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

Abstract

AbstractGenetic 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‐2100 allele frequency was lower, the Gpi‐266 allele frequency increased, but the Gpi‐238 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.