The Physiological Basis of Allometry

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The shapes and sizes of their body parts are the most important features by which different species of animals are recognized and defined. The shapes and relative sizes of body parts, however, change continually during development. As a result, individuals with different final adult body sizes typically differ in the proportions of sizes of their body parts. This phenomenon is called allometry. Although allometry has been extensively described and studied for more than a century, those studies have been largely descriptive and have made simple and unrealistic assumptions about how different body parts grow. This is in part because the physiological processes responsible for producing allometries are still poorly understood and because the theoretical tools used to analyze and interpret allometries cannot deduce growth processes correctly. As a result, the mechanisms that control size, shape and the relative sizes of body parts remain among the great unsolved puzzles in Biology. The proposed work will develop new practical and theoretical tools for the analysis of how, and why, the relative sizes of body parts vary. Understanding how organs grow to their correct size and shape has profound implications for understanding the causes and mechanisms of normal development and of developmental abnormalities. User-friendly software will be developed and freely distributed that will allow students and researchers to implement the equations developed in this research and analyze allometries in novel and more productive ways. This project will provide interdisciplinary training in biological mathematics and physiology for a graduate student and a diverse group of undergraduates. Outreach to local schools and regional science museums, with talks and hands-on exercises on insect biology, laboratory visits by junior-high school students from underserved schools, and continuing participation and mentorship with the North Carolina Museum of Life and Science on the biology of insects are integral parts of the Principal Investigator's commitment to disseminating science and making the resources provided by NSF more broadly available to the local community.The proposed research has three principal aims: (1) to develop an improved theory and new equations for static allometry, (2) to test and validate the theory against rich and diverse data sets from insects and mammals, and (3) to investigate the physiological factors that give rise to allometric relationships. The experimental work will focus on wing-body allometry in Lepidoptera, where the control of growth and size is best understood. Growth and size are controlled by developmental hormones and by the timing and duration of hormone secretion. This work will use several genetic strains of Manduca sexta that differ in body size and that can be reared under different environmental conditions of temperature and nutrition, which also affect size and allometry. This will produce a rich data set that will permit a functional interpretation of the effects of genes and environment on growth patterns and on the resulting allometries. The results of this work will allow researchers to analyze the causes of complex non-linear allometries, and deduce the underlying growth patterns that give rise to those allometries. This work will also provide new insights into the physiological mechanisms by which variation in genetic background and environment alters size, shape and allometry.