Population genetics of a rare wetland species, the Tennessee yellow-eyed grass (Xyris tennesseensis, Xyridaceae)

Abstract

Federally endangered Xyris tennesseensis is a perennial monocot found in imperiled wetlands such as calcareous seeps and riparian habitats within its disjunct distribution (one county in Tennessee, three in Alabama and four in Georgia). This species belongs to a genus of wetland plants for which very little genetic work has been carried out. Because of the rarity of this species, we hypothesized that it would have low genetic variability overall and that populations were likely to be genetically differentiated due to the species’ disjunct distribution. Fourteen microsatellite loci polymorphic at the species level showed limited variability at the population level, averaging 16.3% polymorphic loci, 1.17 alleles per locus, an observed heterozygosity of 0.017, and an expected heterozygosity of 0.054. The discrepancy between observed and expected heterozygosity resulted in a relatively high FIS of 0.71, suggesting that X. tennesseensis experiences high levels of inbreeding. We also found evidence of varying levels of vegetative reproduction in this species. Analysis of molecular variance estimated that differentiation among the regions (states) accounted for the majority (60%) of the genetic variation in this species, with an additional 31% due to genetic differences among the populations of each state and only 9% due to variability within populations. These data indicate X. tennesseensis possesses low levels of genetic diversity and experiences virtually no gene flow among populations. To preserve the genetic diversity of this species, multiple populations must be protected, with priority given to the largest and most variable populations in each region.