Reproductive division of labour without dominance interactions in the queenless ponerine ant Pachycondyla (=Ophthalmopone) berthoudi

Abstract

In the queenless ponerine ant Pachycondyla (=Ophthalmopone) berthoudi, a variable proportion of the workers in each colony are mated and lay diploid eggs ("gamergates"). Virgin workers do not reproduce. The mechanism of reproductive regulation was investigated by splitting colonies to create groups of workers containing one, several or no gamergates. In the monogynous groups, no aggressive interactions were observed and virgin workers showed no signs of ovarian development. In polygynous groups, aggressive interactions were also not observed and the gamergates rarely interacted with each other; again, virgin workers showed no signs of ovary development. The groups without gamergates consisted of a large proportion of callows, with a variable number having developed ovaries in each. No aggressive interactions were observed, and there was no correlation between inter-individual behaviours and reproductive status. Although the eggs produced in these virgin groups were embryonated, none hatched. When sterile workers were separated from gamergates by a double mesh screen, several developed their ovaries and laid eggs. However, when separated by a single mesh antennate screen and allowed to gamergates, virgin workers remained infertile. Our results suggest that chemical signals produced by reproductive individuals are important in reproductive regulation in this species. The absence of any form of behavioural interactions in the regulation of reproduction is unusual for a queenless ant.