Amphibians: Sex Imbalance in Suburban Ponds

Yale researchers found that the number of female green frogs is increasing in local ponds that are near shrubs, vegetable gardens, and manicured lawns. These landscapes in suburban areas are causing disruptions in the amphibians' endocrine systems. The scientists studied 21 ponds in southwestern Connecticut in 2012, according to a release.

"In suburban ponds, the proportion of females born was almost twice that of frog populations in forested ponds," Max Lambert, lead author and a doctoral student at the Yale School of Forestry & Environmental Studies, said in the release. "The fact that we saw such clear evidence was astonishing."

Each pond that the researchers examined had varying degrees of suburban neighborhood impact, from entirely forested ponds to ponds heavily surrounded by residential homes. Some of the pond sites were also linked to septic systems or sewer lines.

"Our work shows that, for a frog, the suburbs are very similar to farms and sewage treatment plants," Lambert explained. "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."

According to a Yale news release, the common plants found in lawns, such as clovers, naturally produce phytoestrogens. Lawn maintenance may be a source of this contamination. The researchers noted that this study, could help other suburban pond species.

"Some of our lab's current work is trying to understand how the suburbs influence sexual development in other species," Lambert said in the release.

Their findings were recently published in the journal Proceedings of the National Academy of Sciences.

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