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The theory of ecological speciation posits that adaptive divergence among incipient species raises incidental barriers to reproduction, thus catalyzing the emergence of new species. In this study, we conducted an experimental test of this theory in Galápagos finches, a clade in which beaks and mating songs are mechanistically linked. We forecasted the acoustic structure of songs for a set of possible evolutionary futures (successive droughts spurring increasingly large beaks) and, in a field assay, presented resulting song simulations to territorial males. We found that responses to songs dropped off after six simulated drought events, to degrees roughly comparable to drops in response to songs that diverged through cultural drift and acoustic adaptation. Our results support, in DarwinÕs finches, the feasibility and mechanistic bases of an ecological speciation hypothesis. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2006.11.001 Byline: Jeffrey Podos Abstract: Geographical variation in the structure of mating signals can influence the processes of mate recognition and reproductive isolation. In Darwin's finches of the Galapagos Islands, Ecuador, prior studies of geographical variation in vocal mating signals (songs) have focused on populations on small islands, on which there is presumably little opportunity for the evolution of within-island song variation or discrimination abilities. The situation on larger islands, however, is less clear. I characterized aspects of song variation and discrimination in the medium ground finch, Geospiza fortis, in the southeastern coastal region of the large island of Santa Cruz. Songs from two sites, Bahia Academia and El Garrapatero, separated by approximately 11km, differed in mean minimum frequency and in a corresponding principal component factor, and could be distinguished with moderate success in discriminant function analysis. Territorial males at El Garrapatero showed strong discrimination of songs by site: in response to playback of local songs, birds showed higher rates of singing and flying, and significantly closer approaches to the playback speaker. Successful discrimination of songs by site, in the face of overlap in song structure between these sites, suggests that these birds rely on an exemplar-based mechanism of song perception. Moreover, the results support the hypothesis that birds in these populations are relatively philopatric, and thus suggest an opportunity for within-island evolutionary divergence. Author Affiliation: Department of Biology, Graduate Program in Organismic and Evolutionary Biology, University of Massachusetts, Amherst, U.S.A. Article History: Received 27 April 2006; Revised 19 June 2006; Accepted 7 November 2006 Article Note: (miscellaneous) MS. number: A10432

The songs of swamp sparrows are compared for their ability to attract mates, depending upon the relative innovation of the song syntax. Female birds are shown to be more conservative about song syntax than male birds.

Author(s): Jeffrey Podos (corresponding author) Speciation in many animal taxa is catalysed by the evolutionary diversification of mating signals [1]. According to classical theories of speciation, mating signals diversify, in [...]