Dissertation Research: Barriers to Genetic Exchange Between Two Species of Mimulus

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This research will determine the mechanisms and processes underlying the evolution, maintenance, and enhancement of reproductive isolation. Mimulus guttatus and M. nasutus (Scrophulariaceae) two naturally hybridizing species of wildflowers, are used as a model system for studying reproductive isolation. Studies of this nature are important in determining the causes and consequences for gene flow between closely related taxa, and are therefore ultimately important in understanding early processes of speciation. To date, major reproductive isolating mechanisms have been identified in these two species: differences in flowering phenology, a predominantly selfing mating system of M. nasutus, and preliminary evidence of hybrid breakdown in the form of pollen inviability. This study will determine the fitness of hybrids relative to both parent species in a common garden setting. One experiment will place hybrid and parental organisms in a naturally occurring hybrid zone, and measure fitness, phenological overlap, and selfing rates for hybrid individuals relative to the parentals. This experiment will allow examination of the nature of reproductive isolation, and prediction of the consequences to gene flow this breakdown causes.