Head, Plant and Microbial Biology Department
Wardle Chair in Microbial Ecology
Symbiosis, Evolution, Population Genomics, Plant-microbe interactions, Legume-Rhizobia, Association Genetics (GWAS)
If you are interested in post-doc or graduate-student opportunities, please contact me.
Evolution and genomics of mutualism
We are interested in understanding how symbionts shape the evolution of their symbiotic partners. Among the questions we are asking: Are symbiotic species coevolving in contemporary populations? Does the strength or efficacy of selection differ between symbiotic partners? How important is selection related to symbiosis relative to selection acting outside of the symbiosis? How rapidly does the genetic architecture of symbiosis evolve?
We address these questions by integrating manipulative experiments, population genomics, association genetics (GWAS). To assay the effects of naturally occurring genetic variation we developed a select and resequence approach that we can use to screen strain performance when growing in competitive communities.
Most of our work on symbiosis focuses on the model legume Medicago truncatula and its rhizobial symbionts (Ensifer sp.). This symbiosis is both ecologically and economically important, due to fixation of atmospheric nitrogen to a plant-usable form that occurs when rhizobia are growing in symbiosis with legumes. This work has also led us to become interested in the population geneomics of bacteria. Although analytical approaches for population gneomic analyses of eukaryotes are well developed, the nature of recombination in bacteria create challanges, how to address those challanges is not completely clear.
Complementing the research on symbiosis, we have worked with Liz Dengate, a teacher at the School for Environment Studies in Apple Valley Minnesota, and Michael Winikoff of the Univ. of Minnesota Science Communication Lab to develop Symbiosis in the Schools for hands-on scientific inquiry for High School Teachers and students. We;d love to hear from you if you are interested in using these materials.
Evolutionary history and targets of selection in cacao
Identifying the genes that confer resistance against pathogens is challenging. This is esecially true for large and long-lived species for which standard genetic analysis are particularly difficult. Working with collaborators at Penn State University we are using population genomic scans to filter through the genome to identify genes that warrant the labor intensive functional analyses. Specifically, we have conducted genomic scans to look for signatures of local adaptation on genes that also have annotations related to pathogen resistance. These genes are then subject to functional analyses. We have also used data generated for this project to characterize selection acting on genomic rearrangments, and to understand how rearrangements can affect how selection shapes genome diversity.
Evolution in Urban Environments
Selection populations experience in urban environments is often substantially different than selection in rural environments and provide interesting environments to explore evolutionary processes. Moreover, urban area are not homogenous, but are a collection of distinct patchy environments. Students and I have been interested in understanding the extent to which urban populations are adaptively diverged from rural populations, the selective heterogeity in urban environments, and how urban populations migh affect the evolution of populations outside of cities.
Dept. of Plant and Microbial Biology
Univ. of Minnesota
St. Paul, MN 55108