Conservation genetics of edaphic endemics in naturally isolated habitats: a case study with Geocarpon minimum (Caryophyllaceae)

Theory predicts that edaphic endemics should exhibit high levels of population differentiation due to restricted gene flow among patchily distributed habitats. Here, we tested this prediction with the federally threatened annual Geocarpon minimum, an edaphic endemic restricted to sandstone outcrops and slick spots associated with saline prairies in the Southeastern United States. We used AFLP data to quantify population genetic variation and structure in 13 G. minimum populations using a bulked sampling scheme. Modest but significant components of genetic variance are partitioned among populations (16%) and among regions (north, south; 3%). The maintenance of private bands within most G. minimum populations suggests limited gene flow among geographically isolated populations. However, a Mantel test failed to detect a pattern of isolation by distance. Estimates of within population variation in G. minimum are relatively low compared to other edaphic endemics with similar life-histories. Results suggest conservation efforts should focus on protecting genetically unique populations and ensuring that genetic variability is adequately captured in ex situ collections.