Research

With climate change, upslope migration might be expected. However, seasonal differences across elevations may select for differing life history across elevations. It is important to understand how initial gene flow between populations from different elevations affects individual survival and reproduction, and how that may scale up to influence population dynamics. 

As part of the IntBio Project, we performed crosses between populations from across the latitudinal and elevational range of S. tortuosus. We planted the resulting F1 offspring at a low and high elevation site. F1 offpsring were monitored weekly for size, mortality, and phenology. Total seed mass was measured at the end of the growth season as an estimate of reproductive output. 

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Understanding the factors that contribute to population persistence or extinction is critical for predicting future population dynamics and managing biodiversity in a changing world. Population persistence is determined by genetic composition, ecological habitat, environmental stresses, and interactions among these factors. The IntBio Project, will integrate advances in genomics, remote sensing, and statistical modeling to develop new predictive models of population persistence and extinction. I will assist with the integration of demography and genomics for those predictive models. The models created in this project will be critical for understanding population dynamics, predicting responses to future change, and providing tools to direct the implementation of genetically-informed conservation strategies.

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The ability of a plant species to move its seeds across space determines its rate of invasion or range expansion, geographic range size, and ability to withstand climate change and habitat fragmentation. Spatial sorting theory predicts that when dispersal-related traits have a genetic basis, assortative mating can increase the rate of population spread at dispersal fronts. However, little is known about how environmental variation may influence dispersal dynamics. If dispersal-related traits exhibit gene-by-environment effects, rates of dispersal may diverge from spatial sorting expectations.

In a field-greenhouse study, I set-up seed capture trays at 2 distances (Close and Far, see figure to the left) from GrENE-net source trays consisting of ~200 native ecotypes of Arabidopsis thaliana in a field site in North Carolina. The seed capture trays were brought into the greenhouse after the natural seed dispersal season and given optimal growth conditions. I counted the number of plants that emerged, measured various individual traits, and pool-sequenced leaf tissue in trays from both distances. 

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With habitat fragmentation increasing globally, it is important to experimentally investigate the effects of seed dispersal on population genetics and demography. Continuous seed dispersal among populations can affect population size, the distribution of phenotypic and genetic variation within and between populations, and density-dependence. Dispersal can supplement population sizes and increase the genetic variation within populations, both of which can increase the probability of population persistence. 

In an add-on to GrENE-net, I set-up population trays that were either open to dispersal (no cages) or closed to dispersal (open-top cages). These populations with high starting genetic variation were allowed to naturally cycle for 3 years. Throughout the experiment, I collected floral tissue for pool-sequencing and measured population size, size at reproduction, reproductive output, and various reproductive traits. 

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As the effects of climate change become more prevalent, it is critical to investigate the traits that may facilitate population persistence in the face of variable and  changing seasonal environments. Seed dormancy can delay germination timing to more favorable growth conditions, not only increasing seedling survival, but potentially increasing lifetime fitness. As such, seed dormancy can be a form of seasonal environmental tracking. In addition, seed dormancy can act as a bet-hedging strategy by spreading the germination risk across time, within or between years. Through both environmental tracking and bet-hedging, seed dormancy can stabilize population demography, potentially enhancing long-term population persistence.

I established 112 genetically variable experimental populations of A. thaliana with about 620 seeds from one of three recombinant inbred line sets (RIL sets) that differed at 2-3 major dormancy loci. I imposed environmental manipulations of soil composition, temperature, and moisture conditions. 48 “Mixed” populations were composed of both dormant and non-dormant genetic lines to investigate the evolution of dormancy itself during the experiment. I monitored environmental conditions, germination timing, population size, population persistence, and measured various individual traits.

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