The flowering plant group Carex subgenus Vignea is a large and difficult group of sedges (Cyperaceae), including approximately 300 species worldwide. Dr. Eric H. Roalson (Washington State University) and Dr. Andrew L. Hipp (The Morton Arboretum) propose to conduct a thorough evolutionary study of this diverse group. Sedges are critical but poorly understood ecological components of riparian, alpine/tundra, and meadow habitats worldwide. Characterizing species differences and evolutionary patterns is critical to conserving biodiversity and defining the ecological function of the species. Drs. Roalson and Hipp will use variation in DNA sequences and genome structure to study the diversification of major lineages and evolutionary innovations in the genus. These studies will also lead to a taxonomic revision of the group and new tools for species identification.
This proposal involves training undergraduate, graduate, and postgraduate researchers in gathering and analyzing biosystematic data. Online resources will be developed to aid scientific and lay workers in identifying species in this group, which will greatly facilitate ecological and biodiversity studies. Finally, our results will be disseminated to the wider scientific and general audience communities through scientific publication, presentation of results at national and international meetings, and enhanced collaborations.
In this project, researchers from Washington State University and The Morton Arboretum collaborated with colleagues around the world to investigate the biodiversity of sedges. The group of sedges they studied, Carex subgenus Vignea (Family Cyperaceae) comprises approximately 275 to 300 species and is broadly distributed across six continents. North America, with nearly 200 species, has the greatest diversity of Carex subg. Vignea species. A secondary center of diversity, with approximately 150 species, is located in northern and temperate Asia and Europe and includes major circumpolar species complexes. Ecologically, this group is an critical component of many wetland and riverine habitats, boreal ecosystems, floodplain forests, and sedge meadows, among others. The research they conducted included (1) field collecting throughout North America and China (the latter in collaboration with colleagues at Kunming Botanical Institute of Botany); (2) rearing live plants from more than 100 species in a greenhouse at The Morton Arboretum; (3) counting chromosomes and measuring genome sizes for more than 200 live plants in the greenhouse; (4) sequencing DNA from more than 500 individual collections, representing approximately 250 Carex species; and (5) using this information to understand how Carex species are related, and how the evolution of genome rearrangements drives the diversification of sedges worldwide. Our major findings and results from this project to date include the following: 1. Chromosome rearrangements in sedges are rapid, and do not entail changes in genome size. It appears that changes in chromosome number do not entail changes in the number of genes that a Carex possesses. This allows chromosome number to evolve rapidly. 2. Chromosome rearrangements drive genetic diversification in sedges. We know from our phylogenetic work that the genus Carex has undergone a rapid diversification relative to the remainder of the sedge family Cyperaceae; this means that it has more species than we expect, given the age of the genus (work from The Morton Arboretum suggests that the core group of Carex originated between 22 and 31 million years ago). A question biologists have long had is, "why are there so many sedges?" Work we conducted in this grant demonstrates that chromosome rearrangements affect gene flow patterns within species: two individuals that differ by many chromosome rearrangements are less likely to interbreed than two individuals that differ by one or a few rearrangements. This suggests that chromosome evolution may play an important role in the evolution of new sedges species. 3. Adjustments to our understanding of sedge classification. The sedges of genus Carex can be difficult to learn. They are numerous, and the differences between them can be very subtle. Our work provides a framework for placing sedges into a new classification, which we expect will provide useful tools to identifying species in this ecologically important genus. In addition to these research findings, our project trained four WSU undergraduates in the methods of plant biodiversity research.
