Water disrupts frogs’ development

By Allegra Krasznekewicz
Contributing Reporter
Wednesday, September 23, 2009

There’s something in Connecticut’s water — and Yale ecology professor David Skelly is in the process of investigating it.

Thanks to a $30,000 grant from the Hartford Foundation for Public Giving, Skelly is set to continue his research examining why growing numbers of male green frogs inhabiting Hartford ponds are exhibiting female sexual traits. Central to his research is the possibility that hermaphrodite frogs might be harbingers of human health problems resulting from water contamination.

Skelly’s preliminary research, carried out at 23 ponds in 14 Connecticut communities, has led him to conclude that male green frogs living in suburban and urban areas exhibit female sexual traits more frequently than their rural counterparts. Using histology — a process that involves dissecting frog gonads, cutting them into small slices, staining them and mounting them on slides — he found that 21 percent of male frogs in suburban ponds and 18 percent in urban ponds exhibit immature eggs growing in their testes, whereas only 7 percent of frogs in agricultural regions demonstrate this abnormality.

“Amphibians appear to be relatively indestructible — this is a group of animals that has weathered just about everything nature has thrown at them,” Skelly said in a podcast called “It’s Not Easy Being a Frog” on the Yale School of Forestry & Environmental Studies’ Web site. “[But] in the last 20 to 30 years, we’ve recognized a real phenomenon, that all over the world, the frogs are disappearing; we’re losing species, we’re losing populations, and we have this deformity phenomenon going on.”

The importance of Skelly’s research lies in its implications for human health. Previously, it was thought that agricultural pesticides, such as atrazine, were the key factors causing amphibian abnormalities. In past studies, Skelly and other biologists have found populations of frogs with missing or additional limbs in several parts of North America and linked it to agricultural practices.

Now, frogs’ sexual development is becoming equally abnormal.

Based on the lower numbers of hermaphrodites in agricultural areas compared to those near urban and suburban developments, Skelly is forwarding a new hypothesis linking sexual abnormalities with pharmaceutical pollution.

“We are seeing a lot of pharmaceutical companies advertising all sorts of drugs to cure all sorts of maladies, and we are encouraged to use pills instead of implementing lifestyle changes,” said Oswald Schmitz, professor of population and community ecology at the environment school. “One of the consequences of this overmedication is that the residue of drugs, passed out of the body through urine, is building up in our sewage systems.”

Because sewage systems are not equipped to deal with these types of chemicals, they remain in the water that ends up in rivers and lakes. According to Skelly and Schmitz, one possibility is that rising levels of estrogenic compounds, the major ingredient of birth control medications, in the water might be affecting the developmental pathways of frogs and create the observed gender abnormalities.

Frogs are good for studying effects of environmental degradation because they spend the majority of their time in water, where pollutants accumulate.

Although Skelly’s work highlights a formidable threat to green frog species, the larger question remains: Are amphibian deformities due to environmental changes a warning sign of human health issues to come?

George Chappell, communications officer at the Hartford Foundation for Public Giving, the study’s funding source, said the Foundation funded this research due to these potentially very important implications.

“While we have no information linking illness in amphibians to human health, the fact remains that they are vertebrates like us and share similar physiological and developmental pathways,” Skelly said in a statement. “Understanding the cause [of abnormalities] in amphibians can help us characterize risks to other species, including humans.”

Though a definitive link between chemicals in the water, amphibian deformities and human health risks has yet to be established, one thing remains clear. As Schmitz put it, “Nature is telling us that we’re doing something to the environment and we better start paying attention to exactly what it is.”

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