A corollary of island biogeographical theory is that islands are largely colonized from their nearest mainland source. Despite Madagascar’s extreme isolation from India and proximity to Africa, a high proportion of the biota of the Madagascar region has Asian affinities. This pattern has rarely been viewed as surprising, as it is consistent with Gondwanan vicariance. Molecular phylogenetic data provide strong support for such Asian affinities, but often not for their vicariant origin; most divergences between lineages in Asia and the Madagascar region post-date the separation of India and Madagascar considerably (up to 87 Myr), implying a high frequency of dispersal that mirrors colonization of the Hawaiian archipelago in distance. Indian Ocean bathymetry and the magnitude of recent sea-level lowstands support the repeated existence of sizeable islands across the western Indian Ocean, greatly reducing the isolation of Madagascar from Asia. We put forward predictions to test the role of this historical factor in the assembly of the regional biota.
© The Willi Hennig Society 2009.