ON THE ROLE OF BODY-SIZE FOR LIFE-HISTORY EVOLUTION

1. Body size is a central element in current theories of life-history evolution. Models for optimal age at maturity are based on the assumpt ions that there is a trade-off between development time and adult size and that larger size provides a reproductive advantage. 2. The result s of large, replicated experiments with the water strider Gerris bueno i (Heteroptera: Gerridae) contradict both these assumptions. Individua l rearings under field conditions showed that there is a negative, not a positive, correlation between development time and adult size. The physiological basis of growth, with stretch-induced moulting, may prov ide a partial explanation for this correlation. 3. This study examined a number of fitness components for their correlations with female siz e: lifetime fecundity, reproductive life span, average volume per egg, total volume of eggs laid, and the proportion of eggs hatched. None o f these traits was correlated with female size. 4. The data on water s triders suggest an alternative scenario for life-history evolution, in which size is not an adaptive trait, but evolves as a correlated resp onse to selection on other traits. This expands the range of possible models, and opens life-history theory to the debate about adaptation a nd optimality.