Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Biology and Biomedical Sciences: Evolution, Ecology and Population Biology


English (en)

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Peter Raven


This dissertation describes the role of pollination in the floral diversification of Oenothera with an integration of both ecological and phylogenetic approaches. Oenothera: Onagraceae) is a model system for studying plant reproductive biology. It provides excellent examples of shifts in reproductive traits such as pollination and breeding system, features that have been important in angiosperm diversification. These systems are evolutionarily labile; they easily shift between different states. These different reproductive traits may shift in a concerted fashion; therefore, a more comprehensive approach to understanding the evolution of these plant systems simultaneously addresses shifts in pollination and breeding system. Using 54 species of Oenothera, I first collected detailed data describing the pollination systems, breeding systems, and floral traits associated with pollinator rewards; and second I determined the phylogenetic structure, evolutionary history and relationships among these species. Finally, in that phylogenetic context, I examined the timing and position of transitions in reproductive traits and consider how these traits are associated with pollination and breeding systems. My results offer new insights regarding the specialization of pollination systems and the predictive power of pollination syndromes. I find that specialization in pollination is not accurately characterized by visitation rates alone, and that considering functional groups of visitors to the flowers provides the most informative characterization of pollination systems. I also find that pollination syndromes do not sufficiently or accurately describe these pollination systems. My results also clarify phylogenetic relationships in the genus Oenothera, determine that there have been 13 independent transitions to self-compatibity, and provide the first phylogenetic tree for subsection Kneiffia. I find that pollination and breeding system do not correlate consistently with floral traits, and do not show an association with each other. Finally, I find that the transitions in the reproductive traits reveal a complex and diverse pattern in which shifts in floral traits occur prior and post a transition in pollination system. I also document an example of a rare transition from a generalized pollination system to a specialized pollination system. The placement of floral trait transitions with regards to pollinator shifts suggests selective pressures in floral traits that are predictable and follow transitions to novel dominant pollinator groups, rather than changes in pollination system.


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