Gene flow and chromosome rearrangements in Carex scoparia
My work in the area of chromosome rearrangements and gene flow addresses a question of fundamental biological importance: what role does chromosome evolution play in the formation of new species and in population genetic structure within species? Chromosomes in the genus Carex undergo rapid rearrangements both within and between species, due in part to the fact that the chromosomes are holocentric (meaning that centromeric activity is distributed along the entire chromosome rather than localized in a solitary centromere per chromosome, allowing chromosome breakages during meiosis to resolve in viable gametes with an increased chromosome number). The potential role of chromosome evolution in suppressing recombination has not been evaluated in an organism with holocentric chromosomes. Because of the enormous species diversity and chromosomal lability in the genus, as well as the fact that holocentric chromosomes have evolved independently in numerous unrelated groups, Carex is an excellent system for studying the role of chromosome evolution in species diversification.
This project has several components:
- Develop molecular markers for investigating patterns of neutral gene flow. Postdoctoral researcher Karin Kettenring worked in our lab and the Field Museum's Pritzker Lab to develop a set of microsatellite loci for use in Carex scoparia. These markers (manuscript in press; see links at bottom of page) amplify across a wide range of species in the genus.
- Assess the relationship between karyotype rearrangements and gene flow within the species. With collaborator Paul Rothrock we are measuring the relationships among geographic distance, karyotype rearrangements, and genetic distance (based on AFLP data) within the species. Our work (manuscrip in prep) suggests a significant role for chromosome rearrangements in structuring gene flow within species across a wide range of geographic scales.
- Characterize the pattern of chromosome variability at a regional scale. Using the microsatellite markers we developed, we are estimating the relationship between genetic structure and karyotype rearrangement on a regional scale. Our work on this is still in progress, but already we have found chromosome numbers in the Chicago region that range from 2n = 62 to 2n = 68. This work will provide the backdrop for future crossing and reciprocal transplant experiments.
- Estimate the extent of local adaptation. Our plans include developing a common garden experiment using seed collected from the populations we are currently genotyping and karyotyping. Morphological measurements made in the common garden will be used to estimate divergence in quantitative traits among populations (QST), while molecular data will be used to estimate FST. The relationship between these two estimates of population structure allow an esimate of the degree and scale of local adaptation.
- Develop experimental populations to map rearranged areas of the genome and Combine reciprocal transplant experiments with QTL mapping to evaluate whether karyotype rearrangements protect locally adapted gene complexes from recombination. These two aspects of the project build on our current work. They will allow us to directly test how karyotype rearrangement structures gene flow within species and estimate its effect on speciation.
- Midewin National Tallgrass Prairie Restoration Fund, which provided funding for microsatellite development.
- Chicago Wilderness, which provided funding for genotyping and karyotyping Carex scoparia populations across the Chicago region (see KMZ file of surveyed populations).
- Link to primers on the Molecular Ecology Resources database [LINK]
- Download Excel spreadsheet with primers and amplification details [XLS]
Oaks, the genus Quercus
Sedges, the genus Carex
Other projects in plant biodiversity