Dissertation Research: Scaling of Work in Insect Societies

Dissertation Research: Scaling of Work in Insect Societies Dissertation Research: Scaling of Work in Insect Societies Body size has profound consequences for the structure, function, and ecology of organisms, as manifested by the presence of scaling patterns or rules within and across species. Likewise, properties of social groups may be influenced by changes in group size, a phenomenon known as social scaling. Insect societies are excellent models for social scaling. They exhibit tremendous variation in colony size, both during development and across taxa. Moreover, highly eusocial insect colonies, including those of most ants, are tightly integrated units that can be viewed as superorganisms. The central hypothesis of this research is that the functional integration of ant colonies gives rise to intraspecific scaling relationships that shape the organization and output of work, and that are analogous to scaling effects found in other integrated biological entities, such as organisms. One objective is to determine whether increased colony size leads to (1) increased division of labor, (2) decreased total work effort, and/or (3) workloads that are more or less evenly distributed among colony members. These hypotheses are based on theoretical principles, organismal scaling patterns, and previous results; however, empirical tests are rare or nonexistent. A controlled, manipulative experiment is proposed to directly test how colony size affects the organization of work in the California harvester ant, Pogonomyrmex californicus, a common species in southwestern North America whose colonies grow from one or more queens to 1000-2000 workers. Another objective is to examine the scaling of brood production, the major form of work output in a social insect colony. Per capita brood productivity (number or mass of brood per worker) is commonly thought to decline in larger colonies. Independent studies have yielded mixed results, but data have not been quantitatively reviewed. A formal meta-analysis is proposed to determine whether there is a general intraspecific relationship between colony size and per capita brood productivity in ants, using published data from whole-colony collections. Intellectual Merit The proposed research activities will provide valuable insight into the functional scaling of eusocial insect colonies and other social groups. Empirical tests of how the organization and output of work scale with colony size are essential to evaluating theoretical scaling relationships and ultimately to understanding how insect societies develop and evolve. Hypothesized scaling effects involve division of labor, a fundamental attribute of sociality that is considered to be of paramount importance to the success of social insects, and brood production, a key parameter in models of social insect life history and evolution. Moreover, analyses of scaling in insect colonies may reveal general principles of design and function across levels of biological organization, from cells to societies. Broader Impacts PI Fewell and Co-PI Holbrook are strongly committed to undergraduate research training and public outreach; both will be important components of this work. The Fewell laboratory has directly mentored over 30 undergraduates, primarily female and underrepresented minority students. At least two undergraduates will assist in the proposed data collection. One minority student is conducting a related independent research project. The lab regularly hosts school groups and provides demonstration ant colonies for community events. Holbrook has mentored underserved junior high students through Graduate Partners in Science Education (http://gpse.asu.edu) and is a frequent contributor to the popular preK-12 educational resource Ask A Biologist (http://askabiologist.asu.edu). He will continue to integrate his research into these and other outreach activities, including a College for Kids summer course he is helping to coordinate.