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: Packard, Benjamin H
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $111,344
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
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

Progress and Final Reports:

  • 2007
  • 2008
  • Final