Queen-worker conflict over sexual production and colony maintenance in perennial social insects

An important idea from kin selection theory as applied to life-history evolution in perennial insect societies suggests that potential conflict exists between the queen and workers over the relative allocation of resources to colony reproduction and colony growth. This prediction assumed a colony with one singly mated queen, sterile workers, and independent colony foundation by dispersing queens. We argue that this prediction is mistaken because queen and workers under these circumstances can only invest in sexuals (new queens and males) derived from the colony queen. Assuming population sex ratio equilibrium, potential conflict is absent because both parties maximize fitness by maximizing the colony's total output of these sexuals. However, a similar queen-worker conflict is predicted in facultatively polygynous species in which existing queens are superseded. We hypothesize that queens favor the production of relatively more new workers to prolong their lives as reproductives, whereas workers favor raising relatively more new queens as possible replacements. We tested this hypothesis using productivity data from the ant Leptothorax acervorum. As predicted, queen number and worker number were, respectively positively and negatively associated with the investment ratio of new workers to new queens. These findings imply a queen-worker conflict over caste determination in ants.