Eusocial insects, such as honeybees, demonstrate the most complex form of sociality known in nature, involving a reproductive queen supported by thousands of sterile workers. Eusocial species are descended from solitary lineages; and, although the exact evolutionary routes to eusociality are unknown, variations in developmental processes, and the timing and degree of gene expression are all theorized to underlie elaborations in social complexity. Comparative research has provided an opportunity to test the biological reality of these theories by exploring taxa thought to represent biological proxies of ancestral forms of eusocial species. Ceratina japonica is a facultatively eusocial small carpenter bee, meaning it is capable of forming both solitary and social nests in the same populations. Social nests are formed between a mother and daughter: the larger and elder female has developed ovaries (i.e. queen-like) and the smaller female acts as a non-reproductive forager (i.e. worker-like). Solitary nests, by comparison, feature lone females which act as reproductive foragers absent any division of labor. In this study, we use a brain gene expression dataset to examine variations in gene expression, regulation, and functional enrichment by age (old vs. young), nest type (solitary vs. social), and role (queens vs. workers vs. solitary females). . Results of this work reveal molecular elements that may be key to C. japonica’s facultative eusociality and, through comparison to a wide range of other social taxa, point to mechanisms that may play a conserved role in the expression of social traits across lineages.
