Plumage convergence and evolutionary history of the Island Thrush in the Philippines

Abstract

With more than 50 described subspecies occurring throughout Southeast Asia and Micronesia and a wide array of morphological and ecological variation, the Island Thrush (Turdus poliocephalus) is one of the most variable known bird species. However, this bird has been studied surprisingly little from an evolutionary perspective, with no information on its evolutionary history to inform our understanding of its tremendous variation. In this study, we examine the population history of the Island Thrush within the Philippine Islands, sampling 88 individuals from six named Philippine subspecies and three populations currently lacking formal subspecific names, as well as several outgroups. Many subspecies are not reciprocally monophyletic, yet most island populations are, and show up to 2.6% sequence divergence (uncorrected). Philippine populations are not monophyletic; samples from Borneo, Sulawesi, Vanuatu, and the Solomon Islands are nested within the Philippines. Previously hypothesized routes of the colonization of the Philippines assume a single initial colonization event and cannot account for the current distribution of haplotypes, which implies at least two colonization events. Morphologically similar taxa in the Philippines are not each other's closest relatives, thus demonstrating plumage convergence. We emphasize the need for further study of this taxon throughout its range, particularly in light of conservation priorities. © The Cooper Ornithological Society 2008.