Patterns of range-wide genetic variation in six North American bumble bee (Apidae: Bombus) species

The increasing evidence for population declines in bumble bee (Bombus) species worldwide has accelerated research efforts to explain losses in these important pollinators. In North America, a number of once widespread Bombus species have suffered serious reductions in range and abundance, although other species remain healthy. To examine whether declining and stable species exhibit different levels of genetic diversity or population fragmentation, we genotyped a set of microsatellite markers from populations sampled across the geographic distributions of two declining (B. occidentalis; B. pensylvanicus) and four stable (B. bifarius; B. vosnesenskii; B. impatiens; B. bimaculatus) Bombus species. Populations of declining species generally have reduced levels of genetic diversity throughout their range compared to co-distributed stable species. Genetic diversity can be affected by overall range size and degree of isolation of local populations, potentially confounding comparisons among spe...