Hermaphrodite Frogs Found In Suburban Ponds
[Rachel's Introduction: New research has found that 21 percent of male green frogs, Rana clamitans, taken from suburban Connecticut ponds are hermaphrodites, with immature eggs growing in their testes.]
Dr. Skelly's research found that 21 percent of male green frogs, Rana clamitans, taken from suburban Connecticut ponds are hermaphrodites, with immature eggs growing in their testes.
The study is the latest in a decade's worth of research that has found intersex characteristics in water-dwelling species like sharp-tooth catfish in South Africa, small-mouth bass on the Potomac and shovelnose sturgeon in the Mississippi.
Previous studies, particularly those by scientists at the University of California, Berkeley, and in the West Virginia office of the United States Geological Survey, suggested a strong link between the abnormalities and agriculture, as well as a possible link to atrazine, a common herbicide. But the Yale study found that intersex frogs were more concentrated in suburban and urban areas.
Dr. Skelly's study, presented at a seminar at the University of Connecticut, is being submitted for publication. He looked at a common amphibian, the green frog, what he called the "Look, Mom, I found a frog" frog. He analyzed the landscapes within the Connecticut River Valley, where abnormalities were more likely to be found.
In 2006, a Geological Survey study of small-mouth bass in the Upper Potomac Basin found that male fish from the most densely inhabited and farmed sites had the greatest likelihood of having immature eggs in the testes. This year, scientists from the agency identified chemicals present in the effluent discharged in the areas where the abnormalities were found.
"Looking upstream and downstream from wastewater-treatment plants, we see there's obviously been an impact by some of the chemicals discharged in the wastewater," said Vicki S. Blazer, an author of the Geological Survey study. "Things like pesticides, herbicides and flame retardants."
She added that although the Potomac Basin study did not measure high levels of estrogen in the water, either from pharmaceutical waste or other sources, "that's certainly a concern."
The research was in part drawn up to identify endocrine disruptors, or compounds that can interfere with reproductive hormones.
It focused on specific chemicals, including atrazine, a herbicide used in agriculture and on suburban lawns and gardens, and chemicals used to give fragrance to soap and cosmetics.
The latest Geological Survey study, while suggesting possible links, did not directly correlate the prevalence of intersex fish and the presence of these chemicals in wastewater, Dr. Blazer said. The effects of those chemicals remain unclear.
A study in 2002 led by Tyrone B. Hayes at Berkeley found that leopard frogs exposed to atrazine in the laboratory had retarded testicular development and, in some cases, immature eggs in the testes.
Atrazine, manufactured by Syngenta of Basel, Switzerland, had the Environmental Protection Agency renew its approval in 2003. At the request of the agency, Syngenta has been studying atrazine levels in some watersheds. The European Union has banned it.
The environmental agency and the company have been criticized by environmental groups that contend atrazine is harmful to fish and amphibians and may have consequences for other species. The company says the chemical is safe.
Asked what might have caused the reproductive changes found in the new Yale study, Dr. Skelly said, "I don't know."
He noted that many suburban areas in his survey used septic systems and that there had been scant investigation of the chemicals or pharmaceutical residue in them or the likelihood of leaching into streams or ponds. Suburban areas are also associated with using herbicides and pesticides.
In contrast to the Geological Survey study, which implicated agricultural runoff, the frog study found that the more agricultural an area, the lower the rate of abnormalities.
In an interview, Dr. Skelly said of the intersex phenomenon: "This is the first evidence that I think anyone has provided that agriculture is doing anything but pushing those rates higher. I wouldn't say it's definitive by any means, but it's certainly not part of the choir.
"I wouldn't want to go out and tell the world that converting landscapes to agriculture is going to prevent us from facing risks from agricultural contaminants. What we found in most of the agricultural ponds we sampled was no evidence of reproductive deformity."
Dr. Skelly divided his survey into undeveloped, agricultural, suburban and rural components, based on frogs collected from 23 ponds. That was out of 6,000 ponds surveyed and 136 visited in the Connecticut River Valley.
Of the 233 frogs whose reproductive organs were analyzed, 13 percent had abnormalities.
In urban areas, 18 percent of the collected frogs were intersex; in suburban areas 21 percent. Just 7 percent of the frogs from agricultural areas were intersex.
The more suburban the land cover, Dr. Skelly said, the more likely were abnormalities. Frogs from undeveloped, often forested areas showed no intersex traits.
The question of the reproductive health of intersex fish is one that Dr. Blazer said she returned to in a follow-up to her 2006 study.
"We know the intersex males produce sperm," she said. "The question is whether the sperm is as good" as the sperm of normal males.
So far, she said, the sperm of the intersex males has shown some decrease in the ability for self-propulsion, but the males remain able to reproduce.
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