Genetic Variation in Engelmann Spruce Associated With Variation in Soil Moisture

Abstract

The genetic structure of Engelmann spruce populations on adjacent wet and dry sites was studied using two enzyme polymorphisms, PGM and UDP. Although allelic frequencies for PGM did not differ between the sites, striking differences in genotypic proportions were found. The population in the wet environment did not differ from Hardy-Weinberg expectations, but in contrast, excesses of heterozygotes were found for both small and large trees on an adjacent dry hillside (F = −0.246 and F = −0.166). For UDP, young trees in both environments were in Hardy-Weinberg equilibrium, whereas adult trees at one of the two investigated localities had a deficiency (F = 0.218) under dry conditions and an excess of heterozygotes (F = −0.154) on a marsh. At the second locality, which receives considerably more precipitation, large trees had excesses of heterozygotes in both environments.

Proportions of dilocus genotypes on dry and wet sites were compared between the localities. The patterns of differentiation between wet and dry microsites were similar at the two sample localities.

These results suggest that natural selection in stands of Engelmann spruce varies with soil moisture.