DNA Barcoding Reveals Cryptic Diversity in the Underestimated Genus Triplophysa (Cypriniformes: Cobitidae, Nemacheilinae) from the Northeastern Qinghai-Tibet Plateau

Abstract

Background: The northeastern part of the Qinghai-Tibet Plateau (QTP) is one of the areas where the number of species of plateau loach is the largest. As one of the three major groups of fishes distributed on the QTP, plateau loach have very important ecological value. However, their taxonomy and systematics are still controversial, and a large number of new species have been reported. The reason for this phenomenon is that the degree of morphological variation is low, the phylogenetic information provided by morphological and anatomical features used for species identification is relatively poor, and there are many cryptic species. Based on the high-density sampling points from the biodiversity hotspots surveyed, this study aims to evaluate the biodiversity of plateau loach in the northeastern of QTP and reveal the hidden diversity by comparing morphologic species with molecular operational taxonomic units (MOTUs). Results: After careful identification and comparison of the morphology and DNA barcoding of 1,630 specimens, 22 species were identified, 20 of which were considered valid local species and two of which were new species that had not been described. Based on the combination of morphological and molecular methods, a total of 24 native species have been found, two of which are cryptic species: Triplophysa robusta sp1 and Triplophysa minxianensis sp1. Fourteen of the 24 species form clusters of barcodes, which allow them to be reliably identified. The remaining cases involved 10 closely related species, some of which were rapidly differentiated, seemed to have experienced incomplete lineage sorting, or showed introgressions.Conclusions: The results highlight the need to combine traditional taxonomies with molecular methods to correctly identify species, especially in closely related species such as the plateau loach. This study provides a basis for protecting the biodiversity of plateau loach.