Individuality in the hive: Behavioral variation and its proximate causes in insect societies
A fundamental question in biology is "why does one individual have a particular phenotype while another individual of the same species has a different phenotype?" Research on behavioral phenotypes has demonstrated that consistent behavioral variation, termed personality, represents alternative solutions to the various challenges animals face throughout their lives. Although most animal personality research has been done with vertebrates, biologists have begun to accept that many lineages of invertebrates also exhibit personalities. Social insects in particular offer unique insights into how and why personalities exist in invertebrates and more broadly, in social animals. I conducted the first comprehensive study of personality differences across individuals in a eusocial insect. I defined and investigated three dimensions of personality within the worker caste of a model social insect, the honey bee Apis mellifera, as follows: 1) consistent individual behavioral differences over time, 2) consistent individual behavioral differences across contexts, and 3) the presence of correlated suites of behaviors. These findings suggest some individuals may be more likely to be highly interactive with other workers (e.g. engaging in food sharing), while other individuals are consistently less interactive. These results expand upon and contribute to previous models for the organization of worker division of labor in honey bees, suggesting that consistent behavioral differences (personalities) of workers within a behavioral caste have the potential to contribute to subcaste division of labor. I examined a potential proximate cause of this inter-individual behavioral variation in honey bee workers: differential nourishment. I tested the hypothesis that nutritionally stressed bees will be more likely to perform cooperative behavior than satiated worker, and found that diet restriction affected queen mandibular pheromone response (a cooperative behavior), but the direction of the effect was different depending on what life stage workers experience restriction. I suggest that these differences depend upon the extent of reproductive plasticity at these life stages, and that individual worker honey bees may adjust their behavioral and physiological traits in response to nutritional stress to invest nutritional resources in either their own or their colony's reproduction. To further probe the generality of the phenomenon that nutritional stress promotes cooperation observed in honey bees, I expanded this work to investigate the link between nourishment and social cohesion in an independently evolved lineage of social insects, primitively eusocial paper wasps Polistes fuscatus. I found that diet restriction reduced aggressive interactions between nestmates, which we interpret as an indicator of high social cohesion. The research presented in this dissertation contributes to a growing body of work on how the nutritional environment, early-life effects, and tradeoffs between personal and group level reproduction affect cooperative behavior in social animals. This research will inform future investigation of how behavioral variation evolves and why it persists.