Date of Award


Degree Type


Degree Name

Departmental Honors




Floral microbes are an overlooked aspect of the extended floral phenotype. Through altering floral nectar chemistry, they can mediate interactions between flowers, pollinators, and other floral microbes, with significant implications for plant and pollinator health. Interactions between floral microbes and pollinators are critically important to understand, as pollinators provide important ecosystem services in both natural and agriculture systems. Here, I explored how floral nectar traits affected both evolution and competition within the floral yeast Metschnikowia reukaufii, the floral bacterium Bacillus subtilis, and other microbes isolated from Brassica rapa nectar, an important plant model system and oilseed crop. To address this, I conducted a multigenerational evolution study of these microbial species within different artificial nectar environments. To quantify shifts in microbial resource use and performance, I quantified nectar quality via shifts in sugar concentration (BRIX) and colony-forming units (CFUs), respectively. While no difference in CFU counts was observed in the presence of sinigrin, a secondary metabolite common to B. rapa nectar, there were significant differences in nectar use based on both nectar background and generation. Furthermore, BRIX values revealed that both B. subtilis and M. reukaufii evolved to consume less sugar over generational time. Additionally, more sugar was consumed within the sinigrin nectar background than control nectar. To determine how microbe-induced shifts may impact floral evolution, we also conducted pollinator preference assays with isolates from each background using artificial flowers. Our results showed no conclusive evidence of Bombus impatiens preference between species, generation, or nectar background. These results can be further tested using modified methodology to decisively conclude how microbe-induced nectar shifts can change B. impatiens nectar preferences. Understanding the evolutionary relationships between nectar-colonizing microbes and bees can provide more context for complex interactions involved in the pollination of agricultural and natural systems.



Faculty Mentor

Robert Schaeffer

Departmental Honors Advisor

Jennifer Burbank

Capstone Committee Member

Grace Freundlich