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The Causes and Consequences of Phenotypic Plasticity in Clarkia concinna (Onagraceae)

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Organisms can alter traits plastically in response to the biotic and abiotic environment in ways that potentially increase fitness, however not all plasticity is adaptive. Despite much study, the effects of plasticity on mating systems, species interactions, and responses to novel environments need further exploration. In this dissertation I study plasticity in an annual plant, Clarkia concinna (Onagraceae) by using a combination of greenhouse experiments and field observations and manipulations. In chapter one I investigate the plastic responses of multiple traits in a greenhouse droughting experiment, comparing the adaptive value of plasticity among plants from eight populations that varied widely in precipitation. Surprisingly, none of the measured traits show adaptive plasticity, and less plastic genotypes show a smaller reduction in fitness in the stressful drought treatment. Plants from locations with greater and more variable annual precipitation tend to show less plasticity in response to drought. In chapter two I focus on the causes of plasticity in floral traits and seed production. Hand-pollinating early flowers on a plant reduces total flower number as well as floral longevity in later flowers. This effect is independent of the abiotic resource conditions (water or nutrient availability). While pollen quality (self or outcross) does not affect floral traits, later fruits on plants with early outcrossed flowers have fewer seeds than fruits on plants with a background of selfing. In chapter three I examine the effects of floral display on pollination. Most pollinators were more likely to move pollen between flowers on the same plant when floral display size was large, increasing the deposition of self pollen. However, the predicted pollinator attraction benefit of large displays is absent in this species, even when there are few surrounding plants. Exploring plasticity in one species though the use of multiple techniques promotes a comprehensive understanding of the subject and leads me to propose potentially fruitful avenues of new research.

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