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There are weird things happening to frogs in the suburbs

A female green frog. Researchers are finding more females than males in suburbia.
Geoff Giller
Yale University
A female green frog. Researchers are finding more females than males in suburbia.

Past studies have found strange things happening to frogs when they’re exposed to farm chemicals. A new study shows estrogen in suburban areas is messing with frogs’ hormonal systems too.

More females frogs than males

David Skelly is an author of the study. He’s the director of the Yale Peabody Museum of Natural History and a professor of ecology in the Yale School of Forestry and Environmental Studies.

In the study, Skelly and his team studied green frogs living in ponds and suburban areas and they compared them to frogs living in undeveloped forests.

“The most striking thing we saw is that the sex ratio — that is the number of males versus females that we recovered in the ponds that we studied, and we looked at over 20 ponds — gradually trended towards more females when we were working in ponds that were in more developed, more suburbanized sites,” Skelly says. “And that was really surprising.”

A possibility: Male frogs could be turning into females.

Skelly says a potential explanation is that male frogs are being “sex-reversed.”

“So you have genetic males becoming, in terms of their morphology and perhaps their physiology, they’re turning into females because of the chemicals they’re encountering in the environment,” he says.

But Skelly says they need to do more tests to see whether this is happening in these suburban sites.

Unknown consequences

A suburban pond and frog home.
Credit Max Lambert/Yale

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What happens to frog populations when the sex ratio changes and there are more females than males?

“Well, that’s a really good question,” Skelly says. “And we don’t know yet.”

Before the effects on frog populations can be determined, Skelly says it’s crucial to figure out whether the extra females in these frog populations are functional.

“Are they capable of having offspring or are they sterile? We don’t know yet and we’re very anxious to find out,” he says.

So where does the estrogen that’s affecting frogs in suburban areas come from?

Skelly says that answer is complex. He says estrogen in the environment comes from many sources.

“It’s everything from brake pads to components of plastics to — in other contexts, we’ve found that, you know, whatever goes into your domestic wastewater is likely to be getting in there,” he says.

He also says many different kinds of metals can get into the environment from cars and household products.

“So it’s really kind of comprehensive,” he says.

Skelly says there’s probably not a “single smoking-gun-type explanation."

“The idea that atrazine or any single chemical is going to be the one to cause this kind of phenomenon, as broadly as it’s been documented, is probably not right,” he says. “Instead, what we’re probably looking at is that there are a wide variety of sources for the kinds of chemicals that can cause these sorts of changes in animals.”

Tackling the problem

In the same way, Skelly says there’s not a simple fix for this issue. That too must be addressed more comprehensively.  

“We’re not going to be able to just get, for instance, you know plasticizers, like BPA, out of baby bottles or just de-register one kind of pesticide and take care of the problem,” he says. “Not that those things might not make some kind of a difference. But they’re not going to be comprehensive, effective solutions.”

To learn more, see this interview with David Skelly by Yale Environment 360.

Rebecca Williams is senior editor in the newsroom, where she edits stories and helps guide news coverage.
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