Linking mechanisms of low temperature tolerance to species distribution

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The long term goal of my research program is to link physiological mechanisms of environmental stress tolerance to species range and population growth in invertebrates. My current focus is on the role of low temperature physiology in setting poleward range limits. Understanding physiological and genetic constraints on low temperature tolerance is essential for predicting the potential of range expansions under climate change. I propose to use the low temperature tolerance of eastern spruce budworm Choristoneura fumiferana as a model system for investigating these links. This species is native forest pest with regular landscape-scale outbreaks in the North American boreal forest east of the Rockies. Previous efforts have identified that overwintering temperature is a key determinant of C. fumiferana population size, and its range is currently expanding northward due to climate warming. I will use this system in three research themes that link from cellular physiology to species distribution to better understand the role of cold tolerance in insect population outbreaks and range. In the first theme, we will test the hypothesis that mortality following repeated cold exposures is due to accumulation of denatured proteins in aggresomes over multiple cooling and warming cycles. We will use immunohistochemistry on larval slices to quantify subcellular localization of heat shock and ubiquitin-tagged proteins following repeated exposure. In the second theme, my research program will use a set of newly-established C. fumiferana cultures initiated by the Canadian Forest Service (CFS) from nine populations that range from Inuvik to northern New Brunswick to quantify the extent and mechanistic basis of variation in low temperature tolerance. In addition, we will leverage the life history of C. fumiferana to examine potential maternal effects on cold tolerance and estimate local adaptation of cold tolerance across populations. Finally, in the third theme we will use the data we have collected on mechanisms of variation in low temperature tolerance and cellular effects of low temperature exposure to produce physiologically-based models of C. fumiferana outbreaks. With the data we have gathered on phenotypic plasticity and energetic costs of cold tolerance, as well as aerial survey data, we will be able to test hybrid models that allow for evolution of cold tolerance under changing climate. These three themes will help link overwintering physiology to species distribution in a species that is both economically and ecologically important in Canada. This will provide novel insights into the role of biochemical adaptation to low temperature, heat shock proteins in low temperature survival, and evolutionary potential for adaptation to novel climates in a rapidly changing world, while providing training in cutting-edge techniques to several highly qualified personnel.