Social and genetic structure associated with migration in pronghorn

Abstract

Individual behavior promotes genetic structure within many mammalian populations, yet few studies have explored coarse- and fine-scale structure associated with migration. Fewer still have considered the conservation implications of such structure in at-risk populations. Pronghorn (Antilocapra americana) inhabiting Yellowstone National Park are partially migratory, and strong adult fidelity to migratory strategy and breeding areas may promote social and genetic structure within this population. We used 18 nuclear DNA microsatellite loci and fecal samples from 47 individuals to quantify group divergence and pairwise relatedness of Yellowstone pronghorn. The genetics of this population are characterized by individual isolation by distance (P=0.009). Evidence for fine-scale social and genetic structure was strong, with mean relatedness between individuals declining rapidly with geographic distance (0–3km) within areas selected by both migrants and non-migrants. On average, females sampled within social groups were related at the level of first cousins (mean R=0.105±0.192SD). We found low differentiation of the population by migratory strategy (FST=0.019), moderate differentiation among some summer use areas (FST⩾0.033), and an excess of heterozygotes within all migrant groups (FIS⩽−0.017). Weak and inconsistent substructure was detected using spatial and aspatial Bayesian clustering methods. Our results are the first to document fine-scale social and genetic structure in pronghorn, most likely organized along matrilines. Access to a majority of the total summer range available to this population is maintained by social inheritance and individual fidelity to areas of use. The maintenance and reestablishment of migratory routes may therefore hinge on the retention of experienced individuals, the strength of natal and adult philopatry, and the accessibility of seasonal habitat to pioneering females.