Do Jel­ly­fish Dream of Elec­tric Sheep?

Newsweek International - - CONTENT - MEGHAN BARTELS @meghan­bar­tels

we're in­ti­mately fa­mil­iar with what a sleep­ing hu­man looks like, or a sleep­ing dog or bird. But what does a sleep­ing ant look like—or a sleep­ing jel­ly­fish? De­spite spend­ing a third of our lives asleep, we still haven’t cracked all its se­crets, but be­com­ing more adept at rec­og­niz­ing the state in other species could ex­plain why sleep is so im­por­tant to us.

Sleep—or at least some ac­tiv­ity that looks an aw­ful lot like it—is pretty com­mon for all liv­ing crea­tures: among not just hu­mans and our close rel­a­tives but also birds, rep­tiles, fish, in­sects and even a mi­cro­scopic worm, called Caenorhab­di­tis

el­e­gans, found in many sci­ence labs. Still, while sci­en­tists haven’t yet con­firmed that any an­i­mal can go with­out sleep, they also aren’t con­vinced that all an­i­mals need it. That’s par­tic­u­larly true of an­i­mals that don’t even have brains. So when a trio of Cal­tech grad stu­dents no­ticed some lab­o­ra­tory jel­ly­fish were act­ing dif­fer­ently when the lights were turned off, they de­cided to in­ves­ti­gate. “We just went in one night...with our iphones and some pretty sim­ple ap­pa­ra­tuses, and we filmed them,” Michael Abrams, one of the three lead au­thors on the new Cur­rent Bi­ol­ogy pa­per sum­ma­riz­ing their find­ings, tells

Newsweek. “You could re­ally clearly, by eye, see a change in the be­hav­ior be­tween the light and the dark.”

The jel­ly­fish, called Cas­sio­pea, are nick­named up­side-down jel­ly­fish for their pref­er­ence to hang out in shal­low waters near the seafloor with their ten­ta­cles up. Cas­sio­pea are in­trigu­ing to sci­en­tists be­cause they have a ner­vous sys­tem but a very sim­ple one—in­stead of a cen­tral­ized brain like ours, they have a net­work of nerves spread through their bod­ies.

The jel­ly­fish pulse their bells (the non-ten­ta­cle por­tions of jel­ly­fish), cre­at­ing cur­rents around their bod­ies. “They’re pretty big, and it’s a big move­ment,” says Claire Bed­brook, an­other Cal­tech grad stu­dent on the team. And this is what the re­searchers no­ticed that first night watch­ing the tank—the jel­ly­fish pulsed less at night than dur­ing the day. That ob­ser­va­tion sent them on a three-year quest to de­ter­mine whether what they were see­ing met the def­i­ni­tion of sleep.

While you prob­a­bly don’t think about it each night as you put on pa­ja­mas, there is a bi­o­log­i­cal def­i­ni­tion of sleep, based on three cri­te­ria. The body has to move less and be less aware of stim­uli—but those char­ac­ter­is­tics must be read­ily able to turn off (oth­er­wise, you’re in a coma). And there’s some­thing called home­o­static reg­u­la­tion, a fancy way of say­ing that af­ter you go with­out sleep for a long time, you sleep ex­tra to catch up.

So Abrams, Bed­brook and fel­low grad­u­ate stu- dent Ravi Nath de­signed a se­quence of ex­per­i­ments that could me­thod­i­cally de­ter­mine whether those boxes could be checked for Cas­sio­pea.

In or­der to do so, the team needed to fig­ure out a way of in­ter­rupt­ing what­ever sleep the jel­ly­fish might be get­ting. “We had to be pretty cre­ative,” Abrams says, as they needed some kind of prod or nudge they could repli­cate pre­cisely with­out the jel­ly­fish get­ting used to it and ig­nor­ing it.

That meant think­ing like a jel­ly­fish, Bed­brook says. One of the runner-up tech­niques, putting the

Cas­sio­pea in a flask and shak­ing it, vis­i­bly stressed out the jel­ly­fish and was dis­carded. “This is a real is­sue in sleep re­search,” Bed­brook added.

They set­tled on a jel­ly­fish el­e­va­tor of sorts: a tube with a net­ted bot­tom. When they wanted to nudge a Cas­sio­pea, they used the tube to lift the jel­ly­fish up from its hang­out at the bot­tom of the tank. Then they low­ered the tube and let the jel­ly­fish sink back, which Nath imag­ines is like a hu­man wak­ing up from dream­ing of fall­ing.

Once they had their per­fect wake-up nudge, the re­searchers started run­ning the ex­per­i­ments. (And yes, keep­ing jel­ly­fish awake also means keep­ing grad­u­ate stu­dents awake.) They counted jel­ly­fish pulses dur­ing the day and at night, af­ter feed­ing and af­ter fast­ing, while nudg­ing them awake through­out the night, and dur­ing the day af­ter a rest­less night. Step by step, their re­sults checked off each com­po­nent of a sleep-like state, plus the pos­si­bil­ity that they were just see­ing the ef­fects of tired mus­cles. All told, they think

Cas­sio­pea re­ally do sleep, even if it isn’t ex­actly how hu­mans do.

Bed­brook is ea­ger to see whether other re­searchers find sim­i­lar be­hav­iors in their own jel­ly­fish and other brain­less species whose sleep habits haven’t yet been closely stud­ied. That would tell sci­en­tists some­thing im­por­tant about the value of sleep, ac­cord­ing to Is­abella Capellini, a re­searcher at the Univer­sity of Hull in the U.K. who has stud­ied the evo­lu­tion of sleep. If all species that have no brains sleep, she wrote in an email to mul­ti­ple me­dia out­lets, “the pre­sumed ben­e­fits of sleep are more univer­sal and far more broadly shared across the tree of life than pre­vi­ously thought; sleep is in essence evo­lu­tion­ar­ily older than we thought.” It would also mean that sleep has a pur­pose be­yond sim­ply let­ting the brain rest.

So next time in­som­nia comes to visit your bed­room, con­sider count­ing jel­ly­fish for in­spi­ra­tion.

One down­side of sleep re­search: keep­ing jel­ly­fish awake also means keep­ing grad­u­ate stu­dents awake.

WAKE­UP CALL Re­searchers had to prod the jel­ly­fish out of what seemed to be their sleep state with­out scar­ing them, or bor­ing them so much that they slept through their “alarm clock.”

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