Increased opportunity for sexual conflict promotes harmful males with elevated courtship frequencies.

Mating systems have a profound influence on the probability of conflict occurring between the sexes. Promiscuity is predicted to generate sexual conflict, thereby driving the evolution of male traits that harm females, whereas monogamy is expected to foster reproductive cooperation, thus rendering such traits redundant. We tested these predictions using experimentally evolved Drosophila pseudoobscura subject to different mating systems. Female survival was not influenced by the mating system treatment of her partner. However, females continuously housed with males evolving under elevated opportunities for female promiscuity produced fewer total progeny, but a relatively greater number of progeny early in their lives, than females housed with males evolving under obligate monogamy. We also found that promiscuous males courted females more frequently than monogamous males. Variation in male courtship frequency and progeny production patterns among treatments reinforces the critical importance of mating system variation for sexual conflict, during both pre- and post-copulatory interactions.