Age-related Variation in Metabolism and Temperature Sensitivity in Muscle: Mechanisms and Evolutionary Implications

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9317969 Marden Physiological processes in animal tissues are strongly affected by temperature, with resultant effects on whole- organism performance and fitness. The precise manner in which tissue and organismal performance are affected by temperature is called "thermal sensitivity". Studies of lower vertebrates have led to an understanding of some of the molecular and cellular mechanisms that determine thermal sensitivity, and to an appreciation of how variation in thermal sensitivity among species affects their geographic distribution and ecology. However, current evolutionary models lack consensus regarding fitness of variation in thermal sensitivity, with competing models concentrating on how thermal sensitivity affects niche breadth, aerobic performance capacity, high-temperature tolerance during peak activity, and compromises between high- and low- temperature performance capacity. Ability to distinguish among these competing hypotheses is hampered by the scarcity of species in which there is both i) variation in thermal sensitivity among individuals, and ii) ability to observe and measure fitness variation among animals possessing different thermal sensitivities. This project takes advantage of the presence of large-scale variation in thermal sensitivity among different-aged individuals in a dragonfly, and the ability to manipulate and observe these abundant and highly active animals in a field setting. Results of these experiments will allow critical tests of the competing models for the evolution of thermal sensitivity. This project will also make a detailed examination of the cellular and molecular mechanisms that affect variation in thermal sensitivity of muscle performance. Preliminary data indicate that a switch from anaerobic to aerobic metabolism accompanies the age-related change in thermal sensitivity, and that variation in expression of a calcium regulatory protein, troponin-t, may be particularly important in determining how mu scle functions in changing thermal and pH conditions. An opportunity to enhance our understanding of the basic physiology of troponin-t is particularly significant, since presence of this molecule in the blood stream has recently become the most sensitive clinical indicator of severe myocardial infraction in humans(i.e. heart attack). In summary, this project will examine physiology and ecology of a model organism in order to provide new data and perspectives that will influence our understanding of both basic evolutionary processes and muscle physiology. ***