Comparative genomics has elucidate the molecular footprints of adaptations to extreme environments at high altitude including hyopxia, but insight into the genomic basis of saline and alkaline adaptation in highland fish has rarely been provided. The increasing of water salinization is a growing threat to Tibetan endemic fish speces. Here we performed one of the first comparative genomics studies and began to characterize genomic signature of alkaline adaptation in a Schizothoracine fish inhabiting soda lake on the Tibetan Plateau. We found that expansions of lineage-specific genes associated with ion transport and transmembrane functions, genome-wide elevated rate of molecular evolution in Schizothoracine fishes relative to other lowland teleost fish species. In addition, we found specific changes in the rate of molecular evolution between G. p. kelukehuensis and other teleost fishes for ion transport-related genes. Furthermore, we identified a set of genes associated with ion tranport and energy metabolism underwent positive selection. Using tissue-transcriptomics, we found that most REGs and PSGs in G. p. kelukehuensis were broadly expressed across three tissues and significantly enriched for ion transport functions. Finally, we identified a set of ion transport-related genes with evidences for both selection and co-expressed which contributed to alkaline tolerance in G. p. kelukehuensis. Althogether, our study identified putative genomic signature and potential candidate genes contributed to ongoing alkaline adaptation in Schizothoracine fish.

Genomic signature of ongoing alkaline adaptation in a Schizothoracine fish (Cyprinidae) inhabiting soda lake on the Tibetan Plateau