Evolution and diversity of batrachoidid vocalizations.

Abstract

Despite the fact that toadfishes are one of the best‐studied taxa for understanding fish vocal communication, vocalizations have only been recorded from a low proportion of taxa within the family. Here, we describe the diverse vocal repertoire and novel swimbladder morphology of a tropical Pacific euryhaline toadfish, Batrachomoeus trispinosus. B. trispinosus produces four classes of vocalizations: long duration hoots, grunts, grunt trains, and grunts exhibiting acoustic beats; the majority exhibiting prominent harmonic features. Calls with acoustic beats, previously unreported for any individual actinopterygian taxon and convergent with songbirds, typically had a predominant frequency around 2 kHz with a beat frequency around 300 Hz. B. trispinosus possesses a bilaterally divided swimbladder, forming two completely separate bladders. Grunts exhibiting beats may be produced by bilateral control of the bladders. Phylogenetic analysis based on available molecular data show that B. trispinosus and Halobatrachus didactylus represent basal lineages in the Batrachoididae, and the separated swimbladders are an independently derived feature of B. trispinosus. Thus, the toadfishes may possess higher levels of vocal, motor, and morphological diversity than previously appreciated, and now provide a framework for understanding integrated mechanisms underlying the evolution of acoustic novelty in fishes.