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GENETIC ADAPTATION TO CHRONIC CONTAMINANT EXPOSURE BY A SMALL ESTUARINE FISH
Citation:
Nacci, D E., D M. Champlin, S. Cohen, A. McMillan, S. A. Roark, AND M Bagley. GENETIC ADAPTATION TO CHRONIC CONTAMINANT EXPOSURE BY A SMALL ESTUARINE FISH. Presented at American Fisheries Society Annual Meeting, Quebec City, Canada, August 11-14, 2003.
Description:
Investigations of the non-migratory fish species Fundulus heteroclitus indigenous to a highly chemically contaminated site is providing novel insights into stressor costs and adaptive strategies. Specifically, we are studying an abundant and persistent population of F. heteroclitus resident to New Bedford Harbor (NBH), MA, USA, contaminated with toxic levels of polychorinated biphenyls (PCBs). We have characterized in this population inherited tolerance to the toxic effects of local contaminants that is profoundly different from populations outside of NBH. The occurrence and maintenance of these adaptive phenotypes suggested that strong divergence has occurred in response to recent and intense chemical contamination, despite potentially high gene flow. We hypothesized that strong directional selection for chemical tolerance may have caused a genome-wide reduction in genetic diversity due to a population bottleneck, or localized reductions in genetic diversity at specific chromosomal regions. We used two complementary techniques to characterize the genetic structure of F. heteroclitus populations residing in and around NBH: amplified fragment length polymorphism (AFLP), a multilocus DNA fingerprinting method, and allozymes. However, genetic diversity in NBH F. heteroclitus was only slightly reduced at allozyme loci, and was not significantly lower based on AFLP analysis. We also examined genetic changes at Major Histocompatibility Complex (MHC) antigen-binding loci to test whether intense selection for chemical tolerance has resulted in reduced genetic diversity at specific loci which might have implications related to pathogen and/or parasite susceptibilities. Although genetic diversity at MHC loci was high, sequence patterns were unique in NBH versus F. heteroclitus populations indigenous to a non-contaminated site. This unique pattern, the reported immunosuppressive effects of PCBs on fish and other vertebrates, and our observations of high and unusual parasitism suggested that NBH F. heteroclitus might display poor immunological responsiveness. In contrast to our predictions, PCB-tolerant NBH populations were slightly, but consistently, more resistant to laboratory bacterial challenges (Vibrio harveryii) than fish from the uncontaminated populations. This pattern was consistent in field-collected fish, and their laboratory-raised, uncontaminated progeny. This model system and these approaches been used to demonstrate a complex pattern of responses and costs in a fish population subject to chronic contaminant exposure.