Evolution of advertisement signals in North American hylid frogs: vocalizations as end-products of calling behavior.

We studied the advertisement signals in two clades of North American hylid frogs in order to characterize the relationships between signal acoustic structure and underlying behavior. A mismatch was found between the acoustic structure and the mechanism of sound production. Two separate sets of phylogenetic characters were coded following acoustic versus mechanistic criteria, and exploratory treatments were made to compare their respective phylogenetic content in comparison with the molecular phylogeny (Faivovich et al., 2005). We discuss the consequences of the acoustic/mechanistic mismatch in terms of significance of acoustic characters for phylogenetic and comparative studies; and the evolution of vocalizations in North American treefrogs. Considering only the acoustic structure of frog vocalizations can lead to misleading results in terms of both phylogenetic signal and evolution of vocalizations. In contrast, interpreting the acoustic signals with regard to the mechanism of sound production results in consistent phylogenetic information. The mechanistic coding also provides strong homologies for use in comparative studies of frog vocalizations, and to derive and test evolutionary hypotheses.