Dwarf Siberian pine, Pinus pumula (Pall.) Rgl., a species of bird-dispersed stone pines, widespread from Baikal region in the west eastward up to Chukotsk Peninsula, Primorye, Sakhalin Isl. and Japan. The species is unique not only by its morphology (crawling or shrub-like living form, branches laying down under snow in winter), but also by its outstanding keystone role in subalpine and coastal ecosystems of East Siberia and the Far East. Genetic structure of dwarf Siberian pine was studied by means of allozyme loci Adh-1, Adh-2, Fdh, Fest-2, Gdh, Got-1, Got-2, Got-3, Idh-1, Lap-2, Lap-3, Mdh-1, Mdh-2, Mdh-3, Mdh-4, Mnr-1, Pepca, 6pgd-2, 6pgd-3, Pgi-1, Pgi-2, Pgm-1, Pgm-2, Skdh-1, Skdh-2, Sdh, Sod-2, Sod-3, and Sod-4. The level of intrapopulation genetic variability (per cent loci polymorphic above 90%, heterozygosity 25-28 % by different loci and data sets) is one of the highest among pines and all conifers). It can be supposed that such high even for conifers values represent adaptations for survival in subalpine conditions considered to be extreme for pines and forest trees in general, and may be associated with long life cycle assuring action of natural selection in favor of heterozygotes. Lack of substantial decreasing of variability measures in marginal stands evidences for stable reproduction of genetic structure and absence of pronounced effects of genetic drift. In the Baikal Lake region P. pumila gene pool may be also enriched due to introgression of genes from sympatric Siberian stone pine (Pinus sibirica Du Tour). The mode of this introgression is unidirectional, since in contrast to mass pollination of P. pumila by P. sibirica pollen in several regions, the reverse cross-specific pollination observed only as exclusively rare events. Genetic subdivision of Dwarf Siberia pine populations (FST=8-14% by different data sets) is higher than in most widespread pines, and different loci made unequal contribution to this differentiation. Some allozyme loci may play an adaptive role in particular ecological conditions. Increasing of allozyme heterozygosity with age of stands evidences in favor of adaptive significance of part of the observed allozyme polymorphism. In P. pumula a substantial deficiency of heterozygotes (as compared to Hardy – Weinberg proportions) is regularly observed at a stage of embryos of intact seeds while an equilibrium or excess of heterozygotes is typical for adult stands (thickets). Multi-dimensional analysis of genetic differentiation by allozyme loci revealed existence of several clusters of populations generally corresponding to geographic origin of the samples: (1) The Baikal Lake region; (2) Stanovoy range (the Baikal – Amur railway zone; and 3) Pacific coast and the islands (Sakhalin, Kurils and Japan). The island populations of the Far East are more differentiated than continental ones due to more complete isolation for longer time. The obtained data can be used in gene conservation programs for the species in current situation of global climate changes. The study is supported by the Programs of Fundamental Research (PFR) of the Presidium of Russian Academy of Sciences «Biological Diversity and the Gene Pools» and «The Origin of Biosphere and Evolution of Geo- and Biological Systems», by PFR of Division of Biological Sciences «Biological Resources of Russia», and by RFBR grant 07-04-00593-а.

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