A coat of many colors: Quantification and analysis of bumble bee color patterns

While the wing color patterns of butterflies serve as the most well-known examples of mimicry, few insects match up to the striking mimetic patterns of bumble bees (Bombus), whose sting is advertised by conspicuous banding patterns that are commonly mimicked by harmless species (Batesian mimics) and noxious relatives (Müllerian co-mimics). While we have a breadth of knowledge concerning the developmental and genetic mechanisms regulating butterfly mimicry, very little is known about the regulation of mimicry in bumble bees, hindering progress toward a general evolutionary model of insect mimicry. An important first step in understanding the mimetic genotype is a quantitative characterization of the phenotype under selection. Because this is lacking in bumble bees, we define the color pattern elements that comprise the phenotypic array of all species using matrix approaches, and comparatively examine the relationships among these elements as a potential foundation for targeting candidate developmental genes that might be involved in generating these patterns. Our analysis, based on 204 species (~80% of known taxa), indicates approximately 11 discrete elements. We discuss the spatial frequency of colors across the body of the bee while also demonstrating that the element boundaries and shapes are closely correlated with thoracic and abdominal segmentation, suggesting a possible role for early developmental genes in the upstream regulation of color pattern formation.