Three is the magic number: disentangling socially-organized gustation in bumble bees using three worker micro-colonies
Kaleigh Fisher, Kaleigh Fisher , Naoki Okamoto , Naoki Yamanaka , S. Hollis Woodard
University of California, Riverside; University of California, Riverside, USA ; University of California, Riverside, USA ; University of California, Riverside, USA ; University of California, Riverside, USA
Taste is the first line of defense for bees to distinguish between nutritious and harmful components in their food. Gustatory receptors (Grs) mediate this process, whereby different receptors are activated by specific compounds (bitter, sweet, etc.); this information is a critical neuronal component that is translated into the decision of whether to feed on the resource or not. Recent studies have demonstrated that Gr expression is dynamic across bee development in bumble bees and honey bees, and their different castes. Further, with the recent sequencing of two bumble bee genomes, it was discovered that bumble bees have more than twice the number of Grs as honey bees. The functional significance of this gene family expansion has yet to be characterized. To begin to address this, we characterized tissue-specific Gr expression in B. impatiens worker and queen larvae and adult workers using qPCR. We also used microcolonies to generate a simple foraging-related division of labor, which can be used to compare Gr expression between workers performing different tasks. We generated micro-colonies with either three, five, or seven workers to examine how group size influences degree of division of labor. We found the highest expression in the adult worker mouthparts, which is consistent with the known role of mouthparts in tasting. Interestingly, the groups of Grs that have expanded in bumble bees have higher expression levels in worker and queen larval brains and adult workers than other Grs, which may further allude to their functional significance. In the microcolonies, we found the same foragers consistently in the foraging arena, with the three-worker colonies showing the greatest degree of division of labor. This demonstrates that a foraging division of labor can be observed in micro-colonies with as few as three workers and that this paradigm can be used to provide future insights into how taste-related differences contribute to bumble bee social organization.