Biophysical Basis of Electric Signal Diversity
The electric sensory and communication signals of electric fish show remarkable diversity in their waveforms, and this diversity is driven by selective pressures related to reproduction, sensory ecology, predation avoidance, and the metabolic costs of signaling. These electric signals are generated by electrocytes, electrically excitable cells that comprise the electric organ. Although the signaling rate is controlled by a brainstem pacemaker or command nucleus that coordinates the discharge of electrocytes within the electric organ, waveform diversity arises primarily from the underlying biophysics of electrocytes, including their passive electrical properties, morphology, voltage-gated ion channels, and regulatory pathways that modify electrocyte function. Electrocyte morphology and innervation patterns are a major source of signal diversity in the African mormyrid electric fishes, whereas diversity of ion-channel expression patterns has a strong influence on waveform diversity in the South American gymnotiforms. Convergent evolution of ion channels in both clades further contributes to signal diversity. Little is known about the ionic mechanisms of signal diversity in mormyrids. Additionally, asynchronous activation of distinct electric organ regions with different electrocyte properties enhances waveform complexity in some gymnotiforms. Signal diversity associated with development and sexual dimorphism arises from the effects of steroid hormones on electrocyte ion channel kinetics, and the rapid changes in signal waveform are mediated by the effects of peptide hormones on electrocyte action potentials and ion channel function. These processes have been investigated primarily in a small number of gymnotiforms, highlighting a great need for broader comparative studies across gymnotiform species and between mormyrids and gymnotiforms.
KeywordsAction potential Electric organ Electric organ discharge Electrocyte Ion channels Melanocortin hormones Sexual dimorphism Steroid hormones
Preparation of this chapter was supported by Grants IOS1644965, IOS1350753, and IOS1257580 from the National Science Foundation and by the Case-Hooper endowment, funded through a gift from Dr. and Mrs. Robert Case to The University of Oklahoma, Norman.
Compliance with Ethics Requirements
Michael R. Markham declares that he has no conflict of interest.
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