Co-Instructor, PBC450, Northwestern University
- Bryophytes (mosses, liverworts, hornworts)
- Peatland ecology
- Population genetics
- Mating system evolution
My research focuses on bryophytes, the collection of early-diverging land plants including mosses, liverworts, and hornworts. I am interested in a broad range of questions applying to the diversity, population genetics, and ecology of bryophytes. My PhD dissertation work focused on the evolution of mating patterns in the peatmoss genus Sphagnum. I studied a connection between biology (mating type) and ecology (microhabitat preference) that predicted mating patterns in this group of ecosystem engineers.
My work at the Gardens is on the Pleurocarp (Moss) Tree of Life project. A pleurocarpous moss has a particular growing habit, creeping along the ground or other substrate (such as trees) with short, lateral reproductive branches. We know that this group is one of the most speciose lineage of bryophytes, and seems to have diversified in an explosion around the same time that flowering plants began to dominate, in the Jurassic. The pleurocarp mosses were very successful at colonizing the new habitats presented by the flowering plant forests.
The sudden appearance of many lineages makes reconstructing the phylogenetic tree of the group difficult. High throughput (“next-generation”) DNA sequencing will allow us to tackle the phylogeny with very large datasets built from transcriptome data for dozens of species. In addition, our data will show whether particular gene families expanded, coinciding with the diversification of the pleurocarps. These genes may have been critical in the development of the pleurocarp growth form, allowing the pleurocarps to colonize new habitats and become one of the most diverse group of land plants.
- M.G. Johnson, E.M. Gardner, Y. Liu, R. Medina, B. Gonet, A.J.Shaw, N.J.C. Zerega, and N.J. Wickett. 2016. “HybPiper: Extracting coding sequence and introns for phylogenetics from high-throughput sequencing reads using target enrichment.” Applications in Plant Sciences. 4(7):1600016 doi:10.3732/apps.1600016 Link
- M.G. Johnson, C. Malley, A.J. Shaw, B. Gonet, and N.J. Wickett. 2016. “A phylotranscriptomic analysis of gene family expansion and evolution in the largest order of pleurocarpous mosses (Hypnales, Bryophyta).” Molecular Phylogenetics and Evolution. 98:29-40. doi:10.1016/j.ympev.2016.01.008 Link
- M.G. Johnson, G. Granath, T. Tahvanainen, R. Pouliot, H. Stenoien, L. Rochefort, H. Rydin, and A.J. Shaw. 2015. “Evolution of niche preference in Sphagnum peat mosses” Evolution. 69(1) 90-103. doi:10.1111/evo.12547 Link