Biogeographic origins of Darwin's finches (Thraupidae: Coerebinae).

Darwin's finches are considered a classic example of an adaptive radiation, and have been the focus of numerous studies from ecological and evolutionary perspectives. Few studies, however, have attempted to investigate the biogeographic origins of Darwin's finches. In this paper, we reconstruct the ancestral biogeography of Coerebinae, the tanager subfamily that contains Darwin's finches and their 14 closest relatives. We use this reconstruction to examine the origin of Darwin's finches, and the diversification of this clade of tanagers. We test multiple biogeographic models using the R package BioGeoBEARS utilizing a recent multilocus phylogeny. We used these models to examine 2 different hypotheses regarding the biogeographic origin of Darwin's finches. The majority of ancestral ranges within this subfamily were estimated as Caribbean restricted. Biogeographic models run using 8 regions suggest Darwin's finches arose from a long-distance dispersal event from the Caribbean Islands as opposed to the geographically closer mainland South America. However, models run using only 5 areas suggest equal probability between a Caribbean and a mainland South America origin to Darwin's finches. This study suggests equal probability for a Caribbean origin to Darwin's finches as a South American mainland origin. Conflict between models run using different biogeographic regimes highlights the sensitivity of these reconstructions to biogeographic region delineation. Overall, the Caribbean Islands appear especially important for the initial diversification of this clade, with many small-island restricted species diversifying early in the radiation. Colonization success was likely coupled with high dispersal ability and highly variable bill morphology to exploit vacant niche space. [ABSTRACT FROM AUTHOR]