Patterns of genetic diversity in the rare Erigeron lemmoni and comparison with its more widespread congener, Erigeron arisolius (Asteraceae)

Analysis of levels and patterns of genetic variation in a rare species is important for determining whether genetic factors associated with small population size, such as genetic drift or inbreeding, may be negatively affecting a species. In this study, we compared estimates of genetic diversity and patterns of population genetic structure in a rare cliff endemic, Erigeron lemmonii, to those of a widespread congener, E. arisolius. Our goals were to assess whether rarity and small population size have negatively affected levels of genetic diversity in E. lemmonii and to identify genetic threats that may limit the ability of E. lemmonii to persist. Levels of observed and expected heterozygosity and allelic richness in E. lemmonii were approximately 60 % of those found in E. arisolius. After correcting for null alleles, inbreeding coefficients in both species of Erigeron were very small, suggesting that both species are highly outcrossing and may demonstrate self-incompatibility. Patterns of genetic structure in both species revealed almost no population substructuring, indicating that widespread gene flow is occurring within each species. Because we found no evidence for inbreeding or a genetic bottleneck in E. lemmonii, it is likely that the species' lower genetic diversity may be the result of genetic drift. Because E. lemmoni exists in a single population, no other populations exist to bolster population size or genetic diversity in the event of declines; thus, conservation efforts should focus on seed collection from as many individuals as possible to protect against possible future losses of genetic diversity. We also recommend continued monitoring of both population size and genetic diversity in E. lemmonii to ensure the species' long-term persistence and viability.