Ecotoxicology (2006) 15:539-548 DO1 10.1007/~10646-006-0090-4 Genetic diversity and,structure of an estuarine fish (Fundulus heteroclitus) indigenous to sites associated with a highly contaminated urban harbor Amy M. McMillan Mark J. Bagley Suzanne A. Jackson Diane E. Nacci Accepted: 23 June 20061Published online: 4 August 2006 @ Springer Science+Business Media, LLC 2006 Abstract Intense selection on isolated populations can cause loss of genetic diversity, which if persistent, reduces adaptive potential and increases extinction probability. Phenotypic evidence of inherited tolerance suggests that polychlorinated biphenyls (PCBs), have acted as strong selective agents on populations of a non-migratory fish, Fundulus heteroclitus, indigenous to heavily contaminated sites. To evaluate population genetic structure and test for effects of intense, multi- generational PCB contamination on genetic diversity, we used AFLP analysis on fish collected from six sites along the east coast of North America that varied widely in PCB contamination. The sites included a heavily contaminated urban harbor (New Bedford, MA), an adjacent moderately contaminated sub-estuary (Buzzards Bay, MA), and an uncontaminated estuary 60 km away (Narragansett, RI). AFLP markers distinguished populations at moderate and small scales, suggesting genetic differentiation at distances of 2 km or less. Genetic diversity did not differ across the study sites. Genome-wide diversity may have been preserved because of large effective population sizes andlor because the mechanism for genetic adaptation to these contaminants affected only a small number of loci. Alternatively, loss in diversity may have been restored with moderate levels of migration and relatively short generation time for this species. Keywords AFLP . Killifish . Migration PCB . Selection This is contribution number AED-05-096 of the US EPA ORD Introduction NHEERL Atlantic Ecology Division. Although the research described in this contributibn has been funded partially by the ~ i ~ h ~ ~ y ~ (1930) fundamental theorem of natural US EPA, it has not been subjected to Agency-level review. Therefore, it does not necessarily reflect the views of the agency. states that the expected rate of increase in Mention of trade names, products, or services does not constitute mean fitness of a population is proportional to the endorsement or recommendation for use. genetic variance for fitness. An important corollary A. M. McMillan (H) Biology Department, State University of New York College at Buffalo, 1300 Elmwood Ave., Buffalo, NY 14222, USA e-mail: mcmillam@buffalostate.edu M. J. Bagley . S. A. Jackson National Exposure Research Laboratory, Ecological Exposure Research Division, US EPA Office of Research and Development, Cincinnati, OH, USA D. E. Nacci National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, US EPA Office of Research and Development, Narragansett, RI, USA for conservation biologists and environmental man- agers is that the capacity of a population to adapt to rapid environmental change is proportional to the amount of standing genetic variation available to selection. When an environmental change results in rapid directional selection, the average fitness of the population may increase in the short-term, but the selective response also can reduce the number of successful breeders to very low numbers if the selection differential is large enough. This would re- duce effective population size, increasing the rate of diversity loss across the genome and diminishing the a Springer