Emergent Homeostasis and Mound Morphogenesis in Colonies of Macrotermes Michaelseni (Isoptera: Macrotermitinae)

Suny College Of Environmental Science And Forestry, Syracuse NY

Investigators

Abstract

Emergent homeostasis and mound morphogenesis in colonies of the termite Macrotermes michaelseni J Scott Turner State University of New York at Syracuse This research will study how colonies of the mound-building termites of southern Africa (Macrotermes michaelseni) provide regulated environments for their nests. These termites, popularly called "white ants" or rysmeere (Afrikaans), build large mounds that are prominent features of the savannas of sub-Saharan Africa. These mounds are devices for capturing wind to power ventilation of the termites' underground nests, which can house as many as two million individuals. In addition, the termites cultivate fungi to aid in cellulose digestion. The termites and fungi form a symbiosis whose collective respiration is similar to a goat's. The viability of this symbiosis depends crucially on the maintenance of a humid, CO2-rich atmosphere in the nest. The atmosphere in the Macrotermes nest is under homeostatic control, the result of a balance between the colony's respiration and the wind-powered ventilation of the mound. If the nest atmosphere is regulated, this implies that the mound itself is a regulated structure, its wind capture for ventilation adjusted to meet the colony's respiratory demands. How do the termites in a colony collectively "know" how to build a mound of just the right structure? How do they collectively "detect" whether their mound's structure is not correct? These questions are the basis of this research. Nest homeostasis follows from coupling the maintenance of the mound structure (mound morphogenesis) to the colony's physiology (emergent homeostasis). Importantly, soil transport by termites within the nest is linked to the distribution of respiratory gases in the mound. Termites translocate soil along gradients of CO2 concentration, effecting a net movement of soil from the nest (high CO2) to mound surface (low CO2). Soil redistribution thus alters the mound's ventilation, thereby altering CO2 concentration within it. Homeostasis involves "tuning" the sensitivity of soil transport to CO2 concentration in the mound. When a mound is damaged, the nest atmosphere is disrupted, and the termites respond with repair of the mound, in which a new network of tunnels is built, restoring the nest atmosphere to its prior state. In this project, the mound will be damaged by drilling a shaft, and inserting a large PVC pipe. Repair will be confined to the pipe, a controlled environment, thereby affording a way to study all aspects of the regulatory system for nest ventilation, and the developing architecture of the new tunnel network. Gas exchange in the tunnels will be assessed via tracer gases. Soil movements will be quantified by marking the soil with colored plastic beads. This research has broad significance both for the biology of social insects and for fundamental questions in ecology, evolution and physiology. Social insect colonies comprise a diverse array of semi-autonomous individuals, from which a degree of homeostasis of the nest environment emerges. This emergent homeostasis is well-documented: how it actually works is less well-understood. This research, by quantifying all aspects of the regulatory process, will be a significant advance in our understanding of emergent homeostasis among social insects. Practically, these termites are dominant factors in the functioning of tropical savanna ecosystems, controlling as much as half the total carbon flow. Understanding how their metabolism works and is controlled therefore has ramifications for our understanding the functioning of tropical savanna ecosystems. Finally, homeostasis in social insect colonies provides a provocative glimpse into the forces that must have driven the emergence of homeostasis in other "proto-organismal" systems that were the ancestors of multicellular organisms. This award is co-funded by EEP and the NSF Office of International Science and Engineering.