A common environmental contaminant affects sexual behavior in the clawed frog, Xenopus tropicalis

Behavior can be a sensitive measure of endocrine disruption from exposure to environmental contaminants. Xenopus tropicalis has become a developmental model system for evaluation of endocrine disrupting compounds because of its relatively rapid development and its sequenced, diploid genome. We used X. tropicalis as a model for endocrine disruption of sexual behavior. We injected frogs intraperitoneally (IP) with a gonadotropin hormone-releasing hormone agonist at 0.31 μg/50 μL or vehicle control solution and determined behavioral outcomes. Next, we used GnRH-induced sexual behavior to determine the effects of a 30-day exposure to aqueous estradiol (E2) at 10(-8) M or a common pollutant, 4-tert octylphenol (OP), at the environmentally relevant concentrations of 10(-7) M OP or 10(-8) M OP. The GnRH-agonist treatment had no effect on female behaviors. In males, GnRH-agonist treatment increased approaches, touches, amplexus, and a sum total of all sexual behaviors (total sexual behavior score). Exposure to E2 or any dose of OP had no effect on female behaviors. In males, E2 and 10(-7) M OP increased incidence of arm waving (a potential pheromone releasing behavior), and E2, and both doses of OP increased calling behavior compared to an unexposed control group. More males in all the exposure groups expressed sexual behavior than in the control group. This study demonstrates that a common pollutant, OP, affects male sexual behavior possibly by acting like an estrogen.