Molecular evidence to reconcile taxonomic instability in mahseer species (Pisces: Cyprinidae) of India

Abstract

The mahseers are an important group of fishes endemic to Asia with most species considered threatened. Conservation plans to save declining wild populations are hindered by unstable taxonomy, and detailed systematic review could form a solid platform for future management and conservation. D-loop and cytochrome c oxidase I (COI) mtDNA sequences were examined in nine mahseer species of Tor, Neolissochilus, and Naziritor. Pseudogenes amplified in a portion of the species limited the utility of the D-loop region. ABGD analysis, NJ, ML, and MP methods and genetic distance (TrN + I + G) using COI data revealed concordant species delimiting patterns. The three genera were monophyletic, separated as distinct clades (TrN + I + G 0.064 to 0.106), and Naziritor was flagged as a separate genus, distinct from Puntius (TrN + I + G 0.196). Out of seven nominal species known for Tor cogeners from India, only five were recovered with mtDNA data (TrN + I + G 0.000 to 0.037) and two species could not be distinguished with the molecular data set employed. Tor mosal, synonymized as Tor putitora, was rediscovered as a distinct species (TrN + I + G 0.031) based on its type locality. Tor mussulah was confirmed as a separate species (TrN + I + G 0.019 to 0.026). Two valid species, Tor macrolepis and T. mosal mahanadicus, were not distinct from T. putitora (TrN + I + G 0.00). The high divergence with mtDNA data failed to validate T. mosal mahanadicus as a subspecies of T. mosal (TrN + I + G 0.031). Morphological outliers discovered within the distribution range of Tor tor (TrN + I + G 0.022 to 0.025) shared the same lineage with T. putitora (TrN + I + G 0.002 to 0.005), indicating a new extended distribution of the Himalayan mahseer T. putitora in the rivers of the Indian central plateau. The findings indicate the need for integrating molecular and morphological tools for taxonomic revision of the Tor and Naziritor genera, so that taxa are precisely defined for accurate in situ and ex situ conservation decisions.