The diversification of the loach genus Schistura McClelland, 1838 (Teleostei, Nemacheilidae) in Sri Lanka

The Palk Isthmus, which connected Sri Lanka to the Indian mainland during periods of low sea levels, has been the only route by which freshwater organisms could enter the island. The endemic aquatic biodiversity of Sri Lanka is dominated by diversifications stemming from founders that immigrated when the Isthmus was both emergent and possessed an aseasonal-mesic climate. The loach genus Schistura McClelland, 1838, among the most speciose of freshwater-fish genera, has three known representative species on the island. Based on two mitochondrial and two nuclear gene markers, we investigate the evolutionary relationships of Schistura in Sri Lanka, showing it to be a monophyletic diversification. Molecular species delimitation analysis recovered eight lineages (MOTUs). These exhibit strong geographical structure; each confined to one or more contiguous basins and two confined to a single basin. There is evidence for gene flow across watersheds, likely due to headwater river-capture. Schistura lineages in the central hills appear to result from multiple independent colonization events. The most widespread lineage in this region likely represents a more recent colonization, following a Late Pleistocene highland extirpation. An analysis of 39 phenetic traits across > 250 specimens revealed marked morpho-molecular incongruence. Taxonomy dependent entirely on phenetic traits is likely to be unreliable in rapidly diversifying populations such as these.