1. Department of Ecology and Evolutionary Biology, University of Arizona , Tucson, Arizona 85721, USA
2. Present address: Department of Biology, University of Massachusetts , Amherst, Massachusetts 01003 USA.

Correspondence to: Jeffrey Podos Correspondence and requests for materials should be addressed to the author (e-mail: Email: jpodos@bio.umass.edu).

Abstract

Speciation in many animal taxa is catalysed by the evolutionary diversification of mating signals¹. According to classical theories of speciation, mating signals diversify, in part, as an incidental byproduct of adaptation by natural selection to divergent ecologies^{2, 3}, although empirical evidence in support of this hypothesis has been limited^{4, 5, 6}. Here I show, in Darwin's finches of the Galápagos Islands, that diversification of beak morphology and body size has shaped patterns of vocal signal evolution, such that birds with large beaks and body sizes have evolved songs with comparatively low rates of syllable repetition and narrow frequency bandwidths. The converse is true for small birds. Patterns of correlated evolution among morphology and song are consistent with the hypothesis that beak morphology constrains vocal evolution, with different beak morphologies differentially limiting a bird's ability to modulate vocal tract configurations during song production. These data illustrate how morphological adaptation may drive signal evolution and reproductive isolation, and furthermore identify a possible cause for rapid speciation in Darwin's finches.

1. Department of Ecology and Evolutionary Biology, University of Arizona , Tucson, Arizona 85721, USA
2. Present address: Department of Biology, University of Massachusetts , Amherst, Massachusetts 01003 USA.

Correspondence to: Jeffrey Podos Correspondence and requests for materials should be addressed to the author (e-mail: Email: jpodos@bio.umass.edu).