The Salamanders that Refuse to Grow Up

In a Wisconsin reservoir, these normally terrestrial animals have managed not only to survive but to thrive underwater

The Eastern Tiger Salamander has managed to survive in an inhospitable and unlikely habitat in Wisconsin. (Courtesy of Tamara Thomsen, Wisconsin Historical Society)

Dead leaves drift on the green, cloudy water that’s nearly to the brim of the six-million-gallon open concrete reservoir. Set on a tree-covered hillside, the reservoir is surrounded by a metal fence, like a community swimming pool long forgotten. It lies on the northern edge of the decommissioned Badger Army Ammunition Plant, a sprawling World War II-era ammunition factory 30 miles northwest of Madison, Wisconsin. Once one of the largest ammunition plants in the world, Badger is polluted by metals, solvents and explosives waste and is now being dismantled, piece by contaminated piece.

Workers strip away siding from nearby buildings and remove bricks. Bulldozers push mounds of dirt and broken concrete blocks, while trucks mounded high with bent metal rods, window frames and other debris create a rush hour of demolition on the heavily secured grounds. The landscape is slowly becoming more open and green, the prairie reappearing from beneath the plant.

The reservoir is unremarkable from the surface. But underwater, it’s home to a surprising animal that has managed to survive in this inhospitable and unlikely habitat. Salamanders cling to the sides, bottom and drain gate of the reservoir and swim through the water. They aren’t just any salamanders. They are adult Eastern Tiger Salamanders—some of the world’s largest salamanders—and they are supposed to live on land. But these salamanders are swimming and living a fully aquatic life with feathery gills, wide jaws, and tail fins.

“We don’t know how long they’ve been in there, but probably a few decades,” says Mike Mossman, an ecologist with the Wisconsin Department of Natural Resources. “We think there’s more than a thousand of them now.”

Mossman is at the reservoir collecting eggs and hopefully a salamander or two for further study. The long rope attached to a buoy and several thermometers in the middle of the reservoir turns out to hold dozens of eggs, black dots stuck to the rope fibers in gelatinous, clear egg sacs. Mossman scrapes them into a plastic bottle, elated at his find and hopeful for what they may allow scientists to learn about these strange salamanders.

Herpetologist Gary Casper of the University of Milwaukee discovered the salamanders while doing a survey of the reservoir for the Army in 1993. “I didn’t know what I had found at first,” says Casper. “We had no idea how uncommon these larval characteristics, like gills, were in the Eastern tiger salamander at the time.”

Ever since, Casper and other researchers from the Army and the state Department of Natural Resources have been trying to determine how these normally terrestrial animals have managed not only to survive but to thrive underwater.

But now time is running out for the salamanders, and scientists are rushing to study and possibly find a new home for them before the reservoir is drained.

Amphibians, such as frogs, toads and salamanders, lay eggs in water, even though most species spend the majority of their adult lives on land. The eggs hatch and develop into larvae—tadpoles in frogs and “efts” in salamanders. But occasionally amphibian development takes an odd turn. Sometimes larvae mature to a reproductive stage without undergoing the normal process of metamorphosis for a land-based adult life. This condition is called “neoteny.” They never lose their gills, tail fins, larval skin coloration and wide heads. They also never leave the breeding pond. This seemed to be exactly what happened to the Badger salamanders.

The open reservoir at Badger provided easy entry for the salamanders looking for a place to lay eggs, but a seven-inch-wide lip prevented them from getting out. Stuck in the reservoir, the breeding salamanders laid eggs and likely died. When their eggs hatched, any of the offspring that metamorphosed into the usual, land-dwelling form also died, unable to swim for long in the deep water. But somehow, others managed to survive by becoming neotenic.

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