Effects of reproductive state and host resource experience on mating decisions in a walnut fly

Prior experience with conspecifics or essential resources, as well as physiological condition, can have important influences on an animal's reproductive behavior. While effects of experience and physiological state (such as reproductive condition) are generally treated separately in theoretical discussions, they often interact. No previous study has attempted to distinguish effects of experience on physiological state from other effects of experience in the context of mating behavior. In a study of a walnut-infesting tephritid fly (Rhagoletis juglandis), we examined the effects of host fruit experience on mating behavior. We manipulated physiological state in terms of egg load (defined as the number of mature oocytes in a female's ovaries) independently of fruit experience to distinguish the effects of these variables. We found that females with high egg loads were significantly more likely to copulate than low-egg load females; the level of fruit experience had no effect on propensity to copulate, except via effects on egg load. In contrast, females with prior exposure to fruit copulated for a significantly shorter duration than control females, while egg load had no effect on copulation duration. These results suggest that female reproductive condition and exposure to essential resources can have important, albeit diverse effects on mating behavior. We discuss how distinguishing different types of variables may provide insight into sexual conflict over mating decisions, as well as which sex controls specific aspects of behavior.