DISSERTATION RESEARCH: What maintains species boundaries between interfertile, sympatric congeners? A test of prezygotic/postzygotic isolating mechanisms and cryptic hybridization

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A critical goal of speciation research is to understand how reproductive barriers evolve among diverging lineages. Reproductive isolating barriers are predicted to increase with increasing divergence time among species and to be reinforced via natural selection against the production of unfit hybrid offspring. Thus, species that co-occur in natural communities are expected to have strong reproductive isolating barriers that prevent hybridization. Despite these predictions, many closely related plant species with weak reproductive barriers co-occur in nature. Two such species are Collinsia linearis and C. rattanii, which overlap in much of their range, flower at the same time, share pollinators, and readily hybridize in hand-pollination experiments. Thus, the proposed research uses these species as a model to better understand how such co-occurring species maintain their separate identities in the face of potential gene flow among the species. This work compliments research currently being conducted in the Kalisz lab by testing two prominent hypotheses on the evolution of reproductive barriers and mating system evolution. In addition, this project will benefit the research community using Collinsia as a model system (seven labs in North America), by expanding understanding of the evolution of isolating barriers and providing a broad-scale analysis of cross-species fertility, ecology, and biogeography in Collinsia.