Contrasting patterns of genetic divergence in twosympatric pseudo-metallophytes: Rumex acetosa L.and Commelina communis L.

BACKGROUND:Patterns of genetic divergence between populations of facultative metallophytes have been investigated extensively. However, most previous investigations have focused on a single plant species making it unclear if genetic divergence shows common patterns or, conversely, is species-specific. The herbs Rumex acetosa L. and Commelina communis L. are two pseudo-metallophytes thriving in both normal and cupriferous soils along the middle and lower reaches of the Yangtze River in China. Their non-metallicolous and metallicolous populations are often sympatric thus providing an ideal opportunity for comparative estimation of genetic structures and divergence under the selective pressure derived from copper toxicity.RESULTS:In the present study, patterns of genetic divergence of R. acetosa and C. communis, including metal tolerance, genetic structure and genetic relationships between populations, were investigated and compared using hydroponic experiments, AFLP, ISSR and chloroplast genetic markers. Our results show a significant reduction in genetic diversity in metallicolous populations of C. communis but not in R. acetosa. Moreover, genetic differentiation is less in R. acetosa than in C. communis, the latter species also shows a clustering of its metallicolous populations.CONCLUSIONS:We propose that the genetic divergences apparent in R. acetosa and C. communis, and the contrasting responses of the two species to copper contamination, might be attributed to the differences in their intrinsic physiological and ecological properties. No simple and generalised conclusions on genetic divergence in pseudo-metallophytes can thus be drawn.