Mitochondrial Introgression With Potential Functional Effects in North American Yak

The domestic yak (Bos grunniens) has experienced introgression with domestic cattle in its native Qinghai-Tibetan Plateau and after introduction to North America (NA), although the extent to which the latter has occurred is not well documented. We used complete mitochondrial (mtDNA) sequences of 12 NA yak and aligned them to the B. taurus reference genome for annotation. Identified variation among the NA haplotypes included a total of 982 variants, of which 99 were nonsynonymous single nucleotide polymorphisms. Among the NA yak, we identified nine unique mitotypes, which a haplotype network separated into two distinct clusters. A maximum likelihood tree including 86 Bovidae taxa revealed six NA yak haplotypes formed a clade with B. indicus; the other three haplotypes grouped with B. grunniens and fell as a sister clade to bison, gaur, and gayal. These data demonstrate two mitochondrial origins of NA yak, likely dating prior to their importation to NA. We isolated satellite cells from seven yak that represented both major mitotypes (B. indicus [N = 4] or yak [N = 3]) to investigate possible differences in ATP production. Oxidative consumption rates and extracellular acidification rates were quantified as measures of mitochondrial respiration and glycolysis using the Seahorse ATP Rate Assay. Cells with the B. grunniens mitotype had less total energy metabolism (p = 0.016). This difference may reflect adaptations to ancestral environments and selective pressures associated with husbandry practices and breeding.