Landscape heterogeneity drives population structure in four western bumble bee species

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The Ohio State University

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Bumble bees are critical pollinators in wild, agricultural, and urban ecosystems—providing the necessary ecological services for food and crop production. In western North America, mountain ranges serve as areas of high bumble bee species richness. However, as climate change increases temperatures and restricts montane populations to higher elevational spaces, their ability to disperse and maintain genetic diversity decreases. This genetic isolation could lead to the extirpation of local pollinator communities and an overall loss of pollinators. My project goal was to analyze the genetic diversity of four broadly sympatric species of bumble bees across mountain regions of western North America to assess habitat isolation's impact on population genetic structure. I expected species restricted to higher elevation habitats to display higher population structure and less genetic diversity across the landscape. I sampled approximately 150 bees per species from seven to eight sites across each species' range. I genotyped bees with an average of 10 loci and used FST and Bayesian Structure analysis to quantify population differentiation. Using isolation by distance and isolation by resistance analyses, I found evidence of habitat suitability restricting gene flow in species occupying both narrow and broad elevation gradients at varying degrees. Although each species showed varying degrees of genetic structure, knowing how habitat heterogeneity drives genetic structure and isolation can help guide conservation efforts and determine regions on which to focus in the face of climate change.



Bombus, Landscape genetics, Isolation by resistance, Conservation units