Three major elements, Carbon, Nitrogen, and Phosphorus, determine how organisms grow, and influence how systems, from groups to ecosystems, function. As a result, organisms have developed behavioral and physiological mechanisms to adjust to limits in element availability and grow successfully in the face of nutritional challenges. Like organisms, social groups that collect and store food must also adapt to changes in nutrient availability. This study focuses on how a complex social group, the leafcutter ant colony, uses behavioral strategies to integrate intake of these elements with colony growth. Because social insect colonies must allocate effort to both foraging and brood care, colony growth and success depend on balancing work allocation across activities. This study will employ biochemical and behavioral techniques to determine how relative balances of these three key elements affect colony growth, as well as foraging and brood-care decisions by the individual workers within colonies. It is expected that colonies will respond to limitations by altering growth patterns and shifting efforts between tasks to balance different tasks associated with colony maintenance, growth, and reproduction around nutrient availability. The findings will integrate our understanding of how fundamental biological properties such as growth scale across levels of organization, especially in complex social groups like the social insects. Social insects are paralleled only by humans in their social complexity and level of organization. Thus, they serve as a relevant model to address the question of how resources and social organization are integrated. This research has broader impact in student training and outreach. Multiple undergraduates will be involved in the project through hands-on research and will participate in an associated seminar: the majority of students move on to the Ph.D. or other postgraduate training. The research will be featured in public educational outreach including the Ask-A-Biologist website (askabiologist.asu.edu) and local K-12 demonstrations.
Three major elements, carbon, nitrogen, and phosphorus, determine how fast organisms grow, and influence how biological systems function. Animals have behavioral and physiological mechanisms to compensate for limits in the availability of these elements, which allow them to grow successfully in the face of nutritional challenges. Like organisms, social groups like ants, bees, and termites that collect, store, and even grow their own food must, as a group, adapt and respond to variation in nutrient availability. This project tested how a complex social group, the leafcutter ant colony, uses behavioral strategies to maximize nutrient intake for fast colony growth. These ants are of particular interest because they function as farmers: leafcutter ants do not directly consume the leaves that they harvest; the leaves are "fed" to a fungus garden that grows within the nest and which serves as food for the growing ants. Through a series of laboratory experiments, we mapped how colonies respond to nutrient limitation, through alterations in task performance and fungus growth. Specifically, we found that supplementing food fed to the fungus with carbon (provided as the plant sugar xylose), nitrogen (provided as soy protein) or phosphorus (provided as potassium phosphate) directly influenced ant foraging rates and the growth and survival of the fungus garden. Colonies supplemented with xylose collected more material for the fungus garden, and grew larger fungus gardens, while colonies given extra soy protein collected less material, and often experienced fungus garden collapse, which leads to starvation of the colony. Further, direct removal or addition of the fungus garden itself caused shifts in worker performance of tasks within the nest: when fungus gardens were reduced in size, overall colony activity levels increased and worker ants increased leaf-collecting rates in particular. In contrast, when fungus gardens were increased, overall activity levels remained similar but workers shifted efforts away from foraging and towards fungus care. These findings contribute to our understanding of how fundamental biological properties such as growth scale across levels of organization, especially in complex social groups like the social insects. Social insects are paralleled only by humans in their social complexity and level of organization. Thus, they serve as a relevant model to address the questions about how resources and social organization are integrated. This research also included student training and outreach: two undergraduates were involved in the project through hands-on research and were able to use the experience to develop their own independent research projects, which they presented at a national scientific meeting. The research has also been featured in public educational outreach including the Ask-A-Biologist website (askabiologist.asu.edu) and local K-12 demonstrations.
