Electric signals and species recognition in the wave-type gymnotiform fish Apteronotus leptorhynchus

Abstract

Gymnotiformes are South American weakly electric fish that produce weak electric organ discharges (EOD) for orientation, foraging and communication purposes. It has been shown that EOD properties vary widely across species and could thus be used as species recognition signals. We measured and quantified the electric signals of various species using a landmark-based approach. Using discriminant function analysis to verify whether these signals are species specific based on different signal parameters, we found that the EOD waveform is a more specific cue than EOD frequency, which shows large overlap across species. Using Apteronotus leptorhynchus as a focal species, we then performed a series of playback experiments using stimuli of different species (varying in frequency, waveform, or both). In an experiment with restrained fish, we found, in contrast to what we predicted, that the choice of stimulus waveform did not affect the production of communication signals. In an experiment with free-swimming fish, the animals spent more time near the playback electrodes and produced more communication signals when the stimuli were within their conspecific frequency range. Waveform again had no measurable effect. The production of communication signals correlated with the frequency difference between the stimulus and the fish's own EOD, but approach behavior did not.