Echoes of Evolution in Holocentridae: Harmony Between Phylogeny, Morphology and Acoustics.

Holocentridae are nocturnal reef fishes that rely on acoustic communication in various behavioral contexts. Using a multidisciplinary approach combining phylogenetics, morphology, and acoustic data from 53 species, we reconstructed the evolutionary history of this communication system within the family. Our results reveal two main clades corresponding to the subfamilies Myripristinae and Holocentrinae, with congruent differences in both the morphology of the sound-producing apparatus and acoustic features. Interestingly, at finer taxonomic scales, closely related species often share similar sound-producing structures but can produce distinct sounds. This suggests that the evolution of acoustic communication in Holocentridae follows a three-step diversification pattern: (1) the emergence of structures enabling sound production; (2) differentiation of sound-producing mechanisms within each subfamily, likely constrained by internal factors such as the swim bladder morphology; and (3) further diversification through differentiated use of conserved mechanisms, consistent with a role of neurophysiological modulation. This scenario mirrors patterns observed in other functional traits, where morphological innovations open new functional pathways, followed by fine-scale diversification based on the flexible exploitation of similar structures. It provides one of the first evolutionary reconstructions of sound production mechanisms in fishes, expanding our understanding of the evolution of complex signaling systems.