Reproductive restraint without policing in early stages of a social insect colony

Abstract

Punishment of cheaters is a widespread means of promoting cooperation in social groups. In the eusocial Hymenoptera, punishment (i.e. ‘policing’) of reproductively active workers is thought to have been essential for the evolution of near-sterile worker castes. Many studies have investigated the evolutionary origin of policing behaviour in social insects, but few have considered the factors that affect the expression of policing behaviour in extant species. One factor that is predicted to affect the expression of policing behaviour is colony age. Specifically, policing is expected to be strongest at early stages of colony growth, when the cost of worker reproduction is high, and weaker at later stages. In a previous study, we found that egg-eating behaviour (i.e. ‘policing’, where workers eat worker-laid eggs) is not expressed in early stages of colony growth in the carpenter ant Camponotus floridanus , contrary to theoretical predictions. Here we test two other mechanisms of policing in incipient colonies: queen policing and destruction of male larvae. We found no evidence of either. We also found that workers from incipient colonies were capable of activating their ovaries and laying eggs. In the absence of evidence of policing in incipient C. floridanus colonies, we suggest that reproductive restraint by workers in early colony stages can arise because the inclusive fitness benefits of helping outweigh the direct benefits of reproducing. • It is argued that social insect worker castes required policing to evolve. • We found no evidence of policing in a carpenter ant in early colony development. • We also found no evidence that male larvae are eliminated at this colony stage. • Policing is not necessary to enforce worker sterility in some extant social insects.