USFWS Grant FWS 0603 Chicago Wilderness How Far is Too Far ? Genetic consequences of Seed Provenance Decisions in Sedges

We investigated the regional patterns of karyotype (chromosome) variation and population genetic structure in 22 Chicago region populations of Carex scoparia, a sedge species that exhibits remarkable chromosomal variation. Karyotype rearrangements are common, with our counts in the species ranging from 2n = 62 to 2n = 68 and multiple counts fixed within at least some populations. As would be expected under these conditions, we found substantial genetic differentiation among populations and significant evidence of inbreeding (low heterozygosity) in most populations. One population, Powderhorn Lake Forest Preserve, showed an intriguing pattern: heterozygosity levels compatible with outbreeding, in combination with evidence of hybridization among two source populations and strong genetic linkage among most markers. This combination may suggest a lack of recombination between two source populations due to karyotype differences. There is a management implication in this interpretation. If in fact non-local genotypes are unable to recombine with local genotypes, then introduction of non-local plants will most likely result in coexistence of the two populations or competitive exclusion of one. The risk is that in the absence of recombination between genotypes, locally adapted genotypes may be outcompeted by nonlocal genotypes, reducing the overall genetic diversity of the species. Whether this theoretical risk, suggested by our study, is a risk in fact is a subject of our ongoing work. Pending further study, our recommendation based on this work is that restorationists should limit seed sources to a broad range of the local populations nearest the restoration site when working with sedges. Unfortunately, the data we have gathered does not present evidence on the relevant spatial scale; however, our interpretation of the data suggests that collecting as locally as possible from a range of sites will minimize the risk of genetic homogenization due to nonrecombination between local and nonlocal populations and maximize genetic variation at the site level.