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In flowering plants, soil heterogeneity can generate divergent natural selection over fine spatial scales, and thus promote local adaptation in the absence of geographic barriers to gene flow. Here, we investigate phenotypic and genetic differentiation in one of the few flowering plants that thrives in both geothermal and non-thermal soils in Yellowstone National Park (YNP). Yellow monkeyflowers (Mimulus guttatus) growing at two geothermal ("thermal") sites in YNP were distinct in growth form and phenology from paired populations growing nearby (<500 m distant) in non-thermal soils. In simulated thermal and non-thermal environments, thermal plants remained significantly divergent from non-thermal plants in vegetative, floral, mating system, and phenological traits. Plants from both thermal populations flowered closer to the ground, allocated relatively more to sexual reproduction, were more likely to initiate flowering under short daylengths, and made smaller flowers that could efficiently self-fertilize without pollinators. These shared differences are consistent with local adaptation to life in the ephemeral window for growth and reproduction created by winter and spring snowmelt on hot soils. In contrast, habitat type (thermal vs. non-thermal) explained little of the genetic variation at neutral markers. Instead, we found that one thermal population (Agrostis Headquarters; AHQ-T) was strongly differentiated from all other populations (all F (ST) > 0.34), which were only weakly differentiated from each other (all F (ST) < 0.07). Phenotypic differentiation of thermal M. guttatus, but little population genetic evidence of long-term ecotypic divergence, encourages further investigations of the potential for fine-scale adaptation and reproductive isolation across the geothermal gradient in Yellowstone.

Although florivores can destroy significant amounts of sexual tissues and indirectly affect pollination, little is known about their preferences, which could shape the evolution of floral traits or defense. In this study, we used a gynodioecious plant Nemophila menziesii, and its main florivore Platyprepia virginalis, to test which floral characteristics are associated with florivory in the field and with florivore choice in the laboratory. Hermaphrodite flowers consistently received more damage than nearby females in the field. In the laboratory setting, florivores also preferred unmanipulated hermaphrodites versus unmanipulated females. Systematic evaluation of hermaphrodite traits, such as corolla size, anther presence, and corolla color, revealed that corolla diameter was the main determinant of florivore preference in this system. Here, we discuss the implications of both pollinator and florivore choice in the evolution of corolla size and sex ratio in gynodioecious species with cytoplasmic male sterility and emphasize the need for more information on the preferences of florivores.