Diversity and evolution of sound production in the social behavior ofChaetodonbutterflyfishes

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 that two sound production mechanisms exist in the bannerfish clade and that other mechanisms are used in the Chaetodon clade, which is distinguished by an auditory specialization, the laterophysic connection (LC). Here, we determine the kinematic action patterns associated with sound production during social interactions in four Chaetodon subgenera and the non-laterophysic fish Forcipiger flavissimus. Some Chaetodon species share the head bob acoustic behavior with F. flavissimus, which along with other sounds in the 100-1000 Hz spectrum, are probably adequate to stimulate the ear, swim bladder or LC of a receiver fish. In contrast, only Chaetodon species produced the tail slap sound, which involves a 1-30 Hz hydrodynamic pulse that is likely to stimulate the receiver's ear and lateral line at close distances, but not the swim bladder or 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 intensities of the tail slap and body pulse sounds in Chaeotodon species are correlated with body size and can provide honest communication signals. Future studies on fish acoustic communication should investigate lowfrequency and infrasound acoustic fields to understand the integrated function of the ear and lateral line, and their evolutionary patterns.

Sound pressure enhances the hearing sensitivity of Chaetodon butterflyfishes on noisy coral reefs

“…Overall, the noise levels are near but below the AEP auditory thresholds to frequency tones. Total noise levels were also below the peak frequency levels reported for the four sounds produced by this species during communication at close distances (Tricas and Boyle, 2015) as shown by representative sound intensity spectral curve plots in Fig. 6.…”

“…Recent work shows that Chaetodon, Forcipiger, Hemitaurichthys and Heniochus species produce several forms of pulsed sounds with peak frequencies and bandwidths from <1 Hz to >1000 Hz during social interactions in the field and lab (Tricas et al, 2006;Boyle and Tricas, 2011;Parmentier et al, 2011a;Boyle, 2014, 2015). In Chaetodon, this includes very low frequency hydrodynamic stimuli (<1-30 Hz) (Tricas et al, 2006;Hanke et al, 2008;Tricas and Boyle, 2015) that can likely stimulate the inner ear by whole body accelerations and the mechanosensory lateral line of the receiver fish. Pulsed acoustic sounds from >100-1000 Hz are produced by all genera by a diversity of motor mechanisms Tricas, 2010, 2011;Parmentier et al, 2011a;Tricas and Boyle, 2015).…”

“…In Chaetodon, this includes very low frequency hydrodynamic stimuli (<1-30 Hz) (Tricas et al, 2006;Hanke et al, 2008;Tricas and Boyle, 2015) that can likely stimulate the inner ear by whole body accelerations and the mechanosensory lateral line of the receiver fish. Pulsed acoustic sounds from >100-1000 Hz are produced by all genera by a diversity of motor mechanisms Tricas, 2010, 2011;Parmentier et al, 2011a;Tricas and Boyle, 2015). Of relevance to perception of these acoustic stimuli by Chaetodon is the strong pairing of monogamous species that defend territories from conspecific competitors (Reese, 1975;Hourigan, 1989;Tricas, 1989a;Roberts and Ormond, 1992).…”

“…Data from the field recordings of ambient noise levels in reef territories of multiband butterflyfish, C. multicinctus, were compared with data on auditory thresholds and spectral levels of their communication sounds (Tricas and Boyle, 2015) to provide a first estimate of the potential constraints on hearing perception in their natural setting. The total background noise levels across the full 10-24 kHz band show variation in intensity of about 10-30 dB among territories and among frequencies that vary with depth ( Fig.…”

“…7B). Comparison of these band-specific background noise levels with the 6 dB bandwidth levels for each sound type (from Tricas and Boyle, 2015) indicates that the signal to noise ratio of the tail slap sound increases with depth of the territory [SNR=(1.57×depth)+3.70, P=0.021, R=0.68], but that for the Relative change in AEP thresholds after sequential displacement of gas from the swim bladder horns and then evacuation of gas from the swim bladder in an individual Chaetodon multicinctus at 600 Hz stimulation. Baseline threshold is at 107 dB re.…”