Size is among the most important factors in determining the biology of an individual animal. Characteristics that correlate with body size include lifespan, metabolism, and growth. Despite the significance of these factors for fields ranging from field ecology to human medicine, scientists have not yet been able to explain the mechanistic link that generates these patterns throughout nature. Recent studies have demonstrated that size not only affects individual animals, but also entire societies such as social insect colonies. The central focus of this study is to test the hypothesis that behavioral organization influences the distribution of work within colonies and results in the allometric scaling of metabolic rate with colony size. Two sets of experiments will make it possible to test this hypothesis, first by measuring colonies as they naturally grow and second by artificially manipulating colony size. In both sets of experiments, metabolic rates, patterns of network connectivity, and and growth rates will be measured to develop an integrative perspective on how size affects whole colony energetics. This research will be conducted with the help of undergraduate students from minority backgrounds all of whom will have the opportunity to develop their own independent projects to develop and present at national conferences. A collaboration with the Estrella Mountain Regional Park in Maricopa County, AZ designed to educate and engage the general public with an interest in insect biodiversity will also be supported by this proposal.

Project Report

The focus of this proposal was to identify the nature of the relationship between behavior and metabolism in social insect colonies. The central hypothesis we tested was that behavioral organization influences the distribution of work within colonies and the allometric scaling of metabolic rate with colony mass. This proposal takes advantage of a study system in which there is great potential to integrate the fields of behavior, physiology, and biomechanics with the goal of addressing one of the broadest and most striking patterns in biology – the ¾ power scaling of metabolic rate. This pattern has consequences throughout biology, including life history theory, broad trends in ecological species range distributions and macro-evolutionary trends in body size. A combination of methods from comparative physiology and animal behavior were developed to investigate scaling relationships in laboratory-reared colonies of the seed-harvester ant, Pogonomyrmex californicus. To determine metabolic rates, flow-through respirometry made it possible to directly measure the carbon dioxide production and oxygen consumption of whole colonies. By recording video of colony behavior, for which ants were individually paint-marked for identification, it was possible to reconstruct the communication networks through which information is transmitted throughout the colony. Whole colonies of seed harvester ants were found to exhibit a robust allometry in which mass-specific metabolic rates decreased with increasing colony size. The distribution of walking speeds also changed with colony size so that larger colonies were composed of relatively more inactive ants than smaller colonies. When colonies were broken into random collections of workers, metabolic rates scaled proportionally, but when entire colonies were reduced in size, they continued to exhibit a metabolic allometry. The scaling of the communication network with colony size is a plausible mechanism for the regulation of whole-colony metabolic scaling. The continued development of a network theory approach to integrating behavior and metabolism will reveal insights into the evolution of collective animal behavior, ecological dynamics, and social cohesion. We have been hosting regular insect adventure nights at the Estrella Mountain Regional Park and Cave Creek Regional Park (Maricopa County Parks & Recreation Department) designed to spark interest in biodiversity and insect biology. These events draw crowds of families and children and feature a range of activities including insect collection using ultraviolet lights to nature walks and hands-on interaction with social insect colonies. With the support of this proposal, we have developed the infrastructure to make this a truly fascinating and enriching regional educational program. We have established strong working relationships with a number of rangers associated with the Maricopa County Parks & Recreations Department. Working together, we have started a museum-quality collection of local insect biodiversity. The insects have been collected by children attending our events, pinned and curated by undergraduate and graduate entomology students at Arizona State University, and then featured at the Nature Center during subsequent events so that the students and children who collected the insects can see their mounted specimens on display, simultaneously taking pride in their work and growing an appreciation for nature, science, and biodiversity.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
Standard Grant (Standard)
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Michelle M. Elekonich
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Arizona State University
United States
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