Evidence of Spatially Extensive Resistance to PCBs in an Anadromous Fish of the Hudson River

Populations of organisms that are chronically exposed to high levels of chemical contaminants may not suffer the same sublethal or lethal effects as naive populations, a phenomenon called resistance. Atlantic tomcod (Microgadus tomcod) from the Hudson River, New York, are exposed to high concentrations of polycyclic aromatic hydrocarbons (PAHs) and bioaccumulate polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs). They have developed resistance to PCBs and PCDDs but not to PAHs. Resistance is largely heritable and manifests at early-life-stage toxic end points and in inducibility of cytochrome P4501A (CYP1A) mRNA expression. Because CYP1A induction is activated by the aryl hydrocarbon receptor (AHR) pathway, as are most toxic responses to these compounds, we sought to determine the geographic extent of resistance to CYP1A mRNA induction by PCBs in the Hudson River tomcod population. Samples of young-of-the-year tomcod were collected from seven locales in the Hudson River, extending from the Battery at river mile 1 (RM 1) to RM 90, and from the Miramichi River, New Brunswick, Canada. Laboratory-reared offspring of tomcod adults from Newark Bay, in the western portion of the Hudson River estuary, were also used in this study. Fish were partially depurated in clean water and intraperitoneally injected with 10 ppm coplanar PCB-77, 10 ppm benzo[a]pyrene (BaP), or corn oil vehicle, and levels of CYP1A mRNA were determined. CYP1A was significantly inducible by treatment with BaP in tomcod from the Miramichi River, from laboratory-spawned offspring of Newark Bay origin, and from all Hudson River sites spanning 90 miles of river. In contrast, only tomcod from the Miramichi River displayed significantly induced CYP1A mRNA expression when treated with PCB-77. Our results suggest that the population of tomcod from throughout the Hudson River estuary has developed resistance to CYP1A inducibility and probably other toxicities mediated by the AHR pathway. Tomcod from the Hudson River may represent the most geographically expansive population of vertebrates with resistance to chemical pollutants that has been characterized

Microarray Analysis of Polychlorinated Biphenyl Mixture-Induced Changes in Gene Expression Among Atlantic Tomcod Populations Displaying Differential Sensitivity to Halogenated Aromatic Hydrocarbons

Several populations of fishes inhabiting contaminated Atlantic Coast estuaries exhibit resistance to early life-stage (ELS) toxicities induced by halogenated aromatic hydrocarbons such as coplanar polychlorinated biphenyls (PCBs). These toxicities include mortality, circulatory failure, edema, and craniofacial malformations. The mechanisms behind resistance to halogenated aromatic hydrocarbon toxicity in these populations are unknown. First and second generation Atlantic tomcod Microgadus tomcod embryos derived from the Hudson River ([HR]; New York, USA) population are highly resistant to PCB-induced cytochrome P4501A (CYP1A) expression and ELS toxicity when compared to embryos of Miramichi River ([MR]; New Brunswick, Canada) and Shinnecock Bay ([SB]; New York, USA) origin. The present study sought to identify novel genes involved in population differences in response to PCB exposure using custom microarrays. Microarray probes consisted of unsequenced inserts of randomly picked clones from a tomcod cardiac cDNA library. Tomcod embryos from three populations (HR, MR, and SB) were exposed to two doses of an environmentally relevant mixture of coplanar PCBs and screened for dose- and population-specific patterns of gene expression. Clones displaying significant differences between populations exposed to the high dose of PCBs were identified by DNA sequencing. Of the 28 identified nonribosomal protein clones, none displayed expression patterns highly similar to CYP1A (altered in MR and SB, but not in HR). However, several transcripts representing biomarkers of cardiomyopathy in mammals (cardiac troponin T2, cathepsin L, and atrial natriuretic peptide) were differentially altered among the three tomcod populations by PCBs. Although the present study did not identify any novel genes associated with PCB resistance in tomcod, several potential molecular biomarkers of PCB exposure were revealed

Fine-scale spatial and temporal genetic structure of Atlantic cod off the Atlantic coast of the USA

Atlantic cod Gadus morhua in US waters are currently managed as 2 stocks: (1) a Gulf of Maine stock and (2) a Georges Bank and south stock. This designation is decades old and warrants re-evaluation in light of concerns that fisheries management units may not reflect biologically meaningful population units. In this study, we used 10 microsatellite loci, the PanI locus, and 5 single nucleotide polymorphism markers to characterize the population genetic structure of cod in US waters. We found significant differentiation among temporally and spatially divergent populations of cod (global F(ST) = 0.0044), primarily stemming from 2 potentially non-neutral loci, and evidence for a population structure that strongly contradicts the current 2-stock management model. This genetic structure was stable over a 5 yr period. Our results indicate that cod in US waters are broadly structured into 3 groups: (1) a northern spring-spawning coastal complex in the Gulf of Maine (GOM), (2) a southern complex consisting of winter-spawning inshore GOM, offshore GOM and sites south of Cape Cod, Massachusetts, and (3) a Georges Bank population. The strongest differentiation occurs between populations in the northern and southern complex (mean F(ST) = 0.0085), some of which spawn in the same bays in different seasons. By means of mixture analysis, young-of-the-year fish sampled on juvenile nurseries were assigned to the spawning complex of their origin. Our findings contribute to a growing body of knowledge that Atlantic cod and other marine fish populations are structured on a finer scale than previously thought and that this structure supports biocomplexity and locally adapted populations. As such, it may be warranted to re-evaluate current management units and tailor management plans toward this finer scale

Evidence of natural reproduction of Atlantic sturgeon in the Connecticut River from unlikely sources

<div><p>Atlantic Sturgeon is listed under the U.S. Endangered Species Act as five Distinct Population Segments (DPS). The “endangered” New York Bight (NYB) DPS is thought to only harbor two populations; one in the Hudson River and a second smaller one in the Delaware River. Historically, the Connecticut River probably supported a spawning population of Atlantic Sturgeon that was believed extirpated many decades ago. In 2014, we successfully collected pre-migratory juvenile specimens from the lower Connecticut River which were subjected to mitochondrial DNA (mtDNA) control region sequence and microsatellite analyses to determine their genetic relatedness to other populations coastwide. Haplotype and allelic frequencies differed significantly between the Connecticut River collection and all other populations coastwide. Sibship analyses of the microsatellite data indicated that the Connecticut River collection was comprised of a small number of families that were likely the offspring of a limited number of breeders. This was supported by analysis of effective population size (<i>Ne</i>) and number of breeders (<i>Nb</i>). STRUCTURE analysis suggested that there were 11 genetic clusters among the coastwide collections and that from the Connecticut River was distinct from those in all other rivers. This was supported by UPGMA analyses of the microsatellite data. In AMOVA analyses, among region variation was maximized, and among population within regions variation minimized when the Connecticut River collection was separate from the other two populations in the NYB DPS indicating the dissimilarity between the Connecticut River collection and the other two populations in the NYB DPS. Use of mixed stock analysis indicated that the Connecticut River juvenile collection was comprised of specimens primarily of South Atlantic and Chesapeake Bay DPS origins. The most parsimonious explanation for these results is that the Connecticut River hosted successful natural reproduction in 2013 and that its offspring were descendants of a small number of colonizers from populations south of the NYB DPS, most notably the South Atlantic DPS. Our results run contrary to the belief that re-colonizers of extirpated populations primarily originate in proximal populations.</p></div

Indices of microsatellite allelic and mitochondrial DNA control region sequence haplotype diversity in 11 (microsatellites) and 12 (mtDNA) collections of Atlantic Sturgeon.

<p>Collection locale, microsatellite DNA results [sample size (<i>n</i>), proportion of polymorphic loci (<i>P</i>), number of alleles (<i>N</i>_<i>A</i>), allelic richness (<i>A</i>), observed heterozygosity (<i>H</i>_O), and expected heterozygosity (<i>H</i>_E)], inbreeding coefficient (<i>F</i>_<i>IS</i>), and mitochondrial DNA results [sample size (<i>n</i>), number of haplotypes (<i>n</i>_H), haplotype diversity (<i>h</i>), nucleotide diversity (π), and mean number of pairwise differences.</p