Conservation Genetics and Population Biology of Helianthus verticillatus
Population Genetics
I have used nuclear and chloroplast SSRs (simple sequence repeats) to investigate the population genetics of an extremely rare sunflower, Helianthus verticillatus Small, which is known from only four locations in North America. I have investigated levels of genetic diversity and population structure compared to a more common congener, Helianthus angustifolius L., using both nuclear and chloroplast SSRs. I have also investigated its proposed hybrid origin from Helianthus grosseserratus Martens and H. angustifolius.
Twenty-two nuclear SSRs originating from the cultivated sunflower (Helianthus annuus L.) expressed sequence tag (EST) database, and known to be transferable to H. verticillatus and its putative parental taxa, were used in this study thereby allowing for statistical control of locus-specific effects in population genetic analyses. Despite its rarity, H. verticillatus possessed significantly higher levels of genetic diversity than H. angustifolius at nuclear loci and equivalent levels of chloroplast diversity. Significant levels of population subdivision were observed in H. verticillatus but of a magnitude comparable to that of H. angustifolius. Inspection of multilocus genotypes also revealed that clonal spread is highly localized. Finally, H. verticillatus is not of hybrid origin as it does not exhibit a mixture of parental alleles at nuclear loci, and it does not share a chloroplast DNA haplotype with either of its putative parents.
Fitness Consequences of Genetic Isolation Knowledge of both the genetic and demographic consequences of rare species is important when evaluating the effects of rarity and fragmentation on such species. Therefore, I sought to assess the fitness consequences of the extreme genetic isolation and small population size of H. verticillatus by conducting a greenhouse crossing study. Specifically I am interested in three related questions 1) is there is evidence for inbreeding depression, 2) is there is evidence for outbreeding depression especially in the F2 generation, and 3) is there evidence for genetic rescue?
Population Genetics in Silene vulgaris
Plant Mitochondrial Recombination
The McCauley lab is interested in the impact of intergenic recombination on the population genetics of plant mitochondrial genomes. The plant mitochondrial genome is capable of both intra- and intermolecular recombination. Intergenic recombination has the potential to create novel multilocus genotypes given the loci involved have intermolecular sequence differences. Recent studies have suggested that heteroplasmy and recombination could play a role in the mitochondrial population genetics of natural populations of plants in the genus Silene. The lab is interested in some related questions 1) what is the magnitude of linkage disequilibrium among mitochondrial genes in S. vulgaris? and 2) what is the role of population structure in generating recombinatorial novelty?
