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Thesis Abstract – Hall (2009)


Synergistic Effects of Endocrine Disrupting Compounds on the Behavior of Gambusia affinis (Western Mosquitofish)

Author and college:

Kathleen Hall, Pomona College


May 1, 2009


Bachelor of Arts in Biology


Gene Fowler, Pomona College


Estrogens are a common and potent type of endocrine disrupting compound (EDC) found in water systems. The synthetic estrogen, ethynylestradiol (EE2), and the natural steroid estrogen, estradiol (E2), are excreted in fairly large quantities into the environment. A variety of species of male freshwater fish have shown reduced reproductive and competitive success when exposed to water containing estrogen. Negative effects also include intersex gonads, reduced sperm counts, and the production of the egg-yolk precursor protein, vitellogenin (VTG). Combinations of low dosages of estrogens have been proven to have additive effects, but the possibility of synergies between estrogens remains largely unexplored. This study used western mosquitofish (Gambusia affinis) to test for reduced mating behavior after a two week exposure to equipotent concentrations of E2, EE2, or a mixture of the two. Mating behavior was assessed for single males with a female, then exposed males were paired with a control male and a female to test for competitive success. In the first day of observations, single males with a female showed significantly reduced mating behavior from control males, indicating that exposure to estrogens can inhibit reproduction. In the competition scenario, males exposed to E2 or EE2 performed comparably to or better than controls, but the combination treatment performed significantly worse than controls. These results lend strong evidence to the hypothesis that synergies exist between estrogenic compounds. Unfortunately, Western blots revealed no VTG production, but this may have been due to the fact that the primary antibody was not specific to mosquitofish.

For more information:

Contact Gene Fowler – gene.fowler@pomona.edu

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