The spectacular success of eusocial insects can be attributed to their sophisticated cooperation, yet cooperation is conspicuously absent during colony foundation when queens are alone. Selection against this solitary stage has led to a dramatically different strategy in thousands of eusocial insect species in which colonies are started by groups of nestmates and the benefits of sociality are retained continuously. Dependent colony foundation (DCF) evolved recurrently multiple times across the ants, bees, and wasps, though its prevalence in termites remains unclear. We review adaptations at both the colony level (reproductive investment shifts from sexuals to workers) and the individual level (wingless queens evolve in ants), and other consequences for life history (invasiveness, parasite transmission). Although few studies have focused on DCF, the accumulated data from anecdotal reports, supported by indirect information including morphology, population genetics, and colony demographics, make it clear that this strategy is more diverse and widespread than is usually recognized.

In insect societies lacking morphologically specialized breeders and helpers, reproduction is often restricted to behaviorally dominant individuals. Such societies occur in about 100 species of ants that have secondarily lost the queen caste. All females, who are morphologically workers, can potentially mate and lay eggs but only a few do so, and we demonstrate in Dinoponera quadriceps that this is regulated by a dominance hierarchy. Six types of agonistic interactions allowed the ranking of 5-10 workers in the hierarchy (n = 15 colonies). In particular, alpha and beta had characteristic behavioral profiles and were easily recognized. Only alpha mated, and workers ranking beta to delta sometimes produced unfertilized, male-destined eggs. Natural replacements (n = 19) and experimental removals (n = 15) of alpha demonstrated that beta was the individual most likely to replace alpha, although gamma and more rarely delta sometimes did, and we discuss the conflict that occurs among high-ranking individuals over who should replace alpha. After such replacements, the new alpha behaved more aggressively than the overthrown alpha. Newly emerged workers tended to reach high ranks and displaced older high-ranking individuals down the hierarchy. Low-ranking subordinates often prevented high-ranking individuals from replacing alpha by biting and holding their appendages (worker policing), which is consistent with the pattern of relatedness associated with monogyny and monandry in D. quadriceps. We investigated the relative importance of chemical communication and dominance interactions to regulate reproduction. Alpha, beta, and sterile workers have different signatures of cuticular hydrocarbons, and these may provide honest information which underpins worker policing by low-ranking individuals.

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-C₃₁). The second-ranking ‘beta’ occasionally lays unfertilized eggs and we show that she has less 9-C₃₁ than the alpha but more than infertile workers. To investigate further the link between 9-C₃₁ 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-C₃₁ on live beta workers which attained alpha status. The proportion of 9-C₃₁ on the replacement alpha increased significantly after six weeks, in parallel with her gain in fecundity. We discuss whether 9-C₃₁ 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.