Comparative transcriptomics reveals unique patterns of convergence in the evolution of eusociality

Eusociality represents a major evolutionary transition that arose independently in at least 12 insect lineages. Despite this prevalence, there remains considerable uncertainty surrounding the catalysing event and underlying genomic changes that enable such modifications. Commonly associated with this evolutionary transition is establishing and maintaining the reproductive division of labour (e.g. a reproductive queen and no-reproductive workers). This division is, at least in part, induced and maintained by highly species-specific pheromones. However, genomic analysis remains conflicted on the role of pheromones in this evolutionary transition. Specifically, if there was co-option of a common pheromone-sensitive genetic pathway present in all progenitor species or strong lineage-specific selection converging on similar transcriptomic signatures. Using a solitary insect model, we sought to determine if various species-specific pheromones induced similar transcriptomic responses, thus activating similar pathways. We measured the transcriptomic and physiological response of a solitary insect, Drosophila melanogaster , to pheromones from bumblebees, honey bees, and termites. Each treatment induced the same strong physiological response - a decreased ovary size. However, employing several methods of transcriptomic analysis, we did not observe conservation in pheromone-mediated gene/pathway regulation. Thus, despite a conserved phenotypic response, the underpinning transcriptome was vastly different. This suggests that pheromone-mediated eusociality is the result of convergent evolution. We propose that mechanisms maintaining eusociality (i.e. proto-pheromone) in early stages of eusocial evolution in each group, thus, acting as a primer for eusociality. This early state is then refined through strong selective pressure, resulting in a converging eusocial phenotype. Visual Abstract Figure 1.