Mating-induced patterns of spermathecal fluid protein expression in two eusocial insect species, Lasius niger and Apis mellifera

Eusocial insect queens exhibit some of the most extreme durations of sperm storage in the animal kingdom. This extended lifespan of sperm within the queen's storage organ (the spermatheca) after mating is largely sustained by the spermathecal fluid matrix-a rich and proteinaceous secretion that fills the void volume within the spermatheca. Here, we conducted a comparative proteomics study on mating-induced changes in spermathecal fluid of two long-lived hymenopteran species, Lasius niger and Apis mellifera. We found some similarities between species; for example, enolase and other enzymes responsible for carbohydrate metabolism were among the top differentially expressed proteins in both A. mellifera and L. niger. Additionally, both species exhibited post-mating upregulation of catalase, glutathione peroxidase, and Mn-conjugated superoxide dismutase (SOD), all of which are important antioxidant enzymes. However, we also identified notable differences, with Cu/Zn-conjugated SODs being consistently downregulated after mating in L. niger but upregulated in A. mellifera. Likewise, canonical immune effectors (phenoloxidase and lysozyme) showed similar patterns of expression in both species, (with phenoloxidase remaining unchanged and lysozyme increasing after mating), but ferritins, which are multifunctional antioxidant proteins that are also induced by immune challenges, differed, increasing in L. niger but decreasing in A. mellifera. Herein, we discuss expression patterns of these proteins and additional immune proteins, hexamerins, odorant binding proteins, and a key carbohydrate metabolism enzyme (glyceraldehyde-3-phosphate dehydrogenase) in the context of the differential life histories of these two eusocial insect species.