Geographic distribution of genetic variation in the rare orchid Isotria medeoloides

Emily Devlin, Colby College

Document Type Honors Thesis (Open Access)


The rare orchid, Isotria medeoloides (Pursh) Raf., is a threatened species native to the Eastern United States. The species' range extends from Maine to Georgia, with many populations including fewer than 25 individuals. The degree of genetic variation among populations could have important implications for conservation strategies. This study evaluated the level of genetic variation within and among I. medeoloides populations through analysis of microsatellite regions, which contain dinucleotide repeats. The lengths of these regions are highly variable and have high mutation rates, making microsatellites a powerful genetic marker. Genetic variation was assessed at two microsatellite loci among 15 populations and three regions (New England, Virginia and Georgia). In this largely self-pollinating species, the inbreeding coefficient was high (Fis =0.964) indicating a high rate of self-fertilization. Populations in New England harbor the most genetic diversity. Southern populations are monomorphic, or nearly so, but distinct from each other, suggesting that they have each independently arisen by long distance colonization from Northern populations.