Abstract
Tibetan loaches are the largest group of Tibetan fishes and are well adapted to the Tibetan Plateau. To investigate the origin of Tibetan loaches and their adaptations to the Tibetan Plateau, we determined 32 complete mitochondrial genomes that included 29 Tibetan loach species, two Barbatula species and Schistura longus. By combining these newly determined sequences with other previously published mitochondrial genomes, we assembled a large mitogenomic data set (11,433 bp) of 96 species in the superfamily Cobitoidea, to investigate the phylogenetic status of the genus Triplophysa. The resulting phylogeny strongly supported that the genus Triplophysa forms a monophyletic group within Nemacheilidae. Our molecular dating time suggests that the lineage leading to the Tibetan loaches and other loaches diverged approximately 23.5 Ma, which falls within the period of recent major uplifts of the Tibetan Plateau in the Early Miocene. Selection analyses revealed that the mitochondrial protein-coding genes of Tibetan loaches have larger ratios of nonsynonymous to synonymous substitutions than do those of non-Tibetan loaches, indicating that Tibetan loaches accumulated more nonsynonymous mutations than non-Tibetan loaches and exhibited rapid evolution. Two positively selected sites were identified in the ATP8 and ND1 genes.
Highlights
Genes Combined data ATP6 ATP8 COX1 COX2 COX3 CYTB ND1 ND2 ND3 ND4 ND4L ND5 ND6
The mitochondrial protein-coding genes (PCGs), transfer RNA genes (tRNA), ribosomal RNA genes (rRNA) and control region (CR) were encoded on the heavy strand except for ND6 and eight tRNA genes, which were encoded on the light strand
The concatenated data set consisted of 11,433 bp from 13 PCGs of 96 mitochondrial genomes
Summary
Genes Combined data ATP6 ATP8 COX1 COX2 COX3 CYTB ND1 ND2 ND3 ND4 ND4L ND5 ND6. Nucleotide composition (%) T C A G Ti/Tv belonging to the family Nemacheilidae within the order Cypriniformes. Studies of the morphological characteristics and geographical distribution of Triplophysa have suggested that the origin and evolution of this group is related to the uplift of the Tibetan Plateau[22,23]. As representative endemic species of the Tibetan Plateau, Triplophysa species are well adapted to the high-altitude environment. We analyzed 32 complete, newly determined mitogenomes along with 64 published mitogenomes of the superfamily Cobitoidea, to 1) confirm the phylogenetic status of the genus Triplophysa within Nemacheilidae based on mitochondrial genomes and broad taxon sampling, 2) date the origin of the Triplophysa lineages, and 3) provide a comprehensive view of the adaptive evolution of the mitogenome in Triplophysa species during their independent acclimatization to high-altitude environments
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