Post-transcriptional regulation of Dufour’s gland reproductive signals in bumble bees

Pheromone communication is a key mechanism by which the reproductive division of labor is maintained within insect communities. Understanding how pheromones evolved to regulate social behavior requires knowledge of the molecular regulation of their production. However, even in cases where pheromones were identified, our understanding of their biosynthesis and molecular regulation remains limited. Bumble bees provide a unique system to explore pheromone biosynthesis since workers produce ester sterility signals in their Dufour's gland that differ from gyne-specific esters and are not produced by queens. These esters are hypothesized to be produced in the exocrine gland where they are stored, and indeed queens, gynes and workers differ significantly in the expression of Dufour's gland genes coding to enzymes involved in the biosynthesis of esters. However, a previous transcriptome analysis revealed no gene expression differences in the Dufour's gland of workers despite differences in both ester production and ovarian activation, suggesting that ester production may be regulated lower down. Proteomics of the Dufour's gland of queens, gynes, and workers recovered over 2400 proteins and broadly matched the previous RNAseq data. However, more than 100 differentially expressed proteins were found between the worker groups, including key enzymes in fatty acid biosynthesis, indicating that the regulation of reproductive signal biosynthesis in workers is done post-transcription. Overall, our data provide evidence that pheromone biosynthesis in the Dufour's gland is caste specific, that gynes and workers are likely using different enzymes to make their respective wax esters, and that the regulation on pheromone production in queens, gynes and workers is likely done at different regulatory levels, with workers signals being subjected to regulation at the protein level.