It isn’t easy being yellow: Analysis of yellow coloration in Perdita (Hymenoptera: Apoidea: Andrenidae)

Bee species have a wide diversity in color, ranging from entirely black to entirely white or yellow. Differences in coloration are thought to play a role in temperature regulation, camouflage, or aposematism. In the speciose Nearctic genus Perdita Smith 1853 (>633 species), entire yellow coloration has evolved at least seven times in more than 25 species, with three of those species displaying extreme color polymorphism.  I use this genus as a model to develop hypotheses to explore whether these shifts in coloration map to floral association, temperature regulation, or predator avoidance. Using historical museum specimens, females from 468 species of Perdita were scored based on the percent of their body with white or yellow coloration. The light and dark species were then analyzed in terms of their floral associations, phenology, and biogeographic distribution. Individual yellow species specialize on a wide variety of plants and do not show affinity to any particular taxonomic group. They also show no clear phenological difference in season of activity compared to their darker counterparts. However, yellow species tend to be found at lower elevations, are especially frequent in sand dunes, and tend to visit yellow flowers. The reasons for the elevational differences are unclear and could represent a mechanism of temperature regulation caused by higher temperatures at lower elevations. Yellow coloration could also be a form of camouflage due to light-colored substrate and/or floral hosts. Future directions for the yellow Perdita include a phylogenetic analysis of the yellow species groups and a taxonomic revision to describe the new species and aid in identification.