These male green frogs are reportedly becoming more feminine due to exposure to estrogen in suburban ponds, scientists at Yale University report in a new Proceedings of the National Academy of Sciences study.
According to Slashgear and United Press International (UPI), the authors of the paper sampled green frogs (Rana clamitans) from 21 ponds in Connecticut. Not only did they find abnormally high numbers of females living in ponds located in the suburbs, but they also discovered that the males in those populations tended to have intersex characteristics.
Lead author Max Lambert, a doctoral student at the Yale School of Forestry & Environmental Studies, suggested that higher levels of estrogen in the water could be turning male green frogs into female by disrupting their endocrine systems. The ponds in question, the authors said, contained high levels of the chemicals called phytoestrogens.
Regular, everyday landscaping may be to blame
Phytoestrogens are estrogenic chemicals produced by plants, and Lambert explained in a press release that clovers and some other types of plants commonly found in lawns naturally produce these substances. In other words, simple landscaping may be the source of the contamination.
“For a frog, the suburbs are very similar to farms and sewage treatment plants,” he said. “Our study didn’t look at the possible causes of this, partly because the potential relationship between lawns or ornamental plantings and endocrine disruption was unexpected… [our lab] is trying to understand how the suburbs influence sexual development in other species.”
The discovery of high estrogen levels in these suburban ponds could also impact other types of creatures that use these waters, including other amphibian species such as wood frogs, gray tree frogs, spring peepers, and salamanders, along with birds, turtles, and even mammals.
According to AFP, the researchers believe future studies are needed to understand exactly why there are such high levels of the female sex hormone in areas where there are lawns, gardens, and shrubbery, as well as to explain the reasons for the link between landscaping and frog offspring sex ratios.
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Feature Image: Geoff Giller/Yale
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