Collaborative Research Proposal: Tipping the Scales - A selection approach to the developmental regulation of morphological scaling

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)The scaling of body parts is the quintessential feature of animal body form. Within species, organs need to be correctly proportioned to the body for the organism to function; larger individuals require larger hearts, longer limbs, etc., whereas smaller individuals generally are composed of proportionally smaller parts. While relative organ size is more or less constant within a species, it can vary dramatically among species; in fact, changes in the relative size of body parts are typically the most pronounced physical difference between species. For example, giraffes derive their distinctive, gracile body form from exaggeration in the size of their necks and limbs relative to their bodies, whereas walrus gain their robust, compact appearance from reduction in the size of their limbs relative to their massive bodies. Despite nearly a century of work describing the body proportions of myriad species, little is known about how scaling is maintained to preserve body form within a species or is modified to alter body form between species. Recent approaches model mathematically the expression and evolution of scaling relationships from first principles. These models focus on the physiological processes that regulate and integrate the growth of individual body parts and identify the specific developmental mechanisms that underlie the control of relative body part size. Importantly, the models can be used to identify which aspects of these mechanisms are likely to change to create differences in body proportions among species This research project will test the validity and predictive power of these models using a three-step approach. First, artificial selection will be used to independently alter the scaling relationship between the wing and body in the fly, Drosophila melanogaster. Second, the physiological mechanisms affecting the scaling relationship between wing and body size will be explored using the flies created through artificial selection. Third, the specific genes responsible for changes in relative wing size will be identified.This research program is the first to test physiological and genetic-based mathematical models of the regulation and evolution of scaling relationships. It promises to answer long-standing questions of how scaling is maintained to preserve form within species or is modified as body form diversifies between species. In addition, the project will provide extensive, cross-campus training for undergraduate and graduate students at the University of Houston and Michigan State University.