Research Results: Wildlife and Ecological Effects
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Critical Stages in Avian Development: Estrogen Hazards to Altricial and Precocial Birds
Michael D. Fry, University of California – Davis
James R. Millam – University of California, Davis
EPA STAR Grant #R825294
- Post-hatch oral administration of estradiol benzoate (EB) to zebra finches produces similar effects at similar doses to parenterally administered EB in that species.
- Post-hatch EB treatment of female zebra finches produces a dose-related increase in the size of the song-control nuclei in their brains as well as singing behavior, which normally is restricted to males.
- Post-hatch EB treatment of male zebra finches alters adult reproductive behaviors in a dose-related manner, demasculinizing copulatory behavior (i.e., failure to mount females) and increasing nesting behavior.
- The effects of post-hatch EB exposure of both males and females can result in total reproductive failure of mated pairs due to an array of behavioral and physiological changes in both sexes.
- Post-hatch oral administration of selected xenoestrogens (i.e., octylphenol) produced no significant effects at the doses tested
Field and Laboratory Studies of the Effects of Polychlorinated Biphenyls and Other Persistent Organic Pollutants on Thyroid Function During Avian Development
F.M. Anne McNabb- Virginia Polytechnic Institute and State University – Blacksburg, VA
EPA STAR Grant #R827400
- Embryonic and prefledgling gulls from polluted areas of the Great Lakes had significantly decreased thyroid function (as determined by lower levels of T4 thyroid hormone) compared to gulls from reference sites.
- Other species (black guillemots and turtles) also showed signs of thyroi d hypertrophy and increased liver PCB levels in areas with high-PCB contamination.
- Thyroid gland T4 content was determined to be a more sensitive marker for alterations in thyroid f unction than plasma hormones or thyroid gland hypertrophy.
- There were no negative effects observed in any measures used to assess thyroid function in chicken embryos exposed to PCB 126 and 77 in the laboratory. This suggests that the mechanisms of toxicity of these PCBs are not through endocrine disruption of thyroid function.
- Activity of the hepatic enzyme UDP-GT (which leads to T4 metabolism and excretion) is not increased appreciably in chicken embryos exposed to PCBs126 and 77. This suggests that these PCB congeners do not affect thyroid function by this mechanism.
Frog Deformities: Role of Endocrine Disruptors During Development
David M.Gardiner - University of California - Irvine
EPA STAR Grant # R827398
- All of the limb deformity phenotypes observed in wild populations of frogs can be induced in the laboratory by TTNPB exposure at appropriate stages of development.
- There are multiple developmental windows of sensitivity during limb bud development, and these windows are remarkably short.
- At high doses and long exposures, TTNPB is acutely toxic at all stages of development, causing death within a few weeks of exposure.
- Using the parameters established from studies of TTNPB effects on stages of Xenopus limb development, a developmental toxicology protocol to screen the activity of a large number of known pesticides was established.
Endocrine Disruption in Marine Gastropods by Environmental Chemical Mixtures
Patricia McClellan-Green - Duke University Marine Lab, Beaufort, NC
EPA STAR Grant #R827401
- Tributyltin (TBT) induces significant levels of imposex (imposition of male sexual characteristics) in female mud snails, which is lessened if females are simultaneously exposed to 3-methyl-cholanthrene (3-MC).
- Injection of the neuropeptide hormone APGWamide into female snails resulted in the initiation of penile bud formation indicating that this peptide is a strong candidate for the penile morphogenic factor (PMF) in mud snails.
- Exposure to TBT causes an increase in the level of APGWamide expression in the tissues of snails. This increase was evident in female (least), imposex female (intermediate), and male (highest) snails exposed to TBT in the laboratory or through environmental exposure.
- Inhibition of cytochrome P450 aromatase activity is not responsible for the induction of imposex but may play a role in the maintenance or severity of penile formation in female snails.
- Inhibition of cytochrome P450-mediated steroid biosynthesis is not responsible for the induction of imposex, but steroids may play a role in the maintenance or severity of penile formation in female snails.
- In summary, TBT likely stimulates the release of PMF (identified as APGWamide) to induce imposex in females (resulting in the growth of the accessory sex organs [ASO] and the production of steroids). Steroids then act as part of a hormonal feedback loop to maintain the ASO.
Endocrine Disruptors and Host Resistance in Lake Apopka Alligators
Trenton R. Schoeb, University of Florida
EPA STAR Grant #R826127
- There appear to be no statistically significant effects of pesticide treatments of eggs or level of natural contamination with EDCs among different lakes on the following measures of immune response in American alligators: p eripheral blood antibacterial activity against Staphylococcus aureus; histology of the spleen, thymus, or bone marrow; spleen weight/body weight ratios; or in vivo lymphocyte response to phytohemagglutinin.
- A significant finding of unknown cause was the presence of focal areas of necrosis in the brains of 6 out of 31 necropsied young animals. Affected animals were either observed with neurologic signs, including ataxia and loss of righting ability, or were found moribund or dead. The affected animals were from Lakes Apopka and Griffin and came from clutches with low clutch viability. Additional studies are necessary to determine whether there is an association with EDC exposure and these brain lesions in alligators.
- There appears to be no evidence of a relationship between clutch viability and exposure to any of the pesticides in organochlorine analyses at the doses examined. This is a significant observation indicating that factors other than pesticide exposure are likely contributing to embryonic mortality and clutch viability that is observed in the free-living alligator populations.
Environmental Endocrine Disruption in Avian Wildlife
Bill L. Lasley , University of California – Davis
EPA STAR Grant # R826298
- A series of experiments demonstrated that female chickens are as sensitive as males to adverse effects from TCDD exposure, and exogenous estrogen administration did not protect birds against those effects, in contrast the findings in mammalian models.
- Estrogen treatment of male birds resulted in qualitatively similar lipid profiles to mature laying hens and reduced secondary male characteristics (i.e., comb size).
- TCDD antagonized several of the feminizing effects of exogenous estrogen administration in male chickens.
- Specific adverse effects of dioxin on key parameters of lipid mobilization may explain the wide range of developmental defects that are observed in egg-laying species exposed to certain halogenated aromatic hyrdrocarbons (HAHs) compared with placental mammals.
Environmentally-Mediated Endocrine Disruption in Estuarine Crustaceans: A 3-Taxon Multi-Generational Study of Sediment-Association EDC Effects from the Genetic to Population Levels
G. Thomas Chandler – University of South Carolina, Columbia, SC
EPA STAR Grant #827397
- Reproduction in the grass shrimp was decreased by exposure to the organochlorine (OC) insecticide endosulfan (ES) in a dose-dependent manner.
- The OC insecticide fipronil (FP) significantly decreased adult grass shrimp survival at 0.2 µg/L; however, it had no significant effects on female reproduction.
- In gravid female grass shrimp, exposure to the organophosphate (OP) insecticide chlorpyrifos resulted in significant increases in ecdysteroid concentrations, but had no significant effects on reproductive parameters.
- In a benthic copepod, trace FP concentrations halted female egg extrusion and altered male spermatogenesis.
- Exposure to the herbicide atrazine increased the incidence of reproductive failure in the copepod and reduced the number of offspring per successful female.
- Elevated yolk deposition occurred in embryos of female copepods cultured throughout their life cycle in sediments contaminated with the PAH chrysene; the biological significance of that finding is unclear.
- Of the five EDCs evaluated in estuarine crustacean models, the OC insecticides and the herbicide adversely affected reproduction; the OP insecticide affected survival and ecdysteroid levels, but not reproduction; and the steroidally- structured PAH, chrysene, increased yolk deposition to embryos without other adverse effects.
Evaluation of Endocrine-Distrupting Chemical Effects Across Multiple Levels of Biological Organization: Integration of Physiology Behavior and Population Dynamics In Fishes
Peter Thomas – University of Texas at Austin, Austin, TX
EPA STAR Grant #R827399
- After exposure of adult Atlantic croaker to representative EDCs, impairment of reproductive function was observed at all reproductive life-history stages examined, including gamete production, gamete maturation, spawning, and early larva survival.
- All of the reproductive and larval stages examined are sensitive to exposure to EDCs; thus, effects at multiple life-history stages need to be taken into account in assessments and modeling of EDC effects on fish populations.
- Methylmercury exposure can impair three critical reproduction stages: gonadal growth, gamete maturation, and fertilization/early egg and larval survival.
- Larval exposure to Aroclor 1254 and methylmercury had negative impacts on many survival parameters, including swimming ability, maximum burst speed, and response to visual stimuli (indicating impaired predator response).
- Three linked population models were developed to simulate population-level effects of low-dose EDC exposure using the measures of reproductive success and larval survival skills measured for EDCs in this study.
Exposure and Response of Morelet’s Crocodile (Crocodylus moreletii) Populations to Endocrine Disrupting Compounds in Belize, Central America
Scott T. McMurry , Texas Tech University
EPA STAR Grant # R826310
- Multiple OCs were detected in all environmental and species matrices examined. DDE was found in every egg analyzed, while OC occurrence and concentrations in scutes were more variable.
- It is unclear whether phallus size and plasma T concentrations observed in crocodiles from Gold Button Lagoon and New River Watershed are normal or altered by some stressor (e.g., EDCs).
- There appears to be no population-level effects of EDC exposure on Morelet's crocodiles inhabiting the two study sites.
- Long-term studies are essential for adequately assessing the effects of EDCs on crocodilian populations, as many of the contaminant-induced effects are organizational in nature, occurring during embryonic development, but not appearing until later in life.
- Plasma vitellogenin induction may serve as a reliable biomarker of estrogen exposure in crocodilians.
Metabolic Androgenization of Invertebrates by Endocrine-Disrupting Chemicals
Gerald A. LeBlanc , North Carolina State University
EPA STAR Grant # R826129
- The biotransformation of testosterone was definitively characterized in both the mud snail and the water flea, and aspects of testosterone metabolism unique to these groups were discovered.
- Tributyltin tin was found to elevate free testosterone levels in the mud snail at environmentally-relevant exposure concentrations through effects on testosterone esterification.
- Juvenoid EDCs were found to alter sex determination in daphnids.
- Ecdysteroids were found to be important in orchestrating discrete processes in early and late embryo development of daphnids.
- EDCs interfered with endogenous juvenoid and ecdysteroid hormone regulatory pathways in Daphnia magna in ways that can inhibit embryo development and reduce fecundity of exposed populations.
Reproductive and endocrine effects of o,p'-DDT, an environmental estrogen, and p,p'-DDE, an antiandrogen, in male and female Atlantic croaker during critical periods of their reproductive life history cycles
Peter Thomas - University of Texas at Austin
EPA STAR Grant # R826125
- Separate genes for three estrogen receptors (ERs), ER alpha, ER beta and ER gamma, were found in Atlantic croaker, the first vertebrate species in which three distinct nuclear ERs have been identified.
- Brain androgen receptor (AR)1 levels in both male and female Atlantic croaker are greatly influenced by gonadal status and circulating levels of sex steroids.
- Plasma membrane receptors for estrogens and androgens and nonclassical, nongenomic actions of these steroids have been identified in croaker gonads.
- O,p’-DDT (a xenbiotic estrogen) and p,p’-DDE (a putative xenobiotic antiandrogen) bind to a variety of steroid receptors in fish reproductive tissues. Greater reproductive impairment was observed with o,p’-DDT compared to p,p-DDE. The differing patterns and degrees of impairment of reproductive and endocrine function observed after exposure to these two DDT derivatives is probably largely a reflection of their different mechanisms of endocrine disruption.
Stages in Sublethal Exposure to EDCs in a Quail Model System
Mary Ann Ottinger – Animal and Avian Sciences, University of Maryland, College Park, MD
EPA STAR Grant #R826134
- Japanese quail represent a sensitive and readily studied model for examining effects of EDCs on the endocrine and neuroendocrine systems of precocial avian species.
- The earlier the exposure of quail to EDCs, the more substantial and permanent the changes in measures of reproductive performance in adults and likely lifetime reproductive sucess.
- Hens can transfer lipophilic EDCs to their offspring through deposition in egg yolks.
- Components of the endocrine and neuroendocrine systems examined, including gonad weight and indicators of maturation, circulating sex hormone levels, and hypothalamic GnRH-I content and aromatase activity, were affected by the EDCs tested, depending on dose and timing of exposure.
- The most sensitive indicators of exposure to EDCs (i.e., effects shown consistently at the lowest doses) of the endpoints examined across all experiments included impaired reproductive behavior and delayed sexual maturation in both males and females.
The Mechanisms and Effects of Endocrine Disruption on Infertility in the Bonnethead Shark on Florida's Gulf Coast
Charles A. Manire, Mote Marine Laboratory – Florida State University
EPA STAR Grant #R826128
- Infertility rates in bonnethead sharks were significantly higher in the Tampa Bay/Anclote River area than in the less contaminated Florida Bay and Apalachicola Bay areas.
- The ability of female sharks to store spermatozoa prior to fertilization was significantly lower in sharks from the Tampa Bay/Anclote River.
- The reproductive biology of male bonnethead sharks from the three study sites did not differ significantly.
- Differences in female reproduction appear to be related to differences in endocrine function, based on low serum concentrations of 17ß-estradiol measured in Tampa Bay/Anclote River sharks.
- High rates of infertility appear to be associated with elevated concentrations of total PCBs and other OCs in Tampa Bay/Anclote River sharks.
- The high infertility rate in Tampa Bay is unlikely to have a profound effect on population status of the bonnethead shark.