To reproduce or work? Insect castes emerge from socially induced changes in nutrition-related genes.

In social species, there is a fundamental trade-off between 'me' and 'we'; that is, should I reproduce, or should I work to help others to reproduce? In this issue of Molecular Ecology, Okada et al. () delve into the evolution and genetic mechanisms of this core question, focusing on social caste formation in insects. The authors take advantage of a unique ant in the genus Diacamma, which has secondarily lost the classic, highly different queens and workers found in many other ants, bees and wasps. Instead, Diacamma ant castes are decided via aggressive dominance interactions among adult females, similar to dominance hierarchies seen in primitively social insects and many social vertebrates. But how does being dominated translate into reproductive shutdown and thus, the creation of a worker caste? The authors use transcriptomics to address this question, and discover that the key may lie in very rapid (within one day) changes in the regulation of nutrient signalling genes, and other genes related to nutrient storage and reproduction. In other words, being aggressed turns on or off genes that tell the ant's brain and physiology to go into 'sterile mode', whereas winning a fight stimulates other genes that ramp up reproductive traits. These results add weight to the idea that caste differences rely on a 'toolkit' of deeply conserved genes involved in core nutritional, reproductive and metabolic functions. In addition, these results emphasize the exquisite and rapid social environmental sensitivity of core toolkit genes during the production of distinct phenotypes.