Correlated evolution of morphology and vocal signal structure in Darwin's finches

Abstract

Speciation in many animal taxa is catalysed by the evolutionary diversification of mating signals. According to classical theories of speciation, mating signals diversify, in part, as an incidental byproduct of adaptation by natural selection to divergent ecologies, although empirical evidence in support of this hypothesis has been limited. 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.

The ability to perform physically challenging songs predicts age and size in male swamp sparrows, Melospiza georgiana

“…The method for quantifying vocal performance is described in detail elsewhere (Podos 2001;Ballentine et al 2004;Ballentine 2006a). Briefly, I plotted trill rate (X axis) and frequency bandwidth (Y axis) of songs, then calculated an upper boundary regression, which estimates the performance limit on trill production (Podos 2001).…”

“…Briefly, I plotted trill rate (X axis) and frequency bandwidth (Y axis) of songs, then calculated an upper boundary regression, which estimates the performance limit on trill production (Podos 2001). Vocal performance was quantified as the orthogonal distance from the upper boundary such that very low numbers refer to songs that are close to the upper boundary and hence close to an estimated performance limit.…”

Especiação e seus mecanismos: histórico conceitual e avanços recentes

“…Os tentilhões de Darwin receberam essa denominação por ser um dos exemplos mais conhecidos de descendência com modificação estudada pelo naturalista inglês durante a viagem a bordo do Beagle (1831-1836) (Darwin, 1890). Esse caso seguiu sendo examinado por outros eminentes pesquisadores como David Lambert Lack (1988) e Jeffrey Podos (2001), com destaque para o trabalho desenvolvido pelo casal Peter e Rosemary Grant ao longo de mais de trinta anos (Grant, Grant, 2002, 2003.…”

“…Inicialmente, os dados sobre a diversificação dos tentilhões foram obtidos por Darwin sem experimentação; no entanto, têm sido sistematicamente corroborados por numerosas análises posteriores (Gibbs, Grant, 1987;Grant, Grant, 2002, 2003Podos, 2001;Vincek et al, 1997). Essas aves são representadas atualmente por 13 espécies no arquipélago de Galápagos (formado por 13 ilhas maiores e seis menores) e uma espécie na ilha Cocos, que variam desde a cor da plumagem e a forma do bico até outros aspectos morfológicos, comportamentais, biológicos, ecológicos e genéticos (Grant, Grant, 2006).…”

“…A pesquisa de Podos (2001) demonstrou que a forma do bico está associada com o tipo de canto que a ave entoa. As espécies com bicos pequenos produzem trinados rápidos e com maior variação de frequência, enquanto espécies com bicos grandes produzem trinados mais lentos com menor número de frequências.…”