Abstract
The evolutionary divergence of animal vocalizations is a complex process shaped by various factors, including morphology, ecology, social pressure, and phylogenetic relationships. This applies even to distress calls, which may appear to be simple expressions of emotion. However, the relative importance of these factors in shaping interspecific divergence of distress call structure remains largely unexplored. In addition, previous studies concerning the factors driving distress call divergence have been mainly conducted in birds, anurans, and lizards, whereas less is known for mammals. Here, we recorded distress calls across 32 bat species belonging to 7 families, and compiled data on body size, foraging habitat types, climatic variables, colony size, and phylogenetic components, aiming to identify the key determinants predicting the cross-species divergence in the incidence and acoustic parameter of distress calls within a comparative framework. Our results supported that bats divergence in distress vocalizations is not an adaptive evolution in response to ecological and social pressure, but constrained by phylogenetic relationship and body size. Phylogenetic components explained the most interspecific variation in the incidence and temporal parameters of distress calls, whereas body size accounts for spectral parameters. This study has revealed that distress vocalizations not only convey the caller's emotional state, but also suffer severe phylogenetic and morphological constraint.