Evaluating the relationship between diploid and tetraploid Vaccinium oxycoccos (Ericaceae) in eastern Canada

Abstract

Vaccinium oxycoccos s.l. is a complex of diploid and polyploid plants. The taxonomic relationship between the cytotypes is uncertain, with conflicting treatments in recent revisions. To clarify this situation, we investigated the relationships among ploidy, morphology, and genetic diversity in this group. We collected samples from a 1000 km transect in eastern Canada. We used flow cytometry to determine DNA ploidy, completed a morphometric analysis of flowering stems, and assessed genetic diversity using AFLPs. Diploids only occurred growing in mixed populations with tetraploids. There were statistically significant morphological differences between ploidies; however, tetraploid variation encompasses the diploid range for most characters. AFLP data demonstrate that the tetraploids have undergone genetic divergence since their formation, obscuring whether they are auto- or allo-polyploids. Our results agree with previous work using isozymes, which revealed genetic divergence of diploids and tetraploids in North America; and morphometry, which demonstrated clear distinctions between diploids and tetraploids in Europe. We found that diploids and tetraploids co-occur much more frequently than previously recognized, which may explain the conflicting treatment of this group by North American taxonomists. We recommend recognizing diploids and tetraploids as distinct species. The distribution of the two species in North America suggests two hypotheses regarding the successful establishment of the tetraploid: the tetraploids’ success is due to their capacity to exploit novel habitats outside the range of the diploid; or the tetraploid has in fact already out-competed the diploid in large areas of its former range, limiting the diploid to the far north. While we cannot rule out ongoing gene flow between diploids and tetraploids, it is likely a rare phenomenon in this group.