Pheromonal emission by pregnant rats protects against infanticide by nulliparous conspecifics

The present studies of experiments focuses on infanticide in the nulliparous rat and asks two questions. First, what do infanticidal nulliparae gain from killing unrelated young? And second, does the recently parturient female have an effective strategy to counter female infanticide? With regard to the first question, we show two benefits from killing unrelated young, namely, that the killer utilizes the young as a food resource and that she occupies the nest site of the mother whose young she has destroyed. With regard to the second question, we show that an extended period of cohabitation with a pregnant female reduces the incidence of infanticidal behavior in nulliparae. Additionally, we demonstrate that the mother emits a pheromone during pregnancy which in itself reduces the incidence of infanticide and, in fact, often makes potentially infanticidal females maternal. The possible endocrine basis of this induced maternal behavior is discussed.