A comparison of isozyme and quantitative genetic variation in Pinus contorta ssp. latifolia by FST.

We employed F-statistics to analyze quantitative and isozyme variation among five populations of Pinus contorta ssp. latifolia, a wind-pollinated outcrossing conifer with wide and continuous distribution in west North America. Estimates of population differentiation (FST) for six quantitative traits were compared with the overall estimate of the differentiation (F*ST) from 19 isozymes that tested neutral to examine whether similar evolutionary processes were involved in morphological and isozyme differentiation. While the FST estimates for specific gravity, stem diameter, stem height and branch length were significantly greater than the F*ST estimate, as judged from the 95% confidence intervals by bootstrapping, the FST estimates for branch angle and branch diameter were indistinguishable from the F*ST estimate. Differentiation in stem height and stem diameter might reflect the inherent adaptation of the populations for rapid growth to escape suppression by neighboring plants during establishment and to regional differences in photoperiod, precipitation and temperature. In contrast, divergences in wood specific gravity and branch length might be correlated responses to population differentiation in stem growth. Possible bias in the estimation of FST due to Hardy-Weinberg disequilibrium (FIS not equal to 0), linkage disequilibrium, maternal effects and nonadditive genetic effects was discussed with special reference to P. contorta ssp. latifolia.