Size-related variation in protein abundance in the brain and abdominal tissue of bumble bee workers.

Female bumble bee workers of the same species often show a profound body size variation that is linked to a division of labour. Large individuals are more likely to forage whereas small individuals are more likely to perform in-nest activities. A higher sensory sensitivity, stronger circadian rhythms as well as better learning and memory performances appear to better equip large individuals for outdoor activities compared to their smaller siblings. The molecular mechanisms underlying worker functional polymorphism remain unclear. Proteins are major determinants of an individual's morphology and behaviour. We hypothesized that the abundance of proteins such as metabolic enzymes as well as proteins involved in neuronal functions would differ with body size and provide insights into the mechanisms underlying size-dependent physiological specialization in bumble bee workers. We conducted protein quantification measurements based on liquid chromatography coupled with tandem mass spectrometry on tissue samples derived from small and large Bombus impatiens and Bombus terrestris workers. Proteins found to differ significantly in abundance between small and large workers belong to the categories of structure, energy metabolism and stress response. These findings provide the first proteomic insight into mechanisms associated with size-based division of labour in social insects.

Behavioral, transcriptomic and epigenetic responses to social challenge in honey bees.

Understanding how social experiences are represented in the brain and shape future responses is a major challenge in the study of behavior. We addressed this problem by studying behavioral, transcriptomic and epigenetic responses to intrusion in honey bees. Previous research showed that initial exposure to an intruder provokes an immediate attack; we now show that this also leads to longer-term changes in behavior in the response to a second intruder, with increases in the probability of responding aggressively and the intensity of aggression lasting 2 and 1 h, respectively. Previous research also documented the whole-brain transcriptomic response; we now show that in the mushroom bodies (MBs) there are 2 waves of gene expression, the first highlighted by genes related to cytoskeleton remodeling, and the second highlighted by genes related to hormones, stress response and transcription factors (TFs). Overall, 16 of 37 (43%) of the TFs whose cis-motifs were enriched in the promoters of the differentially expressed genes (DEGs) were also predicted from transcriptional regulatory network analysis to regulate the MB transcriptional response, highlighting the strong role played by a relatively small subset of TFs in the MB's transcriptomic response to social challenge. Whole brain histone profiling showed few changes in chromatin accessibility in response to social challenge; most DEGs were 'ready' to be activated. These results show how biological embedding of a social challenge involves temporally dynamic changes in the neurogenomic state of a prominent region of the insect brain that are likely to influence future behavior.