ALLOZYME, SI GENE, CYTOLOGICAL, AND MORPHOLOGICAL POLYMORPHISMS IN A POPULATION OF OENOTHERA BIENNIS

The studies of population structure in the North American oenotheras by Cleland and his associates led to the conclusion that "over most of the North American range of the subgenus Oenothera, i.e. the area from the Rocky Mountains eastward, the population consists of innumerable true-breeding and therefore permanent complex-heterozygotes, each isolated from the others by reason of its self-pollinating habit but occasionally or rarely outcrossing, in which case hybrids are formed which tend to disappear if they have other than 014, but which may become the progenitors of new permanent and isolated complex-heterozygous lines if they have 014." (Cleland, 1972, p. 230-231). The popuilation of a given geographical region is composed of local stands which, in the main, appear to be discontinuous and modest in size, generally on the order of a few hundred individuals. Cleland's studies were based on collections which represented the major geographical regions of North America but only included a very limited, fortuitous sampling of particular local stands or unit populations. Population samples were characterized according to the segmental arrangements of the component chromosomal complexes and the phenotype which each complex produced. In the few cases where more than one member of a single stand was analyzed, variations in segmental arrangement were found, suggesting that local stands are heterogeneous, i.e. also composed of numerous, essentially isolated, inbreeding complex heterozygous lines. A precise knowledge of the genetic variability within the local stand can shed light on questions such as the nature of the colonization-extinction cycle, the significance of hybridization, and the degree of phenotypic plasticity exhibited by the inbred lines of complex-heterozygotes. Thus a method is needed which will allow rapid screening of adequate samples of local stands and will detect all inbred lines composing a stand. The determination of the segmental arrangement of a single collection requires on the average the production of 10-15 hybrids and their cytological analysis, an amount not feasible for large numbers of plants. Inbred lines in local stands of the biennis group 1 assemblage of Oenothera biennis have also been identified by analyzing collections for incompatibility alleles (Steiner, 1964; Al Khafaji and Steiner, 1970). This method for obtaining an index of genetic variation requires production of hybrids and extensive compatibility tests which limit the number of plants which can be surveyed during a season. The use of starch gel electrophoresis for identification of allozymes has shown particular promise as a method for rapidly surveying large samples of local stands for genetic variability (Levin et al., 1972; Levin, 1975). The allozyme studies as well as the results of incompatibility allele surveys supported the conclusion that single populations tend to be limited in variability, consisting of only one, or at the most, a few