A molecular phylogeny of the freshwater-fish genusRasbora(Teleostei: Cyprinidae) in Sri Lanka reveals a remarkable diversification-And a cryptic species

The diversity of the freshwater-fish genusRasbora(Cyprinidae) on Sri Lanka (five species) is high compared with the four species reported from the peninsula of India, from which the island's cyprinid fauna is derived. The paucity of characters by which species ofRasboracan be phenotypically distinguished renders field identification difficult, adversely affecting the estimation of populations and distributions, with consequences for conservation and management, increasing also the risk of taxonomic inflation. From a sampling of 90 sites across Sri Lanka and based on phylogenetic and haplotype analyses of sequences ofcox1andcytbmitochondrial, andrag1andirbpnuclear markers, we review the species diversity and phylogeography ofRasboraon the island. Molecular analyses recover, in addition to the five species previously reported, a new (cryptic) species:Rasbora adisisp. nov. Uncorrected pairwisecox1genetic distances between species range from 2.0 to 12.3 percent. The Sri Lankan diversification derives from a common ancestor which arrived from India during a sea-level low-stand in the mid-Miocene (15.1 Ma [95% HPD: 11.5-19.8 Ma]), when the present-day island was subaerially connected to the Indian subcontinent by a broad isthmus. This gave rise to a clade comprising five species-R. adisisp. nov.,Rasbora armitagei,Rasbora microcephalus,Rasbora naggsiandRasbora wilpita-with a crown age of 9.9 Ma (95% HPD: 7.1-13.3 Ma) and to a clade comprising Indian and Sri Lankan populations ofRasbora dandia, which themselves are reciprocally monophyletic. Morphological analysis of 334 specimens discriminates between most species which, however, are most reliably diagnosed by chromatic characters. The four endemic species exhibit a pattern of inter-basin dispersal via headwater capture, followed by vicariance, explaining the high diversity of the genus on the island.