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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Organismic and Evolutionary Biology

Year Degree Awarded

2018

Month Degree Awarded

May

First Advisor

Dr. Lynn S. Adler

Subject Categories

Evolution | Population Biology

Abstract

In species with distinct sexes, differences between the sexes often affect interspecific interactions. In gynodioecious flowering plants, where individuals are female or hermaphrodite, both pollinators and herbivores tend to prefer hermaphrodites. Because pollinators and herbivores affect plant fitness, their preferences have consequences for plant mating patterns, natural selection on mating-related traits, and plant breeding system evolution. Being sessile, the spatial arrangement of females and hermaphrodites in gynodioecious plant populations alters conspecific density and sex ratio locally, which can also have important fitness effects.

My dissertation combines observational studies in natural Silene vulgaris populations and simulation modeling to address questions about how females and hermaphrodites experience intraspecific and interspecific interactions, with consequences for reproductive success, selection on traits, and population sex ratio evolution. Chapter 1 is an introduction. Chapter 2 addresses effects of plant sex and floral and vegetative traits on a recently described interaction between S. vulgaris and Hadena ectypa, a moth that pollinates plants but also deposits eggs in flowers with developing larvae feeding on plant reproductive tissues. Moth oviposition was hermaphrodite-biased and associated with plants having deeper flowers and more stems. However, moth oviposition had limited fitness consequences for host plants, as plants that received moth eggs lost relatively few fruits to predation, receiving eggs did not affect fruit production at the plant level, and oviposition was not associated with enhanced pollination. Chapter 3 demonstrates scale-dependent effects of conspecific density and sex ratio on reproduction and phenotypic selection in S. vulgaris. Fine scale density variation had opposite effects on reproduction in females and hermaphrodites, both sexes experienced enhanced reproductive success with increasing hermaphrodite frequency at high densities, and females and hermaphrodites experienced different effects of density on phenotypic selection. Chapter 4 uses simulation models to assess how pollinator sex bias intensity affects female maintenance and sex ratio evolution in gynodioecious plant populations, finding that even small preferences for hermaphrodites can lead to the loss of females from populations. Taken together, my work sheds new light on the patterns and processes that affect reproduction, selection on floral and vegetative traits, and the maintenance of females in gynodioecious plant populations.

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