Exploring Genetic Drift within the Endangered Species Pityopsis ruthii (Asteraceae)

Pityopsis ruthii, or Ruth’s golden aster, is a federally endangered perennial of the Asteraceae that is found only in southeastern Tennessee. The species grows on unshaded phyllite rock outcrops along the Hiwassee and Ocoee Rivers and is at risk for short-term extinction. Due to the small number of individuals, the species can be relatively easily sampled in its entirety and so is an ideal complex in which to conduct population and conservation studies. While morphology of the species has been examined in depth, molecular studies provide novel information to conservationists. In conjunction with previously developed markers, plastid microsatellites can be used to discover genomic variation and gene flow in natural plant populations, as well as seed dispersal mechanisms. Chloroplast microsatellite markers were used to provide a counterpart to previously published nuclear markers. Twenty-one chloroplast microsatellite markers were identified from genome sequencing of a single genotype, and five markers were seen to be polymorphic among a subsample using tissue from several locations along both the Ocoee and Hiwassee River habitats. Using the polymorphic loci, 11 individuals each from six discrete locations were genotyped. We assume the discrete locations are subpopulations. A total of 16 alleles were identified from the five loci. STRUCTURE was used to examine population structure, and three revealed clusters. Populations did not cluster by river. All three clusters were seen in populations of both rivers. Understanding maternal gene flow within populations of P. ruthii will impact the current conservation methods and plans, as well as provide further information on reintroduction of an endangered species and genetic drift.