DISSERTATION RESEARCH: Does resource limitation promote cooperation? Nutrition restriction and social cohesion in insect societies

Iowa State University, Ames IA

Investigators

Abstract

Why cooperation evolves and how it persists in groups of organisms is a question that biologists are still working to answer. This research will investigate if limited nutrition has led to and continues to promote increased cooperation in one of nature's greatest cooperators: the social insects. The project will integrate behavioral, genetic, and physiological research to investigate how nutrition limitation affects cooperation in two species - one with simple societies (paper wasps) and one with complex societies (honey bees). In experimental colonies of both these organisms, the diets of developing workers will be altered such that some individuals will experience nutritional stress and others will receive normal healthy diets. When these workers reach adulthood, the researchers will examine how cooperatively they behave (more or less aggression toward other workers, tending the queen, raising their sisters), testing the hypothesis that decreased nutritional resources promote increased cooperation. By comparing simple and complex social insect societies, this research will examine whether resource limitation could be a general theme in the evolution of cooperation. By analyzing ovary size, fattiness, and the activity of reproduction and nutrition related genes in starved and un-starved individuals, this research will also examine how nutrition can influence differences in behavior through physiology and gene expression. Research will be paired with insect and evolution education outreach via public talks and freely available and entertaining internet content, as well as direct participation in research activities by undergraduates and research assistants of diverse backgrounds. An essential form of cooperation in a social insect colony is between the queen (the sole reproductive in the colony) and her workers (the queen's daughters). Worker honey bees vary in their responsiveness to the queen a behavior that is essential to colony social cohesion. Nutritionally stressed workers exhibit a high sensitivity to the queen, and workers with high nutrition diets exhibit a low sensitivity. The researchers will investigate if mechanisms underlying the link between nutrition and cooperation are evolutionarily conserved by studying elements of nutritional and reproductive physiology and associated molecular pathways in two eusocial insects, honey bees and paper wasps. They will expand this prior work on honey bees to address whether nutritional stress-induced increases in queen responsiveness are underlain by changes in the regulation of conserved genes related to reproduction and nutrient signaling. Second, the researchers will utilize the primitively social paper wasp Polistes metricus to begin to address the generality and evolutionary conservation of this pattern. Polistes workers will be nutritionally restricted and behavioral observations will be recorded to test whether this leads to higher social cohesion of workers on the nest. The researchers will also measure how these changes affect ovary development and changes in the expression of genes associated with reproduction and nutrient signaling. If nutritionally restricted Polistes workers exhibit higher cooperative behavior, then the connection between nutritional stress and cooperation may represent a conserved mechanism regulating social cohesion in insect societies. Cooperation may be strategic when nutrition is scarce, and the link between nutritional stress and cooperation may be a common theme in social evolution.