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United States Department of Agriculture

Agricultural Research Service


item Ayres, Debra
item Ryan, Frederick

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: This work was carried out in USDA ARS facilities as part of the Ph.D. dissertation work of the first author; funding was from outside grants. The The USDA scientist played an active role in experimental design, interpretation of results and preparation of the manuscript. The population structure of a rare plant with a restricted range, El Dorado Mules Ears, was compared to that of a closely related plant, Wyethia bolanderi, which is more common and widespread. Population structure in this sense is a quantitative assessment of the genetic resources of the plant. The importance of this measure is that it is related to the ability of the plants as a whole to resist disturbance, for instance, destruction of habitat. The rare plant has populations that consist of only a few individuals. Although there may be a large number of plants at a site, there are only a few genetic individuals because of the clonal habit of the eplant. The more widespread plant had a greater number of individuals and more genetic diversity in any population. The population structure of the rare plant was affected by contrasting forces: reproduction isolation, which tends to limit the genetic resources of a population, is counter- balanced by the longevity of the clones. The assessment of genetic resources of rare or endangered organisms, as described in this work, is one factor that must be considered in land use planning. Knowledge of genetic resources and their distribution can also be important in planning mitigation efforts.

Technical Abstract: Wyethia reticulata is an edaphic endemic in the Sierra Nevada foothills. Its sympatric congener, W. bolanderi, is also restricted to the foothills has a north-south range of 250 km, compared to 14 km for W. reticulata. The goals of this study were to determine the clonal diversity, population size, genetic variation and spatial and genetic structure for each species from paired populations in El Dorado County, California, using allzyme and RAPD methodologies. W. reticulata, spreading by rhizomes, had populations dominated by a few large individuals. W. bolanderi, with a basal caudex, had populations of a few hundred evenly sized individuals. Genetic analyses indicated that W. reticulata, compared to its congener, had somewhat less genetic diversity (H:0.28 vs 0.38), had more of its genetic variation partitioned among populations (F:0.25 vs 0.07), and showed a complete absence of inbreeding (F:-0.03 vs 0.22). Cluster analysis of all polymorphic markers revealed population membership in accord with geographically defined populations only in W. reticulata. It was concluded that ecological limits on recruitment of genets results in small population size in W. reticulata. Limited gene flow, drift within small populations, and sexual reproductive dominance of large clones results in the genetic divergence of populations. Genetic diversity is maintained by the longevity of clones and by outbreeding.

Last Modified: 05/24/2017
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