Worker policing

Worker policing is a behavior seen in colonies of social hymenopterans (ants, bees, and wasps) whereby worker females eat or remove eggs that have been laid by other workers rather than those laid by a queen. Worker policing ensures that the offspring of the queen will predominate in the group. In certain species of bees, ants and wasps, workers or the queen may also act aggressively towards fertile workers. Worker policing has been suggested as a form of coercion to promote the evolution of altruistic behavior in eusocial insect societies. Proposed mechanisms for the recognition of worker-laid eggs or active reproductive workers include marker hydrocarbons on the surface of queen-laid eggs, cuticle hydrocarbons on reproductive workers, and recognition of nest-mates. In rare cases, worker-laid eggs carry mimicked queen hydrocarbons and escape policing, a condition known as the anarchic syndrome. Not all forms of policing require the presence of a queen; it also occurs in a few species of ants which establish a dominance hierarchy of reproductive female workers, where top-ranking individuals reproduce. In many social insect communities, sex is determined through haplodiploidy. Haploid male drones develop from unfertilized eggs while diploid females develop from fertilized eggs. Queens of a colony may mate with one or several drones. On average, a queen shares half of her genes with her sons, but only shares a quarter of her genes with the sons of fertile female workers. Therefore, it is in the queen's best interests to have her own sons raised, and not the sons of workers. Workers can reproduce in many ants, bees, and wasps because male offspring come from unfertilized eggs. By contrast, the worker shares half of her genes with her sons and only a quarter with her brothers. Furthermore, the workers in colonies with a single once-mated queen are related to their nephews by three eighths, higher than they are related to brothers. This results in a conflict where the queen and worker females are at odds over the proportion of male offspring they contribute, since each side tries to maximize its reproductive fitness. Queens favor production of their own sons while workers favor production of their own sons, and do not stop their sisters from laying because of the favorable relatedness to nephews. Worker policing occurs when worker bees in the colony are genetically more closely related to the queen than the reproductive female. In many instances, the eggs of the female worker are eaten, or she is repeatedly attacked by other workers. This mechanism of egg removal ensures that the queen's sons predominate. Experiments confirming the role of kin selection in worker policing demonstrate the effects of multiple matings, which can lead to lower average relatedness between workers. Queens of the social wasp Dolichovespula saxonica mate singly or multiply. Researchers who study these wasps have observed a strong positive correlation between worker relatedness and male production. After controlling for the absolute number of eggs laid, these scientists conclude that the queen's multiple matings favor mutual worker policing. Although early theories of worker policing focused on the kin selection component, evidence from honey bees suggests that altruism is sometimes enforced. Fewer workers reproduce as policing effectiveness rises, and policing effectiveness decreases with increasing relatedness except in colonies with no queen. This suggests that worker policing is a social sanction imposed on selfish individuals.