Environmental effects on anuran call design: What we know and what we need to know

Abstract

Long-range acoustic signals are subject to a variety of evolutionary pressures, such as sexual selection, species recognition, body-size constraints, physiological constraints, and natural selection by environmental constraints. Anuran advertisement calls are long-range acoustic signals with two essential functions: to attract females, and to defend a territory against other males. However, the environment offers obstacles to sound transmission. The call can be attenuated and degraded, and the surrounding environment might impose a strong constraint on it by means of sound refraction, reflection, and absorption along the transmission path. The Acoustic Adaptation Hypothesis (AAH) predicts that the acoustic signal could be adapted in order to maximise transmission distance by minimising call attenuation and degradation. The predictions of the AAH have been reviewed twice for birds, and once for mammals and anurans. This study extends the anuran review, focusing on the environmental effects on anuran call design, and their conformity to the AAH predictions. A small number of studies were found, and the results were conflicting. These studies were carefully analysed, and we report a lack of standardised methodology to test for environment effects. We discuss in detail the diverse methodologies and point out how the matter has been treated. We highlight the importance of improving the project design by increasing the sample size, controlling for phylogenetic and body size effects, and using a quantitative representation of vegetation structure. © 2013 Copyright 2013 Dipartimento di Biologia Evoluzionistica dell'Università, Firenze, Italia.