Abstract When females mate with multiple males, ejaculates from different partners compete within the female reproductive tract. Males gain a competitive advantage by transferring seminal fluid proteins (Sfps) that manipulate female post-mating responses, such as reducing female propensity to remate. But in monandrous species, where females typically mate only once, post-mating sexual selection is absent, raising questions about the complexity and identity of Sfps in monandrous seminal proteomes