Comprehensive Transcriptome Analysis Reveals Accelerated Genic Evolution in a Tibet Fish, Gymnodiptychus pachycheilus

restu amalia;

Elucidating the genetic mechanisms of organism aladaptationto the Tibetan Plateau atagenomic scale can provide insights into the process of adaptive evolution. Many high land species have been investigated and various candidate genes that may beresponsible for high land adaptation have been identified. However, we know little about the genomic basis of adaptation to Tibet infishes. Here,we performed transcriptome sequencing of a schizothoracine fish (Gymnodiptychus pachycheilus) and used it to identify potential genetic mechanisms of highland adaptation. We obtained totally 66,105 assembled unigenes, of which 7,232 were assigned as putativeone-to- one orthologs in zebra fish. Comparative gene annotations from several species indicated that atleast 350 geneslost and 41 gained since the divergence between G. pachy cheilus and zebrafish. Ananalysis of 6,324 orthologs among zebrafish, fugu, medaka, and spotted gar identified consistent evidence for genome-wide accelerated evolution in G. pachycheilus and only the terminal branch of G. pachycheilus had an elevated Ka/Ks ratio than the ancestral branch. Many functional categories related to hypoxia and energy metabolism exhibited rapid evolution in G. pachycheilus relative to zebrafish. Genes showing signature of rapid evolution and positive selection in the G.pachycheilus lineage were also enriched infunctions associated with energy metabolism and hypoxia. The first genomic resources for fish in the Tibetan Plateau and evolutionary analyses provided some novel insights into high land adaptation in fishes and served as a foundation for future studies aiming to identify candidate genes underlying the genetic bases of adaptation to Tibet in fishes