A novel female reproductive organ differentiates insemination and postmating responses in bedbugs.

Following the evolution of internal fertilization, the female reproductive tract became the site of two major reproductive interactions, the insemination response and the long-term postmating response. However, our understanding of these two responses is hampered by the fact they coincide in most animals. Traumatic insemination in the common bedbug (Cimex lectularius) presents a unique opportunity to disentangle these effects because females have evolved a novel organ, the mesospermalege, which is the site of insemination, while sperm do not arrive in the reproductive tract until several hours after mating. Here, we show that the mesospermalege exhibits a gene expression profile consistent with functions of the insemination response, including immune responses, that are normally found in the lower reproductive tract in other insect species. We then show that the postmating response in the lower female reproductive tract of bedbugs is delayed, coinciding with the movement of sperm through the female, suggesting that the postmating response has evolved in response to sperm receipt independent of intromission and insemination. Finally, we show male seminal fluid genes are expressed in the female, previously only demonstrated in Drosophila. Seminal fluid genes are more highly expressed in the mesospermalege than the reproductive tract, suggesting co-expression has evolved as part of the insemination response. Our results provide insights into the evolution of novel organs, reproductive traits, and female postmating gene expression in a global pest with an unusual reproductive biology.