The origin and evolution of coral species richness in a marine biodiversity hotspot

The Coral Triangle region of the Indo-Pacific realm harbors an extraordinary number of species, with richness decreasing away from this biodiversity hotspot. Despite multiple competing hypotheses, the dynamics underlying this regional diversity pattern remain poorly understood. Here we use a time-calibrated evolutionary tree of living reef coral species, their current geographic ranges, and model-based estimates of regional rates of speciation, extinction, and geographic range shifts to show that origination rates within the Coral Triangle are lower than in surrounding regions, a result inconsistent with the long-standing center of origin hypothesis. Furthermore, endemism of coral species in the Coral Triangle is low, and the Coral Triangle endemics are older than relatives found outside this region. Overall, our model results suggest that the high diversity of reef corals in the Coral Triangle is largely due to range expansions into this region of species that evolved elsewhere. These ...