Evaluating alterations of genetic diversity in sunfish populations exposed to contaminants using RAPD assay

Bioindicators of pollutant exposure can be more sensitive and ecologically relevant than simply measuring levels of pollutants in the environment and are applied here as a tool for assessing environmental stress on aquatic organisms. DNA polymorphisms, detected by using the randomly amplified polymorphic DNA (RAPD) technique, are used as biomarkers to assess genetic diversity and genetic distance among populations of redbreast sunfish (Lepomis auritus) residing in reference streams and a contaminated stream (East Fork Poplar Creek, EFPC). The RAPD technique uses the polymerase chain reaction (PCR) with short oligonucleotide primers under reduced stringency to produce DNA fragments which, when analyzed by gel electrophoresis, form banding patterns similar to DNA fingerprints. A total of 13 primers were used which produced 45 polymorphic bands among all populations of fish tested. Using this technique, only slight differences in genetic diversity were detected among populations of sunfish within EFPC although the diversity of all EFPC populations analyzed together did differ from the reference populations. Fish populations in EFPC were consistently less genetically distant from each other than they were from each of the reference sites. Differences in genetic distance between populations may be due to selection pressure of pollutants on fish in EFPC which is supported by the finding that frequencies of certain unique genotypes in EFPC sunfish were correlated with the downstream pollutant gradient. These results are discussed in relation to implications of RAPD assays and recent remediation efforts within EFPC.