EVOLUTION OF EUSOCIALITY - THE ADVANTAGE OF ASSURED FITNESS RETURNS

Queller's (1989) head-start hypothesis suggests that workers may gain relatively more inclusive fitness because they have access to young of various ages which can be quickly brought to the age of independence, whereas a solitary foundress has to survive for the entire duration of the development of her brood. Queller's quantitative analysis is incorrect because it gives an unfair advantage to workers, either by giving full credit of rearing an offspring to a worker who only cared for it for a short while or, by assuming that a worker can do much more work per unit time than a solitary foundress. Workers do indeed have an advantage over solitary foundresses because they have assured fitnes returns, even if in small amounts for short periods of work. This results from a different reckoning from that used by Queller and gives a more moderate advantage, arising essentially from saving the wasted effort that occurs when lone foundress nests fail. Using data on the primitively eusocial wasp Ropalidia marginata, and re-analysing data on the four species of polistine wasps used by Queller, the author shows that such an "assured fitness returns' model provides a selective pressure for the evolution of worker behaviour whih is at least about as strong as that of haplodiploidy, but free from such requirements of the latter as high levels of worker-brood genetic relatedness and ability of workers to manipulate brood sex ratios. -from Author