Evolutionary change in garlic mustard (Alliaria petiolata) during the invasion process

While at the Illinois Natural History Survey, I studied how garlic mustard (Alliaria petiolata) interacts with native plants and soil microbes, in order to determine the long-term consequences of this species introduction. As part of a USDA funded project, I found that “older” invader populations (populations from sites with a longer history of invasion) tend to show reduced investment to several allelochemicals, which translated into a weaker effect on native soil microbes and plant growth. These patterns are consistent with the results from the B. nigra research, since older populations may face higher levels of intra-, and lower levels of inter-, specific competition (which favors lower allelochemical concentrations), while newly founded populations must still compete primarily with natives, favoring high levels of allelochemicals.

I have also investigated how knowledge of variation in allelopathy could help prioritize management and restoration practices. Field experiments throughout Illinois showed that the relative efficacy of alternative strategies to promote native seedling growth (garlic mustard removal and soil restoration) depended on the allelochemical concentration of the garlic mustard population. Transplanted red oak seedlings generally performed best in old, less toxic sites, and restoring healthy soil microbes and pulling garlic mustard had the biggest impact on seedlings in young, highly toxic sites. Thus the best management practice could differ according the history of invasion at a site.

I am currently studying the potential evolutionary responses of native plants and soils in response to A. petiolata, and whether this evolution could act to integrate the new species into existing communities. I have found that soil microbial communities tend to decline in richness, but increase in resistance, over time. However, over even longer time scales the evolution of reduced impact in A. petiolata allows for the recovery of sensitive microbial taxa. I am currently performing a large scale reciprocal transplant experiment in sites from Illinois to New York to test how native forest understory plants are adapted to their local conditions and the presence of A. petiolata.

  • Adam Davis, USDA ARS - Weed Science
  • Raghu Sathymurthy, Queensland University of Technology
  • David Rosenthal, University of Illinois, Urbana-Champaign

  • Functional, genetic, and taxonomic diversity of plant-fungal interactions along climatic gradients and their role in climate change driven species migrations

    Climates are currently warming at unprecedented rates. Species must move to track the changing climate or evolve to tolerate warmer conditions; those that fail to do so face extinction. Most plant species, especially forest trees, rely on intimate associations with microbial species living in soil in order to capture the resources they need for proper growth. Little is known about how these invisible, but very important, soil microbes are distributed across the continent, and how they will respond to climate change. With funding from the NSF’s new Dimensions of Biodiversity panel, I will soon start a project investigating the genetic, taxonomic, and functional biodiversity of soil microbial communities from forests across the eastern US to test for parallel latitudinal patterns with respect to climate. Trees and soil microbes will likely not move at equal speeds as climates change. Therefore, I will also use experiments to test the functional consequences for tree growth for situations where microbial species migrate slower or faster than trees. My hope is that this research will allow for more precise predictions about how forests will change as a function of the changing biodiversity of the fungal symbiont community during climate warming.

    Mutual feedbacks in the maintenance of genetic and species diversity:

    During my PhD thesis at UC Davis, I investigated possible feedbacks in the maintenance of genetic diversity in a chemical trait of Brassica nigra and species diversity among several competing plant species. I found that the selective value of sinigrin, a secondary compound of B. nigra with defensive and allelopathic properties, depended on the complexity of the surrounding community, including specialist and generalist herbivores and the species of plant competitor. Additionally, the fitness of competing plant neighbors depended on the sinigrin concentration of B. nigra individual. Together, these effects resulted in a “rock-paper-scissors” type competitive intransitivity between high and low sinigrin B. nigra genotypes and three other plant species. This intransitivity promoted the maintenance of genetic and species diversity because it prevented any one species or genotype from dominating the community. Models parameterized with field data suggest that the observed genetic variation was sufficient to allow long term coexistence of all three species pairs, even though two pairs were not predicted to coexist in the absence of genetic variation. Further work showed that this pattern arose primarily due to feedbacks with altered soil communities, especially mycorrhizal fungi.

  • Emily Wheeler, University of Illinois, Urbana-Champaign
  • Sharon Strauss, University of California, Davis
  • Alison Bennett, University of Wisconsin
  • Mirka Macel, NIOO
  • Jose Maria Gomez, University of Granada
  • Daniel Kliebenstein, University of California, Davis

  • Institute of Natural Resource Sustainability Illinois Natural History Survey University of Illinois

    Created Thu, Jan 8, 2009; Updated Tue, Nov 23, 2010