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  • Sleep is wonderful, but in the animal kingdom, it's also a surprisingly dangerous activity.

  • For many animals, lying in one spot, completely motionless, with basically no awareness of

  • their surroundings is just asking for trouble.

  • It also takes away from time that could be spent finding food or other resources.

  • But all animals do it.

  • And some take it to the extreme.

  • There are some risk-takers who spend almost all of their days sleeping, but they put themselves in harm's way for good reasons.

  • And as a bonus, they're also helping scientists understand why sleep is so useful.

  • So, here are five animals that sleep way too muchat least, by our standards.

  • The big brown bat is probably best known for its weird sleeping style.

  • Like other bats, it sleeps hanging upside-down from caves, trees, or rock faces, thanks to special tendons in its feet.

  • But this bat also has one of the longest sleeping times of any mammal.

  • According to some estimates, it gets around 19.7 hours of shut-eye every day.

  • Scientists think the bats' long snoozes might have developed to give them a perfectly efficient and safe daily schedule.

  • Essentially, sleeping all the time allows them to stay out of trouble and to be awake when their food is.

  • See, these bats are pretty much only active in the few hours around dusk.

  • If they flew around any earlier, birds with keen eyesight and stealthy flying skills could swoop in and make them a meal.

  • So staying asleep and motionless is actually the safest option.

  • Being active for only a few hours each day also helps bats save energy.

  • Their prey includes things like moths and mayflies, which are also primarily active around dusk.

  • So even if a bat stayed up late into the night, they wouldn't really get anything for it, since their food wouldn't be around.

  • They'd just be wasting energy.

  • This makes big brown bats a great case for an idea called adaptive inactivitybasically, an adaptation that leads to animals only being awake when they need to be.

  • Now, another animal that sleeps the day away is the koala.

  • You might have read that koalas sleep for up to 22 hours a day, but that's generally not true.

  • Instead, studies put their total snooze time at around 14.5 hours on average.

  • Which isn't too bad.

  • Koalas likely sleep so much because their diet of eucalyptus leaves isn't all that good for them.

  • This isn't because these leaves contain toxins, though.

  • Koalas' digestive systems seem to have adapted to that pretty well.

  • Instead, it's because these leaves don't have many nutrients.

  • That means koalas don't get much energy out of their food, given how much work it takes to digest it.

  • So sleeping all day is their fuzzy body's way of putting a cap on how much energy they spend.

  • Also, if you're wondering why koalas don't just eat something better for themwell, there aren't many options.

  • As bad as they seem, eucalyptus leaves are actually some of the safer foods in the koalas' environment.

  • Common opossums are some of the best nappers in the animal world.

  • These ratty-looking marsupials have been recorded sleeping for up to 19.4 hours a day.

  • And that might be because they're born really underdeveloped.

  • Gestation in opossums only takes about two weeks, and the animals can have up to 20 or so babies at a time.

  • And these joeys are tiny, too, only weighing about a tenth of a gram.

  • That's less than a dime, but it's likely for a good reason.

  • Most opossums never make it to adulthood, so by having a bunch of huge litters really

  • quickly, an adult can ensure that they have at least some successful offspring.

  • Regardless, these babies spend their first three months or so hanging out in their mom's pouch,

  • basically doing nothing but eating and sleeping until they're grown enough to venture out.

  • Generally speaking, that behavior isn't abnormal for so-called altricial animalsthose that are born immature.

  • Studies have shown that these animals tend to sleep longer and have more rapid eye movement sleep than precocial animals, or those that are born mature.

  • Maybe unsurprisingly, that's because sleeping helps altricial animals put a lot of their energy toward growthespecially rapid eye movement, or REM, sleep.

  • Normally, the opossums would have to put a lot of energy into keeping their bodies warm through thermoregulation, which is a pretty energy-intensive process.

  • But REM sleeps actually shuts down thermoregulation to some extent, which saves them energy.

  • And since these babies are snuggled up close to their parent or littermates, it's not like they need to make all of their own heat, anyway.

  • These processes are all pretty normal, but opossums take them to the extrememaybe because they're born extra small and helpless.

  • As the animals age, they do begin to stay awake for longer, but not by much.

  • And researchers think that behavior is a kind of hangover from their development style.

  • Another altricial animal that you're probably more familiar with is humans.

  • When we're born, we're pretty helpless and can't do much to take care of ourselves.

  • Scientists are still debating exactly what the advantages to this are,

  • but one idea is that someone can't provide enough energy to a fetus and themselves after about nine months.

  • So, out comes a baby.

  • To make up for the lost time in the womb, human newborns sleep a lot.

  • They tend to sleep on and off for up to 16 hours a day,

  • and like with opossums, that time is spent putting energy toward growthespecially toward growing the brain.

  • Multiple studies have found that sleep improved memory and learning in human infants, including language learning.

  • Additionally, two longitudinal studies have linked more sleep as an infant with better impulse control or reasoning a few months or years later.

  • Of course, the tricky thing with these studies is that you can't experimentally change how much sleep babies are getting.

  • That would just be rude.

  • But since these results have been supported in studies with adults, or even ones with infant rats, they seem reliable.

  • For example, in a 2004 study published in Neuron, 18 adults had their brain activity measured while they slept.

  • Researchers found that areas of the brain's hippocampus involved in learning and memory were active during non-REM sleep, also called slow wave sleep.

  • And the more active those areas were at night, the better the study's participants did in a memory task the next day.

  • Overall, scientists think that the connections between brain cells might be formed and reinforced as we sleep.

  • And in infants, some of those connections might be forming for the very first time,

  • making sleep super important for how their brain works over the rest of their lives.

  • In Spanish, “armadillomeanslittle armored one”...

  • but maybe they should be calledlittle sleepy ones”, given that the nine-banded species can sleep for around 18 hours a day.

  • These animals also sleep much more deeply than humans: Around half of their sleep is considered deep sleep, compared to our 5-20%.

  • Scientists think that the reason they can doze off so deeply is because of their distinctive bony plates, called ossified dermal scutes.

  • These iron-like structures cover most of the top side of their bodies, and protect them if a predator tries to take a chomp.

  • And for added safety, these armadillos also dig underground burrows for sleeping.

  • They don't roll up into little balls, thoughonly the three-banded armadillo does that.

  • Still, the nine-banded's anatomy and behavior mean it's protected and can slumber deeply without having to worry about being attacked.

  • That doesn't explain why they sleep so long, though.

  • To figure that out, scientists have had to turn to evolution.

  • Although we'll need more fossil evidence, there's an emerging hypothesis that the evolution of armadillos' hard shells actually determined a lot of the animals' lifestyle, including their sleeping habits.

  • In a 2001 study published in Evolution, biologists found that mammals with armor often walk relatively slowly.

  • That makes sense because, instead of running away, they have a hard shell to protect from predators.

  • But also, because they are so slow, it means armored mammals don't need to have high metabolic rates or eat really high-quality foods to give them lots of energy.

  • They can just forage around for the little they need, and spend the rest of the day snoozing.

  • Now, the last five examples really are the sleep exception, not the rule.

  • Most animals only need a few hours of sleep per night.

  • And even if that still is dangerous, hey, what can you do?

  • Everything needs sleep, right?

  • Wellmaybe not.

  • At least, according to an early 2019 study published in Science Advances.

  • In this paper, researchers tracked the sleep habits of fruit flies.

  • They observed that 6% of their female flies slept for less than 75 minutes a day,

  • with one of those flies sleeping for only 4 minutes on averageapparently, with no adverse effects.

  • Or at least, without any changes to their lifespan.

  • Everything else is kind of hard to measure in a fly, especially when it's in a lab free from predators.

  • To dig into this further, the researchers experimentally sleep-deprived some other fruit flies and waited to see how long they lived.

  • For two weeks, they left the flies in a tube that would shake if the insects became inactive for more than 20 seconds.

  • And again, sleep-deprived flies lived about as long as the controls.

  • This was confusing, because animals have obviously put a lot of time and resources into learning to sleep in safe and efficient ways.

  • But it did lead the scientists to conclude that, while sleep probably serves several biological or evolutionary functions, maybe it isn't always necessary for survival.

  • At least, in fruit flies.

  • One way or another, this study reminds us that we don't fully understand everything about what sleep does.

  • But if armadillos have their fancy shells, and bats have figured out how to take 19-hour napswell, there's gotta be at least some reason for doing it.

  • To try and understand why animals need to sleep, scientists have turned to all kinds of methods, including molecular biology.

  • If you want to learn some of their techniques, you can check out the Order and Information chapter from their Computational Biology course on Brilliant.

  • It's full of great interactive problems and easy-to-understand explanations that make concepts like gene expression easy and interesting to follow.

  • Which is really saying something.

  • Brilliant has all kinds of courses about topics in science, engineering, computer science, and math, so whether it's molecular biology or astrophysics, there's a lot to learn.

  • They also have Daily Challenges, so you can learn something new in just 5-10 minutes every day.

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5 Animals That Sleep Too Much (and One That Might Not Need To)

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    joey joey に公開 2021 年 05 月 11 日
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