Obtaining information about the distribution and levels of genetic diversity in rare species is important for prioritizing the protection of populations so as to represent the bulk of the species’ diversity. Genetic variation is required by species for long-term adaptive evolution, and loss of variability can cause inbreeding depression and impair growth and disease resistance in the short-term. This study examined the population genetic structure and diversity of Xyris tennesseensis, a federally endangered obligate wetland plant found in imperiled seep and riparian habitats. This species has a highly disjunct distribution encompassing 10 counties from three states. Five Tennessee, four Alabama, and five Georgia populations were sampled for this study, including some of the largest and most geographically distant X. tennesseensis populations in each state. An average of 28.5 plants were sampled per population, and 14 polymorphic nuclear microsatellite markers were assayed to determine the species’ genetic structure and diversity.
Results/Conclusions
Results showed limited variability, with a population mean of only 16% polymorphic loci. Observed heterozygosity in all populations was unexpectedly low, ranging from 0.000 to 0.095, with an average of 0.017. This resulted in a relatively high FIS of 0.71, suggesting that X. tennesseensis experiences high levels of inbreeding. Two Alabama populations contain the majority of within-population diversity seen in X. tennesseensis, whereas most others (including all in Tennessee and all but one in Georgia) appear to be genetically depauperate. 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. tennesseesis possesses low levels of genetic diversity and that there is very little, if any, gene flow among the populations. To preserve what remains of the genetic variation of this species, it is essential that multiple populations be protected, with priority given to the largest and most diverse populations in each state.