Plant responses to climate change
I study how California plants cope with the effects of climate change using a native wildflower called Streptanthus tortuosus, or the jewelflower, across an elevational and latitudinal gradient.
Plain language research summary
The jewelflower is adapted to habitats throughout California across elevations in the Sierras. Plants at different elevations will experience the effects of climate change in different ways - those at lower elevations that are hot and dry will have to deal with more intense drought, while those up in the mountains that get lots of snow will have to adapt to lower snowpack.
This species is useful for studying the effects of climate change because we can study their adaptations to these different environments like flowering time, how tall they grow, and the shape of their leaves
They’re also from the mustard family, which is the same family as crops like broccoli and brussels sprouts, so we can apply what we learn from this study system to crops. My research explores how plants are responding to factors like drought, heat waves, and reduced snowpack across an elevation gradient.
We have found that climate change is disrupting the rhythms of plant life, altering when they flower and making it harder for them to survive and reproduce. For example, in places where snowmelt is really early, which is expected to happen more often with climate change, one of the key results I’ve found is that plants are responding to climate change, but not keeping pace with the rate of change.
These findings are important because plants that people depend on like food crops will be dealing with the same things my study species is dealing with. For example, drought is affecting agricultural production, causing economic losses and food shortages. Heat waves can reduce the ability of shade trees like oaks in urban areas to keep cities cool. Meanwhile, fires are devastating forests, reducing their natural ability to mitigate the effects of global warming.
Climate change will bring more extreme and unpredictable changes in weather, like drought followed by intense flooding, which we saw earlier this year in California - and research like mine can help us predict climate change impacts on both humans and nature, build climate resilience, and mitigate the effects of climate change through evidence-based policy.
Technical project descriptions
I study life history responses to environmental cues and the fitness consequences of those responses. S. tortuosus is adapted to a wide range of environments and exhibits remarkable life history and morphological variation in response to climate. Its ability to adapt to disparate environments makes it an ideal study organism for my questions because climate change is predicted to expose organisms to novel combinations of abiotic and biotic conditions.
Phenological responses to snowmelt timing and growing season conditions
In mountainous regions, snow is an important dictator of emergence time and conditions experienced during the growing season such as daylength, temperature, and water availability. However, snowpack is diminishing with climate change and has the potential to disrupt adaptive cue responses and incur negative fitness consequences. If plants flower too early, their buds and flowers may be exposed to damaging frosts; if they flower too late, they may encounter drought conditions at the end of the season. In this project, I aim to elucidate the consequences of phenological differences induced by spatial and temporal variation in snowmelt. To do so, I conducted an observational field study measuring the effects of snowmelt timing on flowering time and fitness across an elevation gradient for four S. tortuosus populations at Lassen Volcanic National Park.
We found that plants are advancing flowering in response to early snowmelt, but nonlinear phenological curves suggest they may be reaching a limit in their ability to keep pace with climate change - in other words, the rate of change in snowmelt timing is exceeding the rate of change in plant responses.
Plants that flower earlier also tend to have higher reproductive fitness, consistent with theoretical and empirical evidence that organisms maximize fitness in the face of climate change by successfully shift phenology in response to changing environmental conditions. However, our results imply that if populations are approaching a threshold in their ability to respond, continued climate change such as reduced snowpack may negatively affect fitness which could result in population decline or extirpation.
Adaptive differentiation in life history traits across climatic gradients
Understanding how traits vary in response to the environment and in what cases this variation is adaptive has important implications for the biological consequences of climate change. Life history traits are commonly adapted to local environmental conditions, but divergence can also be due to neutral factors like genetic drift. Although examples of adaptive divergence are ubiquitous, the relative roles of neutral versus adaptive processes in shaping divergence continue to be debated. Additionally, population connectedness and local adaptation affects divergence: for example, local adaptation can aid evolutionary response when alleles originally adapted to warm environments at lower elevations assist high elevation populations adapt to warming temperatures. However, such adaptation would not take place at all if gene flow is inhibited. I am interested in exploring these factors in the context of adaptation to climate by answering the following questions using a common garden growout of 20 populations across the species range:
Have phenological traits adaptively diverged, and if so, have they diverged in the face of high gene flow?
I will use a variation on Qst-Fst called "Qpc" to evaluate adaptive divergence in relevant life history, morphological, and physiological traits.
Is isolation by environment or isolation by distance more important, and what are the implications for future adaptation?
We performed genotyping-by-sequencing to conduct an Fst study relating genetic differentiation as a function of ecological variables like elevation, precipitation, and temperature vs as a function of geographic distance.