Batia Lavie

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.

Genetic selection of homozygote allozyme genotypes in marine gastropods exposed to cadmium pollution

Five species of marine gastropods (Monodonta turbinata, M. turbiformis, Cerithium scabridum, Littorina punctata and L. neritoides) were exposed to cadmium in the laboratory. The enzyme phosphoglucose isomerase (PGI) tested electrophoretically showed for all five species a statistically significant higher proportion of heterozygotes among the dead animals than among the survivors in the range of concentration tested. This pattern seems to have been established by natural selection. Further, it could be used in developing biological monitors of present and past cadmium pollution based on the genetic response of natural populations to this specific pollutant.

The interactive effects of cadmium and mercury pollution on allozyme polymorphisms in the marine gastropod Cerithium scabridum

Abstract The separate and interactive pollution effects of cadmium and mercury on the electrophoretically detected allozyme frequencies of eight gene loci were tested in the marine gastropod Cerithium scabridum. Our results indicate differential survivorship of allozyme genotypes specific for each type of pollutants and for their interaction. These results reflect the adaptive nature of at least some of the allozymic genotypes in this marine gastropod and seem inconsistent with the neutral theory of allozyme polymorphisms. Furthermore, these findings suggest that the interactive pollution of cadmium and mercury acts as a specific pollutant. Therfore, differential tolerance to pollution can be used as detector of heavy metal pollution in the sea also when more than one pollutant is involved.

Differential viability of phosphoglucose isomerase allozyme genotypes of marine snails in nonionic detergent and crude oil-surfactant mixtures

The effects of a nonionic detergent and of crude oil-detergent mixtures in aqueous solutions on the allozyme frequencies of phosphoglucose isomerase (Pgi) genotypes were tested in the Mediterranean marine gastropods Monodonta turbinata and M. turbiformis. Our results indicate differential survivorship of electrophoretical Pgi allozyme genotypes for both detergent alone and for crude oil-detergent mixtures. These results reflect the adaptive nature of some Pgi genotypes in these marine gastropods and seem inconsistent with the neutral theory of allozyme polymorphisms. Furthermore, these findings suggest that allozyme variants demonstrate a differential tolerance to these organic pollutants and can, therefore, be used as detectors of organic pollutants in the sea.

The niche-width variation hypothesis revisited: genetic diversity in the marine gastropods Littorina punctata (Gmelin) and L. neritoides (L.)

Abstract Allozymic variation encoded by 17 gene loci was compared and contrasted in naturally coexisting populations of two marine gastropods collected along the rocky beach of the Mediterranean coast in Israel. Littorina neritoides (L.) showed considerably more genetic diversity than L. punctata (Gmelin). The results support the niche-width variation hypothesis as L. neritoides may be considered as having a broader ecological niche than L. punctata . Higher heterozygosity appears to be advantageous in a more heterogeneous environment.

Natural selection for resistance to mercury pollution

The survival under conditions of mercury pollution of two natural populations of the marine gastropodCerithium rupestre, derived from mercury-polluted and mercury-free sites, was tested in the laboratory. The results indicate a significantly higher survival rate for animals derived from the mercury-polluted site, in each of six repetitive experiments. We conclude that mercury resistance in marine organisms is reinforced in mercury polluted sites, presumably by natural selection for increased resistance. The evolution of metal tolerance in marine organisms may be as fast as that of metal tolerance in plants and the evolution of industrial melanisms in moths.

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.

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

Abstract 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.

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.

Niche adaptation in two marine gastropods, Monodonta turbiformis and M. turbinata

Abstract Several behavioural, physiological and morphological parameters were studied in two marine gastropods to better define niche differences between the species. M. turbiformis is adapted to a broader more variable niche where as M. turbinata has more stringent niche requirements. This study demonstrated that M. turbinata as compared with M. turbiformis has: a) greater foot muscle strength, b) shorter more squat shell form, c) greater body weight per shell weight and d) greater foot size per body weight. M. turbiformis has a) greater resistance to desiccation and low temperature and b) a more slender shell form. Qualitatively, M. turbiformis appears less effected by elevated temperatures to 40° C. In the laboratory, M. turbinata is more sensitive to crowding. In the field, M. turbinata is found principally in high energy situations with respect to surf action or water flow on or over rocks to which it is attached. On the other hand, M. turbiformis is exclusively found in relatively quiet, shallow wat...