Geological drivers of diversification in Papuan microhylid frogs

Abstract

Studies of the Papuan region have provided fundamental insights into both the evolutionary processes generating its exceptional biodiversity, as well support for alternative hypotheses of geological history. Lying at the junction of five tectonic plates, this region has experienced a turbulent geological history that has not only produced towering mountains allowing elevational specialization, and island archipelagos of varying distance promoting vicariance, but also active margins where land masses have collided and been subsequently rifted apart creating a mosaic of intermixed terranes with vastly different geological histories which may influence the evolutionary history of its biota. Asterophryine frogs are a hyperdiverse clade representing half the world’s microhylid diversity (over 360 species) centered on New Guinea and its satellite islands. We show that vicariance facilitated by geological history, and not elevational specialization best explain this far and wide distribution of a clade that should have poor dispersal abilities. Thus, some of the predictions of island biogeography theory are supported if informed by geological history. We recovered a mainland tectonic unit, the East Papua Composite Terrane (EPCT), as the center of origin for Asterophryinae and no fewer than 71 instances of what appear to be long-distance dispersal events, 29 of which are between mainland regions, with 42 from the mainland to the islands, some presently as far as 200 km away from source populations over open ocean. Furthermore, we find strong support for a “Slow and Steady” hypothesis for the formation of the northern margin of New Guinea by many separate accretion events during the Miocene, over other major geological alternatives, consistent with the 20 M year age of the clade and arrival via the EPCT. In addition, the historical biogeography of our frogs strongly support an affiliation of the Louisiade Archipelago and Woodlark Island with the Owen Stanley Mountain range on the EPCT, and the recent proximity of the large New Britain island. Our results show that Asterophryinae did not have to repeatedly and independently disperse across and large ocean barriers to the offshore islands, but that the current distribution can be explained through vicariance and short-distance oceanic dispersal as historical land connections disappeared and islands slowly became separated from each other. We show that islands have a life history, undergoing changes in area through island-building and erosion, but also change in distance from other land masses, with consequent opportunities for dispersal, isolation, and cladogenesis of their biotas. More broadly, we can begin to see how the geological history of the Papuan region can result in the rapid accumulation and staggering number of extant species.