ABSTRACT
The elaborate songs of songbirds are frequent
models for investigating the evolution of animal signals. However, few
previous studies have attempted to reconstruct historical changes in song
evolution using a phylogenetic comparative approach. In particular, no
comparative studies of bird song have used a large number of vocal characters
and a well-supported, independently derived phylogeny. We identified 32
features in the complex vocal displays of male oropendolas (genera Psarocolius, Gymnostinops, and Ocyalus) that are relatively invariant within
taxa and mapped these characters onto a robust molecular phylogeny of the
group. Our analysis revealed that many aspects of oropendola song are
surprisingly evolutionarily conservative and thus are potentially useful
characters for reconstructing historical patterns. Of the characters that
varied among taxa, nearly two thirds (19 of 29) showed no evidence of
evolutionary convergence or reversal when mapped onto the tree, which was
reflected in a high overall consistency index (CI = 0.78) and retention index
(RI = 0.88). Some reconstructed patterns provided evidence of selection on
these signals. For example, rapid divergence of the songs of the Montezuma
oropendola, Gymnostinops montezuma, from those of closely
related taxa suggests the recent influence of strong sexual selection. In
general, our results provide insights into the mode of vocal evolution in
songbirds and suggest that complex vocalizations can provide information about
phylogeny. Based on this evidence, we use song characters to estimate the
phylogenetic affinities of three oropendola taxa for which molecular data are
not yet available.