Congruence of morphometric and cultural evolution in Atlantic island chaffinch populations

Abstract

Cultural and morphometric evolution of populations of chaffinches from the Azores, Madeira, and Canary Islands were compared using songs and external measurements from seven populations. Cultural evolution was assessed by computing distances among island syllable pools, based on presence or absence coding of syllables. Morphometric differentiation was assessed by computing average taxonomic distances among populations using data from Grant (P. R. Grant. Biol. J. Linn. Soc. 11: 301–332. 1979). Separate analyses of the syllable pool and morphometric distances using cluster and principal coordinates analysis revealed that populations within archipelagos are more similar to one another than they are to populations in different archipelagos. The Madeira population occupies an intermediate position, consistent with its geographic location between the Azores and Canaries archipelagos. Congruence of the patterns of morphometric and cultural evolution in these islands suggests to us that the differentiation has been influenced by a colonization history involving restricted gene and meme flow between archipelagos, subsequent drift, and possibly founder effects. Although directional selection has been implicated in the morphometric differentiation (Grant 1979), cultural evolution (like neutral gene evolution) does not seem to have been subject to selective forces.