Taxonomy and Phylogenesis of Chinese Yak Based on the Complete Sequence of Mitochondrial Cytochrome b Gene in Tianzhu White Yak, Poephagus grunniens

摘要

It is well known that yak is originated from China but fact regarding its taxonomy and evolutionary relationship with other species of Bovini, is largely disputed. Here, we cloned 1140 bp complete mitochondrial cytochrome b (cytb) gene in Tianzhu with yak (JF946750). The origin, taxonomy of the Chinese yak and its phylogenetic relationship with other 8 species of Bovini were discussed based on the cytb. Results showed that Tianzhu white yak had high identity to Qinghai black breed with the minimum sequence divergence of 0.5%. The sequence divergence between yak and cattle/zebu (8.0-8.5%) was higher than that between yak and American bison (3.4-4.1%). Phylogeny analysis also found that domestic yak and wild yak clustered first of all, then gathered with American bison and other Bovini species, indicating yak and American bison were higher genetic comparability than that of other species. The findings sustained the idea that in the choice of nomenclature both the domestic yak and the wild yak belong to the subgenus of Poephagus . The approximate divergence time between domestic yak and wild yak was 0.50 Million Years Ago (MYA), while the yak and cattle/zebu, American bison, European bison, Asian buffalo/African buffalo was 4.00-4.25, 1.7-2.05, 3.80-3.85 and 6.70-6.95 MYA, respectively. We speculated that the ancient yak lived in the northeastern part of Eurasia during the Quaternary had been shifted south to the cold area of the Qinghai Tibetan Plateau (QTP) during the metaphase of the Pleistocene era. Some of them acclimated to today?s wild yak, the others were domesticated by the ancient Qiang people at least 4500 years ago. The sequential evolution could be predicted that buffalo was first to divided into Asian buffalo and African buffalo among the species of Bovini during the end of Miocene and the early of Pliocene. In the end of Pliocene, the Bovini genera were evolved to Bos , Bison and Poephagus . Poephagus which branched off from the middle of Pleiocene, was the latest evolved genera among the Bovini species.