The effect of bumble bee gynes’ reproductive status on the response to CO₂ narcosis

Many organisms undergo extreme physiological and behavioral changes that dictate their responses to different stimuli during their life cycle. Bumble bees (Bombus sp.) display an annual life cycle, in which the virgin gynes emerge, disperse, mate, and undergo several months of winter diapause before establishing new colonies in the spring. CO₂ narcosis induces a direct transition from mating to reproduction, thus diapause can be bypassed. The mechanism underlying the response to CO₂ narcosis remains unclear. Here, we used Bombus terrestris gynes in different reproductive statuses (virgin, mated, and post-diapause) to examine the effect of CO₂ narcosis on ovarian development, body mass, protein uptake, and metabolic rate. We found that the impact of CO₂ narcosis on gynes was inhibited by mating, with virgin gynes showing the strongest effect of CO₂ narcosis on ovary activation and protein turnover. We show that mating inhibits the effect of CO₂ narcosis prior to the diapause period, suggesting that this effect is upstream to that of CO₂ narcosis.