Reproductive conflicts and mutilation in queenless Diacamma ants

Reproductive conflicts are particularly intense in queenless ants because colonies are made up of totipotent workers, all potentially able to mate and produce female offspring. After a gamergate (a mated egg-laying worker) dies, aggressive interactions determine her replacement. In Diacamma, the single gamergate systematically mutilates newly emerged workers (callows) and consequently they can never mate. New callows are expected to resist because, once mutilated, they cannot replace the gamergate. In D. ceylonense and D. australe, we studied the behaviour of new callows confronted with dominant individuals of different fertility or age. Faced with a young unmutilated worker (the future gamergate with poorly developed ovaries), callows were aggressive, whereas they did not resist gamergates. We interpret this dichotomy in terms of reproductive differentials between actors and victims. We discuss the selective advantages of mutilation relative to dominance hierarchies which other queenless ants use to regulate monogyny. Mutilation seems to maximize colony productivity by creating irreversibly sterile helpers from newly emerged individuals. © 2006 The Association for the Study of Animal Behaviour.