Abstract

This study examines the genetic structure of subalpine fir along an elevation gradient in the Olympic Mountains, Washington. Starch gel electrophoresis was used to-resolve 15 isozyme loci from 9 populations on 3 mountains. First, we describe the genetic variation of these 9 populations in the Olympic Mountains, and compare these results to those of other tree species. Then we compare genetic differentiation (G(ST)) among populations to test if selective pressures alter genotypic frequencies in response to steep environmental gradients over the elevation range of this species.

Genetic variation is relatively uniform throughout most of the sites sampled (H-0 range = 0.103-0.139 in the eastern Olympic Mountains), with notably lower diversity observed at the western extent of subalpine fir's range (H-0 = 0.70 in the central Olympic Mountains). Lower diversity in the western Olympics may result from either founder effects as the species expanded its range from a glacial refugium, or from selection pressures on the loci considered. Genetic differentiation is greater among high elevation sites on different mountains, than among different elevation sites on the same mountain, or lower elevation sites on different mountains. Estimates of gene flow (N-m = 7.8) are high among all sites.