GENETIC-STRUCTURE AND VARIABILITY IN JACK PINE POPULATIONS - EFFECTS OF INSULARITY

To determine the effects of insularity on the genetic structure and variability of jack pine (Pinus banksiana Lamb.) populations at a regional scale, stands from two different landscapes were studied: two islands in a lake and two mainland areas. The two landscapes have been affected by different fire regimes. The genetic structure and variability of the four populations were analyzed using cellulose acetate gel electrophoresis of 11 enzyme systems. The analysis of 22 loci showed an average polymorphism of 60.0%, a mean of 2.3 alleles per locus, a mean of 1.185 effective alleles per locus, and an observed level of heterozygosity of 0.171. The F(is) values (i.e., fixation index of individuals relative to their population) for all but two loci indicated an excess of heterozygotes compared with the expected numbers under Hardy-Weinberg equilibrium. The genetic differentiation among populations was weak (F(st) = 0.018). There were no significant differences among the four populations for five genetic parameters (mean number of alleles per locus, mean number of effective alleles per locus, percentage of polymorphic loci, and observed or expected heterozygosity). Although the allelic frequencies were homogeneous between island populations, a significant heterogeneity in allele frequencies was observed between mainland populations. The results suggest that gene flow in island populations is sufficiently high to maintain a level of genetic variability similar to that found in mainland populations and to counteract the effect of isolation and differential selective pressures resulting from different disturbance regimes.