Do body size and habitat shape call frequencies of Brazilian hylids (Amphibia: Anura)?

Abstract

Despite acoustic signals playing a fundamental role on animal behavior and reproduction, our understanding of the mechanisms driving their evolution is still scarce. Due to the high cost of signaling, several adaptive bioacoustics hypotheses have been proposed to explain call design. While Acoustic Adaptation Hypothesis (AAH) postulates the habitat influence on shaping acoustic signals, Morphological Adaptation Hypothesis (MAH) emphasizes the constraints that animal structure imposes to their calls. Yet, when testing those hypotheses, phylogenetic comparative methods have been scarcely applied so far. Here we evaluated the AAH and MAH in 163 anurans (i.e., Brazilian species of the family Hylidae), based on a broad review of the dominant frequency of their advertisement calls. Comparative methods revealed a negative relationship between dominant frequency and body size, supporting the MAH. AAH was partly rejected, as vegetation density, habitat type and calling microhabitat did not affect species’ dominant frequency. However, species calling from higher perches had higher dominant frequencies, partially supporting habitat effect on call features. Our results not only highlight the role of morphology on shaping Hylidae call design, but also arise questions about scale effect, behavioral strategies and other sound propagation characteristics while testing AAH in frogs.