Physical Aspects of Superorganism Physiology: Construction, Circulation, and Homeostasis in Fire Ant Colonies

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Major transitions in the history of life occurred when individual biological entities came together to form interdependent groups with emergent properties that differed from the individuals. The most recent of these transitions occurred when solitary organisms joined together to form cooperative societies. This transition to sociality has been particularly remarkable because many distinct individuals are able to behave as a single organism through the coordinated actions of society members. The best examples of such "superorganisms" are colonies of social insects. Social insect super-organisms breathe, feed, grow, breed and modify their environments. Although each life system is important on its own, the balance at the colony level arises from coordinated action of all systems. The purpose of this research program is to discover physical principles that play important roles in super-organism physiology. Super-organism regulatory principles will be of use in systems where information and physical networks coexist, such as in pedestrian and vehicle traffic, urban and disaster landscapes, and neural and artificial networks. The proposed studies could also help explain why the biological transition to sociality has been so successful.The proposed studies will probe physical aspects of super-organism physiology from a "top-down" approach to discover emergent behavioral, biomechanical, and social features. This will be complemented by a "bottom-up" approach that will discover how aspects of super-organism physiology (exoskeleton, organization of circulatory system, healing mechanisms) depend on soil properties, ant morphology, grain manipulation biomechanics, and genetics. This research will be conducted using the red imported fire ant, Solenopsis invicta, as a model super-organism system. Fire ants possess highly developed social systems and work together to complete complex tasks. The goal of this research is to elucidate principles governing the functioning of the super-organism and the processes responsible for super-organism stability and success. Specifically, this program will study super-organism features that are analogous to those in single organisms including: (1) Super-organism exoskeleton construction: this research will investigate processes by which the super-organism constructs a robust exoskeleton, its nest, from cohesive granular media. Such processes will include biomechanics of excavation in different media, social interactions upon nest formation (like communication, recruitment, workload distribution) and intelligent construction methods (e.g. can ants probe grain level stresses). (2) Super-organism circulation: This research will deduce traffic optimization strategies in confined spaces. Such strategies may include separation of work tasks in space and time, localization of movement in nest space, organization of information hubs, and modification of the carrier's behavior in response to heavy traffic. (3) Super-organism nervous system: This research will discover how information is transmitted through a patterned environment through tactile interactions of individuals. The approaches used will lead to an understanding of how the superorganism nervous and circulatory systems co-exist. (4) Super-organism homeostasis of physical properties of the nest: This research will determine the response of the super-organism to perturbations arising from flooding, mechanical insults to nest networks, invasion of competitive species, and genetic variation derived from hybridization of fire ant species. The research team will leverage the representation of female group members to attract female students to study of the interface between biology and physics, which should attract students who might be discouraged by the barriers in more established fields. The research team will also explore strategies of public involvement through hands-on and DIY initiatives, collaboration with public education clubs and integration of science with the entertainment industry.