last update December 1, 1998
Elucidation of the complex interactions of life-history characteristics that affect genetic structure within and among populations is important in assessing implications for a species' conservation and evolutionary potential. Gene frequency data from 245 individuals from the four California populations of Cupressus forbesii, a serotinous, edaphically restricted, near-endemic conifer were used to investigate temporal and spatial patterns in population genetic structure. Mean values for the proportion of polymorphic loci (P), observed heterozygosity (Ho), expected heterozygosity (He) and mean number of alleles per locus (A) of 0.314 (+/-) 0.035, 0.080 (+/-) 0.021, 0.112 (+/-) 0.019 and 1.224 (+/-) 0.059, respectively, for the four C. forbesii populations are lower than those reported for most conifer species. Significant spatial heterogeneity in allele frequencies was observed on both a populational and subpopulational level. Approximately 16% of all allozymic variation documented in C. forbesii was attributed to populational differences, whereas 2 to 20% was attributable to differences among subpopulations within populations. There was a strong positive correlation between heterozygosity and age and a strong positive correlation between mean number of alleles per locus and mean fire interval of the subpopulations studied. Randomization testing revealed that these associations are not likely to have arisen purely by chance. Though significant spatial barriers exist in this species, genetic distance was not significantly associated with geographic distance.
