DISSERTATION RESEARCH: Genetic and Ecophysiological Causes of Differential Fitness in a Natural Plant Hybrid Zone

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Natural hybridization is an important process in the evolution of many plant species. Determining how selection acts against different hybrid genotypes is necessary for understanding the likelihood of different outcomes of hybridization. This study uses a model natural hybrid system between Ipomopsis aggregata and I. tenuituba to examine potential causes of fitness differences among hybrids, and thus what processes are important in limiting and promoting hybridization. Using field and greenhouse experiments, this study examines: (1) the distribution of nuclear and cytoplasmic genotypes in a natural hybrid population; (2) the influence of nuclear and cytonuclear interactions on fitness of hybrid genotypes, and if these interactions are environment-dependent; (3) ecophysiological variation among hybrid and parental genotypes that may affect relative performance across environmental conditions in a hybrid zone. This work uses an integrated approach that examines both genetic and ecological factors that may influence the outcome of natural hybridization. Understanding how these factors affect differential hybrid fitness is necessary for understanding the evolutionary consequences of hybridization, and ultimately gene flow between species. Such information about hybrid zone dynamics has broad implications for evaluating the potential impacts of hybridization between native and exotic or genetically modified species.