A molecular phylogeny of Asian barbets: Speciation and extinction in the tropics

• Not all named species are monophyletic.
• Five clades raised to species level.
• Most species originate before the Pleistocene.
• Phylogenetic evidence for extinction in island lineages.
• Support for “museum hypothesis” origin of tropical diversity.

We reconstruct the phylogeny of all recognized species of the tropical forest associated Asian barbets based on mitochondrial and nuclear sequence data and test for the monophyly of species and genera. Tropical regions are well known for their extraordinarily high levels of biodiversity, but we still have a poor understanding of how this richness was generated and maintained through evolutionary time. Multiple theoretical frameworks have been developed to explain this diversity, including the Pleistocene pump hypothesis and the museum hypothesis. We use our phylogeny of the Asian barbets to test these hypotheses. Our data do not find an increase in speciation in the Pleistocene as predicted by the Pleistocene pump hypothesis. We do find evidence of extinctions, which apparently contradicts the museum hypothesis. However, the extinctions are only in a part of the phylogeny that is distributed mainly across Sundaland (the Malay peninsula and the islands off southeast Asia). The theory of island biogeography predicts a higher rate of extinction on islands than on mainland areas. The data from the part of the phylogeny primarily distributed on the mainland best fit a pure birth model of speciation, and thus supports the museum hypothesis.

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