New research shows higher levels of estrogen found in the manicured lawns of U.S. suburban lawns is changing the gender ratio of local frogs.
The findings reveal these hormones are disrupting frogs' endocrine systems, causing the number of females to spike while the male population dwindles, Yale University reported. Past studies have suggested similar effects associated with agricultural pesticides and wastewater effluent, but the recent study shows the phenomenon also exists at a smaller suburban scale.
To make their findings, the researchers conducted tests at 21 ponds in Southwestern Connecticut in 2012.
"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 ponds looked at in the study were exposed to varying levels of suburban neighborhood impacts, with some surrounded by forest and others in the midst of suburban sprawl. The analysis also included ponds linked to septic systems and sewer lines.
"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."
The researchers noted some of the lawns included in the research produced plants such as clover, which naturally produce phytoestrogens. In the future, the researchers plan to take a closer look into the issue and determine if the changes are occurring in other animal populations.
The findings were published in a recent edition of the journal Proceedings of the National Academy of Sciences.