We tcsted in the laboratory three pairs of species belonging to three genera and families of marine gastropods, Monodonto turbinata, M . turbifrrnis (Trochidae), Litiorina punctata, L. neritoides (Littorinidae), Cerithiurn scabridurn, C. rupestre (Cerithiidae), for resistance to diverse inorganic (heavy metals and NaCI) and organic (detergents and crude oil) pollutants. Each pair consisted of one narrow-niche species with low genetic diversity and one broad-niche species with higher genetic diversity. Evidence is presented that in all three cases the species with a higher level of genetic diversity was more resistant to all pollutants than its counterpart. These results suggest that fitness is positively correlated with heterozygosity and support the niche-width-variation hypothesis in regard to pollutants. The results also have practical implications for the identification of optimum marine species as genetic monitors of pollution.

The geographic distributions of mercury-tolerant allozyme genotypes of the enzyme phosphoglucomutase in the shrimp Palaemon elegans and the enzyme phosphoglucose isomerase in the marine gastropod Monodonta turbinata were compared in a mercury-polluted site versus several unpolluted sites on the Israeli coast of the Mediterranean sea. We conclude that in both phosphoglucomutase and phosphoglucose isomerase, the level of the mercury-tolerant allozyme genotypes was higher in the polluted as compared with the unpolluted sites. These results suggest that mercury selection is operating in nature on allozyme genotypes of these marine organisms along patterns comparable with those found previously in laboratory experiments. We suggest that the enzymes studied here display an adaptive pattern in polluted environments. Therefore, they may be used as potential indicators and monitors of marine pollution.The evolutionary significance of allozyme polymorphisms was tested by gene-frequency analyses in barnacles under thermal (1) and chemical (2) pollution in the sea. Later, we tested by controlled laboratory experiments the effects of heavy metal pollutants (Hg, Zn, Cd, Pb, Cu) on allozymic frequencies of 15 phosphoglucomutase, PGM, genotypes in the shrimp Palaemon elegans (3, 4) and on 5 phosphoglucose isomerase, PGI, genotypes in two closely related species of marine gastropods, Monodonta turbinata and Monodonta turbiformis (4, 5). All these studies, but most importantly the controlled laboratory tests, indicated significant differential survivorship among allozyme genotypes. The differential viability of allozyme genotypes is probably associated with the different degree of heavy metal inhibition, uniquely related to each specific pollutant (4). Thus, we conclude that these results reflect an adaptive nature of the allozyme polymorphisms tested and suggest that their differential sensitivity to the quality and quantity of specific pollutants can be used as a potential genetic indicator and monitor of pollution (3)(4)(5). We missed, however, the crucial link between laboratory and nature. Can the laboratory results be confirmed in the sea?We focus our testing on mercury pollution because along the Israeli Mediterranean Coast, the Akko site is highly polluted due to industrial discharge, whereas elsewhere along the coast, waters are relatively mercury free. Here we present evidence derived from nature, verifying our laboratory predictions. The most mercury-tolerant allozyme genotypes, the MS heterozygote in Palaemon PGM and the MM homozygote in Monodonta PGI, were found at highest frequency near the mercury-polluted Akko site, as predicted from laboratory experimentation. MATERIALS AND METHODSWe tested electrophoretically PGM variation in 341 individuals from seven populations of the shrimp P. elegans and PGI variation in 192 individuals from three populations of the marine gastropod M. turbinata. We compared in both species allozyme frequencies in the nonpolluted versus the polluted Akko site. The electrophoretic pr...

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Assuming that dispersal from optimal environments evolved as a colonizing device, it is expected that dispersants will possess reproductive characteristics enhancing the probability of successful colonization. Two approaches were used to clarify the relationship between dispersal behavior and two major components of reproductive fitness (developmental time and fecundity) in the flour beetle Tribolium castaneum: (a) comparison between two lines, one selected for low dispersal and the other selected for high dispersal, for several components of reproductive fitness, and (b) calculation of the correlation coefficients between each fitness component investigated and dispersal behavior. The results obtained by both approaches indicate, as expected, shorter developmental time and higher fecundity for dispersants than for nondispersants.

Flour beetles of the genus Tribolium are suitable for the study of dispersal. In an attempt to gain an understanding of the genetic basis of this trait in T. castaneum, a two-way selection experiment was carried out, for 11 successive generations, in a stock derived from an Israeli wild population. When dispersants were defined as beetles that disperse more than once in several attempts, separation between the lines was achieved after one generation of selection. The difference between the lines remained more or less constant in subsequent generations of selection, and did not disappear when selection was relaxed. Reciprocal crosses between the lines suggest that the tendency to disperse is determined by the genotype at a single, sex-linked locus. The allele for dispersal is dominant. Males tend to disperse more readily than females of equivalent genotypes.

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