DISSERTATION RESEARCH: How is the Selfing Syndrome Assembled? A Common Garden Fitness Study of its Component Parts

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This project will test five evolutionary explanations for why plants self-pollinate, which will deepen our understanding of an important characteristic of plant evolution and will improve our breeding of self-pollinating crops such as tomatoes, corn and soybeans. Plants reproduce in a variety of ways, and 10-15% of plant species are primarily self-pollinating. The evolutionary transition from outcrossing to selfing is often accompanied by reductions in many floral traits. The researchers will determine the genetic bases for these changes in the morning glory. The study species are closely related to the sweet potato, a key global food resource that has proven challenging for modern selective breeding. Genetic resources developed in this study may help in the creation of more vigorous and disease-resistant sweet potatoes.The transition to selfing is often accompanied by reductions in flower size, nectar production, pollen-ovule ratio, pigmentation, and the distance between the anther and stigma, collectively called the selfing syndrome. Five models of selfing syndrome evolution (resource allocation, marginal environment and florivory, efficiency of autogamous selfing, and general size reduction in response to inbreeding depression) will be tested by a combination of field and greenhouse experiments. Researchers will develop hybrid backcrossed lines between the morning glory species Ipomoea lacunosa, a selfing species, and its sister species, I. cordatotriloba, which both outcrosses and self-pollinates. The project will determine (1) whether traits in I. lacunosa characteristic of the selfing syndrome evolved in response to direct selection or were correlated responses to selection on other traits and, (2) what selective pressures encourage the adoption of the selfing syndrome. The investigators will measure selection on three selfing syndrome traits (pollen number, nectar volume, and corolla size) in a field experiment comprising 2400 individuals from a set of nearly isogenic lines and wild-type controls. Fitness will be assessed through three proxy measures: survival after transplant, seed set, and outcross paternity.