Collaborative Research: Linking thermal tolerance to invasion dynamics: Environment and physiological capacity as regulators of geographical spread

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Invasive species are an increasing threat to native ecosystems, agriculture, and forestry. This research addresses fundamental questions about how the environment, habitat, local life history, and local physiological traits interact to determine the geographic range of gypsy moths. Introduced from Europe to Massachusetts in 1869, gypsy moth now occurs over nearly a million square kilometers of eastern North America, extending from Minnesota to North Carolina. It is a highly damaging pest of hardwood forests, causing extensive economic and ecological damage to public and private property, as well as negatively impacting the forest products industry. In some parts of its range, gypsy moth is spreading rapidly across the landscape, while in other areas, the invasion front is static or retracting. So far, only one-third of susceptible forest types in the United States have been invaded, leaving large portions of the country still at risk. This project addresses how the invasive potential of a species can change along its leading edge and how a changing environment can determine whether ranges expand or contract. This research also includes training and outreach components that will reach a wide range of student learners, educators, and community stakeholders. The objective of this project is to use patterns of expansion, stasis, and contraction at gypsy moth range limits to examine how local changes in gypsy moth traits influence the potential for future spread. Specifically, the project tests for range-wide variation in tolerance to high and low temperature extremes, local adaptive changes in those physiological limits, and how these traits interact with temperature to influence invasive spread under predicted changes in regional environments. To determine how temperature extremes impact the survival and growth of populations from across the invasion front, experiments will be performed to quantify temperature-dependent growth rates, critical thermal limits, and temperature-specific metabolic rates. Additionally, the effects of current and future environmental conditions will be tested using growth chambers programed with region-specific current and future temperature regimes. The effects of current overwintering conditions at the range extremes on hatching success will be tested by deploying egg masses from a range of populations at both the northern and southern range edge. Publically available climate data, as well as the exhaustive sampling effort by state and federal agencies that annually measures the abundance of gypsy moth along the entire 2000 km range edge, will be used to examine future spread potential. These experimental approaches, combined with information on the current distribution and spread rate will lead to a greater understanding of traits underlying the success of invasive species and help to identify areas that may become more or less susceptible to invasions in the future.