Communication in the weakly electric brown ghost knifefish, Apteronotus leptorhynchus

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Triefenbach, Frank Alexander

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Maintaining a stable social organization necessitates that animals recognize their own dominance status relative to that of other conspecifics. The weakly electric brown ghost knifefish emits a sexually dimorphic sinusoidal electric organ discharge (EOD) for electrolocation. High-quality (larger, dominant) males discharge at the highest and females at the lowest EOD frequencies (EODFs). Each individual is most sensitive to its own EODF, which can be modulated for communication. In order to examine how sensitivity and quality influence an individual’s response to mimics of EODs, I recorded electrical signals emitted by ten males and seven females in response to playbacks of sine waves mimicking a wide range of con- and extraspecific EODFs. While all individuals emit small chirps (LoCs) mostly to stimuli around their own EODF, they are more likely to emit rises (gradual non-chirp signals) to frequencies to which they are less sensitive; males similarly emit larger chirps (HiCs) to frequencies more distant from their own, especially to female mimics. Larger males are less likely to emit rises, stimuli in the female range elicit more rises from both sexes, and females emit rises to male EOD mimics. Although low male EOD mimics elicit more LoCs from all, and especially from smaller males, larger males chirp more at progressively higher male EOD mimics than do smaller males. I conclude that a) although much of the variation in an individual’s response is attributable to its sensitivity, individuals recognize sexual and size cues and have some internal representation of their own quality, and b) whereas LoCs appear to function in intrasexual aggression, HiCs and rises could be used in both courtship and submissive signalling.