Biogeography of the neotropical freshwater stingrays (Myliobatiformes: Potamotrygoninae) reveals effects of continent-scale paleogeographic change and drainage evolution

Aim Paleogeographic changes have had profound effects on the evolution and diversity of the Neotropical biota. However, the influence of marine incursions on the origin, diversification, and distribution of fishes is still incompletely understood. We investigate the biogeographical and chronological patterns of diversification for the marine-derived Neotropical freshwater stingrays (subfamily Potamotrygoninae) at a continental scale. Location Neotropics, South America. Taxa Neotropical freshwater stingrays. Subfamily Potamotrygoninae (Myliobatiformes: Chondrichthyes). Methods We generated a time-calibrated phylogeny for 35 of the 38 valid species of Neotropical freshwater stingrays, from most of the major river basins of South America, using four genes. We used BEAST2 to determine the chronology of population and species divergence events, and ``BioGeoBEARS{''} to infer historical biogeographic patterns. Results The Potamotrygoninae originated during the early/middle Miocene in the upper Amazon region. We recover clades associated with particular geographic areas and detect a recurrent pattern of upper Amazon clades sister to clades in adjacent basins. The timing of dispersals from the upper Amazon to adjacent areas corresponds with the end of the Pebas wetlands. Lower Amazon and Shield associated taxa are relatively young. Main conclusions We propose that the origin of the Neotropical freshwater stingrays is related to marine incursions that occurred during the Oligocene/Miocene. Subsequent diversification of Potamotrygoninae occurred in the Pebas wetland system in the upper Amazon with colonization of adjacent basins. These movements were generally unidirectional, with few lineages returning to the upper Amazon, and we speculate that ecological factors drove this pattern. We observed a burst of potamotrygonine diversification 5 Ma that appears to be related to the modern channelization of the Amazon Basin. (AU)