Island-hopping anurans: diversification dynamics in a widespread frog family

Abstract Examining diversification patterns associated with dispersal, vicariance, and local adaptation is critical in elucidating drivers of speciation. Frogs of the family Ceratobatrachidae are a widely distributed, largely insular, lineage occurring from Indo-Burma to Fiji with their highest diversity in Melanesia and the Philippines. We estimate evolutionary relationships among ceratobatrachids to test hypotheses about diversification dynamics. Ancestral-state estimates indicate that the basal ecotype of these direct-developing frogs was most likely terrestrial, with semi-aquatic, arboreal, and scansorial ecotypes evolving multiple times within Cornufer (N = 4) and Platymantis (N = 5). Divergence between Cornufer and Platymantis, and divergences within Cornufer during the past 35 Myr, occurred under conditions in which the geological terranes inhabited by these frogs formed a string of islands extending from near present-day Palau far out into the Pacific. Placement of these islands during that time would have provided ideal conditions for frogs to island hop far out into the Pacific with the North Equatorial Countercurrent (NECC) c. 25–12 Mya. Subsequent rearrangement of the underlying tectonic plates moved the islands colonized by Cornufer out of the NECC, with most subsequent diversification occurring within present-day archipelagos. Our findings corroborate a growing body of evidence that these ancient island-arc systems have been an important source of diversification within the Southwest Pacific.