‘Out-of-Africa’ dispersal of tropical floras during the Miocene climatic optimum: evidence from Uvaria (Annonaceae)

Abstract

African-Asian disjunctions are common in palaeotropical taxa and have been the focus of considerable biogeographical research. Alternative hypotheses for these biogeographical disjunctions have been proposed, including ‘rafting’ on the Indian tectonic plate, dispersal via Eocene ‘boreotropical’ forests, and long-distance dispersal. These hypotheses are tested using the angiosperm genus Uvaria (Annonaceae), with divergence times estimated using a Bayesian relaxed molecular clock. Uvaria originated in continental Africa, ca. 31.6 Ma, and migrated into Asia in the early to middle Miocene. ‘Rafting’ on India and the Eocene boreotropical hypotheses are rejected due to incongruence with divergence times, and the genus is shown to be dispersed by primates, making it an unlikely candidate for transoceanic dispersal. Here we show that dispersal is likely to have occurred via boreotropical forests associated with the late Middle Miocene thermal maximum. This is the most convincing evidence yet for such a dispersal route for a tropical plant group.