Direct effects of polyandry on female fitness in Callosobruchus chinensis

In many insect species with high levels of polyandry, females benefit directly from remating. The effects of remating on female fitness have generally been examined by comparing the fitness of females in multiple-mating and single-mating treatments. In this standard approach, females in the multiple-mating group that refuse to remate are often excluded from the analysis. We investigated the effects of remating in the adzuki bean beetle, Callosobruchus chinensis, a species with low levels of polyandry. Females that refused to remate when given an opportunity to do so were less fecund and shorter lived than females that accepted remating. In this case, excluding females that refuse to remate from the multiple-mating treatment biases the composition of the two treatment populations, and is thus problematic. When we included such females, we found no difference in fecundity, fertility and longevity between females given an opportunity to remate and those that were not. In addition, when we compared females that were allowed to complete remating naturally and those whose remating was interrupted before sperm transfer we found significantly negative effects of female remating on fecundity, suggesting that remating reduces the fitness of polyandrous females in C. chinensis, which is inconsistent with many studies on polyandrous species.