Genetic variation and structure in natural and reintroduced populations of the endangered legume, Pyne’s ground plum (Astragalus bibullatus)

Rare species with limited geographic distributions and small census populations are particularly susceptible to genetic drift and inbreeding. Assessing genetic variation within and among populations of imperiled species is key to the development of effective conservation management strategies. Reintroduction programs may prove more successful in the long term if baseline genetic data are available to inform seed-source selection. In this study, we assessed genetic diversity in natural and reintroduced populations of Pyne’s ground plum (Astragalus bibullatus; Fabaceae), a plant species narrowly endemic to the limestone glades of Middle Tennessee, USA. Using seven nuclear microsatellite loci to survey six natural and three recently introduced populations, we found evidence for moderate diversity within and limited diversity among populations, with no evidence for inbreeding or recent bottlenecks. All three reintroduced populations exhibited effective number of alleles and mean expected and observed heterozygosities similar to those recovered for natural populations, indicating that the current reintroduction program has successfully captured the breadth of observed variation. One geographically disjunct natural population exhibited the greatest genetic divergence relative to all other populations and should be considered a primary target for future conservation management efforts. We outline suggestions for future demographic and genetic monitoring, and we emphasize the need for breeding system and pollination biology experiments to clarify factors limiting reproductive success in this narrowly endemic legume.