Isozyme variation within the Fraser fir population on Mt. Rogers, Virginia

Abstract

The Fraser fir (Abies fraseri (Pursh) Poir.) on Mt. Rogers is an isolated relic population and part of the southern Appalachian spruce-fir ecosystem. The population has, so far, been able to withstand the impacts of insect infestation and the possible influence of atmospheric deposition factors which may be causing mortality in other regions of the southern Appalachians. It was hypothesized that population vigor may be due to a unique genetic structure. The objective of this study was to determine the amount of genetic diversity within this population and to relate observed diversity to environmental variables.

To quantify the genetic structure 304 trees from 35 plots were genotyped for 13 isozyme loci. Four loci were polymorphic using the 95% criterion. At a fifth locus there were two rare alleles with a combined frequency of approximately 3%. Range wide studies of eastern fir species have shown that other populations are more diverse.

There were no significant differences in gene frequencies among three arbitrarily defined subpopulations or among the 35 plots. There were no significant correlations between any environmental characters and isozyme frequencies.

There was a significant difference among subpopulations for seed weight and germination value as well as a slight, yet significant, correlation between seed weight and elevation, germination value and elevation, and germination value and aspect. Spatial autocorrelation analysis, Wright's F-statistics, Nei's genetic distances, and Gregorius' "𝜹" index all indicated little or no substructuring of the population. It is suggested that a population bottleneck (a drastic reduction of population numbers), which may have occurred following the last glaciation, is the cause for the relatively low genetic diversity found in the population. The lack of substructure is likely due to extensive gene flow.