THE CLONAL-STRUCTURE AND POPULATION-STRUCTURE OF A RARE ENDEMIC PLANT, WYETHIA-RETICULATA (ASTERACEAE) - ALLOZYME AND RAPD-ANALYSIS

Genetic structure arises when limited gene flow between populations fa vours the development of distinct arrays of genetic characters within each population. Determining the spatial scale at which this different iation occurs is critical to our understanding of population biology a nd microevolution of species. The genetic structure and spatial patter n of genetic variation in an endemic, clonal perennial, Wyethia reticu lata E. Greene, was investigated using random amplified polymorphic DN A (RAPD) markers and allozyme alleles. Large stands (250-360 m(2)) wer e found to contain few genetic individuals. Despite the small populati on sizes and endemism of the species, W. reticulata was highly diverse genetically, with most of the variation (75-81%) distributed within p opulations. A population structure in full agreement with spatially de fined populations was achieved only by combining RAPD and allozyme mar kers. Analysis using both types of markers appeared to provide estimat es of genetic similarity between individuals that were most consistent with empirical data on plant distributions. We postulated that large, long-lived clones dominated genetic relationships within populations but also provided opportunities for gene flow between populations on a longer time scale. The two marker types yielded different estimates o f between-individual similarity and revealed disparate patterns of pop ulation structure. This result will arise because allozymes and random DNA segments have dissimilar evolutionary dynamics with respect to mu tation and selection.