Still here after all these years: the persistence of the Uncompahgre fritillary butterfly

Abstract

The US federally endangered Uncompahgre fritillary butterfly (Boloria acrocnema) lives in isolated alpine habitats of the San Juan Mountains of Colorado, USA. Its apparent extirpation from the type locality and its low genetic diversity raised concern in the late 1980s, thus monitoring for this species has continued and genetic samples were collected in 2008 and 2009 from all but one known site, each on a separate peak. Data for five new microsatellite markers were collected from 316 total specimens, including 26 from wings preserved from 1987 and 1988 seasons. Only three main colonies had high enough sample sizes for adequate analyses. We estimated levels of genetic variability and structure, and effective population size. Despite low demographic numbers at these sites, the species has maintained relatively high heterozygosity ranging from 0.41 to 0.46 at three sites. Allelic richness corrected by sample size ranged from 5.3 to 5.9. Genetic structure assessed with non-spatially explicit methods indicated that despite separation on high mountain peaks, colonies were fairly well mixed, which is surprising for these weak fliers with very short growing and adult flight seasons. Estimates of effective population sizes were low, reflecting the life history and limited habitat range for the species. Comparisons at the site with historic and modern specimens revealed a consistent pattern in genetic indices. Our data suggest that the three focal butterfly colonies exist as a metapopulation that persists due to low-level migration between sites and “temporal leakage” via flexibility in development time in this biennial species.