Demographic predisposition to the evolution of eusociality: a hierarchy of models.

I present a hierarchy of models that illustrate, within the framework of inclusive fitness theory, how demographic factors can predispose a species to the evolution of eusociality. Delayed reproductive maturation lowers the inclusive fitness of a solitary foundress relative to that of a worker. Variation in age at reproductive maturity makes the worker strategy more profitable to some individuals than to others and thus predicts the coexistence of single-foundress and multiple-foundress nesting associations. Delayed reproductive maturation and variation in age at reproductive maturity also select for mixed reproductive strategies so that some individuals whose reproductive maturation is expected to be delayed can first act as workers and later switch over to the role of a queen or foundress. Assured fitness returns shows how identical mortality rates can have different consequences for workers and solitary nest foundresses because a solitary foundress will have to necessarily survive for the entire duration of development of her brood, whereas a worker can hope to get proportional fitness returns for short periods of work. In concert with assured fitness returns, delayed reproductive maturation and variation in age at reproductive maturity become more powerful in selecting for worker behavior, and mixed reproductive strategies become available to a wider range of individuals. These phenomena provide a consistently more powerful selective advantage for the worker strategy than do genetic asymmetries created by haplodiploidy.