The biogeography and phylogeny of schizothoracine fishes (Schizopygopsis) in the Qinghai-Tibetan Plateau

Freshwater fish belonging to the genus Schizopygopsis are widespread in drainages throughout the Qinghai-Tibetan Plateau and, thus, a model group with which to investigate how paleo-drainage changes linked to historical uplifting within the Qinghai-Tibetan Plateau influence speciation. To date, the phylogenetic and taxonomic relationships within Schizopygopsis remain controversial. In this study, we constructed a comprehensive molecular phylogeny of Schizopygopsis based on six mitochondrial gene sequences. We compared the taxonomic relationships revealed by this phylogeny with those obtained from morphological data. We also used this phylogeny to assess the extent to which the evolution of Schizopygopsis has been driven by paleo-drainage changes linked to uplifting of the Qinghai-Tibetan Plateau. Results indicated that all Schizopygopsis taxa formed a monophyletic group comprising five major clades, which were inconsistent with the taxonomic relationships based on morphology for this group. Our results also strongly supported the validity of S.anteroventris and S.microcephalus as distinct species within Schizopygopsis. Molecular calibrations showed that species within the middle Yangtze species diverged earlier (similar to 4.5Mya) than species within the Indus River (similar to 3.0Mya), the Mekong River (similar to 2.8Mya) and the Tsangpo+Salween rivers (similar to 2.5Mya). The most recent evolutionary splits occurred among species from the upper and lower Yangtze River, the Yellow River and the Qiadam Basin at about 1.8 to 0.3Mya. Our molecular evidence and use of the molecular clock calibration have allowed us to associate speciation events within the genus Schizopygopsis to the formation and separation of paleo-drainage connections caused by tectonic events during the uplifting of the Qinghai-Tibetan Plateau (similar to 4.5Mya). This work underlines the dominant role of vicariance in shaping the evolutionary history of the genus Schizopygopsis. Further research using multiple loci and more extensive sampling will reveal a more complete picture of the phylogenetic relationships and biogeography of Schizopygopsis fishes.