Range-wide variation in mating system and reproduction of Clarkia pulchella: what are the important drivers?
Climatic gradients underlying a species’ range may create gradients in pollinator availability or flowering season length. These factors can cause variation in selection for reproductive assurance across the range. Similarly, underlying gradients in climate or biotic interactions are likely to be important in shaping geographic ranges. I’m using several approaches to investigate the links between climate, range position, and mating system in Clarkia pulchella. First, I measured traits on a large set of herbarium specimens and related these traits to climate and estimated isolation (Bontrager and Angert 2016, American Journal of Botany), showing that climate may be an important driver of mating system and reproduction, but that important climatic gradients are sometimes heterogeneous across the range.
In a follow-up experiment, I set up pollinator exclusion plots across the range of C. pulchella and I’m evaluating how climate drives variation in reproductive assurance and overall reproduction. To complement this project, an awesome Angert Lab undergraduate, Devin Gamble, is growing C. pulchella in a common environment and examining variation between populations in floral traits and the response of those traits to drought stress.
What factors determine the effects of gene flow on northern range edge populations of Clarkia pulchella? A test using simulated gene flow and common gardens.
Theory offers several competing predictions about the effects of gene flow on range edge populations. One possibility is that gene flow from populations in different environments may disrupt local adaptation in edge populations. An alternative possibility is that edge populations may lack the genetic variation necessary for them to adapt to their local environment, in which case, gene flow may provide beneficial genetic variation. A further complicating factor in the era of climate change is that populations now need to track a rapidly changing environment to avoid extinction. To examine how gene flow from a variety of climatic and geographic distances affects northern edge populations of C. pulchella, I simulated gene flow between populations and planted the resulting seeds into common gardens at the northern range edge. Preliminary results show a strong signal of adaptation to temperature, and indicate that the effect of gene flow depends on the climatic conditions that the source population is adapted to.
A video of my Evolution 2017 presentation on this project is available here.
How do geography and climate contribute to shaping population genetic structure of Clarkia pulchella?
The role of gene flow in shaping geographic ranges ultimately depends on how the movement of individuals or gametes is structured across geographic distance and environmental heterogeneity. Using GBS data from 32 populations across the northern half of the range of C. pulchella, I’m examining how geographic distance and environmental differences between populations shape genetic structure. Initial results show that there is a signal of isolation by distance, but with some interesting heterogeneity. Stay tuned!
Is climate change disrupting local adaptation?
Common garden and transplant experiments are frequently employed to test whether populations are adapted to their environments. As the climate changes, populations will more frequently experience climate that differs from the conditions that they have adapted to. Amy Angert and I are leading an effort to see if there is already a signal of climate change disrupting local adaptation in published studies. We’ve expanded existing databases of transplant studies, and we’re using climate and fitness data to test how signatures of local adaptation have changed over time and in relation to climate anomalies. We’ll be presenting some exciting results at upcoming conferences, so stay tuned.