Potential costs of learning have no detectable impact on reproductive success for bumble bees

Development and maintenance of neural architecture supporting learning and memory, as well as active storage of learnt information, are predicted to carry significant energetic costs. Here we explored whether the demands of learning about fitness-relevant stimuli come at a cost to the reproductive success of an insect model. Bumble bee (Bombus spp.) queens found nests alone, and early in the colony cycle must invest simultaneously in learning about rewarding floral resources and colony founding. We exposed queens of Bombus terrestris audax emerging from diapause to a 6-day reversal learning task and compared colony founding success of these individuals to two control groups that did not learn but received equal food. Additionally, we limited carbohydrate intake in half of queens across all treatments. Nutritionally stressed queens had a lower probability of egg laying, delayed nest initiation and lower offspring production compared with nutritionally unrestricted queens, suggesting resource availability at this life cycle stage is crucial to founding successful colonies and population growth. Nevertheless, potential energetic demands of learning did not reduce colony founding success in a laboratory set-up, even in nutritionally stressed groups. Our findings provide a rare real-world test of the costs associated with learning and suggest they do not affect reproductive potential in bumble bee queens.