Differential Survivorship of Allozyme Genotypes in Mosquitofish Populations Exposed to Copper or Cadmium

Abstract

Laboratory stocks of mosquitofish (Cumbusia uffinis) 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.

Salinity-related fitness differences amongst GPI genotypes in the mosquitofish Gambusia holbrooki (Poeciliidae: Teleostei)

“…At maturity female Gambusia are considerably larger than males (Stearns & Sage, 1980;Diamond et al, 1989) suggesting observed sexratio differences may reflect a size/salinity relationship, larger fish having increased tolerance to high saline conditions, or that sexes differ in their sensitivity to increasing salinity. A similar relationship has been observed between body size and susceptibility to various heavy metal pollutants (Diamond et al 1989;Chagnon & Guttman, 1989).…”

“…In vitro functional differences between GPI molecules have been observed previously in response to temperature variation (Watt, 1983;Watt, Cassin & Swan, 1983), and heavy metal stress (Nevo et al, 1981;Lavie & Nevo, 1982, 1986Gillespie & Guttman, 1989;Chagnon & Guttman, 1989;Diamond et al, 1989). For both temperature and heavy metals it is hypothesized that selection directly affects GPI enzyme activity (Watt, 1983;Watt et al, 1983;Nevo, Lavie & Ben-Shlomo, 1983;Chagnon & Guttman, 1989). A lack of correlation between salinity and GPI allele frequencies in the mussel M. edulis (Koehn et al 1976) suggests GPI enzyme eficiency is not directly affected by high salt concentrations.…”

“…Therefore, increased mortality of fish from the present study may relate to a higher proportion of either smaller fish, and/or susceptible alleles in the populations sampled. A similar relationship between body size, allelic frequency and susceptibility to various heavy metals has also been observed in G. ajinis (Diamond el al., 1989;Chagnon & Guttman, 1989).…”

Survival of copper-exposed juvenile fathead minnows (Pimephales promelas) differs among allozyme genotypes

“…Fish weight and five enzyme loci (GPI-I*, GPI-2*, IDHP-I *, MDH-2*, and PGM*) were related to TTD during the copper exposure. Several studies [7][8][9]231 have also found correlations between genotypes at specific loci and TTD. Variants at an enzyme locus, allozymes, have the same functional properties, but a different molecular structure.…”

“…Researchers [6,7,24,35] have suggested that genetic structure could serve as an effective biological monitor (biomarker). Direct monitoring of the genetic structure of a population has the advantage of being able to detect shortand long-term effects of environmental stress on a population prior to its extinction.…”