Genetic support for the evolutionary theory of reproductive transactions in social wasps

Recent evolutionary models of reproductive partitioning within animal socie ties (known as 'optimal skew:'concessions' or 'transactional' models) predi ct that a dominant individual will often yield some fraction of the group's reproduction to a subordinate as an incentive to stay in the group and hel p rear the dominant's offspring. These models quantitatively predict how th e magnitude of the subordinate's 'staying incentive' will vary with the gen etic relatedness between dominant and subordinate, the overall expected gro up output and the subordinate's expected output if it breeds solitarily. We report that these predictions accord remarkably well with the observed rep roductive partitioning between conesting dominant and subordinate queens in the social paper wasp Polistes fuscatus. In particular, the theory correct ly predicts that (i) the dominant's share of reproduction, i.e. the skew, i ncreases as the colony cycle progresses and (ii) the skew is positively ass ociated both with the colony's productivity and with the relatedness betwee n dominant and subordinate. Moreover, aggression between foundresses positi vely correlated with the skew, as predicted by transactional but not altern ative tug-of-war models of societal evolution. Thus, our results provide th e strongest quantitative support yet for a unifying model of social evoluti on.