Allozyme evidence for genetic autopolyploidy and high genetic diversity intetraploid cranberry, Vaccinium oxycoccos (Ericaceae)

Polyploidy has been important in the evolution of angiosperms and may signi ficantly affect population genetic diversity and structure. Nineteen isoenz yme loci were studied in diploid and tetraploid populations of Vaccinium ox ycoccos (Ericaceae), and the results are compared with data previously repo rted for the related V. macrocarpon. Diploid V. oxycoccos and V. macrocarpo n were readily discriminated based on their allozymic variation. No evidenc e for fixed heterozygosity was found in tetraploid V. oxycoccos. In contras t, all polymorphic loci exhibited both balanced and unbalanced heterozygote s, with some individuals exhibiting a pattern consistent with the presence of three alleles. These results support an autopolyploid origin for tetrapl oid V. oxycoccos. However, tetraploid V. oxycoccos possessed a suite of all eles not found in diploid V. oxycoccos; half of these alleles were shared w ith V. macrocarpon. This suggests that autotetraploid V. oxycoccos may have undergone hybridization with V. macrocarpon or that the autotetraploid ret ained the genetic variation present in an ancestral diploid species. Follow ing theoretical expectations, proportion of polymorphic loci, mean number o f alleles, and observed heterozygosity were significantly higher for the au totetraploid than for the diploid. Mean inbreeding (F-IS) was similar for d iploid and tetraploid V. oxycoccos. The latter exhibited population differe ntiation (F-ST) exceeding both diploid species.