The effect of male size, age, and mating behavior on sexual selection in the seed beetle Callosobruchus maculatus

Abstract

We use laboratory mating experiments to examine the effect of male size, age, and mating behavior on fecundity selection and sexual selection in the seed beetle, Callosobruchus maculatus (Coleoptera Bruchidae), a species in which females are larger than males. Female C. maculatus gain a fitness advantage, in the form of increased lifetime fecundity, from mating with large males (which contribute larger ejaculates), but the partial correlation between male size and fecundity is weaker than the partial correlation between female size and her fecundity. Large males had a mating advantage relative to small males, both when a single male was presented to a female and when two males were present. However, this did not appear to be due to females rejecting male courtship attempts, but instead may be due to male-male competition. When females were mated to two males sequentially, neither the size of the first male nor the size of the second male influenced whether or how quickly a female remated. None of the other potential bases for sexual selection — male age, male mating experience, and male courtship persistence — appeared to influence male mating success. We discuss how patterns of sexual selection on body size and sexual size dimorphism in C. maculatus differ from patterns of sexual selection and dimorphism in another seed beetle, S. limbatus.