Invasive species often encounter novel climatic conditions when they spread outside of their native ranges. Invading populations can respond to novel conditions by acclimation or adaptation of physiological capacities, which may facilitate their spread. We investigated differences in physiological traits among three populations of an invasive lizard, the brown anole (Anolis sagrei), along the latitudinal extent of its invasion in the southeastern United States. We predicted latitudinal clines

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... r most traits based on models of adaptation to climate. Consistent with the latitudinal cline in temperature and moisture, the mean critical thermal minimum and the mean rate of water loss were lowest for lizards in the northern population. Furthermore, these traits acclimated to either temperature or humidity in a direction consistent with adaptive phenotypic plasticity. By contrast, metabolic rates varied among populations but did not conform to our prediction based on a latitudinal cline in temperature. Critical thermal maxima, endurances, and sprint speeds were similar among populations. Despite the idea that tropical lizards have limited capacity for acclimation, we found variation among invasive populations of brown anoles, which could have partially resulted from acclimation. This physiological variation within the invasive range raises questions about the roles of plasticity and adaptation in the success of the invasion.