Increased genetic diversity of Viola tricolor L. (Violaceae) in metal-polluted environments

Changes in DNA sequences affecting cryptic intraspecific variability are very important mechanisms of plant microevolutionary processes, initiating species diversification. In polluted environments, intra- and interpopulation changes at the molecular level proceed rapidly and lead to the formation of new ecotypes in a relatively short time.We used ISSR PCR fingerprinting data to analyze the genetic diversity and genetic structure of seven populations of Viola tricolor: four growing on soil contaminated with heavy metals (Zn, Pb, Cd; waste heaps) and three from control soil. The populations from the polluted sites showed higher genetic polymorphism (%poly = 84%) and gene diversity (HT = 0.1709) than the control populations (%poly = 75% and HT = 0.1448). The number of private markers we detected within metallicolous (MET) populations was more than double that found within non-metallicolous (NON) populations (15 vs. 7). The STRUCTURE and UPGMA analyses showed clear genetic differences between the NON and MET populations.Based on broad analyses of the genetic parameters, we conclude that the effect of these polluted environments on the genetic diversity of the MET populations, separating them from the NON populations, is evidence of microevolutionary processes at species level, leading to species divergence and the emergence of local ecotypes better adapted to their different environments.

Research highlights
► The populations of Viola tricolor from polluted (MET) localities exhibited higher genetic differentiation (FST = 0.27) than those from unpolluted (NON) sites (FST = 0.16).
► The results of the STUCTURE and UPGMA analyses showed clear difference between NON and MET populations and their divergence with a high 89.6% bootstrap.
► Metal-polluted populations increase total genetic diversity of Viola tricolor.