Role of the queen in regulating reproduction in the bulldog ant Myrmecia gulosa: control or signalling?

Ant queens generally monopolize reproduction, even though workers are able to produce males in orphaned colonies. The mechanisms maintaining worker sterility in the presence of a queen remain inadequately understood. In species with small societies, queens may use agonistic interactions, whereas pheromones are more efficient in large colonies. Whether such pheromones represent coercive tools or honest signals has not been established. We investigated behavioural interactions between queen and workers in the bulldog ant Myrmecia gulosa, a species with limited queen-worker dimorphism and small colonies. About 1.6% of a queen's time budget was spent visiting nest chambers, but there was no aggression and the workers sought contact with their queen, suggesting that pheromones are involved. Cuticular hydrocarbons deposited on the nest substrate by the queen were attractive to workers, but were not necessary for regulating their sterility. Confined queens were able to prevent worker oviposition. Myrmecia gulosa is monogynous and probably monandrous, and workers could maximize their fitness by producing sons and rearing nephews. None the less, they refrained from reproduction in the presence of a fertile queen, even though there was no queen policing. Worker sterility seems to be selected to maximize colony productivity. Our results provide evidence against the notion that queen pheromones inhibit worker oviposition.