Unraveling unique island colonization events in Elachistocleis frogs: phylogeography, cryptic divergence, and taxonomical implications

Over the last two decades, molecular work on the reptile and amphibian fauna of the island of Trinidad (West Indies) has revealed the presence of cryptic species and island endemics resulting in the re-description of species for northern South America. In this study, we assess the taxonomy of a population of Elachistocleis sp. formerly assigned to the invalid species E. ovalis , and E . surinamensis , both present in Trinidad and throughout South America. We conduct phylogenetic, morphological, and call characteristic analyses to assess their taxonomy and discuss the phylogeography and evolutionary history of the genus. We find an Andean origin of the genus dating to the Oligocene and two sister clades within Elachistocleis with a Mid-Miocene divergence, coinciding with marine incursions at the time. We discuss their likely dispersal throughout South America following the dry-out of the Pebas mega-wetland system and attempt to find the routes of expansions, probably aided through the Amazon basin and hydrological systems towards the north and east. We find that each of the species is highly divergent and recovered in both sister clades, and we time the colonization of each Trinidad population at 2.1 and 0.5 million years ago, arriving from different regions (Venezuela and Guyana) facilitated by sea-level drops at the time. Lastly, we select a neotype for E . surinamensis from Trinidad to stabilize the nomenclature and describe the frog formerly considered E . ovalis in Trinidad as E . nigrogularis sp. nov.