Samples taken from throughout the ranges of distribution of lodgepole pine (Pinus contorta Dougl. ex. Loud.) and jack pine (Pinus banksiana Lamb.) were assayed for Sal I and Sst I chloroplast DNA restriction fragment variation. Although the chloroplast genome is often regarded as highly conserved, at least 2 distinct Sal I and 13 distinct Sst I restriction fragment banding patterns occur in these closely related species. None of the chloroplast DNA restriction fragment banding patterns observed in allopatric lodgepole pine was observed in allopatric populations of jack pine, and vice versa, even though the two species share an extensive zone of sympatry, and gene flow between the species has been reported for nuclear genes. However, several atypical Sst I restriction fragment banding patterns occur only in or near the zone of sympatry. Chloroplasts have been reported to be inherited maternally in the great majority of species studied; however, restriction fragment analyses indicated that chloroplasts are inherited paternally in controlled matings between lodgepole pine (Y) and jack pine (i).The chloroplast genome, which averages about 150 kilobase pairs (kbp) in size, encodes gene products that are involved in photosynthesis (1). It is inherited maternally in the great majority of species that have been studied, but biparental inheritance has been reported in at least 20 species (2, 3). Although studies of chloroplast DNA (cpDNA) have usually been based on one or a few samples per species, they have demonstrated that diversity among species is common and they have been informative phylogenetically (4-6). There have been few studies of intraspecific cpDNA polymorphisms. Although examples of intraspecific cpDNA polymorphisms have been reported (7-11), small sample sizes have been employed or the variants observed have been at low frequency; Consequently, little is known of the extent of intraspecific cpDNA diversity. In this paper we present evidence, from large samples, that lodgepole pine (Pinus contorta Dougl. ex. Loud.) and jack pine (Pinus banksiana Lamb.) differ in their Sal I and Sst I cpDNA phenotypes and that there are a large number of distinct Sst I restriction fragment variants throughout the wide allopatric distributional ranges ofboth species, as well as within a zone of sympatry in which the ranges of the two species overlap. We also present evidence that introgression of Sal I and Sst I variants is rare between the species and that cpDNA is inherited paternally in matings of P. contorta (9) with P. banksiana (d).MATERIALS AND METHODS Plant Materials. In total, 371 individuals were sampled, including 153 individuals of lodgepole pine from 63 populations in the allopatric (nonoverlapping) region, 115 individuals ofjack pine from 68 populations in the allopatric region, and 95 individuals from 16 populations in the zone of sympatry (Fig. 1); all four subspecies of P. contorta were represented in the sample of lodgepole pine. To maximize the number of populations represented, only a single indi...

Microsatellite DNA markers from 13 simple sequence repeat (SSR) loci were used to compare genetic diversity between preharvest pristine and postharvest residual gene pools of two adjacent virgin, old-growth ( approximately 250 years) stands of eastern white pine (Pinus strobus L.) in Ontario. There was concurrence in genetic diversity changes in the postharvest gene pools of the two stands. The total and mean numbers of alleles detected in each stand were reduced by approximately 26% after tree density reductions of approximately 75%. Approximately 18 and 21% of the low-frequency (0. 25 > P > or = 0.01) alleles and 76 and 92% of the rare (P < 0.01) alleles were lost from residual stands A and B, respectively, after harvesting. Multilocus gametic diversity was reduced by 38 and 85% and genotype additivity by approximately 50% in the residual stands after harvesting. Latent genetic potential of each stand was reduced by approximately 40%. Although heterozygosity was reduced (1-5%) in the postharvest residual stands, the reductions were not substantial and not comparable to those using other genetic diversity measures. The reductions in genetic diversity measures were slightly higher than those theoretically expected in postbottleneck populations according to drift theory. In the absence of substantial gene migration that could ameliorate the genetic losses, the ability of the postharvest white pine gene pools to adapt to changing environmental and disease conditions may have been compromised. The microsatellite DNA results for genetic effects of harvesting in old-growth eastern white pine stands were similar to those that we reported earlier from allozyme analysis (Buchert et al. 1997). The results indicate that silvicultural practices should ensure that the gene pools of remaining pristine old-growth stands are reconstituted in the regenerating stands.

Effects of asexual reproduction as a primary reproductive strategy on population structure and levels of variability were investigated electrophoretically in natural populations of a woody plant species, trembling aspen (Populus tremuloides Michx.), from Alberta. As expected, levels of genic diversity, 42%, and proportion of polymorphic loci, 92%, averaged over all clones are considerably greater than those reported for comparable samples of sexually reproducing plant and animal species. These measures of genic variability of a primarily asexual plant species are similar to those reported for asexual species of insects, fish and bacteria. In addition, each of the 222 clones was electrophoretically unique. Since neutral theory would predict each individual clone to be heterozygous for a unique mutation at each gene locus at equilibrium, these results can be interpreted in a number of ways: (i) insufficient time to reach equilibrium, (ii) inability of electrophoresis to detect all variation at a locus, (iii) periodic establishment of sexually derived propagules in the population, and (iv) selection for similar genotypes at each location or against mutations at particular gene loci. Re-invasion of Pleistocene-glaciated areas by trembling aspen likely was by sexual means, with subsequent reproduction being primarily asexual.

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Isozyme analysis was conducted on individuals of Populus alba L., P. tremula L., and P. × canescens Smith to genetically characterize and differentiate species, hybrids, and individuals, and to determine genetic relationships among them. Thirty gene loci, with 71 alleles, coding for 15 enzymes were observed. Individuals could be identified on the basis of their multilocus genotypes. There were 21 unique multilocus genotypes among 23 P. alba clones. Five P. alba clones from Canada were genetically distinct from each other. Each of the 18 P. tremula and 15 P. × canescens clones had unique multilocus genotypes. Thirteen clones had a unique genotype at a single locus. Percentage of polymorphic loci, average number of alleles per locus, and mean observed heterozygosity were, respectively, 50.0, 1.86, and 0.085 in P. alba, 51.7, 1.66, and 0.096 in P. tremula, and 51.7, 1.86, and 0.157 in P. × canescens. Populus alba and P. tremula were genetically distinct from each other and could be distinguished by mutually exclusive alleles at Aco-3, P. tremula-specific gene Mdh-3, and allele frequency differences at 6 loci. Populus × canescens had allele contributions of P. alba and P. tremula. However, their allele frequencies were closer to those of P. alba than being truly intermediate. The mean genetic identity was 0.749 between P. alba and P. tremula, 0.987 between P. alba and P. × canescens, and 0.817 between P. tremula and P. × canescens. Canonical discriminant analysis of multilocus genotypes separated P. alba, P. tremula, and P. × canescens into three distinct groups and portrayed similar interspecific relationship as above. Our results suggested that the putative P. × canescens individuals consisted of a mixture of F1 hybrids of P. alba and P. tremula and their backcrosses to P. alba.