Abstract Biotic dispersal between regions is mediated by a suite of geographical, environmental, and biotic factors. Australia and Melanesia—with the latter centred on New Guinea—are geographically proximate regions that show differing abiotic environments and geological histories, providing an opportunity to document how environmental variation may interact with geographical proximity in shaping dispersal and evolution. Here, we present a phylogenomic framework and analysis of dispersal history for geckos in the genus Gehyra, a radiation of ∼70 species that occur across Australia, Melanesia, and nearby regions. Despite an evident history of numerous overwater dispersals in species groups occurring in Melanesia, we find very low rates of historical dispersal between Australia and Melanesia and no evidence of an increase in dispersal rate as land bridges formed between Australia and New Guinea from the late Miocene onwards. Analyses of body-size evolution suggest that ‘giant’ large-bodied forms have evolved on islands, but rather than evolving repeatedly on different islands, these are mostly members of a single old clade that dispersed across multiple islands. In contrast to some other Australasian vertebrate radiations, for Gehyra geckos, environmental differences appear to have strongly impeded dispersal between Australia and Melanesia, while also favouring differing trajectories of body size evolution.
Oliver et al. (Fri,) studied this question.