Understanding the mimicry complexes of bumble bees (Bombus sp.) in North America

Mimicry has served as an example of evolution in action that can inform the processes that drive microevolutionary and ultimately macroevolutionary change. Bumble bees (Bombus sp.) exhibit exceptional diversity of color patterns, displaying >600 different color patterns across ~250 species.  This diversity is largely attributed to Müllerian mimicry. Müllerian mimicry occurs when a similar warning indicator, such as color pattern, is utilized by multiple harmful sympatric species. In areas where bumble bee species co-occur they often converge onto a central color pattern. When mimicry zones are crossed they tend to converge on the patterns of each region.  In North America, color patterns are grouped into three mimetic regions: Pacific, Rocky Mountain, and Eastern.  To better understand the evolutionary forces involved in mimicry complex formation, we examine the distribution of bumble bee color pattern variation in the western U.S.  We utilize extensive georeference data to examine the distribution of color monomorphic and color polymorphic species. Color is assigned to polymorphic species, with a focus on Bombus melanopygus, B. bifarius, and B. sylvicola, by examining phenotypes of previously georeferenced specimens at museums and of recent field-collected specimens. Using these data we address the  overlap between mimetic range and phenology of similarly colored species, utilize ecological niche modeling to determine how different ecological factors constrain  mimicry complexes to specific localities, and determine whether the extent of these mimicry complexes have shifted geographically over time. These data will refine our understanding of the evolutionary process that has generated extensive mimicry patterns in these bees.