反复冻融的实验睡美虫的一生

它既不算是昆虫也不像正常的动物，长度大概只有1毫米，形状像一只小熊软糖，有8条腿，身体被坚硬但看着很酥脆的鳞片覆盖：没错，它就是水熊虫。

“它们看起来介于蠕虫和多腿熊之间，因缓慢笨拙的步态而得名：走起来左右摇摆，非常可爱。”德国斯图加特大学（University of Stuttgart）的科学家杰茜卡·伊曼（Jessica Ehmann）说道，她对水熊虫非常着迷，“看到这一幕的我从此爱上了水熊虫，它坐在我的双目镜之下，然后站起身来面朝我，向我招了招手。”

水熊虫存在的历史甚至比恐龙还要长——大约有2亿年，它们已经演化出了一些非常巧妙的方式，在极为恶劣的条件下也能生存，当环境变得太干或太冷时，水熊虫的新陈代谢几乎会降低到零，然后休眠多年。

伊曼：“它们把所有的爪爪攒在一起，团进身体里，然后你就再也看不到这些小腿了，这让它们看起来像小舌头一样。把所有的腿藏起来之后，它们就会降低新陈代谢，基本上停止所有代谢。”然后，当条件再次合适时，它们就会苏醒过来，继续原本的生活，就像睡美人在王子到来前睡了一个世纪一样。

Tardigrades, an Unlikely Sleeping Beauty

Ashleigh Papp:?Imagine a little critter that isn’t quite an insect or an animal. It’s about one millimeter in length, shaped like a gummy bear with eight legs and covered in tough, almost crunchy-looking scales. Ladies and gentlemen, meet the?tardigrade!

Jessica Ehmann:?They basically look like, more or less, something between a worm and a bear with more legs. They get the name water bears from their?lumbering?gait?that—when they walk, they kind of sway from side to side, which is quite cute.

Papp:?That’s Jessica Ehmann (“ee-mahn”), a research scientist and former student researcher at the University of Stuttgart in Germany, and she's pretty obsessed with the water bear.

Ehmann:?So that’s basically when I fell in love with the tardigrade, because it sat there under my?binoculars, and it got up in the front of the body, and it was waving at me.

Papp:?Tardigrades have been around for even longer than the dinosaurs—by, like, 200 million years. And over all of this time, they’ve developed some pretty?nifty?ways to survive harsh environmental conditions. When things get too dry or too cold, a tardigrade can lower its metabolism to nearly zero and go?dormant?for years.

Ehmann:?They take all their arms, and they pull them inside, and you can’t see their arms anymore; they just look like small tongues. And they, like, pull in all their?extremities. And then they slow down their metabolism, basically, to a standstill.

Papp:?And then, when conditions are right again, they wake up and go on with their life, almost like Sleeping Beauty lying asleep for a century before her prince arrives.

Papp:?Here’s why that matters. Researchers are really interested in what happens to tardigrades while they’re in that dormant state, which they call “cryptobiosis.” If nearly everything can be turned off and then, decades later, turned back on and fully functional, the tardigrade and its...[full transcript]