Genetic Structure And Gene Flow Barriers Among Populations Of An Alpine Bumble Bee (Bombus Balteatus) In The Central Rocky Mountains

This study investigated the relative extent of genetic connectance among populations of Bombus balteatus, an ecologically important native bumble bee species in alpine habitats of the central Rocky Mountains, Colorado. This species has experienced recent declines in relative abundance, likely facilitated by climate-mediated decreases in floral resources coupled with increased competition from upwardly mobile lowland Bombus species. I examined population genetic structure (microsatellites) and estimated habitat suitability (MaxEnt) and connectivity (Circuitscape). My data suggest that populations of B. balteatus have low but significant pairwise population genetic differentiation, with evidence of inbreeding that may be a result of evident population structuring. Structure analysis revealed six genetic clusters among the nine populations sampled, with two clearly defined groups. Populations did not exhibit isolation by distance nor isolation by resistance. Habitat suitability was predicted to occur at high elevations in areas with high perennial snow and ice, with high habitat connectivity along high elevation ridgelines, while dispersal appeared to be limited by low elevation forested valleys and major highways. Results suggest that there may not be direct barriers to gene flow, rather the current arrangement of suitable habitat at the regional scale may sufficiently explain the observed levels of population differentiation.