Differential survivorship of allozyme genotypes in mosquitofish populations exposed to copper or cadmium

Abstract

Laboratory stocks of mosquitofish (Gambusia affinis) were acutely exposed to copper (0.16–0.24 mg/L) or cadmium (6.7–9.5 mg/L) for 48 h using a static renewal system. Allozyme genotypes at three polymorphic loci: phosphoglucomutase‒2 (PGM‒2), glucose phosphate isomerase‒2 (GPI‒2), and isocitrate dehydrogenase‒2 (ICD‒2) were resolved using a modified starch gel (13%) electrophoretic technique. Differential survivorship of allozyme genotypes was analyzed using a Wilcoxon matched pair signed‒rank test. Copper significantly (p < 0.05) decreased the overall survivorship of fish heterozygous at the GPI‒2 locus. The frequency of the (ab) genotype was significantly higher in the dead fraction of the test populations than in the surviving fraction. The frequencies of the (aa) genotype and the (a) allele at the ICD‒2 locus were significantly higher in female fish surviving exposure to copper than in nonsurviving females. The frequencies of the (bb) genotype and the (b) allele at the GPI‒2 locus were significantly higher in fish surviving exposure to cadmium than in nonsurvivors. These results indicate that some electrophoretically detectable allozymes are more sensitive than others to the toxic effects of environmental pollutants. This suggests that the genetic structure of natural populations should be considered for use as a biological monitor of environmental pollution.

Biological monitoring of wild thicklip grey mullet (Chelon labrosus), golden grey mullet (Liza aurata), thinlip mullet (Liza ramada) and flathead mullet (Mugil cephalus) (Pisces: Mugilidae) from different Adriatic sites: meristic counts and skeletal anomalies

“…So, while the other mullets fed mainly on filtering organisms, L. aurata seems to be obliged by mullet fry competition to eat organic detritus and adult insects, and thus bio-accumulates fewer toxic substances. Another possible explanation for the low malformation load observed in L. aurata batches could be a loss of genetic variability in this species through the elimination of sensitive individuals and alleles due to the increased selective pressure resulting from contamination stress Nevo, 1982, 1988;Diamond et al, 1989): several laboratory and field studies have shown that an acquired resistance to polluted environments can be obtained at the expense of a diminution in genetic variability (Chagnon and Guttman, 1989;Klerks and Levinton, 1989;Cognetti, 1991;Heagler et al, 1993;Keklak et al, 1994). Furthermore, the genetic adaptation of a fish population under chronic stress and the development of genetic resistance in fish used as environmental sentinels was found to have the capacity to reduce the sensitivity and efficacy of monitoring programs (Kirchhoff et al, 1999).…”

Genetic Adaptability of Sarotherodon Melanotheron to Polycyclic Aromatic Hydrocarbons (PAHs) in Some Senegal Hydrosystems

“…In addition, according to Kopp et al (1994), genotypes that survive exposure to pollution or salinity may be the most tolerant individuals to environmental stress. in addition, Chagnon & Guttman (1989) and Gillespie & Guttman (1989) mention that the degree of genetic variation maintained by a population may be evidence of its ability to survive in future environmental alterations by moderating or modulating the stressful effects of pollutants and providing the population with the necessary genetic plasticity.…”

Loss of genetic diversity in Harpacticoida near offshore platforms

“…The eventual result of this differential selection would be that the stressed Near population would genetically resemble a subset of the relatively less stressed Far population. Losses in genetic variation associated with contamination or habitat loss have been demonstrated for a variety of aquatic organisms, including fish (Changon and Guttman 1989;Murdoch and Hebert 1994), polychaetes Grassle 1974, 1977), and even seagrasses (Alberte et al 1994). The results of the present study are also consistent with such a hypothesis.…”