Accounting for Phylogenetic Uncertainty in Biogeography: A Bayesian Approach to Dispersal-Vicariance Analysis of the Thrushes (Aves: Turdus)

The phylogeny of the thrushes (Aves: Turdus) has been difficult to reconstruct due to short internal branches and lack of node support for certain parts of the tree. Reconstructing the biogeographic history of this group is further complicated by the fact that current implementations of biogeographic methods, such as dispersal-vicariance analysis (DIVA; Ronquist, 1997), require a fully resolved tree. Here, we apply a Bayesian approach to dispersal-vicariance analysis that accounts for phylogenetic uncertainty and allows a more accurate analysis of the biogeographic history of lineages. Specifically, ancestral area reconstructions can be presented as marginal distributions, thus displaying the underlying topological uncertainty. Moreover, if there are multiple optimal solutions for a single node on a certain tree, integrating over the posterior distribution of trees often reveals a preference for a narrower set of solutions. We find that despite the uncertainty in tree topology, ancestral area reconstructions indicate that the Turdus clade originated in the eastern Palearctic during the Late Miocene. This was followed by an early dispersal to Africa from where a worldwide radiation took place. The uncertainty in tree topology and short branch lengths seems to indicate that this radiation took place within a limited time span during the Late Pliocene. The results support the role of Africa as a probable source area for intercontinental dispersals as suggested for other passerine groups, including basal diversification within the songbird tree.