Conflict over sex allocation drives conflict over reproductive allocation in perennial social insect colonies

Queen-worker conflict in the social Hymenoptera has become a cornerstone of sex-ratio theory. Extending that theory to conflict over life-history decisions, however, has proven controversial. Pamilo first proposed that queen-worker conflict over reproductive allocation should be important in perennial, social insect colonies, but Bourke and Chan have questioned the generality of that claim. Here, we reexamine this problem for the simplest case of a monogynous and monandrous hymenopteran society by relaxing assumptions of Pamilo's model. In populations with monomorphic sex ratios, queens and workers agree on allocation to growth versus reproduction. However, variation in sex allocation across colonies can induce queen-worker conflict over reproductive allocation; the former is a necessary condition for the latter. We explore how conflict over reproductive allocation depends on the population-wide sex ratio, the survivorship probabilities for existing colonies, and the likelihood of establishing new colonies. We then test our theory for two ant species, each with two years of data. We find considerable support for our contention of queen-worker conflict over reproductive allocation and suggest how future studies should be structured to explore this conflict further.