Abstract:
A population genetics study of BOECHERA LAEVIGATA, the most widespread Boechera species in the eastern United States, was conducted using 15 populations from 11 states throughout its range. Sixteen polymorphic microsatellite loci were resolved for the species. Three populations exhibited nearly fixed heterozygosity at multiple loci, which was attributed to apomictic reproduction based on this study’s data and other Boechera research. Because of this likelihood of clonal reproduction, only unique multilocus genotypes (MLG) were used for most analyses of the apomictic populations. From 300 total samples, 153 unique MLGs were identified, with no MLGs shared across populations. Percent polymorphic loci at the population level ranged from 6.3-93.8%, with sexual populations averaging 40% and apomictic populations averaging 71%. Observed heterozygosity was lower than expected heterozygosity for sexual populations (H¬o = 0.052, He = 0.169), while the opposite was true for apomictic populations (Ho = 0.679, He = 0.441), resulting in a high FIS of 0.709 for sexual populations (probably due to inbreeding) and an extremely negative F¬IS of -0.927 for apomictic populations, as is commonly found with clonal reproduction. While 69% of the genetic variability in the sexual populations was due to differences among the populations, the majority of genetic variation in the apomictic populations was found within individuals. Widespread species often harbor greater genetic diversity than rare species, so this trend was tested by comparing B. laevigata with the federally endangered B. PERSTELLATA, which was previously found to have extremely low levels of genetic diversity. Such congeneric comparisons of genetic diversity provide phylogenetic context and a more nuanced understanding of evolutionary forces that have shaped a species. Considering the 11 loci assayed in both species, sexual B. LAEVIGATA populations averaged higher allelic richness, observed heterozygosity, and expected heterozygosity than its rare congener, although differences did not reach statistical significance. The rare species had significantly greater population differentiation than B. LAEVIGATA, possibly reflective of the very disjunct distribution of B. PERSTELLATA. This study provides context to the low diversity reported for the endangered B. PERSTELLATA as well as adding to the growing literature on the model genus Boechera.
