Genetic and demographic responses of mosquitofish (Gambusia holbrooki) populations exposed to mercury for multiple generations

Abstract

Abstract-Genetic and demographic responses of mosquitofish were examined after multiple generations of exposure to mercury. Previous studies of acute lethal exposures of mosquitofish to either mercury or arsenic demonstrated a consistent correlation between time to death and genotype at the glucosephosphate isomerase-2 (Gpi-2) locus. A mesocosm study involving mosquitofish populations exposed to mercury for 111 d showed significant female sexual selection and fecundity selection at the Gpi-2 locus. Here the mesocosm study was extended to populations exposed to mercury for several (approx. four) generations. After 2 years, control and mercury-exposed populations met Hardy-Weinberg expectations and showed no evidence of genetic bottlenecks. The mean number of heterozygous loci did not differ significantly between the mercury-exposed and control populations. Significant differences in allele frequencies at the Gpi-2 locus were observed between the mercury-exposed and control populations. Relative to the initial and control allele frequencies, the Gpi-2 100 allele frequency was lower, the Gpi-2 66 allele frequency increased, but the Gpi-2 38 allele frequency did not change in mercury-exposed populations. No significant differences were found in standard length, weight, sex ratio, or age class ratio between the control and mercury-exposed populations. Allele frequency changes at the Gpi-2 locus suggest population-level response to chronic mercury exposure. Changes in allele frequency may be useful as indicators of population response to contaminants, provided that the population in question is well understood.

Genetic variation, inbreeding and chemical exposure—combined effects in wildlife and critical considerations for ecotoxicology

“…At the same time, there is also evidence that individuals that are more genetically diverse (greater heterozygosity and lower 'internal relatedness') within populations derived from exposure areas are more able to tolerate higher levels of exposure than those from less contaminated areas (Bourret et al 2008). Tolerance to mercury exposure in mosquitofish (Gambusia affinis) has been related specifically to genetic polymorphism at the glucose isomerase locus, and the distribution of genotypes in natural and artificial contaminated environments were shown to be consistent with this (Heagler et al 1993;Tatara et al 1999). …”

Spatial segregation of Darwinula stevensoni (Crustacea: Ostracoda) genotypes in lentic and lotic habitats of Northern Italy

“…In Daphnia pulex Weider (1985) and Weider & Hebert (1987) described microgeographic genetic heterogeneity due to differences in low-oxygen and salinity tolerance among different clones. Moreover, different adaptation value of different Gpi genotypes has been found in several organisms (Patarnello & Battaglia 1992;Gaffney 1994;Beaumont & Toro 1996;Tatara et al 1999). In Daphnia pulicaria an increase in the frequency of homozygotes at Gpi locus was associated with decreasing dissolved oxygen (Ross et al 1996).…”

Biomarkers, Bioindicators, and Ecological Risk Assessment—A Brief Review and Evaluation

“…In another study involving mosquito fish (G. holbrooki), Tatara et al (1999) attempted to correlate changes in allele frequencies for glucosephosphate isomerase (Gpi) allozymes with reproductive impacts measured over several generations of fish exposure to mercury in laboratory mesocosm experiments. This study produced statistically significant shifts in allele frequencies between control and treatment mesocosms.…”