Cheryl Grunwald

Sea lamprey Petromyzon marinus: an exception to the rule of homing in anadromous fishes

Anadromous fishes are believed to make regular circuits of migration in the sea before homing to their natal rivers. Sea lamprey Petromyzon marinus is an anadromous fish that is an exception to this life-history pattern. It also differs from other anadromous fishes in that its adult phase is parasitic, a feeding strategy that should make homing problematic for lamprey cohorts that become widely dispersed through transport by the diverse hosts they parasitize. We sequenced a portion of the mitochondrial DNA control region from sea lampreys collected from 11 North American east coast rivers to test for genetic evidence of homing. There were no significant differences (Χ2=235.1, p=0.401) in haplotype frequencies among them, with almost 99 per cent of haplotypic diversity occurring within populations. These findings, together with concordant genetic results from other geographical regions and ancillary information on pheromonal communication, suggest that sea lamprey does not home but rather exhibits regional panmixia while using a novel ‘suitable river’ strategy to complete its life cycle.

A comparison of the dose and time response of CYP1A1 mRNA induction in chemically treated Atlantic tomcod from two populations

Abstract Quantification of cytochrome P4501A1 (CYP1A1) mRNA levels in environmentally exposed Atlantic tomcod (Microgadus tomcod) has revealed significantly induced gene expression in fish from contaminated locales including the Hudson River, New York, and the Miramichi River, New Brunswick. In order to calibrate this response, determine its sensitivity and dose-responsiveness, levels of hepatic CYP1A1 mRNA were quantified in depurated Atlantic tomcod intraperitoneally (i.p.) injected with various concentrations of: β-naphthoflavone (β-NF), the PAH benzo[a]pyrene (B[a]P), the non-ortho coplanar PCB congener-3,3′,4,4′- tetrachlorobiphenyl (IUPAC: PCB-77), and the dioxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Additionally, the rates of CYP1A1 mRNA induction and disappearance were quantified in depurated Atlantic tomcod i.p. injected with single doses of these chemicals and sacrificed at times ranging up to 72 days. Levels of CYP1A1 mRNA were dose-responsive for all four chemicals with maximum induction ranging from 50- to 460-fold and first significant induction being observed in the low mg per kg fish (wet weight) range for β-NF and B[a]P, μg/kg range for PCB-77 and ng/kg range for 2,3,7,8-TCDD. However, while tomcod from the Miramichi River responded to both PAHs and halogenated aromatic hydrocarbons (HAHs), Hudson River tomcod responded only to PAHs indicating population level differences in CYP1A1 mRNA inducibility in tomcod. Furthermore, differences in the responsiveness to PAHs and HAHs suggest that more than one molecular mechanism mediates CYP1A1 transcription in Atlantic tomcod. Kinetic profiles of CYP1A1 mRNA induction differed greatly between tomcod treated with HAHs and PAHs. Initial induction occurred within hours of treatment with PAHs and peaked after 1–3 days, compared to initial induction 4–7 days after treatment with HAHs, and maximum induction not occurring for up to 72 days after exposure. Quantification of halogenated aromatic hydrocarbons (HAH) in the livers of tomcod caught in the Hudson and Miramichi Rivers confirmed exposure and accumulation of known CYP1A1 inducing chemicals including 2,3,7,8-TCDD at concentrations as high as 1.5 μg/kg lipid (554 ng/kg w.w.) and PCB-77 at concentrations as high as 108 μg/kg lipid (15 μg/kg w.w.). These results suggest that hepatic CYP1A1 mRNA concentration can be a useful bioindicator of exposure to some aromatic hydrocarbon compounds in the aquatic environment and that profiles of gene induction and disappearance may help identify environmental inducers provided that gene responsiveness is also evaluated under controlled laboratory conditions.

Population genetics of shortnose sturgeon Acipenser brevirostrum based on mitochondrial DNA control region sequences

Shortnose sturgeon is an anadromous North American acipenserid that since 1973 has been designated as federally endangered in US waters. Historically, shortnose sturgeon occurred in as many as 19 rivers from the St. John River, NB, to the St. Johns River, FL, and these populations ranged in census size from 101 to 104, but little is known of their population structure or levels of gene flow. We used the polymerase chain reaction (PCR) and direct sequence analysis of a 440 bp portion of the mitochondrial DNA (mtDNA) control region to address these issues and to compare haplotype diversity with population size. Twenty‐nine mtDNA nucleotide‐substitution haplotypes were revealed among 275 specimens from 11 rivers and estuaries. Additionally, mtDNA length variation (6 haplotypes) and heteroplasmy (2–5 haplotypes for some individuals) were found. Significant genetic differentiation (P < 0.05) of mtDNA nucleotide‐substitution haplotypes and length‐variant haplotypes was observed among populations from all rivers and estuaries surveyed with the exception of the Delaware River and Chesapeake Bay collections. Significant haplotype differentiation was even observed between samples from two rivers (Kennebec and Androscoggin) within the Kennebec River drainage. The absence of haplotype frequency differences between samples from the Delaware River and Chesapeake Bay reflects a probable current absence of spawning within the Chesapeake Bay system and immigration of fish from the adjoining Delaware River. Haplotypic diversity indices ranged between 0.817 and 0.641; no relationship (P > 0.05) was found between haplotype diversity and census size. Gene flow estimates among populations were often low (< 2.0), but were generally higher at the latitudinal extremes of their distribution. A moderate level of haplotype diversity and a high percentage (37.9%) of haplotypes unique to the northern, once‐glaciated region suggests that northern populations survived the Pleistocene in a northern refugium. Analysis of molecular variance best supported a five‐region hierarchical grouping of populations, but our results indicate that in almost all cases populations of shortnose sturgeon should be managed as separate units.

Conservation of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus: delineation of stock structure and distinct population segments

The anadromous Atlantic sturgeon Acipenser oxyrinchus oxyrinchus, a wide-ranging species along the Atlantic Coast of North America, is being considered for federal listing under the U.S. Endangered Species Act. Identification of distinct population segments (DPS) is necessary but problematic for highly vagile species such as Atlantic sturgeon which may spend a high proportion of their lives outside of their natal estuaries. Characterization of genetic differentiation and estimates of gene flow provide a quantitative measure of the number of DPS into which species could be divided over their distribution and the reproductive independence of each unit. We sequenced a portion of the mitochondrial DNA control region to characterize population structure and gene flow across all naturally reproducing populations from which specimens could be obtained. We then considered these genetic data along with ancillary information on life history characteristics, historical fisheries data, and trajectories of abundance to determine the number of DPS into which this species should be divided. Our results suggest that philopatry is high for Atlantic sturgeon and that each U.S. estuary analyzed hosts genetically distinct populations of Atlantic sturgeon. We conclude that at least nine DPS of Atlantic sturgeon exist along the Atlantic Coast of the U.S. In contrast, the Atlantic Sturgeon Status Review Team has proposed a five DPS scheme for this subspecies based largely on results from nuclear DNA microsatellites, but with fewer populations represented and lower samples sizes. These different conclusions illustrate the somewhat arbitrary nature of the DPS concept, at least as applied to Atlantic sturgeon.

Effects of prior exposure history on cytochrome P4501A mRNA induction by PCB congener 77 in atlantic Tomcod

Abstract Levels of P450IA mRNA in tomcod collected from the Miramichi River, Canda and the Hudson River, New York were measured by slot blot analyses after the fish had been depurated and i.p. injected with Aroclor 1254, PCB congener 77, or PCB congener 105. Elevated expression of P450IA mRNA was observed in congener 77-treated Miramichi tomcod, whereas no induction was seen in the Hudson River fish. Tomcod from both rivers were induced by injection with beta-naphthoflavone. These results suggest that the prior exposure history of the Hudson River tomcod may have affected their non-inducibility by treatment with PCB congener 77.

Induction and clearance of cytochrome P4501A mRNA in Atlantic tomcod caged in bleached kraft mill effluent in the Miramichi River

Abstract Levels of cytochrome P4501A mRNA were measured in Atlantic tomcod caged in the effluents of a bleached kraft pulp and paper mill on the Miramichi River, NB, Canada and two sites downstream, and compared to levels in fish caged upstream of the mill and in unexposed laboratory-maintained tomcod. Additionally, the rate of clearance of CYP1A mRNA in tomcod exposed at the mill and transferred to clean water was compared to that observed in tomcod treated in the laboratory with a single dose of 2,3,7,8-TCDD (0.5 μg/kg). Levels of CYP1A mRNA in tomcod caged upriver of the mill were low and comparable to those observed in untreated laboratory control fish. Levels of CYP1A mRNA were elevated up to 11-fold in tomcod caged at the mill site and a gradient in levels of gene expression was seen at the two downstream sites. Tomcod i.p. injected with a single dose of 2,3,7,8-TCDD exhibited a profile of prolonged CYP1A mRNA induction of at least 25 days. Levels of CYP1A mRNA in tomcod caged at the mill site and transferred to clean water remained significantly induced for at least 3 days post-transfer. In combination, these results suggest that CYP1A mRNA was induced in caged tomcod by constituents of the mills effluents and that the rates of clearance of CYP1A mRNA may provide additional information concerning the identity of environmental inducers.

Use of DNA Fingerprinting in the Identification and Management of a Striped Bass Population in the Southeastern United States

Abstract Historically, striped bass Morone saxatilis were indigenous to many major drainages of the Gulf of Mexico (Gulf). It is believed that almost all natural populations were depleted by the 1950s and 1960s with the exception of fish in the Apalachicola–Chattahoochee–Flint (A–C–F) river system in northwestern Florida, Georgia, and Alabama. Striped bass of Atlantic ancestry were introduced into the A–C–F system during the 1960s and 1970s to enhance population size. We compared DNA fingerprints of striped bass collected from four Atlantic river systems with those offish from the A–C–F system to determine if genetic differences still exist. Moderate levels of polymorphism were observed with two probes, the bacteriophage M-13 genome and mouse sequences related to the Drosophila Per gene. Striped bass DNA digested with single restriction enzymes and hybridized to these two probes generated single DNA fragments shared by 71 out of 75 A–C–F fish but not seen in any of 51 Atlantic fish. Heritability of DNA fi...

Mitochondrial DNA Analysis Indicates Sea Lampreys Are Indigenous to Lake Ontario

Abstract The parasitic sea lamprey Petromyzon marinus occurs throughout North Americas Great Lakes, where it has an immense economic impact on commercially and recreationally important fishes. Sea lampreys indisputably invaded Lake Erie and the upper Great Lakes from Lake Ontario in the mid-1900s, but their official status as a nonnative species in Lake Ontario is based on circumstantial evidence and has long been subject to controversy. Presently, sea lampreys are considered by U.S. and Canadian government agencies to be an invasive species within the entire Great Lakes watershed, and millions of dollars are spent annually to suppress them. We sequenced 330 base pairs of the mitochondrial DNA control region of 224 sea lampreys collected from 10 locations (3 within the Lake Ontario drainage, 2 within the Lake Superior drainage, and 5 rivers between Quebec and New York that are tributary to the Atlantic Ocean). Eighteen haplotypes were revealed, of which 17 occurred in specimens from Atlantic coast rivers...

GENETIC DIVERSITY AT AN ONCOGENE LOCUS AND IN MITOCHONDRIAL DNA BETWEEN POPULATIONS OF CANCER-PRONE ATLANTIC TOMCOD

It has been reported that Atlantic tomcod (Microgadus tomcod) from the Hudson River exhibit an extremely high incidence of liver tumors. More than 90% of spawning 2-year-old fish display hepatocellular carcinomas. In contrast, representatives of this species from a relatively pristine environment show a much lower incidence of tumors. Genomic DNA and mitochondrial DNA (mtDNA) were isolated from tomcod from the Hudson River, New York, and the Saco River and Royal River, Maine. We found a statistically significant difference in the frequency ofPstI-generated restriction fragment length polymorphisms in theabl cellular oncogene between Hudson and Maine tomcod. Allelic variation was observed at two of the threeabl domains scored. A single composite genotype seen in approximately 40% of Hudson River fish was seen in only one Maine fish. This polymorphism enabled us to differentiate a Hudson River population from that encountered in the Maine rivers. This is the first demonstration of a population-specific polymorphism at a cellular oncogene locus in any species. In contrast, no restriction site polymorphisms were seen in mtDNA between the populations. The lack of mtDNA diversity in these fish is consistent with the geological history of the area. In combination, these results suggest that the genetic diversity observed at the c-abl oncogene locus must have been a fairly recent event and that oncogene loci may be particularly sensitive to mutational change.

Annual Run Size and Genetic Characteristics of Atlantic Sturgeon in the Altamaha River, Georgia

Abstract Although the Altamaha River, Georgia, once supported one of the largest fisheries for Atlantic sturgeon Acipenser oxyrinchus in U.S. waters, the fishery was closed in 1997 because of severe overfishing. Since then, no studies have been conducted and population trends have remained unknown. The objective of this study was to estimate annual run size and age structure of the spring spawning migration and to determine genetic relatedness between this population and other Georgia populations. In spring of 2004 and 2005, we sampled the annual spawning run of Atlantic sturgeon in the lower 30 km of the Altamaha River using large-mesh gill nets. Captured fish were marked with passive integrated transponder tags and released to facilitate a run estimate using a simple Schnabel mark-recapture estimator. Over the 2 years of the study, we captured 213 individuals, yielding mark-recapture run estimates of 324 (95% confidence interval [CI] = 143-667) in 2004 and 386 (95% CI = 216-787) in 2005. Catch curve ana...