Evolution and adaptations of the seminal proteome in an insect with traumatic insemination

The protein composition of sperm and seminal fluid are key to male fitness. However, we currently lack an understanding of the factors that shape seminal proteome composition. The common bedbug (Cimex lectularius) mates by traumatic insemination, subjecting the ejaculate to a unique selective environment as sperm traverse the female genital and paragenital system. We provide the first high-throughput proteomic characterisation of the sperm and seminal fluid proteome in a hemimetabolous insect and the first in-depth proteomic characterisation of the male bedbug reproductive system. Our analysis revealed conserved and unique features of the bedbug sperm and seminal fluid proteome possibly linked to traumatic insemination. The sperm proteome showed elevated rates of molecular evolution, unlike most other studied insect species, yet also contained many conserved proteins. Notably, we found that bedbugs and other hemimetabolous insects share an expansion of Sperm-leucylaminopeptidases (S-Laps). Using in silico protein-ligand binding predictions, we show that S-Laps have likely retained catalytic activity in bedbugs. Our results provide a foundation for future studies of this expanding global pest.