Allozyme and Leaf Morphological Variation of Eastern Cottonwood at the Northern Limits of Its Range in Ontario

Abstract

Allozyme variation of 84 trees of eastern cottonwood (Populus deltoides Bartr. ex. Marsh. var. deltoides) from 9 populations in Ontario was studied at 33 loci coding for 11 enzyme systems in root tips. Morphological variation of 7 leaf characters was studied for 57 trees. On average, 42.4% of the loci per population was polymorphic, the number of alleles per locus was 1.7, and the observed heterozygosity was 0.063. The overall mean for genetic distances among populations was 0.007. Principal component analysis (PCA) of allozyme data separated the populations into five groups with a slight separation of eastern and western populations. Leaf characters showed significant variation among (P ≤ 0.003) and with one exception within (P ≤ 0.027) populations. Vein numbers showed significant correlation with longitude (r = 0.81, P < 0.009) and latitude (r = -0.69, P < 0.05). None of the other leaf characters was related to latitude and longitude. PCA of leaf characters separated the Long Point population from the others. Significant (P < 0.01) Mahalanobis distances for leaf characters were observed among populations. There was no concordance between the patterns of variation and differentiation based on allozymes and morphological parameters. The results suggest moderate allozyme and high leaf morphological variation in eastern cottonwood in Ontario. For. Sci. 37(2):688-702.