Self assessment in insects: honeybee queens know their own strength

Most animals fight to gain access to mates and copulate [1,2]. In many animal contests, fighting abilities of opponents are assessed directly during the physical interaction or indirectly when visual, auditory or chemical cues are correlated with fighting ability [1,3– 10]. These assessments enable an individual to gauge whether it should engage in a contest, and once engaged, to assess whether to persist if it is likely to win or to withdraw if the costs associated with losing become unacceptably high [4,11,12]. Escalation of fighting occasionally leads to fatalities [references in 2,13], but lethal fights over resources are the general rule in a few species [14]. A textbook example of a species using lethal fights to settle a reproductive conflict is the honeybee, Apis mellifera [15]. Reproduction in honeybee colonies is achieved by colony fission. The mother queen leaves the nest with a group of workers to establish a new colony while several daughter queens are reared in the old nest. Rearing several replacement queens ensures that at least one will reach maturity and replace the departed queen. The first newly emerged queen kills her rivals within the cells in which they develop [16]. If several queens emerge simultaneously, they typically fight for reproductive supremacy until only one survives and takes over reproduction in the colony [17]. During the fights, the honeybee queens mount, grapple, and sting each other. Stinging is the usual cause of death and is only successful when queens have a good purchase with their mandibles on their opponents and can position themselves suitably [15,18]. In China, beekeepers found a way to prevent queens from killing one another by ablating their mandibles. By forcing several queens to cohabit (Fig. 1), they create more productive colonies for commercial exploitation. In order to understand how manipulating the fighting ability of queens affects the social structure of honeybee colonies, we studied the effects of mandibular ablation on the strategic decisions of opponents during the fights