“Many scientists have studied similar effects from exposure to pharmaceuticals and pesticides, but now we’re seeing it from chemicals found in common road salt and leaf litter,” said Max Lambert
, a doctoral student at the Yale School of Forestry & Environmental Studies (F&ES) and lead author of the paper.
“The health and abundance of females is obviously critical for the sustainability of any population because they’re the ones that make the babies,” Lambert said. “So if you have a population that is becoming male-based, the population might be at risk.”
The results were published in the Canadian Journal of Fisheries and Aquatic Sciences
. Other authors included David Skelly
, the Frank R. Oastler Professor of Ecology at Yale; Meredith Smylie
, a research associate at F&ES; and scientists from Rensselaer Polytechnic Institute.
For the experiment, conducted at the Rensselaer Aquatic Lab in Troy, N.Y., the researchers created a series of water treatments in 500-liter tanks containing varying levels of road salt and leaf litter from maple and oak trees. Many of the water treatments contained tree litter levels that mimicked natural leaf litter found in typical forest ponds.
According to the study, frogs reared in oak leaf litter in the absence of salt exhibited a female-biased sex ratio (63 percent). But when salt was added it decreased the proportion of female frogs by 10 percent.
Meanwhile, within populations exposed to oak litter, developing female tadpoles were always larger than male tadpoles, which is fairly common among species that lay eggs. But when salt was added the female tadpoles decreased in size.