How does mating system influence niche evolution?
Why are some plant species better able to adapt to new or changing environments? Niche expansion requires populations to avoid extinction in stressful environments while responding to natural selection - a challenging combination of demographics, genetic variation, and gene flow! In flowering plants, mating system can have a big effect on each of these factors. Interestingly, many species respond to environmental stress in ways that increase self-fertilization (e.g. smaller flowers, self-incompatibility breakdown). Higher selfing under stress can increase population sizes, expose new genetic variation, and isolate populations from gene flow. However, it can also cause inbreeding depression and reduce genetic variation over time. I'm using stochastic source-sink models to compare the eco-evolutionary consequences of selfing during niche expansion. I've found that intermediate selfing rates (e.g. mixed mating) promote niche expansion over a broad range of ecological and genetic scenarios (pdf). I'm currently interested in how source-sink dynamics alter the evolution of self-fertilization during niche expansion.
The ecology and evolution of UV floral variation in monkeyflowers
Flowering plants often use patterns in the ultraviolet spectrum to attract and guide insect pollinators to floral rewards. In addition to shaping plant-pollinator interactions, these cryptic signals are also involved in interactions with florivores and physiological responses to UV irradiance, heat, and water stress. Thus, UV floral variation is likely shaped by complex selective landscapes. In collaboration with Tim Miller and Kathleen Kay, we recently documented a widespread UV polymorphism between annual and perennial populations of M. guttatus. We used captive and wild bee choice trials to demonstrate that bee pollinators learn common UV patterns and discriminate against unfamiliar UV patterns in this species (pdf). Given the association between UV pattern and life history divergence, this trait has the potential to mediate assortative mating with respect to life history. We are currently interested in the genetic basis and adaptive significance of UV variation in natural populations.
This work has been featured in the new Color of Life exhibit at the San Francisco Academy of Sciences!
How does life history interact with adaptive divergence in monkey flowers?
Organisms must balance multiple components of fitness, including survival, growth, and reproduction, as part of an overall life history strategy. Particular environments favor different life history strategies, which in turn (as components of fitness) shape the overall pattern of phenotypic selection. Thus, adaptive divergence can involve interesting feedbacks between life history evolution and adaptive divergence in other traits. I'm using life history divergence within the model plant species Mimulus guttatus to test for the role of life history in structuring local adaptation, phenotypic selection, and reproductive isolation. I've found that perennial life history traits, including greater vegetative growth, are favored in more mesic habitats (pdf). In turn, selection in perennials is often mediated through clonal growth rather than reproduction. This has interesting implications for the evolution of reproductive barriers, such as post-pollination barriers and hybrid fitness.
Annual (left) and perennial (right) populations have flowers that look similar in the visible spectrum (top) but are associated with different patterns in the UV spectrum (bottom: runway pattern (left) and bulls-eye pattern (right)). Bee pollinators are more likely to visit the UV pattern that they have previously experienced.
Dissecting climate responses in alpine plants
Alpine plants are uniquely threatened by changing climate because they are unable to shift upward in elevation to track cooler conditions. Understanding individual and population responses to climate is crucial for accurate predictions of how future climates will impact alpine species. In a long-term demographic study, Dan Doak and Bill Morris found evidence for climatic "tipping points" in two alpine plant species - moss campion (Silene acaulis) and alpine bistort (Polygonum viviparum). In collaboration with Dan and Bill, we're investigating the role of local adaptation and phenotypic plasticity in determining individual and population-level responses to climate. Through a combination of transplant and controlled-temperature experiments, we're asking whether and how local adaptation and genetic variation in climate responses may influence the severity of such "tipping points" in the future.