Animal acoustic communication has a conserved optimal rhythm within the neural delta range

Acoustic communication is crucial for survival across the animal kingdom, with acoustic signals being shaped by the interaction of producer and receiver selective pressures. While spectral features' variation reflects species-specific selection, the evolutionary history of acoustic communication rhythms, i.e., the rhythmic modulations of acoustic signals, remains unknown. Using data from 98 species spanning primarily mammals and birds, with additional representation from amphibians, reptiles, fishes, and insects, we investigate the origins of acoustic communication rhythms, notably whether they are shaped by the producer's anatomical characteristics, environmental constraints, or social complexity. Regression models which controlled for phylogenetic relatedness did not support an influence of these species-specific selective forces; instead, explicit phylogenetic models of trait evolution showed that most species' rhythms are conserved around an evolutionary optimum of 2.7 Hz that falls within the neural delta range (1-4 Hz) and predates mammalian divergence. Given the known conserved brain oscillations across species and delta involvement in active sensing, we propose that, unlike spectral features, acoustic rhythm could be governed by a universal neural mechanism facilitating effective intra and interspecific communication via a shared channel that has persisted through evolutionary times.