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Wyethia reticulata is an edaphic endemic in the Sierra Nevada foothills. Its sympatric congener, W. bolanderi, is also restricted to the foothills, but has a north‐south range of 275 km, compared to 14 km for W. reticulata. The goals of this study were to determine clonal diversity, population size, genetic variation, and spatial and generic structure for each species from paired populations in El Dorado County, California, using allozyme and RAPD (random amplified polymorphic DNA) methodologies. Wyethia reticulata, spreading by rhizomes, had populations dominated by a few large individuals, while 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 T: 0.28 vs. 0.38), had more of its genetic variation partitioned among populations (FST: 0.25 vs. 0.07), and showed a complete absence of inbreeding (FIS: 20.03 vs. 0.22). Population membership in accord with populations defined by geographical location resulted only when all markers were included in the analysis. Ecological limits on recruitment of genets appears to result in small population size in W. reticulata. Limited gene flow, drift within small populations, and sexual reproductive dominance of large clones result in the genetic divergence of populations in this species, while genetic diversity is maintained by the longevity of clones and outbreeding. The amount of genetic variation within a species and its distribution within and among populations provide clues to factors that govern the maintenance of variation, inbreeding, and gene flow. These factors are useful for defining functional populations (those with members that exchange genes), for identifying potential selection domains and evaluating opportunities for speciation, and in measurements of genetic diversity in crop lines and wild plants. Various studies (Hamrick, Linhart, and Mitton, 1979; Loveless and Hamrick, 1984; Hamrick and Godt, 1990) have used the isozyme data from hundreds of investigations to examine the relationship between genetic variation and various aspects of life history. Geographic range was positively correlated with genetic diversity at the species level, but had no bearing on the distribution of genetic variation among populations. The factors most highly associated with the development of genetic structure were those related to the vagility of pollen and seeds. Reduced pollen exchange due to inbreeding, localized pollination, and/or short life span, and dispersal of seed 1 |
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