Workers respond to unequal likelihood of future reproductive opportunities in an ant

Abstract

In cooperatively breeding or eusocial societies, opportunities may arise for helper individuals to gain direct fitness by reproducing. However, the extent to which helpers respond differentially, in terms of their reproductive behaviour, to the probability that reproductive opportunities will arise is not fully known. In many eusocial Hymenoptera, workers lay eggs only in queenless conditions following the death of the queen or queens. Relative to polygyny (multiple queens per colony), monogyny (single queen per colony) increases the probability that queenless conditions arise. We therefore tested the hypothesis that ant workers respond differentially to queenless conditions as a function of the probability of queenlessness. We compared worker behaviour and reproduction before and after removal of queens from monogynous and polygynous colonies of the ant Leptothorax acervorum . We found that, in queenless conditions, workers from monogynous colonies were significantly more likely to lay eggs, showed a significantly reduced latency to egg laying and laid eggs at a significantly higher rate per capita than workers from polygynous colonies. In addition, before queen removal, workers that laid eggs in queenless conditions across both monogynous and polygynous colonies performed a range of behaviours associated with reproduction at significantly higher rates than nonreproductive, control workers. These ‘future reproductive’ workers also significantly reduced their rates of brood care following queen removal. These findings show that workers under monogyny reproduce more readily in queenless conditions than workers under polygyny, and that would-be reproductive workers alter their behaviour before they experience the opportunity for future reproduction. They therefore suggest that workers adaptively modulate their reproductive behaviour as a function of the likelihood of opportunities for direct reproduction arising, and that workers' behaviour is affected by the ability to gain direct fitness even when reproduction is currently not occurring. • We removed all queens from single- and multiple-queen ant colonies. • We monitored the extent of worker egg laying in queenless conditions. • Workers previously under single queens were significantly more reproductive. • Workers laying eggs when queenless differed behaviourally before queen removal. • Results suggest workers respond adaptively to the likelihood of future reproduction.