UBC Theses and Dissertations

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UBC Theses and Dissertations

Ecological genomics of invasive thistle, diffuse knapweed Turner, Kathryn Grace


Invasive species are able to move into new environments, with new abiotic conditions and biotic interactions, survive, and even dominate, often within a hundred years. Much research in invasion biology has assessed whether populations of invasive plants show phenotypic or evolved genetic differences in growth and reproduction compared to their native range (such as the evolution of increased competitive ability hypothesis), in an effort to understand the causal drivers of invasion. Using diffuse knapweed (Centaurea diffusa) I assessed evolution in its invaded range in multiple ways. Chapter 2 describes two greenhouse common garden experiments that evaluated phenotypic and life history trait variation between the two ranges under benign and stressful conditions (drought, flooding, nutrient deficiency, and herbivory). Invasive individuals grew larger and flowered later in benign conditions, and performed as well or better under most of the tested stress conditions than native individuals. The strongest evidence for a trade-off in tolerance was exhibited under drought conditions, but only among native populations. Chapter 3 employs a field common garden to compare phenotypes, drought response, and adaptation to environmental conditions in a more natural setting. This study incorporates a large dataset of occurrence locations to look at the different relationships that populations in the two ranges have to their bioclimatic environments. I found that invasive C. diffusa individuals were larger, matured later, and have lost adaptation to environmental conditions apparent in native populations. More plastic invasive genotypes may have expanded the climatic niche inhabited in the invaded range. Chapter 4 attempts to identify a genetic mechanism underlying these phenotypic changes by comparing gene expression between the two ranges under benign and drought conditions. Genes were identified whose expression either varied constitutively or responded to drought stress differently between ranges. Based on these data, invasive populations may have constitutively higher levels of energy production, while native populations have a stronger cellular drought defense. This dissertation presents ample evidence of evolution in the invaded range and suggests that plasticity and rapid evolution had a significant impact on the successful invasion of North America by C. diffusa.

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Attribution 2.5 Canada