UBC Theses and Dissertations
Pollination, genetic structure, and adaptation to climate across the geographic range of Clarkia pulchella Bontager, Megan
Every species experiences limits to its geographic distribution on the landscape. Sometimes the barriers that limit geographic ranges are obvious. For example, oceans and topographic features may prevent a species from colonizing the areas beyond them. However, species' distributions frequently end at places on the landscape where no obvious barrier or abrupt shift in the environment occurs, and this raises the question of what limits the range at these edges, both proximately and in evolutionary time. This thesis investigates the contributions of pollination, climate, and gene flow to limiting range edge populations of an annual wildflower, Clarkia pulchella. Pollinators may be important at range edges because many of the proposed characteristics of edge populations (small, isolated, or low density) are also features that might make pollination less reliable and in some cases favour the evolution of self-pollination. I found that climate influences floral morphology and that the capacity of plants to set seed in the absence of pollinators was slightly higher in northern range edge populations. All populations benefit from the service of pollinators. Another factor that may limit populations at geographic range edges is the influence of asymmetric gene flow from central populations, which could prevent local adaptation in range edge populations. Alternatively, edge populations might have low genetic variance and therefore might benefit from gene flow. I tested these competing predictions by simulating gene flow between populations from across the species' range in the greenhouse and planting the progeny into common gardens at the northern range edge. This experiment took place during an extremely warm year. As a result, gene flow from warmer provenances improved performance. I also found a small benefit of gene flow independent of climate. Finally, I found no evidence that environmental differences contribute to genetic differentiation of populations, though geographic distance is a strong predictor of genetic differentiation. Contrary to expectations, genetic variation was higher near the northern range edge. Together, these chapters shed light on important drivers of reproductive success and local adaptation in this species and allow for insights into what processes are likely (or unlikely) to generate range limits.
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