Genetic adaptation of plants in the subarctic environment

The general feature when the northern limit of distribution of spruce Picea abies L. and meadow fescue Festuca pratensis Huds. is approached, is that individuals tend to become more homozygous at their gene loci, but different alleles are still retained in the populations. This is due to the fact that individuals within populations differ strongly in their genotypes – i.e. not one but many different genotypes are retained also at the species margin. This polymorphism in the marginal populations is probably due to some form of frequency dependent selection. Clines in gene frequency are much more pronounced in spruce than in meadow fescue probably due to a much higher environmental autocorrelation in the spruce case with its very long generation interval.