The Significance of Estrogen in Reproductive Copulatory Success in African-clawed Frog (Xenopus laevis)

Hormones are a vital component of reproductive processes, intimately acting on both sexes through proteins of pituitary origin that affect the gonads, and steroids of gonadal origin that affect the accessory organs and secondary sexual characters. Reproductive behavioral success is the capability of an organism to outcompete other organisms for a mate and to achieve copulation. Aside from its crucial role in courtship dynamics, testosterone works with its counterpart estrogen to regulate these behaviors. Once released by the testes, testosterone is converted by the aromatase enzyme into estradiol, which then acts similarly in its effect on male behavior. Although the influences of testosterone and estrogen are known in male African clawed frogs (Xenopus laevis), little is known about the minimum amount of estrogen needed to inhibit testosterone and its effects on frog mating behavior. I performed breeding assays to determine how estrogen treatment of male frogs influenced reproductive behavior in both noncompetitive and competitive environments. I found that male frogs treated with estrogen were significantly less likely than non-treated frogs to copulate in a non-competitive setting. However, I found that treated and untreated male frogs achieved reproductive success at equal rates in a competitive setting. Thus, these unexpected results call into question the role of concentrating a specific amount of hormone in understanding how successful reproductive copulation can be achieved. Determining the threshold level of estrogen is necessary to understand the sensitivity of the amphibian endocrinology system and vital to addressing populations drastically affected by minute traces of endocrine disruption compounds.