Experience-dependent plasticity in brain structure and olfactory learning capacities in honey bees (Apis mellifera): Amélie Cabirol.

Learning capacities, and the structure of the brain centres supporting them, vary greatly between individuals, partly due to different life experiences. In honey bees, experience - dependent plasticity has been reported in multisensory brain centres involved in learning and memory: the mushroom bodies (MBs). T he consequences of such plasticity on learning performances are still unknown. The aim of my thesis was to examine the relationships between experience, learning capacities and MB organization in honey bees. The age - related division of labour in honey bees gave me the opportunity to study experience - dependent plasticity both in young bees working inside the hive, and in older bees foraging outdoors. I first observed that bees exposed to a sensory - impoverished environment for the first days of adulthood had a higher number of synaptic boutons in the MBs, and a reduced performance in a MB - dependent learning task ; reversal learning. This suggests the occurrence of experience - dependent synaptic pruning in the natural environment, which improves learning capacities. I observed similar effects of environmental enrichment when the bees start ed foraging . Foraging onset was accompanied by a decrease in the number of synaptic boutons in the MBs, as well as b y an improvement in reversal learning performance. Prolonged foraging activity, however, had the opposite effects, especially when a stress applied to the colony induced bees to forage earlier. Therefore , I highlighted a negative relationship between the n umber of synaptic boutons in the MBs and performance in reversal learning. I then confirmed the negative impact of foraging activity on learning capacities using a different MB - dependent task; positive patterning . I revealed the involvement of the cholinergic signalling pathway in this experience - dependent cognitive decline. This thesis presents the first integrated analyses of experience - dependent plasticity in both brain structure and cognitive capacities in honey bees. It help s to understand the mechanisms linking synaptic connectivity to learning performances, and will encourage further studies on the role of environmental stressors in the reported cognitive decline in foragers.