Low impact of metal pollution on genetic variation in the earthworm Dendrobaena octaedra measured by allozymes

SummaryNumerous previous studies have reported significant effects of metal pollution on earthworm populations. In this study we investigated the effects of heavy metal pollution on the genetic diversity of populations of the earthworm Dendrobaena octaedra sampled along well-defined metal gradients at two different locations. One hundred and sixty-two specimens, representing six locations along a gradient of heavy metal pollution in Poland (Olkusz), and 193 specimens, representing seven locations along a similar gradient in Sweden (Gusum), were collected. All worms were analysed for 10 isozymes. The fraction of unique clones was 0.61 for the Polish specimens and 0.84 for the Swedish. The number of individuals sharing the same clonal type was low both within the local populations and between populations in the different locations. Only three clones were shared by the two countries for a total of eight individuals. No homogeneity among the samples within each country was observed. The variation in two enzymes, esterase and superoxide dismutase, was weakly correlated to a metal toxicity index calculated using EC50 values for earthworms. Such a correlation was neither observed for the fraction of unique clones nor for clonal diversity. The results suggest that genetic diversity of D. octaedra populations is only weakly affected by pollution with heavy metals despite clear effects on population densities.