Communication signals serve crucial survival and reproductive functions. In Gabon, the widely distributed mormyrid fishParamormyrops kingsleyae emits an electric organ discharge (EOD) signal with a dual role in communication and electrolocation that exhibits remarkable variation: populations of P. kingsleyae have either biphasic or triphasic EODs, a feature that characterizes interspecific signal diversity among the Paramormyrops genus. We quantified variation in EODs of 327 P. kingsleyae from nine populations and compared it to genetic variation estimated from microsatellite loci. We found no correlation between electric signal and genetic distances, suggesting that EOD divergence cannot be explained by drift alone. An alternative hypothesis is that EOD differences are used for mate discrimination, which would require P. kingsleyae be capable of differentiating between divergent EOD waveforms. Using a habituation-dishabituation assay, we found that P. kingsleyae can discriminate between biphasic and triphasic EOD types. Nonetheless, patterns of genetic and electric organ morphology divergence provide evidence for hybridization between these signal types. Although reproductive isolation with respect to signal type is incomplete, our results suggest that EOD variation in P. kingsleyae could be a cue for assortative mating. K E Y W O R D S : Animal communication, electric organ, electrocytes, genetic drift, signal evolution, weakly electric fish.

This study examines evolutionary causes underlying the maintenance of diversity in electric courtship signals (EODs) emitted by the mormyrid electric fish species Paramormyrops kingsleyae. P. kingsleyae are polymorphic for an EOD feature which characterizes interspecific signal diversity among the rapidly diverged Paramormyrops genus. We collected 338 specimens and recorded EOD signals from 9 populations distributed throughout Gabon, west central Africa, collected in 1999Africa, collected in -2009. First, we demonstrate using microsatellite genotyping a significant signature of isolation by distance between populations. Second, utilizing principal components analysis of 21 landmarks measured from EOD waveforms, we find that EOD duration and the magnitude of a small head negative pre-potential (P0) are highly correlated with patterns of spatial and genetic structure. Finally, utilizing a behavioral assay, we demonstrate that P. kingsleyae individuals can discriminate between P0-absent and P0-present EOD waveforms, although genetic and morphological analysis indicate no assortative mating between signal types. Together, these results support the hypothesis that patterns of signal variation in P. kingsleyae have resulted from genetic drift acting upon isolated populations. As P. kingsleyae represents a microcosm of signal diversity among mormyrids, these findings illustrate a potential mechanism by which interspecific patterns of EOD diversity may originate at the population level.