Comprehensive transcriptome analysis reveals accelerated genic evolution in a Tibet fish, Gymnodiptychus pachycheilus

Area of Science:

• Evolutionary biology
• Genomics
• Molecular biology

Background:

• Understanding organismal adaptation to extreme environments like the Tibetan Plateau is crucial for evolutionary studies.
• While many highland species have been studied, the genomic basis of adaptation in Tibetan fishes remains largely unknown.
• Schizothoracine fishes are endemic to the Tibetan Plateau, making them ideal models for studying highland adaptation.

Purpose of the Study:

• To elucidate the genetic mechanisms underlying adaptation to the Tibetan Plateau in fishes using genomic approaches.
• To identify potential candidate genes and pathways involved in highland adaptation in the schizothoracine fish, *Gymnodiptychus pachycheilus*.
• To establish genomic resources for Tibetan fishes and provide insights into their evolutionary history.

Main Methods:

• Transcriptome sequencing of *Gymnodiptychus pachycheilus* to generate genomic data.
• Assembly of unigenes and identification of orthologs in related species like zebrafish.
• Comparative genomic analysis, including gene gain/loss estimations and Ka/Ks ratio calculations.
• Analysis of accelerated evolution and positive selection in gene lineages.

Main Results:

• Generated 66,105 assembled unigenes, with 7,232 identified as one-to-one orthologs with zebrafish.
• Identified significant gene gain and loss events between *G. pachycheilus* and zebrafish since their divergence.
• Detected genome-wide accelerated evolution in *G. pachycheilus*, particularly on the terminal branch, with an elevated Ka/Ks ratio.
• Found enrichment of genes related to hypoxia and energy metabolism among those showing rapid evolution and positive selection.

Conclusions:

• The study provides the first genomic resources for fish inhabiting the Tibetan Plateau.
• Rapid evolution in hypoxia and energy metabolism pathways suggests key adaptations to the high-altitude environment.
• These findings offer novel insights into fish adaptation to Tibet and lay the groundwork for future research on specific adaptive genes.