Relationship between reproductive success and male plasma vitellogenin concentrations in cunner, Tautogolabrus adspersus

The gene for vitellogenin, an egg yolk protein precursor, is usually silent in male fish but can be induced by estrogen exposure. For this reason, vitellogenin production in male fish has become a widely used indicator of exposure to exogenous estrogens or estrogen mimics in the aquatic environment. The utility of this indicator to predict impacts on fish reproductive success is unclear because information on the relationship between male plasma vitellogenin and reproductive end points in male and female fish is limited. In the research reported in this article, we investigated whether the presence of male plasma vitellogenin is a reliable indicator of decreased reproductive success in mature fish. Adult and sexually mature male and female cunner (Tautogolabrus adspersus) were exposed to 17β-estradiol, ethynylestradiol, or estrone, three steroidal estrogens that elicit the vitellogenic response. Data were gathered and pooled on egg production, egg viability, egg fertility, sperm motility, and male plasma vitellogenin concentrations. All males, including two with plasma vitellogenin levels exceeding 300 mg/mL, produced motile sperm. Neither percent fertile eggs nor percent viable eggs produced by reproductively active fish demonstrated a significant correlation with male plasma vitellogenin concentrations. Male gonadosomatic index and average daily egg production by females showed significant, but weak, negative correlation with male plasma vitellogenin concentrations. Results suggest that male plasma vitellogenin expression is not a reliable indicator of male reproductive dysfunction in adult cunner exposed to estrogens for 2-8 weeks during their reproductive season, at least in relation to capacity to produce motile sperm or fertilize eggs. Male plasma vitellogenin expression may serve as an indicator of reduced female reproductive function caused by estrogen exposure

Population genetic diversity and fitness in multiple environments

<p>Abstract</p> <p>Background</p> <p>When a large number of alleles are lost from a population, increases in individual homozygosity may reduce individual fitness through inbreeding depression. Modest losses of allelic diversity may also negatively impact long-term population viability by reducing the capacity of populations to adapt to altered environments. However, it is not clear how much genetic diversity within populations may be lost before populations are put at significant risk. Development of tools to evaluate this relationship would be a valuable contribution to conservation biology. To address these issues, we have created an experimental system that uses laboratory populations of an estuarine crustacean, <it>Americamysis bahia </it>with experimentally manipulated levels of genetic diversity. We created replicate cultures with five distinct levels of genetic diversity and monitored them for 16 weeks in both permissive (ambient seawater) and stressful conditions (diluted seawater). The relationship between molecular genetic diversity at presumptive neutral loci and population vulnerability was assessed by AFLP analysis.</p> <p>Results</p> <p>Populations with very low genetic diversity demonstrated reduced fitness relative to high diversity populations even under permissive conditions. Population performance decreased in the stressful environment for all levels of genetic diversity relative to performance in the permissive environment. Twenty percent of the lowest diversity populations went extinct before the end of the study in permissive conditions, whereas 73% of the low diversity lines went extinct in the stressful environment. All high genetic diversity populations persisted for the duration of the study, although population sizes and reproduction were reduced under stressful environmental conditions. Levels of fitness varied more among replicate low diversity populations than among replicate populations with high genetic diversity. There was a significant correlation between AFLP diversity and population fitness overall; however, AFLP markers performed poorly at detecting modest but consequential losses of genetic diversity. High diversity lines in the stressful environment showed some evidence of relative improvement as the experiment progressed while the low diversity lines did not.</p> <p>Conclusions</p> <p>The combined effects of reduced average fitness and increased variability contributed to increased extinction rates for very low diversity populations. More modest losses of genetic diversity resulted in measurable decreases in population fitness; AFLP markers did not always detect these losses. However when AFLP markers indicated lost genetic diversity, these losses were associated with reduced population fitness.</p

Evaluation of the effects of dioxin and PCBs on Fundulus heteroclitus populations using a modeling approach

The U.S. Environmental Protection Agency (EPA) is reevaluating the risks associated with 2,3,7,8-tetrachlorodibenzo-p-dioxin and related chlorinated hydrocarbons (CHCs). Most information currently available concerning CHC toxic action and biological effects focuses on the responses of individual organisms, as opposed to the potential impacts of CHCs on populations, communities, or ecosystems. In support of EPA\u27s reevaluation, survivorship and reproduction data from two previous studies involving the estuarine fish. Fundulus heteroclitus (Linnaeus), exposed as adults to either dioxin or polychlorinated biphenyls (PCBs), were interpreted at the population level using a stage-classified model of F. heteroclitus population dynamics. The studies differed with respect to the route of exposure of the parental stock: dietary exposure to dioxin in the laboratory and natural exposure to PCBs at the New Bedford Harbor, Massachusetts marine Superfund site. The CHC effects documented in these studies were used to modify fertility and survivorship in the population model. The finite population multiplication (growth) rate, estimated using the model, was used as the measure of population-level effect. In both cases, a negative relationship was observed between CHC dose (quantified as dioxin whole-body burden and liver burden of non-ortho- and mono-ortho-substituted PCB congeners) and population growth rate. The dose- response relationships developed in this study provide useful information for assessing the ecological risks of CHCs to estuarine fish populations

An injectable, slow-release implantation method for exposing fish to chemicals over a period of weeks

A slow-release, injectable implant method was developed for administering test chemicals to cunners Tautogolabrus adspersus.The implant is composed of amatrix of a test chemical homogenized in a mixture of Ethocel (Dow Chemical) and coconut oil. The effectiveness of a subcutaneous implant of this matrix in vivo was determined by tracing plasma concentrations of three separate chemicals (estradiol, ethynylestradiol, and atrazine) over time in treated male cunners. Release from the implant was determined based on the percentage of the implanted concentration of test chemical (plus metabolites) that was detected in fish plasma over a 1-2-week period after implantation. Circulating estrogen concentrations measured in plasma from two different cunners that received the estradiol implant were almost identical, indicating that there is a reasonably even distribution of test chemical within the Ethocel-coconut oil preparation and that individual variability may be minimal for release of test chemical from the implant. Metabolites of estradiol and atrazine were a major portion of the circulating concentration of these chemicals. Estradiol and atrazine demonstrated metabolic and clearance profiles that were very different from those of the xenoestrogen ethynylestradiol. A follow-up in vitro study was conducted to further characterize the release of estradiol from the implant matrix. Results showed a rapid release of estradiol from the matrix bolus during the first 24 h, followed by a more gradual release over subsequent days. The in vitro tests indicated that measuring in vivo plasma concentrations may not accurately reflect the release rate of a chemical from the implant matrix, in part because metabolism and clearance affect the circulating concentrations in vivo. © American Fisheries Society 2012