional migration along an EF guiding cue. As an outlook, we discuss questions concerning the fluctuation of EF and the frequencies and mapping of the "electric" interior of the cell. Another exciting topic for further research is the modeling of field concepts for such distant, non-chemical cellular interactions.

@article{doi103389fphys201500143,
    author = "Funk, Richard H. W.",
    title = "Endogenous electric fields as guiding cue for cell migration",
    year = "2015",
    journal = "Frontiers in Physiology",
    abstract = {This review covers two topics: (1) "membrane potential of low magnitude and related electric fields (bioelectricity)" and (2) "cell migration under the guiding cue of electric fields (EF)."Membrane potentials for this "bioelectricity" arise from the segregation of charges by special molecular machines (pumps, transporters, ion channels) situated within the plasma membrane of each cell type (including eukaryotic non-neural animal cells). The arising patterns of ion gradients direct many cell- and molecular biological processes such as embryogenesis, wound healing, regeneration. Furthermore, EF are important as guiding cues for cell migration and are often overriding chemical or topographic cues. In osteoblasts, for instance, the directional information of EF is captured by charged transporters on the cell membrane and transferred into signaling mechanisms that modulate the cytoskeleton and motor proteins. This results in a persistent directional migration along an EF guiding cue. As an outlook, we discuss questions concerning the fluctuation of EF and the frequencies and mapping of the "electric" interior of the cell. Another exciting topic for further research is the modeling of field concepts for such distant, non-chemical cellular interactions.},
    url = "https://doi.org/10.3389/fphys.2015.00143",
    doi = "10.3389/fphys.2015.00143",
    openalex = "W1605126740",
    references = "doi101016jproghi200807001, doi101016s0092824005800084, doi101038nature04925, doi101038nrm3141, doi101038nrn3708, doi101083jcb10162023, doi101083jcb632614, doi101098rstb19520012, doi101098rstb20140218, doi101152physrev000202004"
}

@incollection{doi101016b9780128035924000195,
    author = "Dunlap, Kent D. and Silva, Ana and Smith, G. Troy and Zakon, Harold H.",
    title = "Weakly Electric Fish: Behavior, Neurobiology, and Neuroendocrinology",
    year = "2016",
    booktitle = "Elsevier eBooks",
    url = "https://doi.org/10.1016/b978-0-12-803592-4.00019-5",
    doi = "10.1016/b978-0-12-803592-4.00019-5",
    openalex = "W2584683512",
    references = "doi101242jeb059444"
}

@article{doi101016jjphysparis201610004,
    author = "Waddell, Joseph C. and Rodríguez-Cattáneo, Alejo and Caputi, Ángel A. and Crampton, William G. R.",
    title = "Electric organ discharges and near-field spatiotemporal patterns of the electromotive force in a sympatric assemblage of Neotropical electric knifefish",
    year = "2016",
    journal = "Journal of Physiology-Paris",
    url = "https://doi.org/10.1016/j.jphysparis.2016.10.004",
    doi = "10.1016/j.jphysparis.2016.10.004",
    openalex = "W2542456417",
    references = "doi101242jeb082628"
}

@article{doi101016jnanoen201607028,
    author = "Jie, Yang and Jiang, Qian and Zhang, Yue and Wang, Ning and Cao, Xia",
    title = "A structural bionic design: From electric organs to systematic triboelectric generators",
    year = "2016",
    journal = "Nano Energy",
    url = "https://doi.org/10.1016/j.nanoen.2016.07.028",
    doi = "10.1016/j.nanoen.2016.07.028",
    openalex = "W2483577093",
    references = "doi101113jphysiol1953sp004849, doi101242jeb082628"
}

Direct electric power generation using biological functions have become a research focus due to their low cost and cleanliness. Unlike major approaches using glucose fuels or microbial fuel cells (MFCs), we present a generation method with intrinsically high energy conversion efficiency and generation with arbitrary timing using living electric organs of Torpedo (electric rays) which are serially integrated electrocytes converting ATP into electric energy. We developed alternative nervous systems using fluid pressure to stimulate electrocytes by a neurotransmitter, acetylcholine (Ach), and demonstrated electric generation. Maximum voltage and current were 1.5 V and 0.64 mA, respectively, with a duration time of a few seconds. We also demonstrated energy accumulation in a capacitor. The current was far larger than that using general cells other than electrocytes (\textasciitilde pA level). The generation ability was confirmed against repetitive cycles and also after preservation for 1 day. This is the first step toward ATP-based energy harvesting devices.

@article{doi101038srep25899,
    author = "Tanaka, Yo and Funano, Shun-Ichi and Nishizawa, Yohei and Kamamichi, Norihiro and Nishinaka, Masahiro and Kitamori, Takehiko",
    title = "An electric generator using living Torpedo electric organs controlled by fluid pressure-based alternative nervous systems.",
    year = "2016",
    journal = "Scientific reports",
    abstract = "Direct electric power generation using biological functions have become a research focus due to their low cost and cleanliness. Unlike major approaches using glucose fuels or microbial fuel cells (MFCs), we present a generation method with intrinsically high energy conversion efficiency and generation with arbitrary timing using living electric organs of Torpedo (electric rays) which are serially integrated electrocytes converting ATP into electric energy. We developed alternative nervous systems using fluid pressure to stimulate electrocytes by a neurotransmitter, acetylcholine (Ach), and demonstrated electric generation. Maximum voltage and current were 1.5 V and 0.64 mA, respectively, with a duration time of a few seconds. We also demonstrated energy accumulation in a capacitor. The current was far larger than that using general cells other than electrocytes (\textasciitilde pA level). The generation ability was confirmed against repetitive cycles and also after preservation for 1 day. This is the first step toward ATP-based energy harvesting devices.",
    url = "https://pmc.ncbi.nlm.nih.gov/articles/PMC4886531/",
    doi = "10.1038/srep25899",
    openalex = "W2466402301",
    pmcid = "PMC4886531",
    pmid = "27241817",
    references = "doi101038260799a0, doi101038nature01748, doi101038nature08721, doi101038nature11477, doi101038nbt2269, doi101038nmat3606, doi101039c5lc00685f, doi101126science1146885, doi101126science1188302, doi101126science1217412"
}

Weakly electric freshwater fish use self-generated electric fields to image their worlds and communicate in the darkness of night and turbid waters. This active sensory/communication modality evolved independently in the freshwaters of South America and Africa, where hundreds of electric fish species are broadly and abundantly distributed. The adaptive advantages of the sensory capacity to forage and communicate in visually-unfavorable environments and outside the detection of visually-guided predators likely contributed to the broad success of these clades across a variety of Afrotropical and neotropical habitats. Here we consider the potentially high and limiting metabolic costs of the active sensory and communication signals that define the gymnotiform weakly electric fish of South America. Recent evidence from two well-studied species suggests that the metabolic costs of electrogenesis can be quite high, sometimes exceeding one-fourth of these fishes' daily energy budget. Supporting such an energetically expensive system has shaped a number of cellular, endocrine, and behavioral adaptations to restrain the metabolic costs of electrogenesis in general or in response to metabolic stress. Despite a suite of adaptations supporting electrogenesis, these weakly electric fish are vulnerable to metabolic stresses such as hypoxia and food restriction. In these conditions, fish reduce signal amplitude presumably as a function of absolute energy shortfall or as a proactive means to conserve energy. In either case, reducing signal amplitude compromises both sensory and communication performance. Such outcomes suggest that the higher metabolic cost of active sensing and communication in weakly electric fish compared with the sensory and communication systems in other neotropical fish might mean that weakly electric fish are disproportionately susceptible to harm from anthropogenic disturbances of neotropical aquatic habitats. Fully evaluating this possibility, however, will require broad comparative studies of metabolic energetics across the diverse clades of gymnotiform electric fish and in comparison to other nonelectric neotropical fishes.

@article{doi101093icbicw104,
    author = "Markham, Michael R. and Ban, Yue and McCauley, Austin G. and Maltby, Rosalie",
    title = "Energetics of Sensing and Communication in Electric Fish: A Blessing and a Curse in the Anthropocene?",
    year = "2016",
    journal = "Integrative and Comparative Biology",
    abstract = "Weakly electric freshwater fish use self-generated electric fields to image their worlds and communicate in the darkness of night and turbid waters. This active sensory/communication modality evolved independently in the freshwaters of South America and Africa, where hundreds of electric fish species are broadly and abundantly distributed. The adaptive advantages of the sensory capacity to forage and communicate in visually-unfavorable environments and outside the detection of visually-guided predators likely contributed to the broad success of these clades across a variety of Afrotropical and neotropical habitats. Here we consider the potentially high and limiting metabolic costs of the active sensory and communication signals that define the gymnotiform weakly electric fish of South America. Recent evidence from two well-studied species suggests that the metabolic costs of electrogenesis can be quite high, sometimes exceeding one-fourth of these fishes' daily energy budget. Supporting such an energetically expensive system has shaped a number of cellular, endocrine, and behavioral adaptations to restrain the metabolic costs of electrogenesis in general or in response to metabolic stress. Despite a suite of adaptations supporting electrogenesis, these weakly electric fish are vulnerable to metabolic stresses such as hypoxia and food restriction. In these conditions, fish reduce signal amplitude presumably as a function of absolute energy shortfall or as a proactive means to conserve energy. In either case, reducing signal amplitude compromises both sensory and communication performance. Such outcomes suggest that the higher metabolic cost of active sensing and communication in weakly electric fish compared with the sensory and communication systems in other neotropical fish might mean that weakly electric fish are disproportionately susceptible to harm from anthropogenic disturbances of neotropical aquatic habitats. Fully evaluating this possibility, however, will require broad comparative studies of metabolic energetics across the diverse clades of gymnotiform electric fish and in comparison to other nonelectric neotropical fishes.",
    url = "https://doi.org/10.1093/icb/icw104",
    doi = "10.1093/icb/icw104",
    openalex = "W2509763671",
    references = "doi101242jeb059444, doi101242jeb082628"
}

ABSTRACT The bluntnose knifefish genus BrachyhypopomusMago-Leccia, 1994, is diagnosed from other Rhamphichthyoidea (Rhamphichthyidae + Hypopomidae) by the presence of a disk-like ossification in the anterior portion of the palatoquadrate, and by the following external characters: short snout, 18.7-32.6% of head length (vs. 33.3-68.6% in Hypopomus, Gymnorhamphichthys, Iracema, and Rhamphichthys), absence of a paired accessory electric organ in the mental or humeral region (vs. presence in Hypopygus and Steatogenys), presence of 3-4 pectoral proximal radials (vs. 5 in Akawaio), presence of the antorbital + infraorbital, and the preopercular cephalic lateral line canal bones (vs. absence in Racenisia). Brachyhypopomus cannot be diagnosed unambiguously from Microsternarchus or from Procerusternarchus on the basis of external characters alone. Brachyhypopomus comprises 28 species. Here we describe 15 new species, and provide redescriptions of all 13 previously described species, based on meristic, morphometric, and other morphological characters. We include notes on ecology and natural history for each species, and provide regional dichotomous keys and distribution maps, based on the examination of 12,279 specimens from 2,787 museum lots. A lectotype is designated for Brachyhypopomus pinnicaudatus (Hopkins, Comfort, Bastian & Bass, 1990). Brachyhypopomus species are abundant in shallow lentic and slow-flowing freshwater habitats from southern Costa Rica and northern Venezuela to Uruguay and northern Argentina. Species diversity is highest in Greater Amazonia, where 20 species occur: B. alberti, new species, B. arrayae, new species, and B. cunia, new species, in the upper rio Madeira drainage; B. batesi, new species, in the central Amazon and rio Negro; B. beebei, B. brevirostris, B. regani, new species, B. sullivani, new species, and B. walteri, widespread through the Amazon and Orinoco basins and the Guianas; B. belindae, new species, in the central Amazon basin; B. benjamini, new species, and B. verdii, new species, in the upper Amazon basin; B. bennetti, in the upper, central, and lower Amazon, lower Tocantins, and upper Madeira basins; B. bullocki in the Orinoco, Negro and Essequibo drainages; B. diazi in the Orinoco Llanos; B. flavipomus, new species, and B. hamiltoni, new species, in the central and upper Amazon basin; B. hendersoni, new species, in the central Amazon, lower Negro and Essequibo basins; B. pinnicaudatus in the central and lower Amazon, lower, upper Madeira, lower Tocantins and Mearim basins, and coastal French Guiana; and B. provenzanoi, new species, in the upper Orinoco and upper Negro basins. Five species are known from the Paraná-Paraguay-Uruguay basin and adjacent southern Atlantic drainages: B. bombilla in the lower Paraná, upper, central, and lower Paraguay, Uruguay and Patos-Mirim drainages; B. brevirostris in the upper Paraguay basin; B. draco in the lower Paraná, lower Paraguay, Uruguay, Patos-Mirim, and Tramandaí basins; B. gauderio in the lower Paraná, upper, central, and lower Paraguay, Uruguay, Patos-Mirim and Tramandaí basins; and B. walteri in the lower Paraná and upper Paraguay basins. Two species occur in small Atlantic drainages of southern Brazil: B. janeiroensis in the São João, Paraíba and small intervening drainages; and B. jureiae in the Ribeira de Iguape and Una do Prelado. One species occurs in the middle and upper São Francisco basin: B. menezesi, new species. Three species occur in trans-Andean drainages: B. diazi in Caribbean drainages of northern Venezuela; B. occidentalis in Atlantic and Pacific drainages of southern Costa Rica and Panama to Darién, and the Maracaibo, Magdalena, Sinú and Atrato drainages; and B. palenque, new species, in Pacific drainages of Ecuador.

@article{doi1015901982022420150146,
    author = "Crampton, William G. R. and de Santana, Carlos David and Waddell, Joseph C. and Lovejoy, Nathan R.",
    title = "A taxonomic revision of the Neotropical electric fish genus Brachyhypopomus (Ostariophysi: Gymnotiformes: Hypopomidae), with descriptions of 15 new species",
    year = "2016",
    journal = "Neotropical Ichthyology",
    abstract = "ABSTRACT The bluntnose knifefish genus BrachyhypopomusMago-Leccia, 1994, is diagnosed from other Rhamphichthyoidea (Rhamphichthyidae + Hypopomidae) by the presence of a disk-like ossification in the anterior portion of the palatoquadrate, and by the following external characters: short snout, 18.7-32.6\% of head length (vs. 33.3-68.6\% in Hypopomus, Gymnorhamphichthys, Iracema, and Rhamphichthys), absence of a paired accessory electric organ in the mental or humeral region (vs. presence in Hypopygus and Steatogenys), presence of 3-4 pectoral proximal radials (vs. 5 in Akawaio), presence of the antorbital + infraorbital, and the preopercular cephalic lateral line canal bones (vs. absence in Racenisia). Brachyhypopomus cannot be diagnosed unambiguously from Microsternarchus or from Procerusternarchus on the basis of external characters alone. Brachyhypopomus comprises 28 species. Here we describe 15 new species, and provide redescriptions of all 13 previously described species, based on meristic, morphometric, and other morphological characters. We include notes on ecology and natural history for each species, and provide regional dichotomous keys and distribution maps, based on the examination of 12,279 specimens from 2,787 museum lots. A lectotype is designated for Brachyhypopomus pinnicaudatus (Hopkins, Comfort, Bastian \& Bass, 1990). Brachyhypopomus species are abundant in shallow lentic and slow-flowing freshwater habitats from southern Costa Rica and northern Venezuela to Uruguay and northern Argentina. Species diversity is highest in Greater Amazonia, where 20 species occur: B. alberti, new species, B. arrayae, new species, and B. cunia, new species, in the upper rio Madeira drainage; B. batesi, new species, in the central Amazon and rio Negro; B. beebei, B. brevirostris, B. regani, new species, B. sullivani, new species, and B. walteri, widespread through the Amazon and Orinoco basins and the Guianas; B. belindae, new species, in the central Amazon basin; B. benjamini, new species, and B. verdii, new species, in the upper Amazon basin; B. bennetti, in the upper, central, and lower Amazon, lower Tocantins, and upper Madeira basins; B. bullocki in the Orinoco, Negro and Essequibo drainages; B. diazi in the Orinoco Llanos; B. flavipomus, new species, and B. hamiltoni, new species, in the central and upper Amazon basin; B. hendersoni, new species, in the central Amazon, lower Negro and Essequibo basins; B. pinnicaudatus in the central and lower Amazon, lower, upper Madeira, lower Tocantins and Mearim basins, and coastal French Guiana; and B. provenzanoi, new species, in the upper Orinoco and upper Negro basins. Five species are known from the Paraná-Paraguay-Uruguay basin and adjacent southern Atlantic drainages: B. bombilla in the lower Paraná, upper, central, and lower Paraguay, Uruguay and Patos-Mirim drainages; B. brevirostris in the upper Paraguay basin; B. draco in the lower Paraná, lower Paraguay, Uruguay, Patos-Mirim, and Tramandaí basins; B. gauderio in the lower Paraná, upper, central, and lower Paraguay, Uruguay, Patos-Mirim and Tramandaí basins; and B. walteri in the lower Paraná and upper Paraguay basins. Two species occur in small Atlantic drainages of southern Brazil: B. janeiroensis in the São João, Paraíba and small intervening drainages; and B. jureiae in the Ribeira de Iguape and Una do Prelado. One species occurs in the middle and upper São Francisco basin: B. menezesi, new species. Three species occur in trans-Andean drainages: B. diazi in Caribbean drainages of northern Venezuela; B. occidentalis in Atlantic and Pacific drainages of southern Costa Rica and Panama to Darién, and the Maracaibo, Magdalena, Sinú and Atrato drainages; and B. palenque, new species, in Pacific drainages of Ecuador.",
    url = "https://doi.org/10.1590/1982-0224-20150146",
    doi = "10.1590/1982-0224-20150146",
    openalex = "W2584841654",
    references = "doi101007s003590050098, doi101242jeb082628"
}

In most electric fish species, the electric organ (EO) derives from striated muscle cells that suppress many muscle properties.In the gymnotiform Sternopygus macrurus, mature electrocytes, the current-producing cells of the EO, do not contain sarcomeres, yet they continue to make some cytoskeletal and sarcomeric proteins and the muscle transcription factors (MTFs) that induce their expression.In order to more comprehensively examine the transcriptional regulation of genes associated with the formation and maintenance of the contractile sarcomere complex, results from expression analysis using qRT-PCR were informed by deep RNA sequencing of transcriptomes and miRNA compositions of muscle and EO tissues from adult S. macrurus.Our data show that: 1) components associated with the homeostasis of the sarcomere and sarcomere-sarcolemma linkage were transcribed in EO at levels similar to those in muscle; 2) MTF families associated with activation of the skeletal muscle program were not differentially expressed between these tissues; and 3) a set of miRNAs that are implicated in regulation of the muscle phenotype are enriched in EO.These data support the development of a unique and highly specialized non-contractile electrogenic cell that emerges from a striated phenotype and further differentiates with little modification in its transcript composition.This comprehensive analysis of parallel mRNA and miRNA profiles is not only a foundation for functional studies aimed at identifying mechanisms underlying the transcription-independent myogenic program in S. macrurus EO, but also has important implications to many vertebrate cell types that independently activate or suppress specific features of the skeletal muscle program.

@misc{doi107287peerj1828v01reviews1,
    title = {Peer Review \#1 of "The myogenic electric organ of Sternopygus macrurus: a non-contractile tissue with a skeletal muscle transcriptome (v0.1)"},
    year = "2016",
    abstract = "In most electric fish species, the electric organ (EO) derives from striated muscle cells that suppress many muscle properties.In the gymnotiform Sternopygus macrurus, mature electrocytes, the current-producing cells of the EO, do not contain sarcomeres, yet they continue to make some cytoskeletal and sarcomeric proteins and the muscle transcription factors (MTFs) that induce their expression.In order to more comprehensively examine the transcriptional regulation of genes associated with the formation and maintenance of the contractile sarcomere complex, results from expression analysis using qRT-PCR were informed by deep RNA sequencing of transcriptomes and miRNA compositions of muscle and EO tissues from adult S. macrurus.Our data show that: 1) components associated with the homeostasis of the sarcomere and sarcomere-sarcolemma linkage were transcribed in EO at levels similar to those in muscle; 2) MTF families associated with activation of the skeletal muscle program were not differentially expressed between these tissues; and 3) a set of miRNAs that are implicated in regulation of the muscle phenotype are enriched in EO.These data support the development of a unique and highly specialized non-contractile electrogenic cell that emerges from a striated phenotype and further differentiates with little modification in its transcript composition.This comprehensive analysis of parallel mRNA and miRNA profiles is not only a foundation for functional studies aimed at identifying mechanisms underlying the transcription-independent myogenic program in S. macrurus EO, but also has important implications to many vertebrate cell types that independently activate or suppress specific features of the skeletal muscle program.",
    url = "https://doi.org/10.7287/peerj.1828v0.1/reviews/1",
    doi = "10.7287/peerj.1828v0.1/reviews/1",
    openalex = "W4242822385",
    references = "doi101242jeb082404"
}

In most electric fish species, the electric organ (EO) derives from striated muscle cells that suppress many muscle properties.In the gymnotiform Sternopygus macrurus, mature electrocytes, the current-producing cells of the EO, do not contain sarcomeres, yet they continue to make some cytoskeletal and sarcomeric proteins and the muscle transcription factors (MTFs) that induce their expression.In order to more comprehensively examine the transcriptional regulation of genes associated with the formation and maintenance of the contractile sarcomere complex, results from expression analysis using qRT-PCR were informed by deep RNA sequencing of transcriptomes and miRNA compositions of muscle and EO tissues from adult S. macrurus.Our data show that: 1) components associated with the homeostasis of the sarcomere and sarcomere-sarcolemma linkage were transcribed in EO at levels similar to those in muscle; 2) MTF families associated with activation of the skeletal muscle program were not differentially expressed between these tissues; and 3) a set of miRNAs that are implicated in regulation of the muscle phenotype are enriched in EO.These data support the development of a unique and highly specialized non-contractile electrogenic cell that emerges from a striated phenotype and further differentiates with little modification in its transcript composition.This comprehensive analysis of parallel mRNA and miRNA profiles is not only a foundation for functional studies aimed at identifying mechanisms underlying the transcription-independent myogenic program in S. macrurus EO, but also has important implications to many vertebrate cell types that independently activate or suppress specific features of the skeletal muscle program.

@misc{doi107287peerj1828v01reviews3,
    author = "Crampton, W",
    title = {Peer Review \#3 of "The myogenic electric organ of Sternopygus macrurus: a non-contractile tissue with a skeletal muscle transcriptome (v0.1)"},
    year = "2016",
    abstract = "In most electric fish species, the electric organ (EO) derives from striated muscle cells that suppress many muscle properties.In the gymnotiform Sternopygus macrurus, mature electrocytes, the current-producing cells of the EO, do not contain sarcomeres, yet they continue to make some cytoskeletal and sarcomeric proteins and the muscle transcription factors (MTFs) that induce their expression.In order to more comprehensively examine the transcriptional regulation of genes associated with the formation and maintenance of the contractile sarcomere complex, results from expression analysis using qRT-PCR were informed by deep RNA sequencing of transcriptomes and miRNA compositions of muscle and EO tissues from adult S. macrurus.Our data show that: 1) components associated with the homeostasis of the sarcomere and sarcomere-sarcolemma linkage were transcribed in EO at levels similar to those in muscle; 2) MTF families associated with activation of the skeletal muscle program were not differentially expressed between these tissues; and 3) a set of miRNAs that are implicated in regulation of the muscle phenotype are enriched in EO.These data support the development of a unique and highly specialized non-contractile electrogenic cell that emerges from a striated phenotype and further differentiates with little modification in its transcript composition.This comprehensive analysis of parallel mRNA and miRNA profiles is not only a foundation for functional studies aimed at identifying mechanisms underlying the transcription-independent myogenic program in S. macrurus EO, but also has important implications to many vertebrate cell types that independently activate or suppress specific features of the skeletal muscle program.",
    url = "https://doi.org/10.7287/peerj.1828v0.1/reviews/3",
    doi = "10.7287/peerj.1828v0.1/reviews/3",
    openalex = "W4234383995",
    references = "doi101242jeb082404"
}

In most electric fish species, the electric organ (EO) derives from striated muscle cells that suppress many muscle properties.In the gymnotiform Sternopygus macrurus, mature electrocytes, the current-producing cells of the EO, do not contain sarcomeres, yet they continue to make some cytoskeletal and sarcomeric proteins and the muscle transcription factors (MTFs) that induce their expression.In order to more comprehensively examine the transcriptional regulation of genes associated with the formation and maintenance of the contractile sarcomere complex, results from expression analysis using qRT-PCR were informed by deep RNA sequencing of transcriptomes and miRNA compositions of muscle and EO tissues from adult S. macrurus.Our data show that: 1) components associated with the homeostasis of the sarcomere and sarcomere-sarcolemma linkage were transcribed in EO at levels similar to those in muscle; 2) MTF families associated with activation of the skeletal muscle program were not differentially expressed between these tissues; and 3) a set of miRNAs that are implicated in regulation of the muscle phenotype are enriched in EO.These data support the development of a unique and highly specialized non-contractile electrogenic cell that emerges from a striated phenotype and further differentiates with little modification in its transcript composition.This comprehensive analysis of parallel mRNA and miRNA profiles is not only a foundation for functional studies aimed at identifying mechanisms underlying the transcription-independent myogenic program in S. macrurus EO, but also has important implications to many vertebrate cell types that independently activate or suppress specific features of the skeletal muscle program.

@misc{doi107287peerj1828v02reviews3,
    author = "Crampton, W",
    title = {Peer Review \#3 of "The myogenic electric organ of Sternopygus macrurus: a non-contractile tissue with a skeletal muscle transcriptome (v0.2)"},
    year = "2016",
    abstract = "In most electric fish species, the electric organ (EO) derives from striated muscle cells that suppress many muscle properties.In the gymnotiform Sternopygus macrurus, mature electrocytes, the current-producing cells of the EO, do not contain sarcomeres, yet they continue to make some cytoskeletal and sarcomeric proteins and the muscle transcription factors (MTFs) that induce their expression.In order to more comprehensively examine the transcriptional regulation of genes associated with the formation and maintenance of the contractile sarcomere complex, results from expression analysis using qRT-PCR were informed by deep RNA sequencing of transcriptomes and miRNA compositions of muscle and EO tissues from adult S. macrurus.Our data show that: 1) components associated with the homeostasis of the sarcomere and sarcomere-sarcolemma linkage were transcribed in EO at levels similar to those in muscle; 2) MTF families associated with activation of the skeletal muscle program were not differentially expressed between these tissues; and 3) a set of miRNAs that are implicated in regulation of the muscle phenotype are enriched in EO.These data support the development of a unique and highly specialized non-contractile electrogenic cell that emerges from a striated phenotype and further differentiates with little modification in its transcript composition.This comprehensive analysis of parallel mRNA and miRNA profiles is not only a foundation for functional studies aimed at identifying mechanisms underlying the transcription-independent myogenic program in S. macrurus EO, but also has important implications to many vertebrate cell types that independently activate or suppress specific features of the skeletal muscle program.",
    url = "https://doi.org/10.7287/peerj.1828v0.2/reviews/3",
    doi = "10.7287/peerj.1828v0.2/reviews/3",
    openalex = "W4246405094",
    references = "doi101242jeb082404"
}

In most electric fish species, the electric organ (EO) derives from striated muscle cells that suppress many muscle properties. In the gymnotiform Sternopygus macrurus, mature electrocytes, the current-producing cells of the EO, do not contain sarcomeres, yet they continue to make some cytoskeletal and sarcomeric proteins and the muscle transcription factors (MTFs) that induce their expression. In order to more comprehensively examine the transcriptional regulation of genes associated with the formation and maintenance of the contractile sarcomere complex, results from expression analysis using qRT-PCR were informed by deep RNA sequencing of transcriptomes and miRNA compositions of muscle and EO tissues from adult S. macrurus. Our data show that: (1) components associated with the homeostasis of the sarcomere and sarcomere-sarcolemma linkage were transcribed in EO at levels similar to those in muscle; (2) MTF families associated with activation of the skeletal muscle program were not differentially expressed between these tissues; and (3) a set of microRNAs that are implicated in regulation of the muscle phenotype are enriched in EO. These data support the development of a unique and highly specialized non-contractile electrogenic cell that emerges from a striated phenotype and further differentiates with little modification in its transcript composition. This comprehensive analysis of parallel mRNA and miRNA profiles is not only a foundation for functional studies aimed at identifying mechanisms underlying the transcription-independent myogenic program in S. macrurus EO, but also has important implications to many vertebrate cell types that independently activate or suppress specific features of the skeletal muscle program.

@article{doi107717peerj1828,
    author = "Pinch, Matthew and Güth, Robert and Samanta, Manoj P. and Chaidez, Alexander and Unguez, Graciela A.",
    title = "The myogenic electric organ of Sternopygus macrurus: a non-contractile tissue with a skeletal muscle transcriptome",
    year = "2016",
    journal = "PeerJ",
    abstract = "In most electric fish species, the electric organ (EO) derives from striated muscle cells that suppress many muscle properties. In the gymnotiform Sternopygus macrurus, mature electrocytes, the current-producing cells of the EO, do not contain sarcomeres, yet they continue to make some cytoskeletal and sarcomeric proteins and the muscle transcription factors (MTFs) that induce their expression. In order to more comprehensively examine the transcriptional regulation of genes associated with the formation and maintenance of the contractile sarcomere complex, results from expression analysis using qRT-PCR were informed by deep RNA sequencing of transcriptomes and miRNA compositions of muscle and EO tissues from adult S. macrurus. Our data show that: (1) components associated with the homeostasis of the sarcomere and sarcomere-sarcolemma linkage were transcribed in EO at levels similar to those in muscle; (2) MTF families associated with activation of the skeletal muscle program were not differentially expressed between these tissues; and (3) a set of microRNAs that are implicated in regulation of the muscle phenotype are enriched in EO. These data support the development of a unique and highly specialized non-contractile electrogenic cell that emerges from a striated phenotype and further differentiates with little modification in its transcript composition. This comprehensive analysis of parallel mRNA and miRNA profiles is not only a foundation for functional studies aimed at identifying mechanisms underlying the transcription-independent myogenic program in S. macrurus EO, but also has important implications to many vertebrate cell types that independently activate or suppress specific features of the skeletal muscle program.",
    url = "https://doi.org/10.7717/peerj.1828",
    doi = "10.7717/peerj.1828",
    openalex = "W2338337517",
    references = "doi101186s1286401512888, doi101242jeb082404"
}

Convergent evolution is widely viewed as strong evidence for the influence of natural selection on the origin of phenotypic design. However, the emerging evo-devo synthesis has highlighted other processes that may bias and direct phenotypic evolution in the presence of environmental and genetic variation. Developmental biases on the production of phenotypic variation may channel the evolution of convergent forms by limiting the range of phenotypes produced during ontogeny. Here, we study the evolution and convergence of brachycephalic and dolichocephalic skull shapes among 133 species of Neotropical electric fishes (Gymnotiformes: Teleostei) and identify potential developmental biases on phenotypic evolution. We plot the ontogenetic trajectories of neurocranial phenotypes in 17 species and document developmental modularity between the face and braincase regions of the skull. We recover a significant relationship between developmental covariation and relative skull length and a significant relationship between developmental covariation and ontogenetic disparity. We demonstrate that modularity and integration bias the production of phenotypes along the brachycephalic and dolichocephalic skull axis and contribute to multiple, independent evolutionary transformations to highly brachycephalic and dolichocephalic skull morphologies.

@article{doi101002ece32704,
    author = "Evans, Kory M. and Waltz, Brandon T. and Tagliacollo., Victor Alberto and Chakrabarty, Prosanta and Albert, James S.",
    title = "Why the short face? Developmental disintegration of the neurocranium drives convergent evolution in neotropical electric fishes",
    year = "2017",
    journal = "Ecology and Evolution",
    abstract = "Convergent evolution is widely viewed as strong evidence for the influence of natural selection on the origin of phenotypic design. However, the emerging evo-devo synthesis has highlighted other processes that may bias and direct phenotypic evolution in the presence of environmental and genetic variation. Developmental biases on the production of phenotypic variation may channel the evolution of convergent forms by limiting the range of phenotypes produced during ontogeny. Here, we study the evolution and convergence of brachycephalic and dolichocephalic skull shapes among 133 species of Neotropical electric fishes (Gymnotiformes: Teleostei) and identify potential developmental biases on phenotypic evolution. We plot the ontogenetic trajectories of neurocranial phenotypes in 17 species and document developmental modularity between the face and braincase regions of the skull. We recover a significant relationship between developmental covariation and relative skull length and a significant relationship between developmental covariation and ontogenetic disparity. We demonstrate that modularity and integration bias the production of phenotypes along the brachycephalic and dolichocephalic skull axis and contribute to multiple, independent evolutionary transformations to highly brachycephalic and dolichocephalic skull morphologies.",
    url = "https://doi.org/10.1002/ece3.2704",
    doi = "10.1002/ece3.2704",
    openalex = "W2588416571",
    references = "doi101016c20100662092, doi101093bioinformaticsbtg412, doi101093oso97801951223430010001, doi101093oso97801985052350010001, doi101111j001438202003tb00285x, doi101111j13652435200701283x, doi101111j155856461985tb00420x, doi101111j17550998201002924x, doi101111j251761611996tb02080x, kirschbaum2008ontogeny, openalexw2611511275"
}

Ostariophysi is a superorder of bony fishes including more than 10,300 species in 1100 genera and 70 families. This superorder is traditionally divided into five major groups (orders): Gonorynchiformes (milkfishes and sandfishes), Cypriniformes (carps and minnows), Characiformes (tetras and their allies), Siluriformes (catfishes), and Gymnotiformes (electric knifefishes). Unambiguous resolution of the relationships among these lineages remains elusive, with previous molecular and morphological analyses failing to produce a consensus phylogeny. In this study, we use over 350 ultraconserved element (UCEs) loci comprising 5 million base pairs collected across 35 representative ostariophysan species to compile one of the most data-rich phylogenies of fishes to date. We use these data to infer higher level (interordinal) relationships among ostariophysan fishes, focusing on the monophyly of the Characiformes-one of the most contentiously debated groups in fish systematics. As with most previous molecular studies, we recover a non-monophyletic Characiformes with the two monophyletic suborders, Citharinoidei and Characoidei, more closely related to other ostariophysan clades than to each other. We also explore incongruence between results from different UCE data sets, issues of orthology, and the use of morphological characters in combination with our molecular data. [Conserved sequence; ichthyology; massively parallel sequencing; morphology; next-generation sequencing; UCEs.].

@article{doi101093sysbiosyx038,
    author = "Chakrabarty, Prosanta and Faircloth, Brant C. and Alda, Fernando and Ludt, William B. and McMahan, Caleb D. and Near, Thomas J. and Dornburg, Alex and Albert, James S. and Arroyave, Jairo and Stiassny, Melanie L. J. and Sorenson, Laurie and Alfaro, Michael E.",
    title = "Phylogenomic Systematics of Ostariophysan Fishes: Ultraconserved Elements Support the Surprising Non-Monophyly of Characiformes",
    year = "2017",
    journal = "Systematic Biology",
    abstract = "Ostariophysi is a superorder of bony fishes including more than 10,300 species in 1100 genera and 70 families. This superorder is traditionally divided into five major groups (orders): Gonorynchiformes (milkfishes and sandfishes), Cypriniformes (carps and minnows), Characiformes (tetras and their allies), Siluriformes (catfishes), and Gymnotiformes (electric knifefishes). Unambiguous resolution of the relationships among these lineages remains elusive, with previous molecular and morphological analyses failing to produce a consensus phylogeny. In this study, we use over 350 ultraconserved element (UCEs) loci comprising 5 million base pairs collected across 35 representative ostariophysan species to compile one of the most data-rich phylogenies of fishes to date. We use these data to infer higher level (interordinal) relationships among ostariophysan fishes, focusing on the monophyly of the Characiformes-one of the most contentiously debated groups in fish systematics. As with most previous molecular studies, we recover a non-monophyletic Characiformes with the two monophyletic suborders, Citharinoidei and Characoidei, more closely related to other ostariophysan clades than to each other. We also explore incongruence between results from different UCE data sets, issues of orthology, and the use of morphological characters in combination with our molecular data. [Conserved sequence; ichthyology; massively parallel sequencing; morphology; next-generation sequencing; UCEs.].",
    url = "https://doi.org/10.1093/sysbio/syx038",
    doi = "10.1093/sysbio/syx038",
    openalex = "W2594557998",
    references = "doi1011861471214811275, openalexw63312880"
}

) is unusual among electric fishes because it has three pairs of electric organs that serve multiple biological functions: For navigation and communication, it emits continuous pulses of weak electric discharge (<1 V), but for predation and defense, it intermittently emits lethal strong electric discharges (10 to 600 V). We hypothesized that these two electrogenic outputs have different energetic demands reflected by differences in their proteome and phosphoproteome. We report the use of isotope-assisted quantitative mass spectrometry to test this hypothesis. We observed novel phosphorylation sites in sodium transporters and identified a potassium channel with unique differences in protein concentration among the electric organs. In addition, we found transcription factors and protein kinases that show differential abundance in the strong versus weak electric organs. Our findings support the hypothesis that proteomic differences among electric organs underlie differences in energetic needs, reflecting a trade-off between generating weak voltages continuously and strong voltages intermittently.

@article{doi101126sciadv1700523,
    author = "Traeger, Lindsay L. and Sabat, Grzegorz and Barrett‐Wilt, Gregory A. and Wells, Gregg B. and Sussman, Michael R.",
    title = "A tail of two voltages: Proteomic comparison of the three electric organs of the electric eel",
    year = "2017",
    journal = "Science Advances",
    abstract = ") is unusual among electric fishes because it has three pairs of electric organs that serve multiple biological functions: For navigation and communication, it emits continuous pulses of weak electric discharge (<1 V), but for predation and defense, it intermittently emits lethal strong electric discharges (10 to 600 V). We hypothesized that these two electrogenic outputs have different energetic demands reflected by differences in their proteome and phosphoproteome. We report the use of isotope-assisted quantitative mass spectrometry to test this hypothesis. We observed novel phosphorylation sites in sodium transporters and identified a potassium channel with unique differences in protein concentration among the electric organs. In addition, we found transcription factors and protein kinases that show differential abundance in the strong versus weak electric organs. Our findings support the hypothesis that proteomic differences among electric organs underlie differences in energetic needs, reflecting a trade-off between generating weak voltages continuously and strong voltages intermittently.",
    url = "https://doi.org/10.1126/sciadv.1700523",
    doi = "10.1126/sciadv.1700523",
    openalex = "W2727348908",
    references = "doi101186s1286401512888"
}

Abstract The evolution of sexually dimorphic traits is thought to have marked effects on underlying patterns of static allometry. These traits can negatively affect organismal survivability by creating trade-offs between trait size and performance. Here we use three-dimensional geometric morphometrics to study the static allometry of two species of sexually dimorphic electric fishes (Apteronotus rostratus and Compsaraia samueli) in which mature males grow elongate jaws used in agonistic male–male interactions. We also estimate jaw-closing performance between the sexes of both species to track changes in kinematic transmission associated with the development of sexual weaponry. We find significantly different patterns of static allometry between the sexes of both species, with males exhibiting more positive allometric slopes relative to females. We also find a negative relationship between skull shape and mandibular kinematic transmission in C. samueli, suggesting a trade-off where males with longer faces exhibit lower mechanical advantages, suggesting weaker jaw leverage. In contrast, males and females of A. rostratus exhibit no difference between sexes in mechanical advantage associated with facial elongation.

@article{doi101093zoolinneanzly076,
    author = "Evans, Kory M and Bernt, Maxwell J. and Kolmann, Matthew A. and Ford, Kassandra and Albert, James S.",
    title = "Why the long face? Static allometry in the sexually dimorphic phenotypes of Neotropical electric fishes",
    year = "2018",
    journal = "Zoological Journal of the Linnean Society",
    abstract = "Abstract The evolution of sexually dimorphic traits is thought to have marked effects on underlying patterns of static allometry. These traits can negatively affect organismal survivability by creating trade-offs between trait size and performance. Here we use three-dimensional geometric morphometrics to study the static allometry of two species of sexually dimorphic electric fishes (Apteronotus rostratus and Compsaraia samueli) in which mature males grow elongate jaws used in agonistic male–male interactions. We also estimate jaw-closing performance between the sexes of both species to track changes in kinematic transmission associated with the development of sexual weaponry. We find significantly different patterns of static allometry between the sexes of both species, with males exhibiting more positive allometric slopes relative to females. We also find a negative relationship between skull shape and mandibular kinematic transmission in C. samueli, suggesting a trade-off where males with longer faces exhibit lower mechanical advantages, suggesting weaker jaw leverage. In contrast, males and females of A. rostratus exhibit no difference between sexes in mechanical advantage associated with facial elongation.",
    url = "https://doi.org/10.1093/zoolinnean/zly076",
    doi = "10.1093/zoolinnean/zly076",
    openalex = "W2903976749",
    references = "doi101002ece32704"
}

, displays a clear-cut example of non-breeding territorial aggression. The asymmetry in the behavior of dominants and subordinates is outstanding. Dominants are highly aggressive and subordinates signal submission in a precise sequence of locomotor and electric traits: retreating, decreasing their electric organ discharge rate, and emitting transient electric signals. The hypothalamic neuropeptide arginine-vasotocin (AVT) and its mammalian homolog arginine-vasopressin, are key modulators of social behavior, known to adapt their actions to different contexts. By analyzing the effects of pharmacological manipulations of the AVT system in both dominants and subordinates, we show evidence of distinct status-dependent actions of AVT. We demonstrate an endogenous effect of AVT on dominants' aggression levels: blocking the V1a AVT receptor induced a significant decrease in dominants' attack rate. AVT administered to subordinates enhanced the expression of the electric signals of submission, without affecting subordinates' locomotor displays. This study contributes a clear example of status-dependent AVT modulation of agonistic behavior in teleosts, and reveals distinctive activation patterns of the AVT system between dominants and subordinates.

@article{doi103389fnbeh201800001,
    author = "Perrone, Rossana and Silva, Ana",
    title = "Status-Dependent Vasotocin Modulation of Dominance and Subordination in the Weakly Electric Fish Gymnotus omarorum",
    year = "2018",
    journal = "Frontiers in Behavioral Neuroscience",
    abstract = ", displays a clear-cut example of non-breeding territorial aggression. The asymmetry in the behavior of dominants and subordinates is outstanding. Dominants are highly aggressive and subordinates signal submission in a precise sequence of locomotor and electric traits: retreating, decreasing their electric organ discharge rate, and emitting transient electric signals. The hypothalamic neuropeptide arginine-vasotocin (AVT) and its mammalian homolog arginine-vasopressin, are key modulators of social behavior, known to adapt their actions to different contexts. By analyzing the effects of pharmacological manipulations of the AVT system in both dominants and subordinates, we show evidence of distinct status-dependent actions of AVT. We demonstrate an endogenous effect of AVT on dominants' aggression levels: blocking the V1a AVT receptor induced a significant decrease in dominants' attack rate. AVT administered to subordinates enhanced the expression of the electric signals of submission, without affecting subordinates' locomotor displays. This study contributes a clear example of status-dependent AVT modulation of agonistic behavior in teleosts, and reveals distinctive activation patterns of the AVT system between dominants and subordinates.",
    url = "https://doi.org/10.3389/fnbeh.2018.00001",
    doi = "10.3389/fnbeh.2018.00001",
    openalex = "W2793318989",
    references = "doi101016s0066185670800012"
}

@incollection{doi10100797830302910514,
    author = "Gallant, Jason R.",
    title = "The Evolution and Development of Electric Organs",
    year = "2019",
    booktitle = "Springer handbook of auditory research",
    url = "https://doi.org/10.1007/978-3-030-29105-1\_4",
    doi = "10.1007/978-3-030-29105-1\_4",
    openalex = "W2988330838",
    references = "doi101002jez10157, doi101007bf01099098, doi101016jbiomaterials201510076, doi101016s0928425703000044, doi1010179781316106280006, doi101126science1254432, doi101152physrev1997773699, doi101186s1286401512888, doi101242dev122113371, doi101242jeb082404, doi101242jeb082628, doi101534genetics115178137, doi1023072485224, kirschbaum2008ontogeny"
}

Mosaic evolution refers to the pattern whereby different organismal traits exhibit differential rates of evolution typically due to reduced levels of trait covariation through deep time (i.e., modularity). These differences in rates can be attributed to variation in responses to selective pressures between individual traits. Differential responses to selective pressures also have the potential to facilitate functional specialization, allowing certain traits to track environmental stimuli more closely than others. The teleost skull is a multifunctional structure comprising a complex network of bones and thus an excellent system for which to study mosaic evolution. Here we construct an ultrametric phylogeny for a clade of Neotropical electric fishes (Apteronotidae: Gymnotiformes) and use three-dimensional geometric morphometrics to investigate patterns of mosaic evolution in the skull and jaws. We find strong support for a developmental, three-module hypothesis that consists of the face, braincase, and mandible, and we find that the mandible has evolved four times faster than its neighboring modules. We hypothesize that the functional specialization of the mandible in this group of fishes has allowed it to outpace the face and braincase and evolve in a more decoupled manner. We also hypothesize that this pattern of mosaicism may be widespread across other clades of teleost fishes.

@article{doi101093icbicz026,
    author = "Evans, Kory M. and Vidal‐García, Marta and Tagliacollo., Victor Alberto and Taylor, Samuel J and Fenolio, Danté B.",
    title = "Bony Patchwork: Mosaic Patterns of Evolution in the Skull of Electric Fishes (Apteronotidae: Gymnotiformes)",
    year = "2019",
    journal = "Integrative and Comparative Biology",
    abstract = "Mosaic evolution refers to the pattern whereby different organismal traits exhibit differential rates of evolution typically due to reduced levels of trait covariation through deep time (i.e., modularity). These differences in rates can be attributed to variation in responses to selective pressures between individual traits. Differential responses to selective pressures also have the potential to facilitate functional specialization, allowing certain traits to track environmental stimuli more closely than others. The teleost skull is a multifunctional structure comprising a complex network of bones and thus an excellent system for which to study mosaic evolution. Here we construct an ultrametric phylogeny for a clade of Neotropical electric fishes (Apteronotidae: Gymnotiformes) and use three-dimensional geometric morphometrics to investigate patterns of mosaic evolution in the skull and jaws. We find strong support for a developmental, three-module hypothesis that consists of the face, braincase, and mandible, and we find that the mandible has evolved four times faster than its neighboring modules. We hypothesize that the functional specialization of the mandible in this group of fishes has allowed it to outpace the face and braincase and evolve in a more decoupled manner. We also hypothesize that this pattern of mosaicism may be widespread across other clades of teleost fishes.",
    url = "https://doi.org/10.1093/icb/icz026",
    doi = "10.1093/icb/icz026",
    openalex = "W2944658967",
    references = "doi101002ece32704"
}

Electroreception, the capacity to detect external underwater electric fields with specialised receptors, is a phylogenetically widespread sensory modality in fishes and amphibians. In passive electroreception, a capacity possessed by c. 16% of fish species, an animal uses low-frequency-tuned ampullary electroreceptors to detect microvolt-range bioelectric fields from prey, without the need to generate its own electric field. In active electroreception (electrolocation), which occurs only in the teleost lineages Mormyroidea and Gymnotiformes, an animal senses its surroundings by generating a weak (50 V) EODs that facilitate communication or predation, but not electrolocation. Approximately 1.5% of fish species possess electric organs. This review has two aims. First, to synthesise our knowledge of the functional biology and phylogenetic distribution of electroreception and electrogenesis in fishes, with a focus on freshwater taxa and with emphasis on the proximate (morphological, physiological and genetic) bases of EOD and electroreceptor diversity. Second, to describe the diversity, biogeography, ecology and electric signal diversity of the mormyroids and gymnotiforms and to explore the ultimate (evolutionary) bases of signal and receptor diversity in their convergent electrogenic-electrosensory systems. Four sets of potential drivers or moderators of signal diversity are discussed. First, selective forces of an abiotic (environmental) nature for optimal electrolocation and communication performance of the EOD. Second, selective forces of a biotic nature targeting the communication function of the EOD, including sexual selection, reproductive interference from syntopic heterospecifics and selection from eavesdropping predators. Third, non-adaptive drift and, finally, phylogenetic inertia, which may arise from stabilising selection for optimal signal-receptor matching.

@article{doi101111jfb13922,
    author = "Crampton, William G. R.",
    title = "Electroreception, electrogenesis and electric signal evolution",
    year = "2019",
    journal = "Journal of Fish Biology",
    abstract = "Electroreception, the capacity to detect external underwater electric fields with specialised receptors, is a phylogenetically widespread sensory modality in fishes and amphibians. In passive electroreception, a capacity possessed by c. 16\% of fish species, an animal uses low-frequency-tuned ampullary electroreceptors to detect microvolt-range bioelectric fields from prey, without the need to generate its own electric field. In active electroreception (electrolocation), which occurs only in the teleost lineages Mormyroidea and Gymnotiformes, an animal senses its surroundings by generating a weak (50 V) EODs that facilitate communication or predation, but not electrolocation. Approximately 1.5\% of fish species possess electric organs. This review has two aims. First, to synthesise our knowledge of the functional biology and phylogenetic distribution of electroreception and electrogenesis in fishes, with a focus on freshwater taxa and with emphasis on the proximate (morphological, physiological and genetic) bases of EOD and electroreceptor diversity. Second, to describe the diversity, biogeography, ecology and electric signal diversity of the mormyroids and gymnotiforms and to explore the ultimate (evolutionary) bases of signal and receptor diversity in their convergent electrogenic-electrosensory systems. Four sets of potential drivers or moderators of signal diversity are discussed. First, selective forces of an abiotic (environmental) nature for optimal electrolocation and communication performance of the EOD. Second, selective forces of a biotic nature targeting the communication function of the EOD, including sexual selection, reproductive interference from syntopic heterospecifics and selection from eavesdropping predators. Third, non-adaptive drift and, finally, phylogenetic inertia, which may arise from stabilising selection for optimal signal-receptor matching.",
    url = "https://doi.org/10.1111/jfb.13922",
    doi = "10.1111/jfb.13922",
    openalex = "W2911749405",
    references = "doi101007bf01047569, doi101016jympev200909017, doi101016s0065345402800092, doi101016s1546509808600515, doi101038167201a0, doi101073pnas1011803107, doi101113jphysiol1953sp004849, doi101242jeb059444, doi101242jeb082404, doi101242jeb082628, doi101242jeb2043543, doi101371journalpone0036287"
}

, and the associated critical oxygen tension was 14.34 mmHg. Routine EOD rate was 5.68 Hz with an associated critical tension of 15.14 mmHg. These metabolic indicators of hypoxia tolerance measured in this study were consistent with those in previous studies on M. victoriae and other weakly electric fishes. Furthermore, our results suggest that some aerobic processes may be reduced in favour of maintaining the EOD rate under extreme hypoxia. These findings underscore the importance of the active electrosensory modality to these hypoxia-tolerant fish.

@article{doi101111jfb14234,
    author = "Moulton, Tyler L. and Chapman, Lauren J. and Krahe, Rüdiger",
    title = "Effects of hypoxia on aerobic metabolism and active electrosensory acquisition in the African weakly electric fish Marcusenius victoriae",
    year = "2019",
    journal = "Journal of Fish Biology",
    abstract = ", and the associated critical oxygen tension was 14.34 mmHg. Routine EOD rate was 5.68 Hz with an associated critical tension of 15.14 mmHg. These metabolic indicators of hypoxia tolerance measured in this study were consistent with those in previous studies on M. victoriae and other weakly electric fishes. Furthermore, our results suggest that some aerobic processes may be reduced in favour of maintaining the EOD rate under extreme hypoxia. These findings underscore the importance of the active electrosensory modality to these hypoxia-tolerant fish.",
    url = "https://doi.org/10.1111/jfb.14234",
    doi = "10.1111/jfb.14234",
    openalex = "W2995207679",
    references = "doi101242jeb059444"
}

The electric eel is a unique species that has evolved three electric organs. Since the 1950s, electric eels have generally been assumed to use these three organs to generate two forms of electric organ discharge (EOD): high-voltage EOD for predation and defense and low-voltage EOD for electrolocation and communication. However, why electric eels evolved three electric organs to generate two forms of EOD and how these three organs work together to generate these two forms of EOD have not been clear until now. Here, we present the third form of independent EOD of electric eels: middle-voltage EOD. We suggest that every form of EOD is generated by one electric organ independently and reveal the typical discharge order of the three electric organs. We also discuss hybrid EODs, which are combinations of these three independent EODs. This new finding indicates that the electric eel discharge behavior and physiology and the evolutionary purpose of the three electric organs are more complex than previously assumed. The purpose of the middle-voltage EOD still requires clarification.

@article{doi101038s41598021857153,
    author = "Xu, Jun and Cui, Xiang and Zhang, Huiyuan",
    title = "The third form electric organ discharge of electric eels",
    year = "2021",
    journal = "Scientific Reports",
    abstract = "The electric eel is a unique species that has evolved three electric organs. Since the 1950s, electric eels have generally been assumed to use these three organs to generate two forms of electric organ discharge (EOD): high-voltage EOD for predation and defense and low-voltage EOD for electrolocation and communication. However, why electric eels evolved three electric organs to generate two forms of EOD and how these three organs work together to generate these two forms of EOD have not been clear until now. Here, we present the third form of independent EOD of electric eels: middle-voltage EOD. We suggest that every form of EOD is generated by one electric organ independently and reveal the typical discharge order of the three electric organs. We also discuss hybrid EODs, which are combinations of these three independent EODs. This new finding indicates that the electric eel discharge behavior and physiology and the evolutionary purpose of the three electric organs are more complex than previously assumed. The purpose of the middle-voltage EOD still requires clarification.",
    url = "https://doi.org/10.1038/s41598-021-85715-3",
    doi = "10.1038/s41598-021-85715-3",
    openalex = "W3139350093",
    references = "doi101186s1286401512888"
}

. Coupling of the proposed methods with a boundary element modeling approach, we are thereby able to model the information gained and provided during agonistic encounters. The data indicate that the passive electrosensory input, in particular, provides sufficient information to localize a contender during the pre-contest phase, fish did not use or rely on the theoretically also available sensory information of the contest outcome-determining size difference between contenders before engaging in agonistic behavior.

@article{doi103389fnbeh2021718491,
    author = "Pedraja, Federico and Herzog, Hendrik and Engelmann, Jacob and Jung, Sarah Nicola",
    title = "The Use of Supervised Learning Models in Studying Agonistic Behavior and Communication in Weakly Electric Fish",
    year = "2021",
    journal = "Frontiers in Behavioral Neuroscience",
    abstract = ". Coupling of the proposed methods with a boundary element modeling approach, we are thereby able to model the information gained and provided during agonistic encounters. The data indicate that the passive electrosensory input, in particular, provides sufficient information to localize a contender during the pre-contest phase, fish did not use or rely on the theoretically also available sensory information of the contest outcome-determining size difference between contenders before engaging in agonistic behavior.",
    url = "https://doi.org/10.3389/fnbeh.2021.718491",
    doi = "10.3389/fnbeh.2021.718491",
    openalex = "W3205629474",
    references = "doi10100797830302910514"
}

Abstract DNA barcoding is a useful tool for identifying species; however, successful barcode-based identification requires a reference library of barcode sequences from accurately identified specimens. Here we present a reference library of COI barcode sequences for the Neotropical electric knifefish, order Gymnotiformes (Teleostei: Ostariophysi), a model taxon for studies of tropical diversification and biogeography, genomics, behaviour and neurobiology. Our library contains barcodes for 167 of the c. 270 valid species of gymnotiforms derived from geo-referenced museum voucher specimens, and includes sequences from 26 type specimens and 21 specimens from type localities, most of which we collected. To assess the state of gymnotiform barcodes in two main public barcode repositories, GenBank and BOLD, we compared the barcodes in these databases to our reference library. Our analysis shows that a considerable proportion of gymnotiform barcodes in GenBank and BOLD are mis- or unidentified. We encourage taxonomists to develop and publish barcode reference libraries composed of carefully curated barcode sequences.

@article{doi101093zoolinneanzlac039,
    author = "Janzen, Francesco H. and Crampton, William G. R. and Lovejoy, Nathan R.",
    title = "A new taxonomist-curated reference library of DNA barcodes for Neotropical electric fish (Teleostei: Gymnotiformes)",
    year = "2022",
    journal = "Zoological Journal of the Linnean Society",
    abstract = "Abstract DNA barcoding is a useful tool for identifying species; however, successful barcode-based identification requires a reference library of barcode sequences from accurately identified specimens. Here we present a reference library of COI barcode sequences for the Neotropical electric knifefish, order Gymnotiformes (Teleostei: Ostariophysi), a model taxon for studies of tropical diversification and biogeography, genomics, behaviour and neurobiology. Our library contains barcodes for 167 of the c. 270 valid species of gymnotiforms derived from geo-referenced museum voucher specimens, and includes sequences from 26 type specimens and 21 specimens from type localities, most of which we collected. To assess the state of gymnotiform barcodes in two main public barcode repositories, GenBank and BOLD, we compared the barcodes in these databases to our reference library. Our analysis shows that a considerable proportion of gymnotiform barcodes in GenBank and BOLD are mis- or unidentified. We encourage taxonomists to develop and publish barcode reference libraries composed of carefully curated barcode sequences.",
    url = "https://doi.org/10.1093/zoolinnean/zlac039",
    doi = "10.1093/zoolinnean/zlac039",
    openalex = "W4225346292",
    references = "doi10100797830302910514"
}

South American and African weakly electric fish independently evolved electric organs from muscle. In both groups, a voltage-gated sodium channel gene independently lost expression from muscle and gained it in the electric organ, allowing the channel to become specialized for generating electric signals. It is unknown how this voltage-gated sodium channel gene is targeted to muscle in any vertebrate. We describe an enhancer that selectively targets sodium channel expression to muscle. Next, we demonstrate how the loss of this enhancer, but not trans-activating factors, drove the loss of sodium channel gene expression from muscle in South American electric fish. While this enhancer is also altered in African electric fish, key transcription factor binding sites and enhancer activity are retained, suggesting that the convergent loss of sodium channel expression from muscle in these two electric fish lineages occurred via different processes.

@article{doi101126sciadvabm2970,
    author = "LaPotin, Sarah and Swartz, Mary E. and Luecke, David and Constantinou, Savvas J. and Gallant, Jason R. and Eberhart, Johann K. and Zakon, Harold H.",
    title = "Divergent cis-regulatory evolution underlies the convergent loss of sodium channel expression in electric fish",
    year = "2022",
    journal = "Science Advances",
    abstract = "South American and African weakly electric fish independently evolved electric organs from muscle. In both groups, a voltage-gated sodium channel gene independently lost expression from muscle and gained it in the electric organ, allowing the channel to become specialized for generating electric signals. It is unknown how this voltage-gated sodium channel gene is targeted to muscle in any vertebrate. We describe an enhancer that selectively targets sodium channel expression to muscle. Next, we demonstrate how the loss of this enhancer, but not trans-activating factors, drove the loss of sodium channel gene expression from muscle in South American electric fish. While this enhancer is also altered in African electric fish, key transcription factor binding sites and enhancer activity are retained, suggesting that the convergent loss of sodium channel expression from muscle in these two electric fish lineages occurred via different processes.",
    url = "https://doi.org/10.1126/sciadv.abm2970",
    doi = "10.1126/sciadv.abm2970",
    openalex = "W4281720259",
    references = "doi101186s1286401512888"
}

The Gymnotiformes, also known as the South American or Neotropical knifefishes, include the strongly electric Electrophorus electricus and many other weakly electric species. These fish possess specialised electric organs that are able to release electric discharges into the water, for electrolocation and communication, and sometimes for predation and defence. All Gymnotiform species possess a myogenic electric organ (mEO) derived from the muscle tissue, and members of the Apteronotidae family uniquely possess a neurogenic electric organ (nEOs) derived from the nervous tissue. A mEO may consist of 'Type A' electrocytes that develop within the tail muscle (for example, in Apteronotus leptorhynchus), or 'Type B' electrocytes that develop below the tail muscle (for example, in Brachyhypopomus gauderio). In this review, we discuss the diversity in the anatomy, electric discharge and development of electric organs found in different Gymnotiform species, as well as the ecological and environmental factors that have likely contributed to this diversity. We then describe various hypotheses regarding the evolution of electric organs, and discuss the potential evolutionary origin of the nEO: a pair of nerve cords that are located on either side of the aorta in B. gauderio, and which may have expanded and developed into a nEO in the Apteronotidae family during its evolution from a common ancestral species. Finally, we compare potential Gymnotiform phylogenies and their supporting evidence.

@article{doi101186s13227022001945,
    author = "Bray, Isabelle E. and Alshami, Ilham J. J. and Kudoh, Tetsuhiro",
    title = "The diversity and evolution of electric organs in Neotropical knifefishes",
    year = "2022",
    journal = "EvoDevo",
    abstract = "The Gymnotiformes, also known as the South American or Neotropical knifefishes, include the strongly electric Electrophorus electricus and many other weakly electric species. These fish possess specialised electric organs that are able to release electric discharges into the water, for electrolocation and communication, and sometimes for predation and defence. All Gymnotiform species possess a myogenic electric organ (mEO) derived from the muscle tissue, and members of the Apteronotidae family uniquely possess a neurogenic electric organ (nEOs) derived from the nervous tissue. A mEO may consist of 'Type A' electrocytes that develop within the tail muscle (for example, in Apteronotus leptorhynchus), or 'Type B' electrocytes that develop below the tail muscle (for example, in Brachyhypopomus gauderio). In this review, we discuss the diversity in the anatomy, electric discharge and development of electric organs found in different Gymnotiform species, as well as the ecological and environmental factors that have likely contributed to this diversity. We then describe various hypotheses regarding the evolution of electric organs, and discuss the potential evolutionary origin of the nEO: a pair of nerve cords that are located on either side of the aorta in B. gauderio, and which may have expanded and developed into a nEO in the Apteronotidae family during its evolution from a common ancestral species. Finally, we compare potential Gymnotiform phylogenies and their supporting evidence.",
    url = "https://doi.org/10.1186/s13227-022-00194-5",
    doi = "10.1186/s13227-022-00194-5",
    openalex = "W4221059480",
    references = "doi10100797830302910514"
}

The electric eel is known as the most powerful creature to generate electricity with a discharge voltage up to 860 V and peak current up to 1 A. These surprising properties are the results of billions of years of evolution on the electrical biological structure and bulk, and now have triggered great research interest in electric eel biomimetics for designing innovated configurations and components of energy storage and conversion devices. In this review, first, the bioelectrical behavior of electric eels is surveyed, followed by the physiological structure to reveal the discharge characteristics and principles of electric organs and electrocytes. Additionally, underlying electrochemical mechanisms and models for calculating the potential and current of electrocytes are presented. Central to this review is the recent progress of electric-eel-inspired innovations and applications for energy storage and conversion, particularly including novel power sources, triboelectric nanogenerators, and nanochannel ion-selective membranes for salinity gradient energy harvesting. Finally, insights on the challenges at the moment and the perspectives on the future research prospects are critically compiled. It is suggested that energy-related electric eel biomimetics will greatly boost the development of next-generation high performance, green, and functional electronics.

@article{doi101002smtd202201435,
    author = "Xiao, Xiangting and Mei, Yu and Deng, Wentao and Zou, Guoqiang and Hou, Hongshuai and Ji, Xiaobo",
    title = "Electric Eel Biomimetics for Energy Storage and Conversion",
    year = "2023",
    journal = "Small Methods",
    abstract = "The electric eel is known as the most powerful creature to generate electricity with a discharge voltage up to 860 V and peak current up to 1 A. These surprising properties are the results of billions of years of evolution on the electrical biological structure and bulk, and now have triggered great research interest in electric eel biomimetics for designing innovated configurations and components of energy storage and conversion devices. In this review, first, the bioelectrical behavior of electric eels is surveyed, followed by the physiological structure to reveal the discharge characteristics and principles of electric organs and electrocytes. Additionally, underlying electrochemical mechanisms and models for calculating the potential and current of electrocytes are presented. Central to this review is the recent progress of electric-eel-inspired innovations and applications for energy storage and conversion, particularly including novel power sources, triboelectric nanogenerators, and nanochannel ion-selective membranes for salinity gradient energy harvesting. Finally, insights on the challenges at the moment and the perspectives on the future research prospects are critically compiled. It is suggested that energy-related electric eel biomimetics will greatly boost the development of next-generation high performance, green, and functional electronics.",
    url = "https://doi.org/10.1002/smtd.202201435",
    doi = "10.1002/smtd.202201435",
    openalex = "W4321996891",
    references = "doi101186s1286401512888"
}

The electric organ discharges (EODs) produced by weakly electric fish have long been a source of scientific intrigue and inspiration. The study of these species has contributed to our understanding of the organization of fixed action patterns, as well as enriching general imaging theory by unveiling the dual impact of an agent's actions on the environment and its own sensory system during the imaging process. This Centenary Review firstly compares how weakly electric fish generate species- and sex-specific stereotyped electric fields by considering: (1) peripheral mechanisms, including the geometry, channel repertoire and innervation of the electrogenic units; (2) the organization of the electric organs (EOs); and (3) neural coordination mechanisms. Secondly, the Review discusses the threefold function of the fish-centered electric fields: (1) to generate electric signals that encode the material, geometry and distance of nearby objects, serving as a short-range sensory modality or 'electric touch'; (2) to mark emitter identity and location; and (3) to convey social messages encoded in stereotypical modulations of the electric field that might be considered as species-specific communication symbols. Finally, this Review considers a range of potential research directions that are likely to be productive in the future.

@article{doi101242jeb246060,
    author = "Caputi, Ángel A.",
    title = "Living life with an electric touch",
    year = "2023",
    journal = "Journal of Experimental Biology",
    abstract = "The electric organ discharges (EODs) produced by weakly electric fish have long been a source of scientific intrigue and inspiration. The study of these species has contributed to our understanding of the organization of fixed action patterns, as well as enriching general imaging theory by unveiling the dual impact of an agent's actions on the environment and its own sensory system during the imaging process. This Centenary Review firstly compares how weakly electric fish generate species- and sex-specific stereotyped electric fields by considering: (1) peripheral mechanisms, including the geometry, channel repertoire and innervation of the electrogenic units; (2) the organization of the electric organs (EOs); and (3) neural coordination mechanisms. Secondly, the Review discusses the threefold function of the fish-centered electric fields: (1) to generate electric signals that encode the material, geometry and distance of nearby objects, serving as a short-range sensory modality or 'electric touch'; (2) to mark emitter identity and location; and (3) to convey social messages encoded in stereotypical modulations of the electric field that might be considered as species-specific communication symbols. Finally, this Review considers a range of potential research directions that are likely to be productive in the future.",
    url = "https://doi.org/10.1242/jeb.246060",
    doi = "10.1242/jeb.246060",
    openalex = "W4389056873",
    references = "doi10100797830302910514"
}

The adaptive-shift hypothesis for the evolution of cave-dwelling species posits that ancestor species in surface habitats had exaptations for subterranean life that were exploited when individuals invaded caves. Weakly electric Gymnotiform fishes, nocturnal South American teleost fishes, have features that appear to be likely exaptations for troglobitic life. These fishes have active electrosensory systems in which fish generate weak electric fields that are detected by specialized electroreceptors. Gymnotiform fishes use their electric fields for navigation, prey capture (scene analysis), and social communication. Although active electrosensory systems appear to be exaptations for troglobitic life, as fish use these systems to “see in the dark”, producing electric fields is energetically costly. Cave habitats, which often are low in resources, may not be able to support such high energetic demands. Eigenmannia vicentespelaea, a species of weakly electric fish that is endemic to the São Vicente II cave in central Brazil, surprisingly generates stronger electric fields than their surface relatives. The increase in strength of electric fields may result simply from differences in size between cave and surface populations, but may also be due to lack of predation pressure in the cave or increases in “sensory volumes” and acuity that improve prey localization and capture. Eigenmannia vicentespelaea exhibits the classical phenotypes of any troglobitic fish: these fish have small to nonexistent eyes and loss of pigmentation. The closest living surface relative, Eigenmannia trilineata, inhabits streams nearby and has eyes and pigmentation. The electrosensory and locomotor behavior of both species of fish were measured in their natural habitats using a grid recording system. Surface Eigenmannia exhibited dramatic circadian changes in social behavior, such as hiding under rocks during the day and foraging in groups at night, while cave Eigenmannia displayed territorial behavior with no apparent circadian modulations. The territorial behavior involved electrical and movement-based interactions that may be a form of boundary patrolling. Electrosocial behavior and scene analysis are mechanistically interlinked because both stem from active sensing tactics.

@article{doi103389fevo20231180506,
    author = "Soares, Daphne and Gallman, Kathryn and Bichuette, Maria Elina and Fortune, Eric S.",
    title = "Adaptive shift of active electroreception in weakly electric fish for troglobitic life",
    year = "2023",
    journal = "Frontiers in Ecology and Evolution",
    abstract = "The adaptive-shift hypothesis for the evolution of cave-dwelling species posits that ancestor species in surface habitats had exaptations for subterranean life that were exploited when individuals invaded caves. Weakly electric Gymnotiform fishes, nocturnal South American teleost fishes, have features that appear to be likely exaptations for troglobitic life. These fishes have active electrosensory systems in which fish generate weak electric fields that are detected by specialized electroreceptors. Gymnotiform fishes use their electric fields for navigation, prey capture (scene analysis), and social communication. Although active electrosensory systems appear to be exaptations for troglobitic life, as fish use these systems to “see in the dark”, producing electric fields is energetically costly. Cave habitats, which often are low in resources, may not be able to support such high energetic demands. Eigenmannia vicentespelaea, a species of weakly electric fish that is endemic to the São Vicente II cave in central Brazil, surprisingly generates stronger electric fields than their surface relatives. The increase in strength of electric fields may result simply from differences in size between cave and surface populations, but may also be due to lack of predation pressure in the cave or increases in “sensory volumes” and acuity that improve prey localization and capture. Eigenmannia vicentespelaea exhibits the classical phenotypes of any troglobitic fish: these fish have small to nonexistent eyes and loss of pigmentation. The closest living surface relative, Eigenmannia trilineata, inhabits streams nearby and has eyes and pigmentation. The electrosensory and locomotor behavior of both species of fish were measured in their natural habitats using a grid recording system. Surface Eigenmannia exhibited dramatic circadian changes in social behavior, such as hiding under rocks during the day and foraging in groups at night, while cave Eigenmannia displayed territorial behavior with no apparent circadian modulations. The territorial behavior involved electrical and movement-based interactions that may be a form of boundary patrolling. Electrosocial behavior and scene analysis are mechanistically interlinked because both stem from active sensing tactics.",
    url = "https://doi.org/10.3389/fevo.2023.1180506",
    doi = "10.3389/fevo.2023.1180506",
    openalex = "W4386373334",
    references = "doi10100797830302910514"
}

@incollection{mcguigan2023nature,
    author = "McGuigan, F. J.",
    title = "Nature of Bioelectrical Phenomena",
    year = "2023",
    booktitle = "Psychophysiological Measurement of Covert Behavior",
    url = "https://doi.org/10.4324/9781003455608-4",
    doi = "10.4324/9781003455608-4",
    openalex = "W4385838279",
    pages = "9-10"
}

Mormyroidea is a superfamily of weakly electric African fishes with great potential as a model in a variety of biomedical research areas including systems neuroscience, muscle cell and craniofacial development, ion channel biophysics, and flagellar/ciliary biology. However, they are currently difficult to breed in the laboratory setting, which is essential for any tractable model organism. As such, there is a need to better understand the reproductive biology of mormyroids to breed them more reliably in the laboratory to effectively use them as a biomedical research model. This review seeks to (1) briefly highlight the biomedically relevant phenotypes of mormyroids and (2) compile information about mormyroid reproduction including sex differences, breeding season, sexual maturity, gonads, gametes, and courtship/spawning behaviors. We also highlight areas of mormyroid reproductive biology that are currently unexplored and/or have the potential for further investigation that may provide insights into more successful mormyroid laboratory breeding methods.

@article{doi101002jezb23242,
    author = "Saunders, Alyssa N. and Gallant, Jason R.",
    title = "A review of the reproductive biology of mormyroid fishes: An emerging model for biomedical research",
    year = "2024",
    journal = "Journal of Experimental Zoology Part B Molecular and Developmental Evolution",
    abstract = "Mormyroidea is a superfamily of weakly electric African fishes with great potential as a model in a variety of biomedical research areas including systems neuroscience, muscle cell and craniofacial development, ion channel biophysics, and flagellar/ciliary biology. However, they are currently difficult to breed in the laboratory setting, which is essential for any tractable model organism. As such, there is a need to better understand the reproductive biology of mormyroids to breed them more reliably in the laboratory to effectively use them as a biomedical research model. This review seeks to (1) briefly highlight the biomedically relevant phenotypes of mormyroids and (2) compile information about mormyroid reproduction including sex differences, breeding season, sexual maturity, gonads, gametes, and courtship/spawning behaviors. We also highlight areas of mormyroid reproductive biology that are currently unexplored and/or have the potential for further investigation that may provide insights into more successful mormyroid laboratory breeding methods.",
    url = "https://doi.org/10.1002/jez.b.23242",
    doi = "10.1002/jez.b.23242",
    openalex = "W4391880700",
    references = "doi10100797830302910514"
}

-ATPase being enriched on the stalklet membrane. Stalklets are distributed and organized in a quite uniform pattern on the posterior face of the electrocyte disc and fuse to terminal stalks. The latter then unite in a mostly dichotomic mode to stalks of increasing thickness, with the main stalk measuring about 100 µm in diameter. We further analyse the structural organization of stalklets and stalks, with a characteristic cytoskeletal system of bundled actin filaments in the centre and nuclei in subsurface position. These results suggest that the stalklet/stalk system is adapted in its structural layout to generate an action potential highly synchronized over the entire disc-portion of the electrocyte, accounting for the short electric organ discharge in this species. Our results suggest that actin-related proteins overexpressed in electrocytes, as shown previously by transcriptome analysis, may be involved in the organization of the unique F-actin system in stalklets and stalks.

@article{doi101007s0044102403938y,
    author = "Baumann, Otto and Cheng, Feng and Kirschbaum, Frank and Tiedemann, Ralph",
    title = "Organization of the stalk system on electrocytes in mormyrid weakly electric fish Campylomormyrus compressirostris",
    year = "2024",
    journal = "Cell and Tissue Research",
    abstract = "-ATPase being enriched on the stalklet membrane. Stalklets are distributed and organized in a quite uniform pattern on the posterior face of the electrocyte disc and fuse to terminal stalks. The latter then unite in a mostly dichotomic mode to stalks of increasing thickness, with the main stalk measuring about 100 µm in diameter. We further analyse the structural organization of stalklets and stalks, with a characteristic cytoskeletal system of bundled actin filaments in the centre and nuclei in subsurface position. These results suggest that the stalklet/stalk system is adapted in its structural layout to generate an action potential highly synchronized over the entire disc-portion of the electrocyte, accounting for the short electric organ discharge in this species. Our results suggest that actin-related proteins overexpressed in electrocytes, as shown previously by transcriptome analysis, may be involved in the organization of the unique F-actin system in stalklets and stalks.",
    url = "https://doi.org/10.1007/s00441-024-03938-y",
    doi = "10.1007/s00441-024-03938-y",
    openalex = "W4405649150",
    references = "doi10100797830302910514"
}

@article{doi101016jest2024111739,
    author = "Bütün, İsmail and Çelik, Süleyman and Dönmez, Koray Bahadır and Yürüm, Alp and Gürsel, Selmiye Alkan and Koşar, Ali",
    title = "The effect of current collectors on polymer-based energy-generating units inspired by the electric organs of eels",
    year = "2024",
    journal = "Journal of Energy Storage",
    url = "https://doi.org/10.1016/j.est.2024.111739",
    doi = "10.1016/j.est.2024.111739",
    openalex = "W4396631405",
    references = "doi101038srep25899"
}

Abstract Electric eels (Electrophorus) are renowned for their ability to generate electric discharge, which is used for prey capture and defense. Their electric organs (EOs) are located along the lateral–ventral region of the tail and contain electrocytes, which are multinucleated syncytium cells. The developmental origin of the electrocyte is mesodermal lineage cells observed in the ventral part of the myotome. However, it is unclear whether these precursor cells are also maintained in later stages and contribute to electric organ growth in adulthood. In this study, we report regional differences in cell morphology within the main EO (mEO) and identify a candidate cell population for electrocyte progenitors at the juvenile stages of Electrophorus. The cell morphology and distribution from the ventral terminal to the dorsal region of the mEO suggest the segregation of progenitors from the ventral cluster and their gradual transformation into mature multinucleated electrocytes via cell fusion and layering along the dorsal axis. Immunohistochemistry revealed strong expression of sodium-potassium adenosine triphosphatase (Na + /K + -ATPase), a key component in generating electric discharge in the mEO, across most mEO regions, except in the ventral cluster cells. Based on these observations, we propose that electrocyte progenitors develop from ventral cluster cells in the mEO and differentiate into mature multinucleated cells as they migrate dorsally. This is the first report to approach the developmental process of Electrophorus electrocytes from cell morphology and genetic profiles. Our findings represent a breakthrough in understanding the differentiation of electrocytes during the growth stages of Electrophorus.

@misc{doi10110120240821606117,
    author = "Senarat, Sinlapachai and Matsumoto, Ayako and Nagasawa, Tatsuki and Sakaki, Shintaro and Tsuzuki, Daichi and Uchida, Kazuko and Kuwahara, Makoto and Nikaido, Masato and Hondo, Eiichi and Iida, Atsuo",
    title = "Ventral-to-dorsal electrocyte development in electric organs of electric eel (Electrophorus)",
    year = "2024",
    booktitle = "bioRxiv (Cold Spring Harbor Laboratory)",
    abstract = "Abstract Electric eels (Electrophorus) are renowned for their ability to generate electric discharge, which is used for prey capture and defense. Their electric organs (EOs) are located along the lateral–ventral region of the tail and contain electrocytes, which are multinucleated syncytium cells. The developmental origin of the electrocyte is mesodermal lineage cells observed in the ventral part of the myotome. However, it is unclear whether these precursor cells are also maintained in later stages and contribute to electric organ growth in adulthood. In this study, we report regional differences in cell morphology within the main EO (mEO) and identify a candidate cell population for electrocyte progenitors at the juvenile stages of Electrophorus. The cell morphology and distribution from the ventral terminal to the dorsal region of the mEO suggest the segregation of progenitors from the ventral cluster and their gradual transformation into mature multinucleated electrocytes via cell fusion and layering along the dorsal axis. Immunohistochemistry revealed strong expression of sodium-potassium adenosine triphosphatase (Na + /K + -ATPase), a key component in generating electric discharge in the mEO, across most mEO regions, except in the ventral cluster cells. Based on these observations, we propose that electrocyte progenitors develop from ventral cluster cells in the mEO and differentiate into mature multinucleated cells as they migrate dorsally. This is the first report to approach the developmental process of Electrophorus electrocytes from cell morphology and genetic profiles. Our findings represent a breakthrough in understanding the differentiation of electrocytes during the growth stages of Electrophorus.",
    url = "https://doi.org/10.1101/2024.08.21.606117",
    doi = "10.1101/2024.08.21.606117",
    openalex = "W4401737795",
    references = "doi10100797830302910514"
}

-ATPase), a key component in generating electric discharge in the mEO, across most mEO regions, except in the ventral cluster cells. Based on these observations, we propose that electrocyte progenitors develop from ventral cluster cells in the mEO and differentiate into mature multinucleated cells as they migrate dorsally. This is the first report to approach the developmental process of Electrophorus electrocytes from cell morphology and genetic profiles. Our findings represent a breakthrough in understanding the differentiation of electrocytes during the growth stages of Electrophorus.

@article{doi101016jydbio202505003,
    author = "Senarat, Sinlapachai and Matsumoto, Ayako and Nagasawa, Tatsuki and Sakaki, Shintaro and Tsuzuki, Daichi and Uchida, Kazuko and Kuwahara, Makoto and Nikaido, Masato and Hondo, Eiichi and Iida, Atsuo",
    title = "Ventral-to-dorsal electrocyte development in electric organs of electric eel (Electrophorus)",
    year = "2025",
    journal = "Developmental Biology",
    abstract = "-ATPase), a key component in generating electric discharge in the mEO, across most mEO regions, except in the ventral cluster cells. Based on these observations, we propose that electrocyte progenitors develop from ventral cluster cells in the mEO and differentiate into mature multinucleated cells as they migrate dorsally. This is the first report to approach the developmental process of Electrophorus electrocytes from cell morphology and genetic profiles. Our findings represent a breakthrough in understanding the differentiation of electrocytes during the growth stages of Electrophorus.",
    url = "https://doi.org/10.1016/j.ydbio.2025.05.003",
    doi = "10.1016/j.ydbio.2025.05.003",
    openalex = "W4410214392",
    references = "doi10100797830302910514"
}

Large-area, flexible pyroelectric sensors have received increasing attention in a range of applications including electronic skin, robotics, and military. However, existing flexible pyroelectric sensors struggle to achieve both high pyroelectric performance and excellent mechanical properties simultaneously. Here, we propose a universal island-bridge percolation structure inspired by the electric organ of the electric ray that can enable flexible nonpyroelectric substrates with excellent mechanical properties to generate a pyroelectric effect. The island-bridge percolation network structure made of pyroelectric particles (island) and carboxyl-functionalized multiwalled carbon nanotubes (bridge) achieved the transmission and superposition of the pyroelectric effect through the film polarization and percolation effect. The pyroelectric sensor based on the island-bridge percolation network structure not only inherits the pyroelectric properties of the pyroelectric particles but also inherits the excellent mechanical properties of the nonpyroelectric substrates. The flexible pyroelectric sensors fabricated from polydimethylsiloxane (PDMS) substrates exhibit a good pyroelectric effect and excellent mechanical reliability even under 30% tensile rate and 5,000 tensile-retraction cycles, and those made from polyimide (PI) substrates can serve as electronic skin for robots to detect heat sources and possess infrared sensing properties with a maximum distance of 8 cm. This study provides ideas to fabricate flexible pyroelectric sensors with highly flexible and high-performance properties.

@article{doi101021acssensors4c02974,
    author = "Cheng, Peng and Hong, Jinhua and Zhu, Xiaohui and Bao, Cheng and Song, Lei and Zhou, Xu and Wen, Peng",
    title = "Electric-Ray-Inspired Universal Island-Bridge Structure for Transforming Nonpyroelectric Substrates into Pyroelectric Sensors",
    year = "2025",
    journal = "ACS Sensors",
    abstract = "Large-area, flexible pyroelectric sensors have received increasing attention in a range of applications including electronic skin, robotics, and military. However, existing flexible pyroelectric sensors struggle to achieve both high pyroelectric performance and excellent mechanical properties simultaneously. Here, we propose a universal island-bridge percolation structure inspired by the electric organ of the electric ray that can enable flexible nonpyroelectric substrates with excellent mechanical properties to generate a pyroelectric effect. The island-bridge percolation network structure made of pyroelectric particles (island) and carboxyl-functionalized multiwalled carbon nanotubes (bridge) achieved the transmission and superposition of the pyroelectric effect through the film polarization and percolation effect. The pyroelectric sensor based on the island-bridge percolation network structure not only inherits the pyroelectric properties of the pyroelectric particles but also inherits the excellent mechanical properties of the nonpyroelectric substrates. The flexible pyroelectric sensors fabricated from polydimethylsiloxane (PDMS) substrates exhibit a good pyroelectric effect and excellent mechanical reliability even under 30\% tensile rate and 5,000 tensile-retraction cycles, and those made from polyimide (PI) substrates can serve as electronic skin for robots to detect heat sources and possess infrared sensing properties with a maximum distance of 8 cm. This study provides ideas to fabricate flexible pyroelectric sensors with highly flexible and high-performance properties.",
    url = "https://doi.org/10.1021/acssensors.4c02974",
    doi = "10.1021/acssensors.4c02974",
    openalex = "W4407391824",
    references = "doi101038srep25899"
}

@incollection{roth2025bioelectrical,
    author = "Roth, Fabian Christoph and Numberger, Markus and Draguhn, Andreas",
    title = "Bioelectrical Phenomena and their Measurement",
    year = "2025",
    booktitle = "Mastering the Patch Clamp Technique: A Practical Guide",
    url = "https://doi.org/10.1007/978-3-662-70745-6\_2",
    doi = "10.1007/978-3-662-70745-6\_2",
    pages = "15-28"
}

The investigation of biological conductivity has evolved from its classical foundation based on ionic fluxes underpinning cardiac and neuronal excitability to a multifaceted regulator of cellular physiology. Traditional approaches for probing electrical events in living matter focused largely on action potentials recording. However, bioelectricity in non-excitable cells governs key phenomena, including developmental patterning, tissue homeostasis, and disease progression. Pioneering studies implicated endogenous bioelectrics in many aspects of morphogenesis, wound healing, regeneration, and cancer. Early findings laid the groundwork for viewing bioelectricity as a means to influence cell fate, cell cycle progression, differentiation, and senescence. More recently, spatial variations in membrane potential within tumor microenvironments were found to correlate with metastatic potential. In parallel, substantial breakthroughs have been achieved in designing advanced bioelectrical interfaces for the study of neuronal networks and cardiac function. This perspective bridges the engineering and biological domains by examining how such technologies might enable new insights into non-excitable cell electrical events at different scales of operation to ultimately manipulate cellular pathways in cancer reprogramming, anti-aging interventions, and gene expression modulation.

@misc{cadinu2026bioelectrical,
    author = "Cadinu, Paolo and Burgess, Matthew K. and Franco Jones, Catarina Franco and Iarossi, Marzia and Schröter, Manuel and Nakatsuka, Nako and Djamgoz, Mustafa B.A. and Gonçalves, Gil and Abayzeed, Sidahmed and Sanjuán-Alberte, Paola and Mendes, Paula M. and Rawson, Frankie J. and Nair, Malavika and Levin, Michael and Moreddu, Rosalia",
    title = "Bioelectrical Interfaces Beyond Excitable Cells: Cancer, Aging, and Gene Expression Modulation",
    year = "2026",
    publisher = "Wiley-VCH",
    abstract = "The investigation of biological conductivity has evolved from its classical foundation based on ionic fluxes underpinning cardiac and neuronal excitability to a multifaceted regulator of cellular physiology. Traditional approaches for probing electrical events in living matter focused largely on action potentials recording. However, bioelectricity in non-excitable cells governs key phenomena, including developmental patterning, tissue homeostasis, and disease progression. Pioneering studies implicated endogenous bioelectrics in many aspects of morphogenesis, wound healing, regeneration, and cancer. Early findings laid the groundwork for viewing bioelectricity as a means to influence cell fate, cell cycle progression, differentiation, and senescence. More recently, spatial variations in membrane potential within tumor microenvironments were found to correlate with metastatic potential. In parallel, substantial breakthroughs have been achieved in designing advanced bioelectrical interfaces for the study of neuronal networks and cardiac function. This perspective bridges the engineering and biological domains by examining how such technologies might enable new insights into non-excitable cell electrical events at different scales of operation to ultimately manipulate cellular pathways in cancer reprogramming, anti-aging interventions, and gene expression modulation.",
    url = "https://www.research-collection.ethz.ch/handle/20.500.11850/798890",
    doi = "10.3929/ethz-c-000798890"
}

@incollection{alexanderNoneelectric,
    author = "Alexander, James B.",
    title = "Electric organs.",
    year = "None",
    booktitle = "The dynamic theory of life and mind: An attempt to show that all organic beings are both constructed and operated by the dynamic agencies of their respective environments.",
    url = "https://doi.org/10.1037/12949-055",
    doi = "10.1037/12949-055",
    openalex = "W4236579962",
    pages = "526-533"
}

@inproceedings{smithNonedirect,
    author = "Smith, W.M.",
    title = "Direct mapping of bioelectrical phenomena",
    year = "None",
    booktitle = "Proceedings of the 20th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. Vol.20 Biomedical Engineering Towards the Year 2000 and Beyond (Cat. No.98CH36286)",
    url = "https://doi.org/10.1109/iembs.1998.745808",
    doi = "10.1109/iembs.1998.745808",
    pages = "5-9"
}