Genetic population substructure in bison at Yellowstone National Park

The Yellowstone National Park bison herd is 1 of only 2 populations known to have continually persisted on their current
landscape since pre-Columbian times. Over the last century, the census size of this herd has fluctuated from around 100
individuals to over 3000 animals. Previous studies involving radiotelemetry, tooth wear, and parturition timing provide
evidence of at least 2 distinct groups of bison within Yellowstone National Park. To better understand the biology of
Yellowstone bison, we investigated the potential for limited gene flow across this population using multilocus Bayesian
clustering analysis. Two genetically distinct and clearly defined subpopulations were identified based on both genotypic
diversity and allelic distributions. Genetic cluster assignments were highly correlated with sampling locations for a subgroup
of live capture individuals. Furthermore, a comparison of the cluster assignments to the 2 principle winter cull sites revealed
critical differences in migration patterns across years. The 2 Yellowstone subpopulations display levels of differentiation that
are only slightly less than that between populations which have been geographically and reproductively isolated for over
40 years. The identification of cryptic population subdivision and genetic differentiation of this magnitude highlights the
importance of this biological phenomenon in the management of wildlife species.