Interpopulation variation in male investment and copulatory behavior in a bruchid beetle (Callosobruchus maculatus)

Sexual selection results in the evolution of traits ranging from mutualistic to antagonistic to the opposite sex. When traits in one sex are harmful to the opposite sex, we expect selection for the harmed sex to either avoid or alleviate harm. Males of the seed beetle, Callosobruchus maculatus, transfer ejaculates containing compounds that inhibit female remating but also increase female lifespan and egg production. Males also possess spines on their genitalia that penetrate the female reproductive organ internally. Variation in ejaculates and spine-induced damage influence female fecundity and lifespan, but how spines and ejaculate size interact to influence male and female fitness has not been examined. In this study, we examine variation in genital spine length and ejaculate size in six geographically and genetically isolated populations of C. maculatus, and test how this variation influences damage done to females during mating. Tracking both mutualistic and antagonistic male traits and their effects on females, we advance understanding of how male traits with differing consequences for females evolve under sexual selection.