Revisiting the Centre Hypotheses of the Indo-West Pacific: Idiosyncratic genetic diversity of nine reef species offers weak support for the Coral Triangle as a centre of genetic biodiversity

AimSeveral biogeographic hypotheses seek to explain the extreme species diversity of the coral reefs in the Coral Triangle (CT) of the Indo-West Pacific (IWP). Here, we investigate processes implicit to the Centre of Origin, Centre of Overlap and Centre of Survival hypotheses. We focus on intraspecific genetic data, where intraspecific diversity can provide information regarding directionality of past dispersal (gene flow) and changes in population size such as expansion from refugia. LocationIndian Ocean, Coral Triangle and West Pacific Ocean. MethodsWe use existing mitochondrial DNA data augmented with new samples from the Philippines, thus filling in key sampling gaps from previous studies, to examine nine reef species. We first test if genetic diversity peaks in the CT. We then estimate gene flow between regionsCT vs. Indian Ocean (IO) and CT vs. Pacific Ocean (PO)to assess concordance with predicted directions of movement (i.e. into the CT or out of the CT). Finally, we investigate the historical demography of these species and evaluate population expansions to ascertain whether genetic diversity is correlated with putative Pleistocene refugia. ResultsGenetic diversity in the CT was not greater than genetic diversity in the IO and PO, and we found highly variable spatial patterns of genetic diversity when species were evaluated individually. Gene flow estimates indicated very limited exchange between regions, consistent with peripheral isolation and/or signals of historical divergence. For some species, however, there were signals of movement out of the CT. While there was no significant correlation between genetic diversity and putative refugia, genetic patterns suggested that some populations have experienced population expansions. The locations of expansion were also variable across species. Overall, there was no signal of concordant processes shaping intraspecific genetic diversity. Main conclusionsGenetic patterns across species were highly variable with some species lending weak support for processes aligned with each of the Centre of diversity hypotheses. But overall there was no compelling evidence for uniform processes underlying all species, which possibly indicate that processes underlying the different Centre have not strongly affected IWP species within the recent past.