Colonies of social insects, such as bees and ants, typically consist of one or more 'queens ' and the 'workers' that support their reproduction. In some social insect colonies, however, workers do lay unfertilised eggs - which develop into males - essentially "cheating" on the other workers who are investing in only the queen's reproduction. Such action can be severely penalized by other workers - in honeybees, where this behavior was first shown, workers remove worker-laid eggs within hours by eating them, and, in some ants, more draconian methods lead to the mutilation of the culprit caught in the act of laying. In the open access journal, PLoS Biology, Rob Hammond and Laurent Keller explain how these policemen arise.

The apparently altruistic behavior of workers in supporting their queen is generally explained by 'kin selection', whereby the worker obtains more 'reproductive payoffs' indirectly by producing the queen's offspring than by having their own. Kin selection revolves around relatedness because relatedness determines the magnitude of the payoffs. Based on a detailed comparative phylogenetic analysis of 50 species of ants, wasps, Hammond and Keller now demonstrate that the 'policing' behavior of workers cannot be accounted for just by relatedness as traditionally thought - but that it is necessary to consider how the efficiency of the colony influences behavior. The key appears to be that energy invested by workers into laying eggs - which would otherwise be used in foraging and legitimate brood rearing - can detract from the overall efficiency and growth of the colony.

To test this, Hammond and Keller estimated the extent to which workers produce their own male offspring and whether this was determined by how related the workers are to each other (e.g. some colonies are run by more than one queen); the 'efficiency hypothesis' predicts no such relationship. Contrary to expectations, they found evidence that a genetic incentive for worker
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Contact: Paul Ocampo
pocampo@plos.org
1-415-624-1224
Public Library of Science
23-Aug-2004

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