Reproductive sharing among queens in the ant Formica fusca

Reproductive sharing among cobreeders, in which reproductive shares may vary from equal contribution (low reproductive skew) to reproductive dominance by one individual (high reproductive skew), is a fundamental feature of animal societies. Recent theoretical work, the reproductive skew models, has focused on factors affecting the degree to which reproduction is skewed within a society. We used the parameters provided by skew models as a guideline to study determinants of reproductive sharing in polygyne ants. As a model system we used two-queen laboratory colonies of the ant Formica fusca in which the reproductive shares of each queen was assessed from offspring by using allozymes and DNA microsatellites. We tested how the different variables included in reproductive skew models (queen-queen relatedness, potential fighting ability, productivity, and worker relatedness reflected by queen number in the colony of origin) affect reproductive sharing among queens. The results showed that the relatedness among queens explained 26% of the variation in reproductive skew. The size difference between queens (reflecting potential fighting ability), colony productivity, and worker relatedness did not have an effect on reproductive partitioning among cobreeders. To our knowledge, this is the first study to test for the effects of various determinants of skew in an experimental setting.