SEXUAL SIZE DIMORPHISM AND SELECTION IN THE WILD IN THE WATERSTRIDER AQUARIUS-REMIGIS - LIFETIME FECUNDITY SELECTION ON FEMALE TOTAL LENGTHAND ITS COMPONENTS

Darwin's fecundity advantage model is often cited as the cause of fema le biased size dimorphism, however, the empirical studies of lifetime selection on male and female body size that would be required to demon strate this are few. As a component of a study relating sexual size di morphism to lifetime selection in natural populations of the female si ze-biased waterstrider Aquarius remigis (Hemiptera: Gerridae), we esti mated coefficients for daily fecundity selection, longevity selection, and lifetime fecundity selection acting on female body size and compo nents of body size for two consecutive generations. Daily fecundity wa s estimated using females confined in field enclosures and reproductiv e survival was estimated by twice-weekly recaptures. We found that dai ly fecundity selection favored females with longer total length throug h direct selection acting on abdomen length. Longevity selection favor ed females with smaller total length. When daily fecundity and reprodu ctive longevity were combined to estimate lifetime fecundity we found significant balancing selection acting on total length in both years. The relationship between daily fecundity and reproductive longevity al so reveals a significant cost of reproduction in one of two years. We relate these selection estimates to previous estimates of sexual selec tion on male body size and consider the relationship between contempor ary selection and sexual size dimorphism.