The selective advantage of low relatedness

Relatedness within colonies of social Hymenoptera is often significantly lower than the outbred population maximum of 0.75. Several hypotheses address the widespread occurrence of low relatedness, but none have measured the covariation of colony fitness and relatedness. In a polyandrous harvester ant, Pogonomyrmex occidentalis, average within-colony relatedness in the population is low but highly variable among colonies, and relatedness is negatively correlated with colony growth rate. Differences in growth rate strongly influence survival and the onset of reproduction, leading to a 35-fold increase in fitness of fast-growing colonies. Benefits of a genetically diverse worker population may favor polyandry in this species.