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Grantee Research Project Results

Grantee Research Project Results

The Effects of Environmental Estrogens on the Reproductive Biology of a Model Species

EPA Grant Number: F6F20426
Title: The Effects of Environmental Estrogens on the Reproductive Biology of a Model Species
Investigators: Parker, Michael Rockwell
Institution: Oregon State University
EPA Project Officer: Jones, Brandon
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $111,344
RFA: STAR Graduate Fellowships (2006)
Research Category: Academic Fellowships , Endocrine Disruptors , Fellowship - Environmental Physiology



The goal of this research is to determine the effects of environmental estrogens on three aspects of vertebrate reproduction:

  1. reproductive organ development in males
  2. pheromone production in males and females
  3. survival rates and sex ratios of offspring.

Understanding how environmental estrogens directly affect a model system is crucial for both anticipating the effects these pollutants will have on exposed taxa and resolving conflicts arising from studies in other surrogate systems, such as amphibians.


I have proposed to use a model, terrestrial ectotherm, the red-sided garter snake (Thamnophis sirtalis parietalis), to address the mentioned questions. We have a wealth of knowledge on this wide-ranging reptile’s biology from over half a century of field and laboratory research, and this snake has the potential to serve as a surrogate organism for ecotoxicological studies. I will use Atrazine and a metabolite of DDT as putative environmental estrogens in this snake, and I plan to administer biologically-relevant levels of these pollutants by either injecting study animals directly or treating their food. I also plan to pair all experimental treatments with neutral and positive controls. I will conduct histological analyses of male gonads after treatment with environmental estrogen and then determine, via radioimmunoassay, the treatments’ effects on circulating steroid levels. Lastly, I will use gas chromatography/mass spectrometry to examine pheromonal responses of males and females after exposure to environmental estrogens.

Expected Results:

I expect males to be feminized (reduction of testes or hemipenis size) by treatment with environmental estrogens, and I may further validate this by showing an increase in natural estrogen production and a decrease in circulating androgen levels. I anticipate that males will produce a female-like pheromone and females will have desynchronized pheromone synthesis occurring when males will rarely mate. Lastly, I expect that offspring born to female snakes treated with environmental estrogens will have reduced survival and female-skewed sex ratios.

Supplemental Keywords:

Environmental estrogen, pheromones, endocrine disruption, feminization, Atrazine, reproduction, Thamnophis, reptile, ectotherm,, RFA, Health, Scientific Discipline, Toxicology, Endocrine Disruptors - Environmental Exposure & Risk, endocrine disruptors, Biochemistry, Endocrine Disruptors - Human Health, endocrine disrupting chemicals, altered sexual development, reptile model, developmental biology, DDT, estrogen response, reproductive processes, atrazine

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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