The Qinghai-Tibetan Plateau is the largest and youngest high land in the world. Because of its particular environment of the high altitude, like hypoxia, coldness and high radiation, animals living on the high land were forced to undergo adaptive changes in morphology, behavior, ecology, physiology and genetics. These animals have acquired particular adaptation traits to the environment of high altitude. To study the genetic basis of those traits and evolutionary history of high altitude animals, we sequenced and analyzed mitochondrial genomes (mt-genome) of three representative high altitude animals: Tibetan antelopes (Pantholops hodgsonii), Tibetan horses (Equns caballus), and plateau pikas (Ochotona curzoniae). The results are as followings: 1. mt-genome and high altitude adaptation of the Tibetan antelope (Pantholops hodgsonii) Analysis on mitochondrial DNA mutations indicates that the COXI (cytochrome c oxidase subunit I) gene has higher non-synonymous mutation rate in Pantholops hodgsonii and Bos grunniens. COX1 is one of the subunits of complex Ⅳin respiratory chain, which transfers electrons to oxygen and generates ATPs. Considering the same climate and environment shared by these two mammalian species, we proposed that the mitochondrial COXI gene is probably relevant for these native mammals to adapt to the high altitude environment. Based on the mitochondrial DNA sequence data, the estimated divergence time between Pantholops hodgsonii and Ovis aries is about 2.25 million years ago, which is closed to the estimated time of the Qinghai-Tibet plateau uplift. 2. The mt-genome of the plateau pika (Ochotona curzoniae) The full length mitochondrial genome of plateau pika (Ochotona curzoniae) is 17566bps, which is longer than American pikas (Ochotona collaris and Ochotona princes) (16968bp & 16481bp respectively). The variation of the mitochondrial genome length is caused by the different copy number and types of repeat fragments. After analyzing the protein coding genes in the mitochondrial genome, again we found that COX1 gene has a higher non-synonymous mutation rate on the branch of Ochotona curzoniae. This indicates that COX1 may be also under selection during the adaptation process of Ochotona curzoniae to the environment of high altitude. 3. mt-genome and estimatary history of Tibetan horses (Equns caballus) We sequenced three mt-genomes of Tibetan horses collected from Naqu (4500m) of Tibetan, Zhongdian (3300m) and Deqin (3100m) of Yunnan province. The structure and length of these three mt-genomes are similar to the Cheju horses. Different from COX1 under selection in the Tibetan antelope and plateau pika, when analyzing the mitochondrial protein coding genes of Tibetan horses, we found NADH6 has higher non-synonymous mutation rate in all of three Tibetan horses. This implies that NADH6 may play a role for Tibetan horses’ high altitude adaptation. NADH6 is one of the subunits of complexⅠin respiratory chain. Although both of NADH6 and COX1 located in respiratory chain, they belong to different complexes and play different roles for respiratory chain. Whether the different evolution patterns of mitochondrial genes caused by different adaptive genetic basises of animals or by other reasons is unclearly. Further works should be undertaken to answer this question. Furthermore, the study of evolutionary history of Tibetan horses suggests that the extant Tibetan horse populations may have multiple origins.
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