The synthetic theory of evolution has postulated and laboratory experiments demonstrated that the division of an integral population into small isolated fragments causes a random abrupt and nonadaptive change of the initial ratio between the frequencies of alleles, genotypes and mutations ("the drift of genes"). It is assumed also that homozygotation and formation of genetically specific populations take place inevitably in a multitude of subsequent generations (especially in insular protractedly isolated populations at the boundaries of the natural habitat) on account of inbreeding, new mutations and selection. However, correctness of the STE postulates as to natural "insulated" settlements of trees has not been confirmed.
To test these hypotheses, we studied specific features of the allozymic polymorphism taking, by way of example, 26 marginal insular isolates of the Scotch pine (occupying the surface area of less than 15–20 km2 or over 50 km2) at the boundaries around the natural habitat of this species in comparison with 20 populations at the central the least disjunctive part of their natural habitat.
The study revealed a reliable relationship of the number of alleles per locus (r = +0.704) and the degree of the observed heterozygosity (r = +0.671) with the surface area of natural insular pine forests at the northern, eastern and southern boundaries of the natural habitat. It was shown that the polymorphism parameters decrease sharply as the surface area of the isolates shrinks to less than the "critical value" of 15–20 km2. When their surface area increases to over 50 km2, the intrapopulation polymorphism parameters (the number of alleles per locus, the expected and the actual heterozygosity) and, to a lesser extent, Wright's fixation indices, which reflect the degree of inbreeding in populations, reach the normal level characteristic of the main central part of the natural habitat of this species. Thus, Wright-Dubinin's "insular model" of genetic-automatic processes and Mayr's hypothesis of homozygotation of small isolated (insular) populations at the boundaries of natural habitats have been confirmed for the first time at the genetic level taking Pinus sylvestris as an example.
Reliable correlations between the number of alleles per locus and the parameters of the observed heterozygosity have been also established for populations of the Scotch pine in Siberia, Central Kazakhstan (r = +0.602), the East European Plain, the Northern Caucasus, and the Carpathians (r = +0.702).
The investigations served as the basis for a three-rank areogenetic classification of marginal (peripheral) populations of the Scotch pine, which was developed considering the degree of their disjunctivity (and the exchange of genes, m), the surface area (the effective number Ne) and "the microevolutionary age" (the time of residence in the landscape as determined from paleobotanical data). The obtained results present interest with respect to advancement of the STE, substantiation of the minimum size of genetic reservations, and applied measures on forest population selection and seed growing.Note. Abstracts are published in author's edition