Compensation of labour by noncompetitive individuals mitigates costs of aggressive succession contest in a social wasp

Cooperative breeders rear young through a division of labour among parents and alloparents (helpers), with reproduction monopolized by one or a few individuals despite all group members being potential breeders. This group-living strategy is found across the animal kingdom in vertebrate and invertebrate taxa. Reproductive succession, in which a previously nonreproductive subordinate female replaces the dominant breeder, is common in these societies and represents a major source of reproductive conflict among group members. The complex trade-offs associated with these social systems have led to a variety of mechanisms that improve individual fitness by mitigating reproductive conflict and maintaining colony cohesion. Social wasps (Vespidae) include a wide diversity of cooperatively breeding species and are highly tractable models for studying how succession conflicts are resolved, yet most of our understanding of cooperatively breeding wasps is based on a small number of species with highly organized, convention-based dominance and predetermined breeder succession systems. Here we investigated the putatively aggression-based succession system of a tropical paper wasp cooperative breeder, Polistes canadensis. We characterized the aggressive interactions and provisioning behaviours of queenright postemergence colonies and, through experimental queen loss, assessed changes in these behaviours at the individual and group level throughout the succession process. We found that social networks broke down, with intense aggressive interactions involving many colony members when the queen was lost. Despite this disruption, provisioning behaviour and affiliative social networks were maintained by previously less-active individuals that switched to foraging roles. Thus, the costs of aggression-based succession were mitigated through compensation by noncompeting group members. Our findings provide support for the hypothesis that aggression-based reproductive succession can be a stable strategy for cooperative breeders when a compensatory mechanism mitigates fitness costs associated with colony failure.