Proteomic diversification of spermatostyles among six species of whirligig beetles

We investigated the proteomic composition of spermatostyles, an understudied ejaculate structure in six species of whirligig beetles (Order Coleoptera: Family Gyrinidae). Ejaculate structures such as copulatory plugs and spermatophores are diverse and assumed to be adaptive, but their composition has not been widely investigated in many taxa, limiting insights into their function inside FRTs. Here we report on the proteomic composition of spermatostyles, an ejaculate structure found in some beetles and true bugs. By combining novel proteomic data with predicted proteins from newly assembled de novo transcriptomes, we learned that spermatostyles are proteolytically enriched and that they contain a large abundance of catalytically active proteins. In addition, assays confirmed that they retain proteolytic activity and are functionally conserved based on orthology inferences. Our study revealed that spermatostyles contain a notably large amount of sperm-leucyl aminopeptidases (S-LAPs), an unusual family of abundant fly flagellar proteins, and confocal imaging of S-LAPs in spermatostyles shows that one route to the formation of ejaculate structures can entail the co-option of canonical sperm proteins.