Chameleon radiation by oceanic dispersal

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Abstract
Historical biogeography is dominated by vicariance methods that search for a congruent pattern of fragmentation of ancestral distributions produced by shared Earth history1,2,3. A focus of vicariant studies has been austral area relationships and the break-up of the supercontinent Gondwana3,4,5. Chameleons are one of the few extant terrestrial vertebrates thought to have biogeographic patterns that are congruent with the Gondwanan break-up of Madagascar and Africa6,7. Here we show, using molecular and morphological evidence for 52 chameleon taxa, support for a phylogeny and area cladogram that does not fit a simple vicariant history. Oceanic dispersal—not Gondwanan break-up—facilitated species radiation, and the most parsimonious biogeographic hypothesis supports a Madagascan origin for chameleons, with multiple ‘out-of-Madagascar’ dispersal events to Africa, the Seychelles, the Comoros archipelago, and possibly Reunion Island. Although dispersal is evident in other Indian Ocean terrestrial animal groups8,9,10,11,12,13,14,15,16, our study finds substantial out-of-Madagascar species radiation, and further highlights the importance of oceanic dispersal as a potential precursor for speciation.