Body size and the neural, cognitive and sensory basis of sociality in bees

Body size is a universal property strongly tied to biological structure, function and complexity, from cell metabolism to animal behavior. The nervous system, the physical generator of the behavioral phenotype, is also affected by variations in body size; hence potentially affecting the way animals perceive, interpret and react to the surrounding environment. When animals join to form groups, such individual differences and requirements become part of the structure of the society, and may even determine social roles. In this dissertation, I explore the association between body size, behavioral phenotype and social organization in two groups of bees, honey bees and bumblebees. Focusing on bumblebees, I explore the link between body size, brain allometry and performance in learning and memory tasks, within the context of task specialization for in-hive and outside of-hive tasks. I show that variation in size goes along with learning and memory performance and with a broad distribution of brain size. I also show that such cognitive and neural features are further affected by an individual’s age and foraging experience. Next, and with a focus on honey bees, I explore the association between body size and foraging task specialization. Previous evidence has shown a link between specialization on pollen or nectar foraging and multimodal sensory sensitivity further demonstrating that sensitivity affects the quality and/or quantity of resource exploited. I hypothesize that, as in solitary bees, larger body size is associated with higher sensory sensitivity. I test this hypothesis by comparing body size and the quality and quantity of the resource exploited by foragers of wild Africanized and European honey bees. I show that, as predicted, nectar foragers are smaller and have fewer olfactory sensilla, which might underlie their lower sensitivity to odors. I also show that larger bees collect more pollen (within pollen foragers) and more dilute nectar (within nectar foragers). To further test the hypothesis that size correlates with sensitivity, I compare strains of bees that have been selected for many generations to store large ("high strain") or small ("low strain") amounts of pollen surplus, respectively. As these strains differ in sensory sensitivity, I predict that the more sensitive high strain bees are larger and have more sensory sensilla. I show that high strain bees are indeed bigger than low strain bees. However, high strain bees do not have more sensory sensilla. Together, my results show that body size is strongly associated with an individual's sensory, neural and cognitive features, which seem to support and strongly affect the organization of bee societies. My results also suggest that body size plays a more important role in the organization of bee societies than generally assumed, and the results serve to indicate future research directions.