Submitted to: BMC Evolutionary Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/15/2013
Publication Date: 1/14/2014
Publication URL: doi:10.1186/1471-2148-14-7
Citation: Proestou, D.A., Flight, P., Champlin, D., Nacci, D. 2014. Targeted approach to identify genetic loci associated with evolved dioxin tolerance in Atlantic Killifish (Fundulus heteroclitus). BMC Evolutionary Biology. 14:7. Interpretive Summary: The objective of this research was to identify genetic variation in genes involved in or related to a key chemical detoxification pathway (the Aryl hydrocarbon receptor (AHR) pathway) and determine associations with tolerance to persistent organic pollutants present in the environment (dioxin-like compounds including PCBs)in the Atlantic killifish (Fundulus heteroclitus). Patterns of genetic variation within and among four PCB-tolerant populations were compared with those of nearby sensitive populations. Genetic variation at 42 AHR-related genes was assessed in these populations and variation at two loci, AHR2 and CYP1A, was associated with PCB tolerance.
Technical Abstract: Extreme tolerance to highly toxic dioxin-like contaminants (DLCs) has evolved independently and contemporaneously in (at least) four populations of Atlantic killifish (Fundulus heteroclitus). Surprisingly, the magnitude and phenotype of DLC tolerance is similar among these killifish populations that have adapted to varied, but highly contaminated urban/industrialized estuaries of the US Atlantic coast. We hypothesized that comparisons among tolerant populations and in contrast to their sensitive neighboring killifish might reveal genetic loci associated with DLC tolerance. Since the aryl hydrocarbon receptor (AHR) pathway partly or fully mediates DLC toxicity in vertebrates, we identified single nucleotide polymorphisms (SNPs) from 42 genes associated with the AHR to serve as targeted markers. Wild fish from the four highly tolerant killifish populations and four nearby sensitive populations were genotyped using 59 SNP markers. Consistent with other killifish population genetic analyses, our results revealed strong genetic differentiation among populations, consistent with isolation by distance models. Pairwise comparisons of nearby tolerant and sensitive populations revealed differentiation among these loci: AHR 1 and 2, cathepsin Z, the cytochrome P450s (CYP) 1A and 3A30, and the NADH ubiquinone oxidoreductase MLRQ subunit. By grouping tolerant versus sensitive populations, we also identified cytochrome P450 1A and the AHR2 loci as under selection, lending support to the hypothesis that the CYP1A and/or AHR2 loci may have evolved in populations adapted to extreme DLC contamination.