Cuticular hydrocarbons correlated with reproductive status in a queenless ant

Reproductive division of labour is regulated behaviourally in social insects lacking morphologically specialized castes. The directional nature of dominance interactions shows that recognition occurs, but little is known about its basis. In the queenless ant Dinoponera quadriceps, the top worker in the hierarchy ('alpha') mates and produces offspring in each colony, while other workers remain virgin. Dominant ants frequently rub one antenna of subordinates against their own cuticle, and alpha and infertile nest-mates consistently differ in their relative proportions of the cuticular hydrocarbon 9-hentriacontene (9-C-31) The second-ranking 'beta' occasionally lays unfertilized eggs and we show that she has less 9-C-31 than the alpha but more than infertile workers. To investigate further the link between 9-C-31 and ovarian activity, we experimentally removed alpha workers (n = 11 individuals) and used solid-phase microextraction (SPME) with gas chromatography to measure changes in 9-C-31 on live beta workers which attained alpha status. The proportion of 9-C-31 on the replacement alpha increased significantly after six weeks, in parallel with her gain in fecundity. We discuss whether 9-C-31 provides honest information about egg-laying ability enabling ants to recognize the different classes of nest-mates involved in reproductive conflicts. Such fertility cues could reliably underpin the antagonistic interactions occurring in insect societies.