• General-purpose genotype;
  • genotype–environment interaction;
  • parthenogenesis;
  • phenotypic variability

1. Parthenogenetic species are often geographically more widely distributed than their sexual relatives. This success in colonizing can be explained either by dispersal of one or a few clones of wide physiological tolerance or by the distribution of many locally adapted clones.

2. Here we compare the influence of salinity on reproductive output, feeding rate, growth rate and size at birth between two genotypes of Potamopyrgus antipodarum to address the questions (i) Do these traits vary in response to changing salinity? (ii) Does the response to a salinity gradient differ between genotypes? (iii) Can the patterns of variation, in relation to salinity, contribute to explaining the geographical distribution of P. antipodarum in Europe?

3. Our results demonstrate that genetic variation among populations of P. antipodarum is reflected in differences in life-history traits and feeding rates in response to a salinity gradient. The phenotypic differences between the genotypes are consistent with the geographical distribution of P. antipodarum clones in Europe.

4. The overall response to salinity of both genotypes of P. antipodarum suggests an optimum at ≈ 5‰ S; however, both genotypes showed a broad salinity tolerance and were able to feed, grow and reproduce over the entire salinity range tested (0–15‰ S). The broad environmental tolerance of both genotypes together with their widespread geographical distribution across Europe provide evidence consistent with the general-purpose genotype hypothesis.