Development of variable microsatellite loci and range-wide characterization of nuclear genetic diversity in the important dryland shrub antelope bitterbrush (Purshia tridentata)

Antelope bitterbrush (Purshia tridentata Pursh DC; Rosaceae) is an arid-land shrub that occupies an important ecological niche in various fire-dominated communities across much of the western United States. Because of its importance as a browse for large mammals and a food source for granivores, P. tridentata is frequently planted by Federal agencies in arid-land revegetation. We are currently analyzing the range-wide genetic diversity of this species as part of a larger effort to develop seed movement guidelines. In this study, we describe the development of eight novel nuclear microsatellite loci and characterize the amount and apportionment of range-wide nuclear genetic diversity. The eight microsatellite loci exhibited a high level of polymorphism (13-33 alleles per locus) and in general, observed levels of heterozygosity did not deviate form Hardy-Weinberg expectations. An initial screen of 196 individuals from 12 widely distributed populations revealed a moderate amount of genetic differentiation (FST = 0.09, p < 0.001). Moreover, these loci successfully produced PCR products in cross-species amplifications with two closely related Purshia species. These results demonstrate the utility of these markers and provide useful measures of neutral genetic diversity and population differentiation.