Caste totipotency and conflict in a large–colony social insect

In most social insects with large, complex colonies workers and queens are morphologically quite distinct. This means that caste determination must occur prior to adulthood. However workers and queens in the swarm-founding epiponine wasps are often morphologically indistinguishable, or nearly so, suggesting that caste determination in these wasps could be quite different. To determine the extent of caste lability in the epiponine, Parachartergus colobopterus, we removed all the queens from one colony and all but one from another colony. Worker aggression diminished after queen removal. A week later the colony with no queens had a new, young cohort of mated queens. These must have been either adults or pupae at the time of queen removal, and so could not have been fed any differently from workers. Relatedness patterns confirmed that these new queens would normally have been workers and not queens. A model of inclusive fitness interests shows that workers ought to suppress new queen production, except at low queen numbers, a prediction supported by our empirical results. The patterns of social conflict over queenship resulting from swarm founding in a many-queen society may help to explain the unusually weak caste differentiation in the epiponines.