Invasive species often encounter climatic conditions that differ significantly from those of their native range. These environmental shifts may trigger phenotypic responses, resulting through some combination of adaptation and plasticity, that enable the invader to persist under novel thermal regimes. In this dissertation, I examine phenotypic changes in a tropical lizard that has successful invaded a cooler temperate climate, specifically examining traits that may promote survival and reproduction in their new range. First, I examined physiological traits, as I predicted greater cold tolerance would be necessary to survival in the invasive range. I found that invasive populations tolerated lower temperatures, exhibited greater maximum sprint speeds, and had higher metabolic rates than native populations. Next, I examined how life-history traits may change in the invasive range in order to facilitate reproduction under shorter breeding and growing seasons. I found that compared to native females, invasive females had shorter interlaying intervals and produced eggs that hatched more quickly. Once I quantified changes physiological and life-history traits that may have aided in successful establishment, I executed a common garden study to determine whether changes were the result of adaptation or plasticity. I found that differences in critical thermal minimum, metabolic rate, interlaying interval, and incubation period were maintained in lab-reared offspring, while measures of sprint speed converged. My results provide evidence that life history and physiology can evolve rapidly during invasion. These findings are useful to understanding contemporary evolution, and also provide valuable insight on how species respond to environmental shifts, both during invasions and as a result of climate change.

When species invade a new area, they often face different climates that make can make survival and reproduction challenging. In response, species may alter traits in order to adjust to new temperatures and conditions. In this dissertation, I examine trait changes in a tropical lizard that has successfully invaded a cooler temperate climate, specifically examining traits that may help them to survive and reproduce in their new range. First, I examined physiological traits, as I predicted greater cold tolerance would be necessary to survival in the invasive range. I found that invasive populations tolerated lower temperatures, could sprint faster, and had higher metabolism than native populations. Next, I examined how reproductive traits may change in the invasive range in order to facilitate reproduction under shorter breeding and growing seasons. I found that compared to native females, invasive females had less time between egg lays and produced eggs that hatched more quickly. Once I assessed how traits may have changed in the new range, I determined whether changes resulted from evolution or not. I found that differences in low temperature tolerance, metabolic rate, the time between egg lays, and incubation period were the result of evolution, while sprint speed did not seem to be the result of evolution. My results provide evidence that traits can evolve rapidly during invasion, allowing invasive species to persist and spread in new areas.

Doctor of Philosophy