Mosaic patterns of diversification dynamics following the colonization of Melanesian islands.

The fate of newly settled dispersers on freshly colonized oceanic islands is a central theme of island biogeography. The emergence of increasingly sophisticated methods of macroevolutionary pattern inference paves the way for a deeper understanding of the mechanisms governing these diversification patterns on lineages following their colonization of oceanic islands. Here we infer a comprehensive molecular phylogeny for Melanesian Exocelina diving beetles. Recent methods in historical biogeography and diversification rate inference were then used to investigate the evolution of these insects in space and time. An Australian origin in the mid-Miocene was followed by independent colonization events towards New Guinea and New Caledonia in the late Miocene. One colonization of New Guinea led to a large radiation of >150 species and 3 independent colonizations of New Caledonia gave rise to about 40 species. The comparably late colonizations of Vanuatu, Hawaii and China left only one or two species in each region. The contrasting diversification trajectories of these insects on Melanesian islands are likely accounted for by island size, age and availability of ecological opportunities during the colonization stage.