Multilocus genetic resistance and susceptibility to mercury and cadmium pollution in the marine gastropod, Cerithium scabridum

The separate and interactive pollution effects of cadmium and mercury on the allozyme frequencies of eight loci were tested in the marine gastropod Cerithium scabridum. When the influence of pollution was analyzed individually on each locus only 4 of the examined loci showed differential survivorship due to pollution. However, examining the genetic multilocus complex invoving the loci that on individual basis showed no differential mortality, we found a 4 locus complex resistant to mercury, a 4 locus complex resistant to cadmium and a 2 loci complex resistant to the combined mercury and cadmium pollution. Theoretically, these results suggest that even in cases where single locus analysis seemingly supports the neutral theory of allozyme polymorphisms the unit of selection may be an adaptive multilocus genetic complex. Practically, since each of the three pollutants displays different multilocus structures resistant or sensitive to pollution, such genetic complexes, and not only single genotypes, can be used as specific indicators of heavy metal pollution in the sea.