Date of Award:


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Doctor of Philosophy (PhD)




James P. Pitts


In 2011, several wild North American bumble bee pollinator species were reported to have declined by up to 96% in relative abundance in comparison to historic estimates, and one species was speculated to be extinct. None of these species have yet been documented to have recovered from these declines and additional species are now suggested to be at risk. Imperiled species in particular show increased specificity to narrow climatic envelopes, as opposed to putatively stable species. My dissertation describes patterns of population genetic diversity, structure, and gene flow pathways associated with climate variation and historical biogeography of bumble bees distributed in western North America. The results of my dissertation research suggests that (1) historic climate variability predicts contemporary patterns of population genetic structure and divergence in an economically important species, (2) color variability in bumble bees is likely associated with lineage diversification and phylogeography, (3) bumble bee community structure across evolutionary time is likely driven by Müllerian mimicry at narrow spatial scales, and (4) bumble bees inhabiting specialized ecological niches are associated with high levels of genetic fixation at regional spatial scales in the Pacific Northwest. The results of my research directly contribute to current efforts to effectively manage, conserve, and advocate for wild bumble bee pollinators in the context of global change.



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