An Issue of Genetic Integrity and Diversity: Assessing the Conservation Value of a Private American Bison Herd

Abstract

There are 600,000 American bison (Bison bison) that exist today, all of which can be traced to the less than 500 bison that were present after a severe bottleneck in the late 1800s. To save the species from extinction and increase the robustness of domestic cattle (Bos taurus), ranchers interbred the two species, creating a hybrid animal. The genetic introgression caused by this hybridization can still be seen in the current bison population. Only two bison herds evaluated to date have shown no domestic cattle genetic introgression: Yellowstone National Park (YNP) and Wind Cave National Park (WC). As such, these herds are very important to the conservation of the bison species. A private herd that was reportedly derived from YNP has shown no introgression during initial testing. Using microsatellites randomly dispersed throughout the genome, the genetic integrity of this herd is evaluated. It was found that this herd has an average number of alleles per loci, but that the unbiased heterozygosity values are low when compared to 11 known Department of Interior (DOI) herds. The low heterozygosity values could be due to a biased sex ratio that is present in the herd. This biased sex ratio would produce inbreeding within the herd, resulting in the low unbiased heterozygosity values. The presence of an average number of alleles per loci suggests that the low heterozygosity value is reversible by removing this biased sex ratio. The relationship of this herd to the reported foundation herd, YNP, is also evaluated. Though this herd is reportedly founded from YNP only, genetic analysis shows this to be untrue. The presence of alleles that are unique to the private herd when compared to YNP supports this claim. A Structure analysis comparing the germplasm of the 11 DOI herds to this private herd shows that the private herd was not founded solely from YNP, shown by the fact that the private herd did not cluster with YNP in this analysis. This information is important for the management of this herd and the overall conservation of the germplasm of this species.