Many birds, mammals and amphibians vary the frequency and intensity of their vocalizations to expand their vocabulary.
Aaron Rice, Bruce Land and Andrew Bass at Cornell University in Ithaca, New York, show that fish also use forms of ‘acoustic nonlinearity’, such as frequency jumps and biphonation — the simultaneous expression of two independent frequencies. Results from their studies have just been published on the prestigius Proceedings of the Royal Society B: Biological Sciences.
Acoustic signals play essential roles in social communication and show a strong selection for novel morphologies leading to increased call complexity in many taxa. Among vertebrates, repeated innovations in the larynges of frogs and mammals and the syrinx of songbirds have enhanced the spectro-temporal content, and hence the diversity of vocalizations. This acoustic diversification includes nonlinear characteristics that expand frequency profiles beyond the traditional categorization of harmonic and broadband calls. Fishes have remained a notable exception to evidence for such acoustic innovations among vertebrates, despite their being the largest group of living vertebrates that also exhibit widespread evolution of sound production. Here, we combine rigorous acoustic and mathematical analyses with experimental silencing of the vocal motor system to show how a novel swim bladder mechanism in a toadfish enables it to generate calls exhibiting nonlinearities like those found among frogs, birds and mammals, including primates. By showing that fishes have evolved nonlinear acoustic signalling like all other major lineages of vocal vertebrates, these results suggest strong selection pressure favouring this mechanism to enrich the spectro-temporal content and complexity of vocal signals.
Keywords: acoustic communication; Batrachoididae; deterministic chaos; sound production; swim bladder; toadfish