Task Performance and Queen Presence Influence the Brain Transcriptome in a Bumble Bee (Bombus terrestris) With a Flexible Division of Labour System

Division of labour in reproduction and in task performance are two hallmarks of insect societies. Bumble bees and honey bees are both classified as eusocial, but differ in the social organization of their colonies and in the hormonal regulation of division of labour. Bumble bees exhibit size-related division of labour among adult workers that is independent of juvenile hormone (JH), whereas honey bees exhibit age-related division of labour among same-size bees that is influenced by JH. We hypothesized that despite these differences, some common molecular pathways for social organization are shared between the two species. We addressed this hypothesis by analysing brain transcriptomes of bumble bee (Bombus terrestris) queenright workers differing in the performance of foraging and brood care activities, as well as of queenless workers. The brain transcriptomes of nurses, foragers and queenless bees were different, with little overlap. qPCR validation shows that some of the genes are associated with task performance even for bees with a similar body size. The set of genes influenced by JH treatment overlaps with the genes influenced by queen presence but not with those associated with division of labour. These results support and extend the evidence that in bumble bees JH regulates reproduction but not the division of labour among workers for colony tasks. Additionally, we found significant overlap between genes differentially expressed among workers performing different tasks or as a function of queen presence in the current study with bumble bees and previous studies with the honey bee Apis mellifera. These findings support the hypothesis that a common ‘toolkit’ of genes is involved in the regulation of division of labour in honey bees and bumble bees for both reproduction and task performance.