Sexual conflict in the wild: Elevated mating rate reduces female lifetime reproductive success

Sexual conflict over mating rate is suggested to play a pivotal role in male-female coevolution, and females are predicted to reject superfluous mating attempts. Recent work suggests that direct effects of multiple mating on female fitness are not fully understood. A major concern in studies of sexual conflict is how well the data obtained under controlled laboratory settings relate to natural conditions. We tested the effect of female multiple mating on reproductive success in a natural population of a polyandrous spider, Stegodyphus lineatus. Previous studies show that a male who succeeds in entering a female nest also mates with her; therefore, we used male encounter rate as a proxy of female mating rate. We further elevated female mating rate by introducing males into females' nests. Female lifetime reproductive success was assessed as the likelihood of successful reproduction, offspring production, and juvenile offspring body mass. Increased mating rate increased the time to oviposition and reduced the likelihood of successful reproduction. Female mating rate negatively affected offspring body mass. Manipulated females produced fewer offspring than control females. The observed patterns imply a net cost of polyandry to females and suggest that natural mating rates can be suboptimal for females under natural conditions.