Green frogs in the suburbs are undergoing a gender switch - but it isn't pesticides doing it, according to a new study in Proceedings of the National Academy of Sciences, the same journal that set off the craze in thinking pesticides were causing frogs to change sex, by letting a member walk a study through peer review for a friend of his, by not mentioning that study had no data.
The issue in the new study is estrogen in suburban yards. It is changing the ratio of male and female green frogs at nearby ponds by disrupting frogs' endocrine systems, according to the study. That, in turn, is driving up the number of female frogs and lowering the number of male frogs. The problem is that some plants commonly found in lawns, such as clovers, naturally produce phytoestrogens. The simple act of maintaining a lawn, in other words, may be the source of the contamination.
The research is based on tests conducted at 21 ponds in southwestern Connecticut in 2012. As noted, some studies have shown similar effects caused by agricultural pesticides and wastewater effluent but this one finds amphibian endocrine disruption in suburban locales.
"In suburban ponds, the proportion of females born was almost twice that of frog populations in forested ponds," said lead author Max Lambert, a doctoral student at the Yale School of Forestry&Environmental Studies. "The fact that we saw such clear evidence was astonishing."
The researchers looked at ponds with varying degrees of suburban neighborhood impact -- with entirely forested ponds at one end of the spectrum, and ponds that were heavily surrounded by suburbia at the other end. The sites included ponds linked to both septic systems and sewer lines. In many cases, the researchers needed to obtain permission from homeowners to survey their back yards.
"Our work shows that, for a frog, the suburbs are very similar to farms and sewage treatment plants," Lambert 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."
