Gynodioecy and Biotic Interactions: Plant Traits, Insect Preferences, and Population-Level Consequences

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

Sex-biased oviposition by a nursery pollinator on a gynodioecious host plant: Implications for breeding system evolution and evolution of mutualism

Dioecy, a breeding system where individual plants are exclusively male or female, has evolved repeatedly. Extensive theory describes when dioecy should arise from hermaphroditism, frequently through gynodioecy, where females and hermaphrodites coexist, and when gynodioecy should be stable. Both pollinators and herbivores often prefer the pollen-bearing sex, with sex-specific fitness effects that can affect breeding system evolution. Nursery pollination, where adult insects pollinate flowers but their larvae feed on plant reproductive tissues, is a model for understanding mutualism evolution but could also yield insights into plant breeding system evolution. We studied a recently established nursery pollination interaction between native Hadena ectypa moths and introduced gynodioecious Silene vulgaris plants in North America to assess whether oviposition was biased toward females or hermaphrodites, which traits were associated with oviposition, and the effect of oviposition on host plant fitness. Oviposition was hermaphrodite-biased and associated with deeper flowers and more stems. Sexual dimorphism in flower depth, a trait also associated with oviposition on the native host plant (Silene stellata), explained the hermaphrodite bias. Egg-receiving plants experienced more fruit predation than plants that received no eggs, but relatively few fruits were lost, and egg receipt did not significantly alter total fruit production at the plant level. Oviposition did not enhance pollination; egg-receiving flowers usually failed to expand and produce seeds. Together, our results suggest that H. ectypa oviposition does not exert a large fitness cost on host plants, sex-biased interactions can emerge from preferences developed on a hermaphroditic host species, and new nursery pollination interactions can arise as negative or neutral rather than as mutualistic for the plant

WTO must ban harmful fisheries subsidies

Sustainably managed wild fisheries support food and nutritional security, livelihoods, and cultures (1). Harmful fisheries subsidies—government payments that incentivize overcapacity and lead to overfishing—undermine these benefits yet are increasing globally (2). World Trade Organization (WTO) members have a unique opportunity at their ministerial meeting in November to reach an agreement that eliminates harmful subsidies (3). We—a group of scientists spanning 46 countries and 6 continents—urge the WTO to make this commitment..