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  • [ intro ]

  • In the 1990s, researchers were puzzled by struggling trout populations in the Great

  • Lakes.

  • Even though pollution levels were low, the fish were acting really weird.

  • They were having a hard time swimming upright,

  • and showing signs of overexcitability

  • all very strange behaviors for these fish.

  • And they weren't just acting weird.

  • A not-small number of them were actually dying before they could reach adulthood

  • and no one could really figure out what was going on.

  • That is, until a team of researchers suggested that these fish might be missing something

  • important: vitamin B1,

  • often referred to as thiamine.

  • And it turns out that hunch was right!

  • When they supplemented their diet,

  • the fish recovered.

  • Only... it turned out it wasn't just these fish.

  • Since this initial discovery,

  • scientists have found dozens of other creatures living in the Northern Hemisphere

  • which were similarly lacking thiamine

  • including fish, birds, reptiles, and maybe even mammals.

  • Some experts think that's evidence that something much bigger is going on: that nature

  • has a vitamin deficiency!

  • And that's led to a flurry of research into what could possibly

  • be causing this impending ecological crisis.

  • Andwell, spoiler alert, the studies basically all point a finger at humans being the problem

  • though, in different ways.

  • And ultimately, while these deficiencies themselves are a big problem,

  • they're also an indicator of an even bigger one: a planet under stress.

  • Thankfully, now that scientists are aware of the potential crisis and have some solid

  • ideas for what could be causing it, they can move forward with trying to alleviate it

  • before it's too late.

  • Now. if you've heard of thiamine before

  • , it was probably because of a multivitamin or health supplement.

  • That's because thiamine is an essential nutrient for all organisms.

  • But we animals can't make it.

  • Only plants and some fungi and microorganisms can.

  • The rest of us have to get thiamine by eating those thiamine makers,

  • or by eating something else that has.

  • Basically, the vitamin slowly spreads up the food chain.

  • Physiologically, thiamine is important because

  • it helps your cells turn the food you eat into fuel that your body can use.

  • It's involved in the chemical reactions that mitochondria use to generate energy for

  • the cell.

  • So, without thiamine, an organism's cells are simply unable to turn food into cellular

  • fuel.

  • And a severe thiamine deficiency will eventually lead to illness and death,

  • because cells basically stop functioning.

  • But what's especially awful about thiamine deficiencies is that even mild ones can have

  • nasty effects.

  • Like, strange behavioral issues, as scientists observed in the Great Lakes trout.

  • That's because brain cells need a lot of cellular fuel,

  • so they're extra sensitive to low thiamine levels.

  • And these quotesublethaleffects can vary widely, so it can be super hard to diagnose

  • what's really happening

  • which makes it harder for people to act quickly,

  • before the problem becomes much harder to solve.

  • Now, scientists have known for a really long time

  • that a thiamine deficiency is a huge problem for people.

  • For example, the disease beriberi, which is caused by a lack of thiamine,

  • was first described by Western physicians in the mid-1600s.

  • But in part because it's so tricky to spot,

  • it wasn't until the 1990s that thiamine deficiency was discovered to be a big problem

  • for wildlife, as well.

  • Those struggling Great Lakes trout populations got a lot of people thinking about thiamine

  • in wild animals.

  • And once they were aware of the potential issue,

  • researchers found deficiencies in all sorts of other creatures.

  • This included other underwater inhibants, like alligators and mussels,

  • as well as land animals, including dozens of kinds of birds!

  • Of course, when people lack thiamine, the usual fix is to change their diet or give

  • them a supplement.

  • Unfortunately, those don't really work for ecosystems.

  • Even if we could figure out how to dole out a supplement,

  • it'd be like slapping a tiny bandaid on a gaping wound.

  • So, in order to devise a solid, long-term solution,

  • researchers need to get at the root cause for the deficiencies.

  • And, well, it's kind of taking awhile to figure that out because there are likely multiple

  • things going on.

  • For starters, in some areas, there seem to be shifts happening in those tiny critters

  • that can make their own thiamine.

  • For example: a study in 2012 of the southern California-Baja coast found

  • that there was a lot more variability in B vitamins than other commonly found nutrients.

  • The researchers think that's because climate change is messing with ocean circulation patterns,

  • which in turn is altering the abundance of certain microbes.

  • You see, researchers think that, in the ocean,

  • the microbes that make thiamine are often found in deeper waters, since that's where

  • they get the parts they need to make it

  • like, dead plankton.

  • So, the thiamine they make wouldn't get into shallow water unless they're dragged

  • up from the depths

  • like, in places where ocean currents move deeper waters to the surface.

  • And that's where the system is starting to break down.

  • As the Earth's atmosphere gets warmer

  • you know, thanks to us and all those greenhouse gases we keep producing

  • the ocean gets warmer as well.

  • But this warmth isn't evenly distributed

  • the top layer of the ocean is absorbing a lot more heat than the depths.

  • And these much warmer waters not only float on top of the colder waters,

  • they don't mix well with the lower layers, leading to a phenomenon called stratification.

  • And this stratification seems to be limiting the upward movement of the thiamine-producers!

  • ~

  • So, they're not ending up where the creatures who need to eat them can easily get to them.

  • Changing water conditions may also be creating an environment that selects for organisms

  • that can't make thiamine, or are inedible.

  • You see, a study published in 2020 looked at thiamine deficiencies in Baltic salmon

  • and found that changes to water conditions, especially things like nutrient input,

  • had led to a shift in the food web.

  • Suddenly, certain kinds of cyanobacteria largely replaced the organisms

  • that had served as the bottom of the food chain.

  • And while these cyanobacteria are rich in thiamine, they're also not really edible.

  • So none of that thiamine was available to the animals in the food web.

  • This kind of fundamental shift of aquatic microbes may also help explain

  • why some birds are suffering from thiamine deficiencies.

  • Though, not because they eat plankton

  • but because their prey do!

  • Take eiders — a seabird fond of mussels.

  • Researchers discovered that these birds and their favorite food were both lacking in thiamine

  • in the mid 2010s.

  • And mussels are filter-feeders that vacuum plankton out of the water

  • so it tracks that a change in microorganisms could underscore their thiamine deficiency.

  • But microbes may not be the problem everywhere these deficiencies are cropping up

  • or, at least not the only one.

  • In 2019, researchers demonstrated how overfishing could cause thiamine deficiencies

  • using a computer model.

  • See, fisheries often target small plankton-eating fish

  • like juvenile cod, for example.

  • In fact, cod are one of the most popular fish in the United States,

  • and Atlantic populations have declined in recent years due to overfishing.

  • Well, this model showed that when young cod and other plankton-eating fish

  • disappear from the food web, their prey populations increase.

  • And these prey munch on theanimal planktonor zooplankton that would otherwise be hanging

  • around in the water.

  • So more of them means less zooplankton.~

  • And those zooplankton typically eat the tiny organisms that produce thiamine.

  • So they're the easy way for thiamine to get from the bottom of the food web to everyone

  • else!

  • But that means, if zooplankton populations drop,

  • there's basically no one to transfer this essential vitamin to all the other, larger

  • creatures.

  • And, like with microbial shifts, this kind of deficiency could be impacting animals that

  • live on land

  • but depend on water-dwellers as a primary food source.

  • Plus, it's not the only way non-microscopic critters may be involved in deficiencies.

  • Because some species make an enzyme called thiaminase.

  • Thiaminase breaks down thiamine, so it lets those species process thiamine that's been

  • damaged or degraded.

  • Basically, it lets them get a little extra from the thiamine in their diet.

  • But this enzyme can destroy perfectly good thiamine.

  • And if an animal eats food containing a lot of thiaminase,

  • the enzyme goes to work destroying all the thiamine in its gut,

  • keeping it from actually getting any from its meals!

  • ~

  • Scientists suspect that this is what underlies recent increases in mortality of mammals that

  • don't love seafood

  • like pronghorns and... camels.

  • This could make sense if their diet has shifted to one that's heavy in grains

  • which promote the growth of thiaminase-rich bacteria in their stomachs

  • or if they're munching on a lot of thiaminase-containing plants, like bracken ferns and horsetails.

  • Researchers know that can happen with livestock and captive animals like deer.

  • And, thanks to our farms, there are plenty of grains around.

  • Plus, those particular thiaminase-rich plants do pretty well in a warming climate,

  • and may even outcompete other forage plants that are more sensitive to changing temperatures.

  • So, basically, our love of fossil fuels may be encouraging thiaminase-rich plants to grow,

  • resulting in a dietary shift that could harm wildlife!

  • And something very similar is already happening underwater.

  • For example, a 2016 paper revealed that Chinook salmon in Western Alaska had lower thiamine

  • levels

  • when they ate thiaminase-containing fish like capelin.

  • And central California salmon are also lacking in thiamine,

  • which was tied to a recent shift towards an anchovy heavy diet

  • another fish rich in thiaminase.

  • And, in a paper published in 2005,

  • researchers found that several salmon species in the Great Lakes were thiamine-deficient

  • because they were eating too many thiaminase-rich alewife and rainbow smelt.

  • And this is where it becomes really clear that,

  • no matter what case you're looking at, this is all ultimately our fault.

  • You see, both alewife and rainbow smelt don't belong in the Great Lakes.

  • They were introduced by humans!

  • And even where people aren't directly responsible for the presence

  • of thiaminase-rich creatures, we're probably to blame for their sudden abundance.

  • Like, we know the type of food available to Chinook salmon

  • depends on the climate and how it affects the way water moves into the Bering Sea.

  • So, all that CO2 we're spewing and its effect on global climate are directly impacting what

  • these salmon can eat.

  • And the same goes for the California salmon.

  • Those anchovy populations exploded thanks to warmer water temperatures

  • which, again, is thanks to climate change.

  • But the upside here is that we have the opportunity to fix what we've broken!

  • The solution is probably not going to be a one size fits all type of thing

  • and yeah, curbing climate change is probably a big part of it.

  • But there are other things we can do, especially at the local level.

  • For example, in Lake Huron and Lake Michigan,

  • the fish issue was managed by adding thiamine to the water in hatcheries.

  • You see, for a while now, both trout

  • and salmon have been artificially bred and released into these lakes to boost their natural

  • populations.

  • So researchers gave those baby fish a little extra thiamine.

  • And not only did the fish not end up deficient as they grew up,

  • they appear to have outcompeted the thiaminase-rich alewife, likely helping cause their numbers

  • to decline!

  • And researchers are working on finding solutions like that for everything we've talked about

  • today.

  • Like, if a deficiency is exacerbated by overfishing, then altering what and how much we remove

  • from an ecosystem could help shift it back in the right direction

  • or at the very least, ensure wild animals have enough of their natural foods to eat.

  • And even in places where problems go all the way to the microbial level, we might have

  • some options.

  • Like, if cyanobacteria are taking over, then regulating the amount of agricultural pollution

  • might help, as they flourish in runoff.

  • Or there may be some other way of cleaning up the water to get conditions back to promoting

  • thiamine-makers instead.

  • Getting rid of nature's vitamin deficiency isn't going to be easy.

  • But all of this knowledge gained over the past three decades is helping governments

  • and organizations move towards

  • taking more sustainable approaches in managing ecosystems.

  • And researchers are continuing to investigate this widespread problem

  • so they can come up with effective, attainable solutions.

  • Thanks for watching this episode of SciShow!

  • And thank you to everyone who supports this channel,

  • whether it's as a channel member here on YouTube, or as a Patreon patron.

  • We wouldn't be able to dive deep into complex topics like this without your support!

  • So thank you.

  • And if you'd like to learn more about how you can help us make free educational science

  • videos,

  • you can find our patron community at Patreon.com/SciShow,

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  • [ outro ]

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B2 中高級 美國腔

我们正在给自然界提供维生素缺乏症(We’re Giving Nature a Vitamin Deficiency)

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    joey joey 發佈於 2021 年 05 月 13 日
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