Demographic and Genetic Consequences of Small Population Size in Remnant Populations of Arabis georgiana Harper (Georgia Rockcress)

The goal of this thesis is to provide a greater scientific understanding of the demographic and genetic consequences of small population size in remnant populations of Arabis georgiana Harper (Georgia Rockcress). Specifically, 1 ) traits associated with phenological progression, fitness and reproductive success were compared between naturally occurring native plants and plants grown ex situ and subsequently restored to one of the largest remaining populations of A. georgiana, and 2) a preliminary analysis of population genetic structure in remnant populations across the species\u27 range was performed. In addition to updating census information on remnant populations of A. georgiana, chapter one represents the first critical evaluation of traits associated with the phenological and reproductive success in this species. Moreover, this chapter explores the possible negative effects of ex situ restoration practices within natural populations. Although results indicate no significant delays in phenological progression (the timing of flowering and fruit dehiscence), traits associated with fitness and reproductive success (plant size, fruit production, and seed output) were significantly lower in restored plots compared to their native cohorts. In restored plots, plants were 9.3% shorter, produced 44.0% less fruit, had 6.5% fewer fruit dehisce, produced 14.4% fewer seeds, and had a 13.0% reduction in seed weight compared to native plants. These results suggest that genetic bottlenecks potentially invoked through ex situ conservation efforts can have a negative impact on the restoration of remnant populations. The second chapter of this thesis includes an updated population census of the species as well as the first confirmation of its genetic identity. To evaluate the magnitude of genetic structuring across the range of A. georgiana, potential variation in ploidy, cpDNA haplotypes and microsatellite markers was also evaluated. Census data revealed no species-wide pattern for population growth or decline compared to data collected in 2005. The rbcL barcode generated for this species were confirmed as a unique haplotype when compared with other co-occurring members of Brassicaceae. Analysis of genomic DNA content using flow cytometry showed no variation in ploidy across the species range and suggests that A. georgiana is most likely octoploid; however, visual confirmation of chromosome number is still required. No sequence variation was found among trnL (UAA) intron cpDNA haplotypes. Of the seven microsatellite loci screened for this study, one locus (DnB220) revealed significant genetic structuring among 101 samples across 10 populations. Three genetic clusters (K=3) were found, each population having a common and private allele, with 1 1% of all individuals sampled being homozygous for the common allele. Collectively, this research program will contribute to the effective management and conservation of a narrow endemic whose fragmented populations are steadily declining