Trade-offs between sperm viability and immune protein expression in honey bee queens (Apis mellifera)

Abstract

Queens of many social hymenoptera keep sperm alive within their specialized storage organ, the spermatheca, for years, defying the typical trade-off between lifespan and reproduction. However, whether honey bee (Apis mellifera) queens experience a trade-off between reproduction and immunity is unknown, and the biochemical processes underlying sperm viability are poorly understood. Here, we survey quality metrics and viral loads of honey bee queens from nine genetic sources. Queens rated as ‘failed’ by beekeepers had lower sperm viability, fewer sperm, and higher levels of sacbrood virus and black queen cell virus. Quantitative proteomics on N = 123 spermathecal fluid samples shows, after accounting for sperm count, health status, and apiary effects, five spermathecal fluid proteins significantly correlating with sperm viability: odorant binding protein (OBP)14, lysozyme, serpin 88Ea, artichoke, and heat-shock protein (HSP)10. The significant negative correlation of lysozyme—a conserved immune effector—with sperm viability is consistent with a reproduction vs. immunity trade-off in honey bee queens.

Queens, but not their stored sperm, are resilient to temperature stress

“…1c). However, upon inspection of proteins quanti ed within the spermathecal uid, we found that one of the six proteins signi cantly correlating with sperm viability (5% false discovery rate) was Mellitin, which is the main protein component of honey bee venom (Table 2), and which we have not observed in our previous spermatheca proteomics dataset [21]. Here, abundance of Mellitin is inversely linked to sperm viability, strongly suggesting that venom contamination during the dissection process impaired our ability to detect differences in sperm viability between experimental groups.…”

“…mM Na 3 C 6 H 5 O 7 ) and sperm viability was measured using dual uorescent staining exactly as previously described [21]. Two days after queens were sacri ced, we returned to the nucs to sample remaining eggs as already described, destroy any queen cells that had been built, normalize colony populations, and introduce new adult queens for the next round of the queen stress trial.…”

Honey bee queen health is unaffected by contact exposure to pesticides commonly found in beeswax

“…Spermathecae were removed from the abdomen with forceps and blotted dry on a Kimwipe, then clean forceps were used to gently remove the tracheal net surrounding the spermatheca. The spermatheca was then lysed in an Ependorf tube containing 100 μl Buffer D and spermathecal fluid proteins were extracted for mass spectrometry analysis exactly as previously described [50].…”

“…Proteins were extracted, digested, and purified from spermathecal fluid exactly as previously described [49, 50]. Briefly, sperm cells were spun down from the Buffer D-diluted spermathecal fluid solution and soluble proteins in the supernatant were precipitated with acetone.…”

Fertility costs of cryptic viral infections in a model social insect

“…Examination of previously published proteomic and transcriptomic data from mated and unmated queen spermathecae, in the absence of identifiable infection, revealed no obvious decrease in the constitutive expression of immune related genes in mated queens, as might be expected if a trade-off was occurring (see Supplementary Fig S1 ). However, we have previously shown that lysozyme, an immune effector, is negatively correlated with stored sperm viability in honey bee queens and that failing queens, even without symptoms of viral infection, have significantly higher titers of black queen cell virus (BQCV) and sacbrood virus (SBV) 33 . This suggests that immune activation and reproduction are negatively associated in honey bee queens, at least in terms of sperm maintenance, but the relationship between immunity and ovary function has not yet been explored.…”