Phylogeny of the hillstream loach genus Mesonoemacheilus reveals widespread diversification through ancient drainage connections in the Western Ghats Biodiversity Hotspot.

Rivers draining the Western Ghats (WG) mountain ranges in peninsular India harbor an exceptionally diverse, unique and evolutionarily distinct assemblage of lower vertebrates with high levels of endemism, attributed to their evolution and potentially long history of isolation during the Late Cretaceous or Early Tertiary. A molecular phylogeny of hillstream loaches of the genus Mesonoemacheilus endemic to the WG revealed the presence of four clades which we designate as 'species groups'. A consensus of various species delimitation methods indicates the likelihood of 'at least' seven more undescribed species within Mesonoemacheilus. Molecular clock analysis dates the basal clade around 38 mya in the Paleogene, and subsequent diversification in the Neogene and Quaternary periods resulting in the current genetic diversity. Biogeographic analysis suggests that vicariance events which separated the rivers on either side of the two geological barriers/gaps, the Palghat and Shencottah, in the Neogene, as well as range contractions and cladogenetic events contributed to the current patterns of diversity and distribution of this genus. Our results also provide preliminary indications on the interconnections and faunal exchange between historical river drainages in the WG region.