Evolution and Population Genomics of Invasive Reynoutria japonica in North America

摘要

Evolution in invasive plants is of interest to land managers for its implications on protecting ecosystems and to evolutionary biologists for the light it can shed on rapid evolution. In this dissertation, I examined the adaptation and population genomics of invasive Reynoutria japonica in its invaded range in North America. This invasive plant is of particular interest in evolutionary terms because of its use of both sexual and asexual reproduction, its hybridization with related plants, and its polyploidy. The examination of adaptive change in the invaded range has revealed insights into the mechanisms invasive plants use to occupy new habitats. My work revealed that R. japonica is able to tolerate a wide range of environmental conditions, despite low genetic diversity. In response to just seven years of herbicide application, some populations evolved increased tolerance to glyphosate herbicide. In contrast, the century since R. japonica occupied North America has been insufficient to permit local adaptation in the populations, rather populations have maintained fitness through plasticity. Thus it is evident that R. japonica is able to adaptively evolve in response to selection, but the normal environmental conditions may not pose sufficient selective pressure to result in local adaptation. My work presents strong evidence that high phenotypic plasticity has aided its invasion. In addition, the research results provide an example of how hybridization can interact with polyploidy to increase invasiveness. Finally, I show that previous estimates of the nuclear genetic diversity in North America have been underestimated. In addition, I demonstrate the complex genetic structure that allows R. japonica to thrive despite relatively low genetic diversity.