Female seed beetles, Callosobruchus chinensis, remate more readily after mating with relatives

Mate relatedness can have an impact on fitness and inbreeding avoidance is a potential factor shaping mating behaviour. When females are unable to avoid mating with kin, they may exploit postcopulatory mechanisms as an alternative means to avoid inbreeding. If females increase their remating propensity after incestuous matings, they could reduce the likelihood of kin siring their offspring. We investigated the effects of male relatedness on the probabilities of female first mating and remating in the adzuki bean beetle, Callosobruchus chinensis. Females showed no precopulatory discrimination against brothers at their first or second mating. In contrast, females mated first with brothers were more willing to remate than females mated first with unrelated males. We found no evidence that males transfer fewer sperm when mating with sisters. This study suggests that C. chinensis does not avoid inbreeding before and during copulation. Instead, females that mated with related males adapted their subsequent mating behaviour to avoid the potential costs of inbreeding. Polyandry in this species may be the result of females attempting to prevent genetic incompatibility by remating after having mated to a relative.