Tainted water can skew population toward males, study reveals – via Herp Digest

By Brian Nearing Thursday, November 24, 2016, Albany Times-Uniion

Salted frog may sound like a gourmet restaurant dish, but it actually could mean real trouble for coming generations of the amphibians.

New research done by Rensselaer Polytechnic Institute and Yale University has found that road salt finding its way to pools where frogs breed tilts the balance of offspring, resulting in more males and fewer females that emerge as tadpoles.

"How the salt is doing this, frankly, we don't yet know," said Rick Relyea, a RPI biologist and co-author of the study that was published this month in a Canadian aquatic science journal. "How many females you have in a population determines how many offspring you have. We are not in a position to make any conclusions about potential population decline, but what we do not need is more males.”

Normally, the ratio of male to female tadpoles is roughly equal, said Relyea, who runs the RPI Aquatic Laboratory in North Greenbush, where he conducted the frog study over the last year using massive 500-liter water tanks.

Some tanks contained leaves from oak and maple trees, which are common around

the forest pools where frogs and other amphibians lay their eggs.

Other tanks contained road salt, which is routinely applied to highways in the winter.

Some salt can get washed into drainage systems and potentially reach other bodies of water. For example, Lake George salt levels have been rising steadily.

During the last three decades, the lake's salt levels have tripled, making it now about 30 times saltier than an undeveloped Adirondack lake.

The problem is happening throughout the Adirondacks wherever there are roads, according to Dan Kelting, executive director of the Adirondack Watershed Institute at Paul Smith's College. He spoke at a regional summit last year aimed at addressing the growing threat of road salt.

In the salted water tanks at the RPI lab, there were 60 male tadpoles for every 40 females — a shift of 10 percent. The effect is called masculinizing. Also, female tadpoles exposed to salt were smaller than normal.

"The continual masculinization of frog populations for many generations in habitats contaminated with high concentrations of road salt ... could potentially affect the abundance of frogs in these habitats," said Relyea, who is also director of RPI's Darrin Fresh Water Institute.

"The research raises the possibility that many other aquatic species could be affected by road salts in sub-lethal ways, not only in terms of altered sex ratios, but potentially in many other traits.”

His experiments were conducted as part of the Jefferson Project at Lake George, a research collaboration among RPI, IBM and The Fund for Lake George, a not-for-profit advocacy group. The project is currently installing a series of water- and land-based sensors around the lake to study its water quality and ecosystem.

Part of that ecosystem includes what are called vernal pools, which are temporary pools of water that routinely form by snow melt in the spring, and where frogs and other amphibians lay eggs. "The vast majority of our amphibians come from vernal pools, not lakes," said Relyea. There are likely hundreds of such pools surrounding the lake, where road salt is applied every winter.

"When it comes to road salt, frogs are like canaries in a coal mine warning us of the need to dramatically cut back salt use," said Eric Siy, executive director of The Fund for Lake George. "An estimated 30,000 metric tons of road salt is applied annually in the Lake George basin — enough to fill 300 rail cars or a train 3 miles long every year.”

Across the U.S. each winter, more than 22 million metric tons of salt is applied on roadways, according to estimates by RPI.

Siy's group just held its second annual "salt summit" at the lake, where local officials and conservationists learn about potential methods to reduce use of road salt during the winter.

Previous studies have found effects on amphibian gender ratios caused by exposure to pharmaceuticals and pesticides, but the road salt study is the first of its kind.

"The health and abundance of females is obviously critical for the sustainability of any population because they're the ones that make the babies. So if you have a population that is becoming male-biased, the population might be at risk," said Max Lambert, lead author of the research study and a doctoral student at the Yale School of Forestry and Environmental Studies.

Other researchers included Aaron Stoler, a postdoctoral researcher at RPI, and Yale researchers David Skelly and Meredith Smylie.

Lambert said previous research suggests that such outcomes could be caused by a phenomenon in which simple elements — such as sodium — can bind to a receptor in cells, mimicking the actions of testosterone or estrogen.

This, in turn, can trigger masculinizing or feminizing functions.

"So there is a very small testosterone-like effect with one salt molecule," he said. "But if you're dumping lots and lots of pounds of salt on the roads every winter that washes into these ponds, it can have a large effect.”