Levels and Patterns of Genetic Diversity in the Rare and Endangered Cumberland Stitchwort, Minuartia cumberlandensis (Caryophyllaceae)

Sequences of a highly variable nuclear gene (G3pdh) were used to characterize genetic diversity within and among populations of the endangered rockhouse endemic, Minuartia cumberlandensis (Wofford and Kral) McNeill (Caryophyllaceae), and compared to a widespread and abundant related species, M. glabra (Michaux) McNeill. By reconstructing phylogenetic relationships among G3pdh variants (haplotypes) and observing the geographical distribution of those ordered variants, an attempt was made to gauge the effects of historical and contemporary population processes acting within the species, particularly those with potential implications for long-term conservation. Both M. cumberlandensis and M. glabra were found to have high overall genetic (haplotype) diversity. In M. cumberlandensis, most of this variation was distributed among populations rather than within them (F_ST = 0.63), while in M. glabra the inverse was true, with variation largely within populations (F_ST = 0.22). This pattern suggests significant divergence among populations of M. cumberlandensis, likely caused by a reduced influence of gene flow relative to genetic drift. Observed heterozygosity in populations of M. cumberlandensis was significantly reduced relative to M. glabra, suggesting the effects of inbreeding within small populations. Minuartia. cumberlandensis maintains broad genetic polymorphism among populations, with genetic similarities between many populations likely resulting from persistent ancestral alleles rather than ongoing gene flow. Lineages of haplotypes with significantly restricted geographical ranges provide further evidence for restricted gene flow among populations of M. cumberlandensis. The bulk of genetic diversity in M. cumberlandensis is maintained within the largest, densest cluster of populations, which occurs primarily in Pickett County, with outlying populations having relatively low, though still significant, portions of the overall diversity in the species. Because of the small overall number of outlying populations, and the unique genetic makeup of each, all occurrences should be given the strongest possible protection from further human habitat disturbance. It is likely that M. cumberlandensis has persisted in its current location through cyclical changes in climate during the Pleistocene, and if protected from habitat destruction and population decimation, it may fare well in the face of future climate change.