GENETIC ECOTOXICOLOGY .2. POPULATION GENETIC-STRUCTURE IN MOSQUITOFISH EXPOSED IN-SITU TO RADIONUCLIDES

In 1977, approximately 250 mosquitofish (Gambusia affinis) from a rela tively uncontaminated site (Crystal Springs) were transplanted into a small pond on the Department of Energy Oak Ridge Reservation which is heavily contaminated with radionuclides (Pond 3513). Starting in 1992, DNA polymorphism was evaluated using the RAPD (Randomly Amplified Pol ymorphic DNA) and allozyme genotype techniques to determine if genetic differentiation had occurred between the two populations. Fish from a second radionuclide-contaminated population (White Oak Lake) and anot her unrelated non-contaminated population (Wolf Creek) were also exami ned. For the RAPD analyes, 15 RAPD primers (from a total of 40) were f ound to produce polymorphic banding patterns in at least two of the fo ur populations and subsequently were used to produce a total of 142 ba nds. Data generated by these RAPD primers indicated an increased genet ic diversity in radionuclide-contaminated sites relative to reference sites. Furthermore, the patterns from six RAPD primers produced a high er average number of bands when using DNA from radionuclide-contaminat ed populations than from non-contaminated, and for three RAPD primers the average number of bands from radionuclide-contaminated populations was lower. In addition, 17 bands occurred at a higher frequency in th e radionuclide-contaminated compared to the non-contaminated populatio ns. For the allozyme analyses, it was found that there was a higher pe rcentage of polymorphism and heterozygosity in the radionuclide-contam inated relative to non-contaminated sites. These findings contribute t o our understanding of the evolutionary effects of contaminant exposur e as well as to the development of population-level biomarkers.