Allozyme variation within and between populations of Ruth's Golden Aster, Pityopsis ruthii (small) small

Genetic structure of the two known populations of Ruth's golden aster, Pityopsis ruthii (Small) Small, was determined. Pityopsis ruthii is a rare, endemic plant species restricted to exposed phyllite and graywacke rock outcrops in the flooding zones of the Hiwassee and Ocoee River drainages in Polk County, Tennessee. There are an estimated 10,000 to 15,000 P. ruthii plants on the Hiwassee and ≈600 on the Ocoee River. Patterns of variation at three enzyme loci were examined. Two loci, Pgm-2 and Prx-1, were polymorphic in both river populations. Despite limited habitat and subsequent restricted ranges (≈ 5 km along each river), populations of this obligately outcrossed species were moderately substructured (mean F_ST = 0.163). Although river populations were separated by ≈ 20 km of mountainous terrain, only 1.05% of the gene diversity was attributable to differences between river populations, while 15.16% was attributable to differences among subpopulations within respective river gorges, and 83.79% was attributable to within subpopulation variation. The low mean F_IS value for _{P. ruthii} (0.062) may indicate that this species is avoiding inbreeding by predominantly reproducing vegetatively.

What has been traditionally considered two separate, breeding river populations of _{P. ruthii} was demonstrated, on the basis of two polymorphic loci, to be many separate "rock populations" within each river population. To determine how many separate breeding groups exist, further allozyme analyses of more rock populations and subsampling within rock populations needs to be conducted. Based on these data each rock outcrop should, unless demonstrated to be the contrary, be considered a "breeding population."