Allozyme Variation in the Athabasca Sand Dune Endemic, Salix silicicola, and the Closely Related Widespread Species, S. alaxensis

Genetic variation was estimated by starch gel electrophoretic resolution of 17 putative isozyme loci in eight populations of the Athabasca sand dune endemic Salix silicicola from northern Saskatchewan, Canada, and five populations of its putative progenitor species, Salix alaxensis, from northern British Columbia, Canada. Thirty-seven alleles were detected at 10 polymorphic loci. Six loci were polymorphic in the endemic species and 10 loci were polymorphic in the presumed progenitor species. Salix silicicola had one unique allele, whereas Salix alaxensis had 17 alleles not found in the former species. Populations of the endemic contained fewer alleles per locus (1.30 vs. 1.85), fewer alleles per polymorphic locus (2.05 vs. 2.85), lower percent polymorphic loci (28.7 vs. 45.9) and lower genetic diversity (0.073 vs. 0.195) than did populations of the putative progenitor species. Genetic identities within species averaged 0.981 for Salix silicicola and 0.973 for Salix alaxensis and between species identities ranged from 0.902 to 0.963 with a mean of 0.932. At polymorphic loci, total gene diversity was relatively high in Salix silicicola (HT = 0.305) and Salix alaxensis (HT = 0.384). Population differentiation was relatively low in both species (Salix silicicola, GST = 0.159; Salix alaxensis, GST = 0.097) whereas estimates of gene flow based on GST values were moderate (Salix silicicola, Nm, = 1.32; Salix alaxensis, Nm, = 2.33), consistent with these trees' dioecious breeding system and wind-dispersed seeds.