Genetic and demographic responses of mercury-exposed mosquitofish (Gambusia holbrooki) populations: temporal stability and reproductive components of fitness.
Two previous mesocosm studies showed changes in glucosephosphate isomerase-2 (Gpi-2) allele frequencies in mosquitofish populations exposed to mercury for 111 d or two years. A previous selection component analysis of single-generation populations exposed for 111 d to 18 microg/L Hg suggested that female sexual selection and fecundity selection could contribute to changes in Gpi-2 allele frequencies. The present multigeneration study was conducted to determine the stability of Gpi-2 allele frequencies over four years of mercury exposure, measure the reproductive fitness of Gpi-2 genotypes inhabiting control and mercury-contaminated mesocosms to determine a mechanism explaining changes in Gpi-2 allele frequencies, investigate differences in the demographic characteristics of mercury-exposed and control populations, and investigate the water quality of the mesocosms to determine if variables other than mercury show concordant patterns among mesocosms. Differences in Gpi-2 allele frequencies between control and mercury-exposed populations were stable over four years (approximately eight generations) of mercury exposure. Mercury-exposed female mosquitofish had a lower probability of being gravid than control females (p = 0.001). Mercury-exposed females also had lower fecundity (total number of eggs and embryos) than control females (p = 0.036). Unlike the results of the more intense mercury exposures in the single generation study, no strong evidence was found that Gpi-2 genotype influenced fecundity or the probability of being gravid in both control and mercury-exposed females. The quantification of fitness components is difficult but has the potential to enhance our understanding of how toxicants alter allele frequencies in exposed populations.
Tatara
Christopher Paul
CP
National Marine Fisheries Service, Manchester Research Station, Washington 98353, USA. chris.p.tatara@noaa.gov
Mulvey
Margaret
M
Newman
Michael C
MC
D000818:Animals; D003532:Cyprinodontiformes / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D005260:Female; D005298:Fertility / Q000187:drug effects* / Q000235:genetics; D005787:Gene Frequency / Q000235:genetics*; D005838:Genotype; D005956:Glucose-6-Phosphate Isomerase / Q000235:genetics; D008297:Male; D008628:Mercury / Q000493:pharmacokinetics / Q000633:toxicity*; D012641:Selection, Genetic; D014874:Water Pollutants, Chemical / Q000493:pharmacokinetics / Q000633:toxicity*
D014874:Water Pollutants, Chemical; D005956:Glucose-6-Phosphate Isomerase; D008628:Mercury