Genetic diversity and population structure of Piceaglauca on an altitudinal gradient in interior Alaska

Abstract

Allozyme variation at 13 loci for 11 enzyme systems was studied in four white spruce (Piceaglauca (Moench) Voss) populations extending from a floodplain at 120 m above sea level to the altitudinal tree limit at 750 m above sea level in interior Alaska. Although 97% of the total genetic diversity was among trees within stands and 1% was among stands within populations, frequencies of several allozymes and allozyme genotypes were significantly different (P < 0.05) among populations. Ninety-two percent of the loci were polymorphic. Total heterozygosity was 0.276. Heterozygosity and allozyme frequencies were not related to altitude. The population at the tree limit was as genetically diverse as populations at low elevations [Formula: see text] and contained four of seven rare alleles observed in all populations. These observations suggested that white spruce is genetically diverse in interior Alaska and the tree-limit population will continue to colonize new habitats. Genetic distance was not related to altitude and geographic distance and was less between the tree-limit and upper slope populations than among other populations A detectable gene substitution rate was estimated at 10−6 per year. Populations on the upper slope and at the tree limit may have diverged about 2500 years ago and reached tree-limit altitudes only recently. Populations at low altitudes may have diverged during early Holocene white spruce expansion. We concluded that white spruce is genetically diverse in a small geographic area in interior Alaska. Results suggested that local white spruce populations should be regenerated from indigenous seed and that provenance research is needed to support afforestation programs.