The Tardigrade: Practically Invisible, Indestructible ‘Water Bears’
When scientists at the American Museum of Natural History mounted an exhibit about creatures that survive under conditions few others can tolerate, they did not have to go far to find the show’s mascot.
“We just got them from Central Park,” said Mark Siddall, a curator of the show, Life at the Limits. “Scoop up some moss, and you’ll find them.”
He was talking about tardigrades, tiny creatures that live just about everywhere: in moss and lichens, but also in bubbling hot springs, Antarctic ice, deep-sea trenches and Himalayan mountaintops. They have even survived the extreme cold and radiation of outer space.
Typically taupe-ish and somewhat translucent, and a sixteenth of an inch or so long, they are variously described as resembling minuscule hippopotamuses, mites or, most commonly, bears.
Many people call them “water bears” or “bears of the moss.” The word “tardigrade” is from the Latin for “slow walker” and pronounced TAR-dee-grade.
Once an object of interest only among zoological specialists, tardigrades now are generating widespread enthusiasm. Admirers have produced artwork and children’s books about them, and have even organized the International Society of Tardigrade Hunters “to advance the study of tardigrade biology while engaging and collaborating with the public.”
According to the society, formed this year at the University of North Carolina at Chapel Hill, people can find tardigrades if they gather some lichen or moss, especially on a damp day, put it in a shallow dish of water, and “agitate” it a bit. Debris will settle to the bottom of the dish, and tardigrades will probably be prowling in it.
The museum exhibit, which runs until January, also includes beetles, flowers, corals and other animals with unusual ways of coping with hostile environments.
Confronted with drying, rapid temperature changes, changes in water salinity or other problems, tardigrades can curtail their metabolism to 0.01 percent of normal, entering a kind of suspended animation in which they lose “the vast, vast, vast majority of their body water,” Dr. Siddall said. They curl up into something called a “tun.”
Tuns have been reconstituted after more than a century and brought back to life as tardigrades, looking not a day older. Little is known about their evolution, which is too bad because biologists think it must have been interesting. But tardigrade fossils are hard to spot.
People who have become transfixed by tardigrades often say they came across a photo or article by chance.
“I just stumbled across it,” said Thomas Gieseke, an artist and illustrator in Merriam, Kan., who created “The Tardigrade Queen,” an acrylic-on-canvas work depicting a tardigrade on a throne, complete with tiara and royal crest, which was shown at the Todd Weiner Gallery in Kansas City, Mo.
In ordinary life, tardigrades don’t get up to much. Dr. Siddall said that like most animals, they spend their time “hanging out and eating” plants and animals smaller than themselves, and possibly even indulging in cannibalism.
“People often say, ‘What’s their purpose? What’s their role in the universe?’ ” Dr. Siddall said. He has no ready answer. They might be useful for the study of suspended animation. But, he added, “are we going to find a way to put humans into suspended animation? I doubt it.”
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