Aspects of fitness of field and laboratory-reared populations of mosquitofish Gambusia affinis from a lake chronically contaminated with radioactive wastes were compared with control populations. The measured dose rate to the field population at the end of the study was 59 mrad/day, primarily received from γ irradiation from contaminated bottom sediments. Fecundity of the laboratory-reared irradiated and control groups did not differ significantly. This suggests that the higher fecundity of the irradiated field population previously reported by Blaylock is a response to high productivity in its eutrophic environment produced by nonradiological causes. The increased frequency of dead embryos relative to controls, which indicates the presence of radiation-induced recessive lethal mutations, has been maintained in the irradiated population since initial studies conducted in 1966. Significantly higher variance of certain morphological and physiological characteristics in laboratory-reared populations taken from the irradiated environment suggests increased heterozygosity resulting from the genetic load, coupled with semidominant effects of recessive lethals in the heterozygous condition. The field population is thriving, which is another indication that genetic load is not an index of population fitness.

This content is only available as a PDF.
You do not currently have access to this content.