Population genetic variation, structure, and evolution in Engelmann spruce, white spruce, and their natural hybrid complex in Alberta

Genetic variation, structure, and evolution of 12 populations of putative E ngelmann spruce (Picea engelmanii Parry), white spruce (Picea glauca (Moenc h) Voss), and Engelmann - white spruce natural hybrids from the sympatric a reas and two populations of white spruce from the allopatric areas in Alber ta were examined using 23 allozyme loci coding for 13 enzymes in needles. A lthough most of the alleles were widespread, unique alleles were found in 9 of the 14 populations. No species-specific allele was observed. However, a llele frequency differences were observed between the putative Engelmann an d white spruce populations at a number of loci. Frequencies of 13 alleles s howed significant correlation with altitude, those of 11 alleles showed cor relation with latitude, and those of 3 alleles showed correlation with long itude. On average, 66.2% (99% criterion) of the loci were polymorphic, the number of alleles per locus was 1.88, the number of alleles per polymorphic locus was 2.88, and the observed and expected heterozygosities were 0.063 and 0.184, respectively. Genetic variability of allopatric white spruce, pu tative Engelmann, sympatric white spruce, and hybrid populations was quite comparable. The mean F-ST estimate was 0.123 for the total populations. Can onical discriminant functions separated four putative Engelmann spruce popu lations from the fifth putative Engelmann spruce population and from the al lopatric and sympatric white spruce and sympatric putative hybrid populatio ns. A cluster analysis from genetic distances generally separated allopatri c and sympatric white spruce populations from the putative Engelmann spruce and hybrid populations. A Wagner tree of the 14 populations produced two m ain branches; one branch consisting of two allopatric and two sympatric whi te spruce and one putative hybrid populations, and another branch consistin g of the remaining nine spruce populations representing putative Engelmann spruce, putative hybrids, and sympatric white spruce. Putative hybrids show ed lower distances to white spruce from the canonical discriminant analysis , whereas they showed lower distances to putative Engelmann spruce from the genetic distance analysis. High allozyme genetic identities between putati ve Engelmann and white spruce and allelic differentiation related to altitu de in Alberta suggest that Engelmann spruce could at best be considered as a subspecies of Picea glauca, with white spruce named as Picea glauca ssp. glauca and Engelmann spruce named as Picea glauca ssp. engelmannii.