Association between mitochondrial DNA and morphological evolution in Canada geese

Summary Variation within and between eight subspecies of Canada geese was assessed by restriction fragment analysis of mitochondrial DNA (mtDNA), electrophoresis of proteins encoded by nuclear DNA, and the morphometric analysis of skeletons. Estimates of mtDNA sequence divergence between Canada goose subspecies ranged from 0.04 to 2.54%. Pairwise comparisons of the three data matrices revealed that only mtDNA variation and body size are significantly correlated. Subspecies with northern breeding grounds are small-bodied and display small variations of one mtDNA clone, whereas those breeding further south are largebodied and show small differences in another mtDNA clone. Canada geese exhibit strong geographic differentiation with respect to mtDNA sequence, but weak structuring in protein-encoding nuclear DNA. This finding can be explained by a lower level of gene flow for the mitochondrial genome than for the nuclear genome, which in turn emanates from the maternal inheritance of mtDNA and male-biased dispersal in Canada geese. Despite male-mediated flow of nuclear genes, strong morphometric differentiation persists among Canada geese subspecies.