Like individual organisms, complex social groups are able to maintain predictable trajectories of growth, from initial colony foundation to mature reproductively capable units. They do so while simultaneously responding flexibly to variation in nutrient availability and intake. This research applies stoichiometric theory to understand how a complex eusocial system, colonies of the leafcutter ant, Acromyrmex versicolor, integrates nutritional intake with colony growth. Stoichiometry, the study of element balances, provides a simple but comprehensive index of nutritional supply and demand, and a universal, measureable currency for determining how colonies balance allocation to nutritional intake and brood production for colony growth. By focusing on the basic elements present in almost all nutrients, Carbon, Nitrogen and Phosphorus (C,N,P), stoichiometry allows comparisons across diverse systems, ranging from cells through ecosystems. Application of this framework to the study of colony growth expands the utility of this approach from analyses of individual organisms to social groups a new and valuable test-bed. The applicability of stoichiometry across diverse systems and biological levels allows us to place questions about the regulation of growth in social groups - questions central to sociobiology - into a broader ecological context. Leafcutter ant colonies provide a valuable context in which to explore the integration of nutritional intake and colony growth (measured as worker production), because they function as tri-trophic systems, in which ants harvest vegetation to grow a fungus that, in turn, serves as food for the colony. Fungal growth rates and colony worker production are interdependent, regulated by nutritional and behavioral feedbacks. Fungal growth and quality is directly affected by worker foraging decisions, while worker production is, in turn, dependent on the amount and condition of the fungus. Because colonies must allocate effort to both foraging and brood care, colony growth is dependent on the balance in allocation to these two activities. To understand how leafcutter colonies regulate growth relative to nutritional input, this work first maps the relationship between worker production and fungal growth during the early, critical stages of colony development. It then tests how changes in the relative balances of the key elements, C,N and P, affect growth and production of fungus and ants. Finally, it asks how colonies make foraging and brood-care decisions in response to shifts in fungus quantity and leaf quality. Collectively, these experiments test how growth and nutritional feedback systems are integrated across trophic levels in this complex social system. The findings will expand our understanding of how fundamental biological properties such as growth scale across levels of organization, to include social groups.
|Effective start/end date||7/1/10 → 6/30/12|
- NSF: Directorate for Biological Sciences (BIO): $13,334.00