Genetic and Demographic Responses of Mosquitofish (Gambusia Holbrooki) Populations Exposed to Mercury for Multiple Generations

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 Diversity of the Major Histocompatibility Complex of Cotton Rats (Sigmodon Hispidus) Inhabiting an Oil Refinery Complex

“…Such changes have the potential to affect both the short-term well-being and longterm evolutionary fate of local populations. Results of studies examining protein loci [3][4][5][6][7][8] and randomly amplified polymorphic DNA (RAPD) [8][9][10][11][12] suggest that selection is operating on populations stressed by natural events and chemical contaminants. However, the relationship between genetic biomarkers and physiological response to environmental contamination typically is not known.…”

Genetic and demographic responses of mercury‐exposed mosquitofish (Gambusia holbrooki) populations: Temporal stability and reproductive components of fitness

“…A subsample (n ϭ 134) of the mosquitofish collected from Risher Pond was used to determine initial allele frequencies for seven polymorphic allozyme loci in 1994. The mesocosm populations were sampled heavily in 1996 for our previous study [8], with caution taken not to harvest at levels that might be detrimental to population viability. The populations were monitored for the presence of gravid female fish during the late spring and early summer of 1998.…”

“…Our previous study [8] detected changes in the genetic composition of mosquitofish populations at the Gpi-2 locus over the course of a two-year, low-level mercury exposure in mesocosms. The frequency of the Gpi-2 100 allele decreased, while the frequency of the Gpi-2 66 allele increased, in mercury-exposed populations relative to the initial and control allele frequencies.…”

“…The use of allozymes as genetic markers for detecting population-level effects of toxicant exposure is gaining popularity in ecotoxicology. Changes in genotype or allele frequencies have been correlated with environmental contamination in several studies of natural and experimental populations [1][2][3][4][5][6][7][8]. Populations inhabiting contaminated environments frequently have different genotype and allele frequencies than reference or control populations.…”

“…Because allozymes are being used increasingly for biomonitoring [12,13], it is important to carefully assess their suitability for that purpose. Several studies have documented changes in the genetic composition of populations exposed to contaminants but have not investigated the stability of the changes over time through repeated sampling [1][2][3][4][5][6][7][8]. For allozymes to be of practical use, the contaminant-correlated changes in genotype and allele frequencies should not be ephemeral.…”