Sleep plasticity due to sexual experience in Drosophila melanogaster

Sleep behavior is quite plastic and can be altered according to the organism\u27s previous wakeful experience. For instance, it was recently demonstrated that female Drosophila melanogaster experience a post-copulatory reduction in daytime sleep that is purportedly mediated by sex peptide (SP), a molecule transferred from male to female during mating via seminal fluid and that has been implicated in other effects of copulation on female behavior, such as increased ovulation and rejection offuture male courtship advances. The present study examines what other variables—pertaining to both the female fly and her mate—might be involved in this sex-specific case of social experience-induced sleep plasticity. The effect of mating on sleep remained stable regardless of a female fly\u27s age and previous mating experience, and persisted in the vision mutants norpA and eya2, the learning mutants amnesiac and dunce, and eggless tudor mutants, suggesting that visual, learning, or egg fertilization-related mechanisms do not contribute to this form of sleep plasticity. Contrary to existing literature, here the complete loss of SP only partially blocked the post-copulatory female siesta sleep reduction, suggesting that the effect cannot be governed solely by SP. The daytime sleep reduction was not eliminated in females mated to mutant males lacking the entire class of seminal fluid proteins or lacking sperm entirely, indicating that this effect does not entirely depend on any of the components of the seminal fluid transferred to females during mating. Surprisingly, the sleep reduction persisted even in females exposed to genitalia-less mutant males capable of courtship but not copulation, suggesting that the true mechanism underlying this form of sleep plasticity is contained in some aspect of the sociosexual experience of courtship. This is substantiated by the observation that the courtship vigor of reproductive mutant males parallels the relative magnitude of the sleep reduction effect their mates undergo. These results present an alternative interpretation of the mechanism by which the post-copulatory changes in female Drosophila sleep behavior are elicited, and demonstrate that sleep is sensitive to even the subtlest aspects of an organism\u27s sociosexual experience