The seminal proteome of a monandrous fly, Drosophila subobscura

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. To address this, we characterized the seminal proteome of the monandrous fly Drosophila subobscura. Using a label-free quantitative proteomics approach, we identified 172 Sfps, comparable in number to the 153 Sfps previously reported in polyandrous Drosophila melanogaster using a similar approach. The D. subobscura seminal proteome contains all the D. melanogaster sex peptide network-proteins that control the female post-mating response-and many proteins known to be involved in post-copulatory sexual selection. We also found a surprising over-abundance of proteins previously shown to be downregulated under monogamy selection in D. melanogaster. Collectively, the patterns suggest that the D. subobscura seminal proteome is characterized more by conflict than cooperation and, despite differences in mating systems, is compositionally similar to that of D. melanogaster, with a complex proteome rich in receptivity-inhibiting Sfps.