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  • I don't know if you've noticed, but animals kind of need oxygen.

  • That's because animals generally get their energy from cellular structures called mitochondria,

  • and those processes require oxygen to work.

  • So if somebody stole all of the Earth's O2, things would end pretty quickly around here.

  • Except, as it turns out, there are at least some animals that would be perfectly fine.

  • Because in 2010, scientists published a paper announcing

  • that they'd found three species of them that straight-up don't need oxygen!

  • Now, to be clear, not all life needs oxygen.

  • There are plenty of single-celled microbes that are anaerobic,

  • meaning they can survive just fine without the stuff.

  • Instead of oxygen, these organisms can use other molecules like sulfate or nitrate.

  • But for years, scientists thought a system like that wouldn't work for animals,

  • since their complex, multicellular bodies have higher energy requirements.

  • Instead, they thought animals needed the more efficient energy production that takes place in mitochondria.

  • And then came that 2010 paper.

  • This discovery happened in the L'Atalante basin,

  • three thousand meters below the surface of the Mediterranean Sea.

  • L'Atalante is a deep hypersaline anoxic basin,

  • meaning it's super salty and completely devoid of oxygen.

  • It's the kind of place you wouldn't expect to find animals.

  • And indeed, when a research team visited three times between 1998 and 2008,

  • that's generally what they saw.

  • They did find a lot of single-celled organisms living in the basin,

  • but most of the animals they saw were dead,

  • the result of a so-calledrain of cadaversfrom oxygenated waters above.

  • Most of the animals, but not all of them.

  • Because the team also found an unusually high abundance of tiny, sediment-dwelling animals

  • called loriciferans, and they were seemingly very alive.

  • Loriciferans are pretty weird creatures to begin with.

  • Their heads are covered in spines, and their bodies are typically encased in a vase-like shell called a lorica.

  • But finding them in an oxygen-free basin was a whole new level of weird.

  • The researchers observed that the loriciferans were still taking up nutrients,

  • and that some had recently molted.

  • Some even had developing offspring inside them.

  • So these animals apparently spend their lives buried in this sediment, with no oxygen,

  • not only surviving, but thriving.

  • Part of this incredible survival might be down to their size.

  • At less than one millimeter long, loriciferans have pretty low energy needs.

  • But they also seem to have some unique adaptations.

  • For one thing, they don't have mitochondria!

  • Instead, they have cellular structures that look a lot like hydrogenosomes.

  • These are organelles that some microbes use to produce energy,

  • and they use hydrogen ions in place of oxygen.

  • Alongside these structures, the researchers also noticed shapes that might be microbes

  • living inside the loriciferans' cells.

  • That's intriguing because some anaerobic, single-celled organisms also have symbiotic microbes

  • that live alongside their hydrogenosomes.

  • All in all, it looks like these loriciferans have developed similar cellular structures

  • to anaerobic microbes for living in the same way,

  • although it's not clear how they did this.

  • One option is that they retained these adaptations from an earlier ancestor

  • more similar to anaerobic microbes.

  • But it's also possible that their ancestors swiped genes from their microbial neighbors,

  • allowing them to use the same cellular tricks for survival.

  • Of course, this is an extraordinary claim, and some researchers have doubts.

  • For example, a study published in 2015 looked in the same basin

  • and was unable to find independent evidence of living loriciferans.

  • The researchers of the original study are still confident in their results,

  • but it may take more confirmation to convince everyone.

  • If these results do hold up, though,

  • it could change how we understand the requirements of complex life.

  • It would have implications for the diversity of animal life in the world today,

  • for scientists interested in how life got started on an oxygen-deficient early Earth,

  • and maybe even for scientists looking for life elsewhere in the solar system.

  • Ultimately, life is so adaptable and endlessly diverse,

  • that we wouldn't be shocked if there are more surprises to be found.

  • Critical thinking in science is obviously a great thing, though,

  • and that's why it's so important for researchers to check each other's work.

  • And if you want to brush up on your critical thinking skills, or just learn some really cool stuff,

  • the Daily Challenges from Brilliant are a great way to do that.

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  • Like, I just completed one about black body radiation in a real life setting: a campfire!

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B1 中級

この動物たちは酸素を必要としないのか? (These Animals Don't Need Oxygen?!)

  • 74 4
    Jerry Liu に公開 2021 年 01 月 14 日