# Mitochondrial Introgression With Potential Functional Effects in North American Yak

## TL;DR

This study shows that North American yaks have two mitochondrial origins, one from cattle, and suggests these differences may affect energy metabolism.

## Contribution

The paper identifies two mitochondrial lineages in North American yak and links mtDNA variation to differences in cellular energy production.

## Key findings

- North American yak have two distinct mitochondrial origins, one from B. indicus cattle.
- Cells with the B. grunniens mitotype showed lower total energy metabolism compared to others.
- The study found 99 nonsynonymous SNPs in NA yak mtDNA, suggesting potential functional impacts.

## Abstract

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.

Little is known about the origin of yak that were imported to North America. Using complete mtDNA sequence, we identified two distinct lineages in North American yak; one of these appears to be the consequence of past introgression from indicine cattle. Variation in the mtDNA included many putatively functional variants. In a pilot study of mitochondrial function, we observed a difference in ATP production of satellite cells associated with the mtDNA haplotype.