Genetic polyethism in leaf-cutting ants

Abstract

Females mating with multiple males (polyandry) is taxonomically widespread but is hard to explain in many animals in which it has no obvious direct benefits. In some, of which social insects are the best example, it is suggested that females benefit from the increased genetic diversity of their offspring. Social insect colonies express division of labor, and if genotypes behave differently (genetic polyethism), then genetically diverse colonies may be fitter. However, unequivocal evidence of genetic polyethism is only known from honey bees. Here, we show that such a genetic influence on behavior is also present in the leaf-cutting ant Acromyrmex echinatior. In 2 of the 3 colonies examined, we found that the offspring of some fathers (patrilines) were more likely to engage in waste management, whereas other patrilines were more likely to engage in foraging. When we increased the stimulus for waste management, the representation of patrilines in the ants that responded was the same as normally engaged in waste management in 2 colonies but differed in the third colony. The leaf-cutting ant A. echinatior therefore shows genetic polyethism. Although other factors such as disease resistance may have also played a role in the evolution of polyandry, the results suggest that genetic polyethism may be widespread in social insects and potentially of general importance in the evolution of polyandry.