The Complicated Relationship Between Floral Volatile Production and Olfactory Signaling Within the Genus Mimulus

Floral odors in the form of volatile organic compounds (VOCs) play a vital role in attracting insect pollinators to flowers. Floral rewards may change in quantity or quality post-visitation from a pollinator and can trigger an odor change that may increase foraging efficiency for pollinators. Many forces, such as pollinators, phylogenetics, or abiotic environmental factors, may shape volatile production and signaling throughout a species' range or within a genus. The relationship between these forces is vital to understanding how species lineages diversify and evolve in the past and in the future. In this thesis, I examined: 1) the behavioral preference with Bombus impatiens to evaluate the ability of bees to discriminate between pollinated and unpollinated floral volatiles in M. guttatus and M. lewisii. 2) I examined the differences in floral volatile profiles between the unpollinated and pollinated flowers to link changes in pollinator behavior with changes in olfactory signaling. 3) I examined how volatile composition varied throughout the genus and across several populations and how pollination biology affected the evolution of volatile composition. My results found that M. guttatus had a shift in volatile composition between unpollinated and pollinated flowers but no significant difference in bumble bee preference. In M. lewisii, I found a significant behavioral preference for unpollinated flowers but no difference in volatile organic compound production. Despite the paradox, my experiments have shown evidence of changes in odor composition post-pollination that require further study and confirm that olfactory signals can maintain honesty over the life of a flower. While my overall study of the genus Mimulus concludes that phylogenetic and pollinator-mediated constraints do not drive interspecific or intraspecific variation, they are likely influenced by individual species' adaptive solutions to entice pollinators or genetic drift.