MATING SYSTEM EVOLUTION, PLANT-POLLINATOR INTERACTIONS, AND FLORAL ULTRAVIOLET PATTERNING IN MIMULUS GUTTATUS

Abstract

The evolution and maintenance of plant mating systems has been a topic of great interest throughout the history of evolutionary biology. Despite a large body of literature describing mating system variation, critical knowledge is lacking regarding the mechanisms involved in mating system transitions, including the rate and magnitude of trait changes. I combine experimental evolution, pollinator behavioral studies, and classic phytomorphology to examine the mating system transition from outcrossing to self-fertilizing (selfing) in flowering plants. Using the wildflower Mimulus guttatus (yellow monkeyflower) as a model, I investigate which traits facilitate outcrossing via mutualistic relationships with pollinators and which traits evolve in response to pollination disruption. In Chapters 1 and 2, I demonstrate that rapid evolution of adaptive floral and genetic traits can occur in populations that lose pollinators and that trait evolution occurs sequentially. In Chapter 3, I find strong pollinator preference for specific floral traits, evidence that pollinator selection maintains attractive traits in wild populations. However, pollinators displayed limited ability to distinguish between subtle population variants and thus are unlikely drivers of ethological speciation. In Chapter 4, I document within and among population variation in a cryptic floral trait, ultraviolet (UV) patterning. UV patterning is a visual stimulant for pollinators, but I found it in a selfing Mimulus species, suggesting that UV patterning in flowers functions beyond pollinator attraction. My research has direct implications for forecasting plant adaptation as anthropogenic environmental disturbance increasingly decouples plant-pollinator relationships. Rapid adaptation is an option for some self-compatible, pollinator-reliant plants; however, a transition to selfing results in decreased genetic diversity which may expose populations to extinction with further environmental disturbances.