D3061: Effects of urbanization on gene flow between bumble bee populations

Bumble bees (Bombus spp.) are important pollinators for a large variety of wildflowers, crops and ornamental plants. However, population declines have been documented for 20% of North American bumble bee species over the last several decades. Habitat losses, including those incurred by urban expansion, have been identified as a significant driver of these declines. Though some studies have explored the effects of urbanization on bumble bee communities, few have focused on the effects of urbanization on gene flow and genetic isolation among populations. In this study, we use 15 microsatellite markers to reveal the genetic structure of populations of B. impatiens, B. griseocollis and B. bimaculatus throughout Columbus, OH and Madison, WI. We use isolation by resistance (IBR) models to examine the relationship between genetic structure and the density of impervious surface surrounding urban bee populations. We test the null hypothesis that there is no significant relationship between impervious surface density in the surrounding landscape and the level of genetic similarity between adjacent bumble bee populations. Prior studies show that urbanization can decrease richness, abundance and functional diversity of bees; thus, we expect to find a significant level of genetic structure and reduction of gene flow corresponding to increasing urbanization. These results could have potential long-term implications for bumble bee species' health, resilience and conservation status, which future research must extricate.