# Phylogeny and Body Size Predict Distress Call Divergence in Bats: A Comparative Analysis

## TL;DR

This study finds that distress calls in bats are shaped mainly by evolutionary history and body size, not just ecological or social factors.

## Contribution

The study identifies phylogeny and body size as primary drivers of distress call divergence in bats, a novel insight in mammalian vocal communication.

## Key findings

- Phylogeny and body size are the main factors explaining distress call differences in bats.
- Ecological and social factors have a minor role in distress call divergence.
- Distress calls are influenced by deep evolutionary and morphological constraints.

## Abstract

Bats often emit loud distress calls when captured or threatened, which can function to startle predators or alert conspecifics. However, little is known about how these calls vary among species and what factors drive such divergence. In this study, we recorded distress calls from 32 bat species in China and examined how evolutionary history, body size, ecology, and social traits shape call structures. We found that both phylogeny and body size were the main factors explaining differences in distress calls across species, while ecological and social factors played minor roles. These findings indicate that distress calls are not merely emotional outbursts but are shaped by deep evolutionary and morphological constraints, providing new insights into the evolution of acoustic communication in mammals.

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.