CAREER: The genetics underlying adaptive diversification of mimicry patterns in bumble bees

New advances in genomics allow for the discovery of the genes responsible for specific traits of organisms and for complex patterns of trait variation that have evolved in species across their geographic range. To better understand the evolutionary mechanisms that determine trait variation and that promote rapid adaptation to environmental change, studies are needed that can link traits to the genes that encode them, especially in species that show extraordinary trait variation. Bumble bees (Bombus) are especially suited for such research: the 250 species worldwide have evolved to exhibit >600 color patterns, in which similar color patterns evolve in different species when they live in the same geographical location. This project will explore how these different color patterns form in Bumble Bee species across North America by identifying the pigments that are responsible for color patterns and then identifying the genes responsible for those pigments and the observed geographic patterns of color variation. This research will provide general insights into how color variation arises in nature, and will also help to address a long standing question in evolutionary biology regarding the repeatability of evolution. Are the same genes in different species responsible for the same color patterns or are different genes able to produce the same color patterns? This research will directly address this question and in answering it help us understand whether evolution is truly repeatable or whether it just looks repeatable and that there are many evolutionary paths to get to the same outcome.

This CAREER project builds foundational knowledge on the genetic and evolutionary processes enabling the mimetic radiation of bumble bees. The project will address the mimetic process by characterizing the geographic distribution of color patterns in North America bumble bees and how they are impacted by climate. It will reveal how these bees are pigmented and the factors that influence their coloration, providing a foundation for further genetic work. Pigment discovery will extend to a diversity of insects through undergraduate research and classroom modules on insect pigment chemistry. As a primary aim, gene mapping and gene expression approaches will be used to identify genes driving red/black and yellow/black bumble bee color variation. Black and yellow pattern morphs of the subgenus Bombus will demonstrate how adaptive gene variants are transferred across species, populations, and sexes. The discovery of the genes behind black and red mimetic convergence in western U.S. bumble bees will inform on the genetic complexity underlying bumble bee mimicry. Identifying these genes will enable a broader comparative approach to examine how adaptive genes have been targeted and transferred across this replicate-rich radiation.