A phylogeny of Darwin's finches based on microsatellite DNA length variation

Allele length variation at 16 microsatellite loci Tvas used to estimate the phylogeny of 13 out of the 14 species of Darwin's finches. The resulting t opology was similar to previous phylogenies based on morphological and allo zyme variation. An unexpected result was that genetic divergence among Gala pagos Island populations of the warbler finch (Certhidea olivacea) predates the radiation of all other Darwin's finches. This deep split is surprising in view of the relatively weak morphological differentiation among Certhid ea populations and supports the hypothesis that the ancestor of all Darwin' s finches was phenotypically similar to Certhidea. The results also resolve a biogeographical problem: the Cocos Island finch evolved after the Galapa gos finch radiation was under way supporting the hypothesis that this dista nt island was colonized from the Galapagos Islands. Monophyletic relationsh ips are supported for both major groups, the ground finches (Geospiza) and the tr ee finches (Camarhynchus and Cactospiza), although the vegetarian fi nch (Platyspiza crassirostris) appears to have diverged prior to the separa tion of ground and tree finches. These results demonstrate the use of micro satellites for reconstructing phylogenies of closely related species and in terpreting their evolutionary and biogeographic histories.