Abstract

Background/Objectives: Phylogenetic relationships within Triplophysa remain unclear due to limited molecular data and complex traits. Mitochondrial genomes are robust markers for teleostean phylogeny and molecular evolution. This study aims to provide Triplophysa brevicauda mitochondrial genome and molecular evidence for its phylogenetic position and high-altitude adaptation. Methods: The complete mitochondrial genome of T. brevicauda was assembled via Illumina NovaSeq 6000 paired-end sequencing. Genomic characteristics were analyzed, with phylogenetic reconstruction based on complete mitochondrial genomes and selective pressure analyses for adaptive evolution. Results: The 16,570 bp circular genome encodes 13 PCGs, 22 tRNAs, two rRNAs, and a D-loop. All PCGs start with ATG (except cox1) and terminate with TAA, TAG, or incomplete Triplophysa Phylogenetic analysis supports four Triplophysa clades, with T. brevicauda sister to Triplophysa nujiangensa. Purifying selection is pervasive, with elevated non-synonymous rates in atp8, nad2, nad4L, nad6, and positive selection in nad2/nad5. Conclusions: Positive selection in nad2 and nad5 may relate to T. brevicauda’s plateau adaptation. This study provides valuable mitochondrial resources, supporting further research on Triplophysa’s phylogeny and high-altitude adaptive evolution.

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