Population genetics of Astragalus bibullatus (Fabaceae) using AFLPs

Astragalus bibullatus (Fabaceae) is an endangered plant species endemic to limestone cedar glades in Tennessee. Data from 134 amplified fragment length polymorphism (AFLP) fragments indicate that populations of this species are genetically very similar, with genetic identity values ranging from 0.976 to 0.991. Approximately 10% of the species' total genetic variation is due to differences among populations (F(ST) = 0.102), and a principle coordinate analysis based on genetic distance among individuals revealed considerable overlap between populations. Averaging across populations, 38.4% of the AFLP markers were polymorphic, and the mean expected heterozygosity was 0.120. These estimates are higher than what has previously been reported for this species based on a survey of allozyme variation. Despite the overall similarity of populations of this species, a model-based clustering approach revealed the presence of 2 (possibly 3) genetically distinct subgroups. The results of this study highlight the utility of DNA-based markers for conservation genetic studies in genetically depauperate species and reveal that detectable levels of genetic substructuring may be present even in relatively undifferentiated species.