Metal resistance in earthworms; genetic adaptation or physiological acclimation

We hypothesised that long-term earthworm colonizers of heavily polluted met alliferous soils in the vicinity of abandoned Pb/Zn-mines have; responded g enetically to the selection pressures imposed upon them by the edaphic cont aminants such that they have evolved into locally differentiated, metal-ada pted, ecotypic populations. The hypothesis was tested by measuring and comp aring the growth rates up to 36 weeks post-hatching of the F1 generation of fspring of adult Lumbricus rubellus collected from four distinct sites: a c lean calcareous reference site; a clean acidic reference site; a calcareous mine site; an acidic mine site. Four subsets of each of the four Fl popula tions separated, with one subset grown on food-supplemented soil of parenta l origin, and one subset allocated to each of the other 'experimental' fiel d-collected soils. Growth did not yield compelling evidence of metal adapta tion in either of the two mine-derived F1s. Different organism groups explo it different life-history strategies to cope with environmental stress. Thi s tenet justifies our intention to extend our observations on F1s beyond 36 weeks to encompass reproduction endpoints. Two further Findings were notwo rthy: fa) soil pH is a major determinant of juvenile earthworm growth; fb) plotting the growth data for individual worms representing the F1 offspring of parents inhabiting the acidic mine soil revealed two distinct phenotype clusters, one with a significantly faster growth rate than the other.