Electric organ discharge variability of Mormyridae (Teleostei: Osteoglossomorpha) in the Upper Volta system

Abstract

The electric organ discharges (EODs) of five mormyrid species (Marcusenius senegalensis, Brevimyrus niger, Petrocephalus bovei, Pollimyrus isidori, Hippopotamyrus pictus) from different sampling sites from the Upper Volta system in West Africa were investigated. EOD waveforms were recorded at high sampling rates in order to compare signal waveform parameters of the different species from different locations. Except for H. pictus, EODs within a species differed significantly from one another in some parameters and waveform variability at least between some sampling sites. In addition, each species showed a continuous spectrum of waveform variations, all or only parts of which were found at certain localities. Although there was variability and sometimes similarities between species, the EOD waveforms were species specific. Knowing their variation spectrum, they can be used for species determination and are probably used for species recognition by the mormyrids. Similarities or differences in EOD waveform expression within a species were not related to geographical distance. By contrast, we suggest that biotic environmental factors at a given location influence the expression of EOD waveforms. These factors affect absolute measurements such as EOD duration and fast Fourier transformation peak frequency as well as the amount of variation for certain waveform parameters across species in a similar manner for a given site. Although EOD waveform might be important for the establishment of reproductive barriers between species, our results suggest that differences in waveforms may not necessarily reflect different species or speciation processes in progress.