Araucaria angustifolia (Bert.) O. Kuntze is a native species of the Tropical Atlantic Forest (Veloso and Goes Filho, 1982; Veloso et al., 1991). Natural populations or plantations can be found mainly in the three southernmost states of Brazil (Paraná, Santa Catarina and Rio Grande do Sul) where it is called "pinheiro-do-Paraná", "araucaria" or "pinheiro brasileiro". This species has also spread throughout other states such as São Paulo and Minas Gerais and in Argentina, particularly in the Province of Missiones (Klein, 1960; Carvalho, 1994).
In its region of natural occurrence, It is one of most important trees in its region of natural occurrence due to its relevant ecological, economic and social functions. As a dominant tree, populations of adult individuals create a microcosmic environment where shade-tolerant plant species of other taxa can grow and develop. Naturally, the seeds feed the wild fauna, including birds and rodents, which are the main araucaria seed dispersors. As the seeds have a high nutritious value, humans also use them for food. Seed collection and trading constitutes a source of income to an undetermined number of families living near the natural araucaria populations of araucaria. Its wood high quality wood, which gives it its main economic value, can be used for almost everything, especially housing, furniture, and pulp (Carvalho, 1994, Reitz et al., 1978).
Prior to European contact, the araucaria forest size was estimated to be 200,000 km2. Uncontrolled exploitation, mainly in the 20th century, led the species to the vulnerable category (IUCN), although some scientists are now aware of its imminent extinction. Most of the remaining araucarias, about 1 to 3% (Guerra et al., 2000), are still under pressure of exploitation pressure by the timber industry. Therefore, conservation and sustainable management strategies for this species should be implemented as soon as possible. A knowledge of the population's genetic structure is crucial to define such strategies properly, a knowledge of the population's genetic structure is crucial.
The genetic structure of natural populations has been studied more intensely since the development and utilization of non-adaptive markers, since they provided the means to interpret observations at the gene level. These studies have characterized how genetic variation is distributed among and within populations and which factors are associated with, or determinant of, the structure itself (Lewontin and Hubby, 1966; Hamrick et al., 1979; Hamrick and Godt, 1989; Reis et al., 1998). Information about the existing extent and organization of genetic variation at species level in their ecosystems helps the definition of strategies not only for breeding, but also for management and genetic conservation.
In this context, isozyme electrophoresis has been widely used in more than a thousand species (Lewontin, 1991) because of its favorable attributes: simplicity of methodology, low cost, simple molecular basis used for polymorphism, and absence of environmental effects, almost without exceptions. Allozymic loci can be effectively identified in a large number of individuals in a short period of time. Since 1980, several studies have been carried out to characterize the genetic structure of natural populations of tropical species by the use of isozyme markers (Hamrick and Loveless, 1986; Loveless and Hamrick, 1987; Buckley et al., 1988; Murawsky and Hamrick, 1991; Hamrick and Murawsky, 1991; Eguiarte et al., 1992; Reis et al., 1998).
Several authors have noted genotypic variation within the araucaria species. The large distribution probably contributes to its differentiation in botanical varieties or ecotypes (Carvalho, 1994). Reitz and Klein (1964) described nine botanical varieties of Araucaria angustifolia: 1) elegans; 2) sancti josephi; 3) angustifolia; 4) caiova; 5) indehiscens; 6) nigra; 7) striata; 8) semi-alba; and 9) alba. The two main criteria used to distinguish them were ripening time and seed color. An additional variety, catarinensis, has an uncovered seed ventral face uncovered (Mattos, 1994).
The existence of geographical races was also demonstrated by Gurgel and Gurgel Filho (1964), who based their inference on the differences shown by distinct provenances. Kageyama and Jacob (1980) detected the existence of genetic variations within and among three natural populations, whose amounts were distinct from those of populations established at different altitudes. The differences in the wood volume from 24 provenances collected in five Brazilian States (MG, SP, PR, SC, and RS) were statistically significant, indicating the existence of genetic variation in this trait (Monteiro and Speltz, 1989).
However, a few studies have been carried out with biochemical and molecular markers in araucaria. Mazza (1997), using RAPDs markers was able to associate lower genetic similarities with larger geographical distances among populations. Later, Shimizu et al. (2000) established the values of 0.240 and 0.248 for the observed and expected heterozygosity, respectively. In this study, the authors detected 2.4 alleles per allozymic locus in 120 individuals from The Parque Nacional do Iguaçu. Using PCR-AFLP of chloroplast DNA, Schogl (2000) detected 12 haplotypes, 72% of which were common to all eight Santa Catarina araucaria populations. In this study, the total diversity (HT) was 0.612 and the average difference among populations (GST) was 0.28.
The objective of this study was to characterize the genetic structure of natural fragmented populations with isozyme markers to provide support for the development of species conservation, sustainable management, and breeding strategies. In addition, inferences about the effects of the fragmentation on the genetic structure of natural populations were made.