Factors affecting the reproductive success of the crab spider Misumenoides formosipes: the covariance between juvenile and adult traits

Abstract

To examine the importance of covariance between stages in traits related to foraging, we quantified the relationships between reproductive success and sizerelated variability in weight gain in juvenile and adult instars of the crab spider Misumenoides formosipes (Araneae: Thomisidae). Prereproductive weight and fecundity are both highly correlated with carapace width, a linear measure of size which does not change within an instar. In field populations, adult females with larger carapaces gain more weight and are more likely to reproduce than females with smaller carapaces. The growth rate of spiders fed ad libitum in the laboratory is unrelated to size, suggesting that size-related differences in the field are due to variation in prey-capture success. Adult females with a carapace width less than 3.4 mm comprised 22% of the population, but were never found to reproduce. Of the individuals that did reproduce, a 17% increase in carapace width resulted in a 100% increase in fecundity. Juvenile stages must be examined to understand adult foraging and reproductive success, because the net weight gained by juvenile instars determines adult size. The final weight gained by spiders in the antepenultimate and penultimate instars explained nearly all the variation in carapace width in the penultimate and adult instars, respectively. We found that constraints on foraging in late juvenile stages are different from the adult stage. Penultimate foraging behavior differs from that of adults, because of constraints on foraging in the period preceding ecdysis. Additionally, in both late juvenile instars, carapace width had little or no effect on the final weight gained within the instar suggesting that factors that affect foraging are different between the juvenile and adult stages. These analyses stress the fact that to fully understand the effects of foraging on reproductive success, we must examine stage-specific constraints throughout an organism's life history.