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)

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“Like tadpoles with legs” is how Mossman describes the Badger salamanders. The adults have the same yellowish color with dark spots as the larvae as well as red feathery gills, but like regular adults, they are nearly a foot in length.

Their aquatic world has been captured on film by maritime archaeologists from the Wisconsin Historical Society. Used to diving for shipwrecks in the Great Lakes, the archaeologists have used their skills to videotape the salamanders’ underwater habitat.

“Based on what we thought we knew about Eastern tigers, we would predict that these salamanders would drown in that reservoir,” explains Michael Lannoo, a professor of anatomy and cell biology at the University of Indiana School of Medicine, who has studied tiger salamanders for more than 30 years.

The Badger salamanders aren’t the first neotenic Eastern tiger salamanders to be found. But the Badger salamanders are perhaps the first human-induced neotenic population and are the only population known to have existed for many generations and to be well established.

The fact that these salamanders became neotenic under unnatural conditions—an Army reservoir—suggests that the species must have done this in the past, says Lannoo. He thinks the key to why salamanders usually don’t exhibit neoteny today is fish. Amphibians and fish rarely live in the same places. Nearly every body of water that can support fish has fish in the modern landscape. Fish often eat amphibian eggs and larvae, so amphibians tend to stick to seasonal and semipermanent wetlands, places where fish do not usually survive. “It’s how fish and amphibians have sorted out the landscape,” explains Lannoo.

But 200 years ago, before people began introducing fish to wild areas, fish were not as widespread as they are now. Some lakes and ponds had no fish. Amphibians likely lived in all kinds of water, including permanent bodies of water like lakes. To test this hypothesis, scientists needed an isolated, fish-free body of water, a situation nearly impossible to find in nature today. That is, until salamanders were discovered in the water reservoir at the Badger Army Ammunition Plant.

The thick-walled concrete reservoir once supplied millions of gallons of water for fire control and the production of propellants for use in firearms and artillery. Constructed in 1942, the war machine at the heart of the Sauk Prairie employed more than 30,000 men and women during its 58-year history, supplying three wars. The operation was massive: more than 7,400 acres covered with 1,400 buildings, many of them made of blast-proof concrete, 130 miles of roads, 200 miles of elevated steam pipe and 26 miles of railway. In the midst of this industrial landscape, nature still crept in.

Badger’s man-made reservoir mimicked the historic landscape: a permanent body of water free of fish. And sometime after the reservoir was dug, salamanders began falling in, either accidentally or to lay eggs.

“The reservoir’s purpose was to hold water for a process that made gunpowder, a destructive process,” says Mossman. “And yet a whole living system developed behind our backs, without our knowledge and control.”

The reservoir population seems to prove that Eastern tiger salamanders are capable of surviving to adulthood in water; that they can become neotenic in the right conditions; and that they may have commonly lived in permanent bodies of water in the past. Casper, Mossman and Lannoo believe that the Badger salamanders may represent one of the last instances of a biological phenomenon that was once widespread.

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