PRF/J: The Evolution of Metabolic Rate in Response to Temperature

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Interspecific comparisons of temperature effects on metabolic rates of ectotherms have long been used as premier examples of physiological adaptation to environment - - typically populations from relatively cold habitats have evolved increased metabolic capacities (compensation) at low body temperatures. Interspecific comparisons provide a perspective on long term evolutionary patterns, but little insight into contemporary dynamics of physiological evolution. The dynamics of metabolic evolution in contemporary populations will be explored using a series of complementary studies of the thermal dependence of metabolic rate in Drosophila melanogaster. First, replicate stocks of the species will be compared. Second, these results will be compared to the same type of data from specimens collected along a 3000 kilometer transect. If compensatory evolution has occurred, flies evolving at low temperatures (or high latitudes) are expected to exhibit elevated metabolic rates relative to flies from high temperature situations. Correlated responses of thermal dependence of metabolic rate to selection for temperature extremes will also be examined. If there are genetic correlations between components of the metabolic response to temperature, selection for tolerance of temperature extremes should influence metabolic rate at other temperatures. %%% Metabolic rate in ectotherms has a profound significance for locomotor performance, competitive ability, and is strongly correlated with an array of life history variables. Recent work in comparative and evolutionary physiology repeatedly stresses the importance of understanding the evolution of thermal sensitivity, but few studies have examined this feature in small ectotherms. One important goal of studying comparative physiology is to ascertain why tradeoffs between life history parameters (for example, the tradeoff between growth rate and asymptotic size) exist. Ultimately such research has implications for understanding the biological limits of human life history traits such as longevity and reproductive life span.