Findings published this week in PLoS Biology claim that worker policing in social insects has a more complex evolutionary basis than even their unusual patterns of genetic relatedness allow. Instead, it is the 'colony efficiency'—the cost that reproducing workers impose on the colony as a whole—that determines how many are tolerated, according to the study.

Rob Hammond and Laurent Keller, both at the University of Lausanne's Department of Ecology and Evolution, carried out a metaanalysis on previously published data on 50 species of social Hymenoptera—colonial ants, bees, and wasps. These species have a haplodiploid genetic system, which results in extremely high levels of relatedness among workers. This means that a typical worker's long-term genetic prospects are usually better served by raising the queen's brood than by reproducing herself.

In most species, however, workers can lay haploid eggs, which develop into males—nephews to the other workers and grandsons to the...

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