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Taxonomic placement and origin of yaks: implications from analyses of mtDNA D-loop fragment sequences
Browse Number:2848
Authors:Guo Songchang, Liu Jianquan, Qi Delin, Yang Jie, Zhao Xinquan
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Keywords:D-loop; mitochondrial DNA, Origin; Taxonomic placement; Yak (Bos grunniens)
Publication Year·Volume·Issue(Page):2006·26·No.4(325-330)
The origin and generic placement of the yak (Bos grunniens), a large ungulate endemic to Qinghai-Tibetan Plateau, remains unresolved. 637 bp of mitochondrial DNA control region of both wild and domesticated yaks were sequenced. We found that D-loop region sequences were similarly informative to commonly used cytochrome b gene in constructing phylogeny for tribe bovini. Based on the genetic variation of this sequence, we firstly constructed a more discernable phylogeny of Bovini with high support than previous analyses. The analyses suggested that in Bovini, two monophyletic lineages were recovered: one comprising Bubalus and the other consisting of all species of Bos and Bison. Two species of Bison, the extinct species B. priscus and the extant species B. bison, clustered as a monophyletic lineage which is a sister to Bos grunniens. These results suggested that yaks are more closely related to North American Bison than to other species of Bos in Asia, and that yaks and North American bison have a common recent ancestor. Our results did not support a previous suggestion of establishing a monotypic genus (Poephagus) to accommodate yaks. Because species of neither Bos nor Bison clustered as respective monophyletic lineages, these two should be taxonomically treated as one genus. Based on our results and other available fossil evidence, we discuss the historical context regarding the origin of yaks. The divergence between yaks and bison may have occurred in the Eurasia during the Quaternary climatic oscillation, when rising temperature following the ice ages restricted yaks to the cold Qinghai-Tibetan Plateau. Bison migrated to North America through the Bering Land Bridge and differentiated two species. It seems likely that American bison originated directly from extinct steppe bison.
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