Lack of physical policing and fertility cues in egg-laying workers of the ant Camponotus floridanus

Abstract

In many kin groups cooperation is maintained by mutual policing and enforcement of fairness, a pattern that is predicted to change with group size. Variation in group size is most pronounced in hymenopteran societies, in which reproductive division of labour between queens and workers exists. Workers should not reproduce because of relatedness patterns and/or productivity costs. In small colonies where workers retain high reproductive potential egg laying is controlled by worker policing in the form of aggression towards incipient egg-layers or as destruction of worker-laid eggs. Egg-layers and worker eggs can be recognized in many species by differences in their surface hydrocarbons. We investigated whether these mechanisms change in species with large colonies and low worker reproductive potential. In the ant Camponotus floridanus, worker policing is based on differences in the hydrocarbon profiles of worker- and queen-laid eggs. However, in this study workers with developed ovaries were never the focus of attacks by nestmates, which contrasts with most studies on species in which workers have high reproductive potential. The lack of aggression towards egg-laying workers fits with the absence of relevant differences in the cuticular hydrocarbon profile between egg-laying and infertile C. floridanus workers, although strong differences existed between highly fertile queens and workers. Large colonies and low worker reproductive potential were thus accompanied by a lack of physical worker policing in C. floridanus, as predicted. Furthermore, we found costs of worker reproduction and we discuss their significance for worker policing.