Differential fitness of allelic isozymes in the marine gastropodsLittorina punctata andLittorina neritoides,exposed to the environmental stress of the combined effects of cadmium and mercury pollution

The present study tested the separate and the interactive pollution effects of cadmium and mercury on the electrophoretically detected allelic isozyme frequencies of the enzyme phosphoglucose isomerase for two species of littoral marine gastropods —Littorina punctata andL. neritoides — and the enzyme amino peptidase forL. neritoides. Our results indicate differential survivorship of allelic isozyme genotypes specific for each type of pollutant and for their interaction, as well as trends common to all pollutants. Theoretically the results reflect the adaptive nature of at least some allozymic genotypes in these marine gastropods and seem inconsistent with the neutral theory of allozyme polymorphisms. Practically, the results reinforce earlier conclusions that changes in the frequency of allelic isozymes may be used as a genetic monitor of pollution.     

Genetic variability in the marine gastropods Patella coerulea and Patella aspera: patterns and problems

Allozymic variation encoded by 15 gene loci was compared and contrasted in naturally coexisting populations of two marine gastropods (Patella coerulea and Patella aspera) collected along the rocky beaches of the Mediterranean sea of Israel in June, 1979. The genetic variability did not differ consistently or significantly between the two species, but in all the populations studied, P. aspera was more heterozygous than P. coerulea. These results are discussed in terms of the potential ecological factors affecting this genetic differentiation.     

Heavy metal selection of phosphoglucose isomerase allozymes in marine gastropods

The effects of zinc and copper pollution on the allozymic variation of phosphoglucose isomerase (Pgi) genotypes were tested in the Mediterranean marine gastropods Monodonta turbinata and M. turbiformis in 26 laboratory tests involving 2 081 adult individuals, with 545 survivors. Our results indicate differential survivorship of electrophoretical Pgi allozyme genotypes for both pollutants. Zinc pollution selected against the allozyme genotype SS in M. turbinata, whereas no differential survivorship was observed in M. turbiformis which lacks this allozyme. Copper pollution selected against the MM genotype in both species. These results are inconsistent with the neutral theory of allozyme polymorphisms and appear to reflect the adaptive nature of some Pgi genotypes in these marine gastropods.     

Mercury selection of allozymes in marine gastropods: Prediction and verification in nature revisited

Previous laboratory studies with mercury pollution revealed that the sensitive alleles are (S) for the phosphoglucose isomerase (PGI) locus in both Littorina punctata and L. neritoides and the allele (M+) for the amino peptidase (AP) locus in L. neritoides (Lavie and Nevo, 1986b). The present study tested the frequencies of these alleles at 8 sites along the Israeli Mediterranean shore. We found the frequencies of the sensitive alleles at the mercury polluted site at Akko to be lower than at all other seven sites. Therefore, we concluded that allozyme frequency distributions found in nature are consistent with survivorship patterns found in the laboratory. These results reinforce the suggestion (Nevo et al., 1980) that a monitoring system based on changes in population genetic structure is not only theoretically commendable but practically feasible in principle.