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

Abstract

I present a hierarchy ofmodels 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 multiplefoundress 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.

Survival and productivity benefits to social nesting in the sweat bee Megalopta genalis (Hymenoptera: Halictidae)

“…If female mortality is higher when constructing nests and/or nest construction substantially increases the time required to rear brood to emergence, then our calculations underestimate the probability of solitary nest failure (Gadagkar 1991). Conversely, if females choose to abandon their nests to nest elsewhere, our calculations overestimate adult mortality.…”

“…Although our estimate is approximate, it shows that independently nesting females face a substantial risk of brood loss that can be reduced by group living. This risk of solitary nest failure is at the lower end of the range reported in other studies of APR models (Gadagkar 1991;Queller 1994;Eickwort et al 1996;Field et al 1998;Hogendoorn and Zammit 2001).…”

“…Assured fitness returns, or "insurance-based" models (hereafter APR models), argue that in such cases adults will be favored to remain at their natal nest as helpers because they may die before successfully raising an offspring (Queller 1989(Queller , 1994(Queller , 1996Strassmann and Queller 1989;Gadagkar 1990Gadagkar , 1991Bull and Schwarz 2001). A solitary individual will lose all parental effort if she dies before offspring independence.…”

Kin structure, ecology and the evolution of social organization in shrimp: a comparative analysis

“…Under such conditions groups are better able to find scattered food, repel enemies, care for young, and thus reduce the risk of brood loss. This scenario has long been a favoured explanation for evolution of eusociality in insects (Wilson 1971;Lin & Michener 1972), and has been termed 'life insurer' eusociality (Queller & Strassmann 1998) in Hymenoptera, in which helpless larvae require extended care and foraging adults are under constant threat from enemies (Queller 1989;Gadagkar 1991). A similar explanation has been offered for sociality in vertebrates threatened by harsh environments with unpredictable food supply.…”

Evolution of social behaviour in the primitively eusocial waspRopalidia marginata: do we need to look beyond kin selection?

“…To examine this possibility, I have constructed a hierarchy of inclusive fitness models that explore different demographic reasons why a worker may have higher inclusive fitness than a single foundress [19]. For lack of space, I will illustrate below only one of these models, the assured fitness returns model [9].…”