Diversity and evolution of sound production in the social behavior of Chaetodon butterflyfishes

Abstract

Fish produce context-specific sounds during social communication but it is not known how acoustic behaviors have evolved in relation to specializations of the auditory system. Butterflyfishes (family Chaetodontidae) have a well-defined phylogeny and produce pulsed communication sounds during social interactions on coral reefs. Recent work indicates two sound production mechanisms exist in the bannerfish clade and others for one species in the Chaetodon clade which is distinguished by an auditory specialization, the laterophysic connection (LC). We determine the kinematic action patterns associated with sound production during social interactions in four Chaetodon subgenera and the non-laterophysic Forcipiger. Some Chaetodon species share the head bob acoustic behavior with Forcipiger which along with other sounds in the 100-1000 Hz spectrum are likely adequate to stimulate the ear, swim bladder or LC of a receiver fish. In contrast, only Chaetodon produced the tail slap sound which involves a 1-30 Hz hydrodynamic pulse that likely stimulates the receiver's ear and lateral line at close distances, but neither the swim bladder nor LC. Reconstructions of ancestral character states appear equivocal for the head bob and divergent for the tail slap acoustic behaviors. Independent contrast analysis shows a correlation between sound duration and stimulus intensity characters. The intensity of the tail slap and body pulse sound in Chaeotodon is correlated with body size and can provide honest communication signals. Future studies on fish acoustic communication should investigate low frequency and infrasound acoustic fields to understand the integrated function of the ear and lateral line, and their evolutionary patterns.