Analyses of gene diversity in some species of conifers

Abstract: Genetic variation at 21 to 25 loci in extracts of individual megagametophytes was surveyed in Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco), Sitka spruce (Picea sitchensis [Bong.] Carr.) and lodgepole pine (Pinus contorta ssp. latifolia [Engelm.] Critchfield). The overall mean proportion of polymorphic loci was 61.19 percent, and the overall mean heterozygosity per individual was 15.81 percent. Sitka spruce was on the low side and interior Douglas-fir on the high side of overall mean genetic variation. Distribution of loci relative to frequency of heterozygotes was rather even for heterozygosities between 0.05 and 0.60: however, between 38 to 56 percent of the loci had heterozygosities lower than 0.05. More than 90 percent of the total gene diversity resided within populations. Although subpopulations were differentiated by only 2.6 to 7.9 percent, level of population subdivision was considered significant for the species tested. The overall pattern of genetic differentiation agreed with the expected on the basis of the neutral-mutation theory. Some loci, however, demonstrated conspicuous clinal variation patterns that are not readily compatible with this stochastic model. he recent use of gel electrophoresis in isozyme Tstudies of genic variability in natural populations of conifers (Rudin 1976) has permitted researchers to investigate many basic questions of evolutionary biology. These questions concern levels of heterozygosity within populations, distribution of genic variation within and between local populations, and relative amounts of genetic variation in central, as opposed to, marginal populations. Until recently, most investigators addressing these questions on conifers were restricted to a small sample of loci. A striking feature of the more recent and extensive isozyme surveys, however, has been the demonstration of a high degree of interlocus variation in heterozygosity within