Experimental removal of sexual selection reverses intersexual antagonisticcoevolution and removes a reproductive load

Although sexual selection can provide benefits to both sexes, it also can b e costly because of expanded opportunities for intersexual conflict. We eva luated the role of sexual selection in a naturally promiscuous species, Dro sophila melanogaster. In two replicate populations, sexual selection was re moved through enforced monogamous mating with random mate assignment or ret ained in promiscuous controls. Monogamous mating constrains the reproductiv e success of mates to be identical, thereby converting prior conflicts betw een mates into opportunities for mutualism. Random mate assignment removes the opportunity for females to choose beneficial qualities in their mate. T he mating treatments were maintained for 47 generations, and evolution was allowed to proceed naturally within the parameters of the design. In the mo nogamous populations, males evolved to be less harmful to their mates, and females evolved to be less resistant to male-induced harm. The monogamous p opulations also evolved a greater net reproductive rate than their promiscu ous controls. These results indicate a potentially widespread cost of sexua l selection caused by conflicts inherent to promiscuity.