Abstract |
Environmental noise can be an important selective force modulating signal evolution in species with acoustic communication. Many anuran species breed alongside streams; hence, the sound produced by the flowing water is an important source of noise for acoustic communication. Since calling is physiologically very expensive in anurans, and communication is essential for reproduction, we expected adaptations that reduce environmental masking effects and allow acoustic communication in streamside breeders. This basic assumption of the acoustic adaptation hypothesis has not been yet evaluated at a large phylogenetic scale. We combined ahistorical and phylogenetic methods to test whether anuran species that breed alongside streams call at higher frequencies than species that breed away from streams. We compiled primary and secondary data on body size, breeding habitat, and the dominant frequency of the advertisement call for 110 species; 40 of them breed alongside streams and 70 away from streams. Call frequency was slightly higher and body size was significantly smaller in streamside breeding species. After controlling for the effects of body size and phylogenetic signal, only differences in body size persisted between species breeding at both kinds of habitats. Our data suggest that habitat filtering rather than acoustic adaptation explains the high call frequency of stream breeders. Species with large body size, pleiotropically constrained to utter low-frequency calls, would have succeeded less often in establishing viable populations alongside streams, due to the masking effect of low-frequency noise. Thus, small species calling at relatively high frequencies would be more common there. Although our data do not preclude adaptations to noisy habitats in some anuran species, they do not provide support for the acoustic adaptation hypothesis at a wider phylogenetic scale. |