Sexual conflict and the environment: teasing apart effects arising via males and females

When males and females differ in their reproductive interests, each sex attempts to increase its own reproductive success, sometimes to the detriment of its mate. The environment that individuals experience has been shown to be fundamental in mediating this sexual conflict, since it can alter the balance between the costs and benefits that males and females obtain from mating. In the seed beetle Callosobruchus maculatus water availability is an important environmental factor that can alter this balance, with consequences for female mating strategies and the strength of sexual conflict. Whether the effect of water availability arises via effects on females or males, however, has not been explored. Here we manipulated access to water independently for adult males and females and explored how this environmental variation affected male and female mating behaviour, female fitness and offspring development. We found that access to water did not alter the size of ejaculates that males transferred, but that males with water available had longer copulation durations. We also found that females with access to water, despite living longer and laying a similar number of eggs during their lifetime, had offspring with longer development times and lower eclosion success than those of females with no access to water. Our results suggest that water availability has detrimental effects on female fitness, but despite changes in male mating behaviour these effects are not related to changes in the costliness of males as mates.