Bioacoustic behavior of African fishes (Mormyridae): potential cues for species and individual recognition in Pollimyrus.

An analysis of the natural bioacoustic signals made by two closely related African fishes (P. adspersus and P. isidori) revealed that these species separated along several acoustic dimensions that are likely to be important for species isolation. Both species produced grunts that were composed of a trains of pulses, but the pulse repetition rates were distinctly different (56 +/- 3 s.d. vs 44 +/- 4 s.d. pps). Complex tone bursts (moans) were also used, but the species differed substantially in the location of the fundamental peak (240 Hz +/- 12 s.d. vs 332 Hz +/- 34 s.d.). Some P. adspersus males sustained these tones for over a second (812 ms +/- 495 s.d.), whereas P. isidori produced shorter tones (121 ms +/- 35 s.d.). During interactions with females, the two species produced the grunts and moans in distinct species-typical patterns: P. adspersus males alternated grunts with moans and P. isidori produced a single grunt followed by a succession of moans. A detailed analysis of identified individual P. adspersus showed that acoustic features constituted individual signatures which could be used by conspecifics to identify individuals. Grunt spectral peak frequency was shown to be a good predictor of male mass, with peak frequency decreasing at 72 Hz per gram. Simulated standardized courtship encounters with females revealed that males differ markedly in their apparent ability to produce sustained moans and it is suggested that this may be particularly important to females in mate selection.

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