Worker reproduction in ants -: a genetic analysis

Workers of social insects may enhance their inclusive fitness by laying unfertilized eggs that develop into males. In particular, workers may gain from rearing worker-produced males if their average relatedness to them exceeds their relatedness to queen-produced males. These relatedness values depend both on the queen mating frequency and on the number and relatedness of nestmate queens. We examined the occurrence of worker reproduction in field colonies of four ant species of the genera Formica and Myrmica. Based on relatedness arguments alone, worker reproduction was expected in all species because of low queen mating frequency, or low effective queen numbers. Nevertheless, genotype matching of workers and males showed that worker reproduction was absent or rare in two of the three Formica species studied here. In M. ruginodis, queens may have been the sisters of the workers in many cases, which means that workers of this species may regularly rear nephews. In the three species in which worker reproduction was not found, workers bias colony sex ratios to enhance their inclusive fitness. We therefore hypothesize that sex ratio biasing and male production may be mutually exclusive strategies for workers.