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Duration:09:43
Uploaded:2021-02-28
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This episode is brought to you by the Music for Scientists album! Stream the album on major music services here: https://streamlink.to/music-for-scientists. Check out the “For Your Love" music video here: https://youtu.be/YGjjvd34Cvc.

Thievery is a known survival strategy in the wild. But you couldn’t steal a toxin...or could you? Meet 5 animals that turn someone else’s poison into their own weapon of choice.

Hosted by: Stefan Chin

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Sources:
https://www.nature.com/nrmicro/journal/v14/n2/full/nrmicro.2015.3.html
https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/pore-forming-toxin
https://www.nature.com/articles/s41467-019-09681-1
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https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/cardenolides
https://royalsocietypublishing.org/doi/full/10.1098/rspb.2011.1169
https://link.springer.com/referenceworkentry/10.1007%2F978-1-4614-1533-6_247
https://genomebiology.biomedcentral.com/articles/10.1186/gb-2003-4-3-207
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/bufadienolides
https://biologydictionary.net/atp/
https://link.springer.com/referenceworkentry/10.1007%2F978-3-642-11274-4_135
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1892995/
https://royalsocietypublishing.org/doi/full/10.1098/rspb.2016.2111
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1892995/
https://www.chemeurope.com/en/encyclopedia/Batrachotoxin.html
https://rupress.org/jgp/article/137/5/397/42910/Structural-studies-of-ion-selectivity-in
https://www.pnas.org/content/101/45/15857
https://www.pnas.org/content/97/24/12948
https://www.intechopen.com/books/toxicology-new-aspects-to-this-scientific-conundrum/a-review-of-cyanogenic-glycosides-in-edible-plants
https://www.ncbi.nlm.nih.gov/books/NBK507796/
https://www.intechopen.com/books/toxicology-new-aspects-to-this-scientific-conundrum/a-review-of-cyanogenic-glycosides-in-edible-plants
https://www.researchgate.net/profile/J_P_A_Angseesing/publication/274457763_Cyanogenesis_in_Bird's_Foot_Trefoil_and_White_Clover_-_differentiation_with_respect_to_aspect/links/55206c660cf2f9c13050b080/Cyanogenesis-in-Birds-Foot-Trefoil-and-White-Clover-differentiation-with-respect-to-aspect.pdf
https://www.sciencedirect.com/science/article/abs/pii/S0965174813001975
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#SciShow
This episode is brought to you by  the Music for Scientists album, now available on all streaming services. [♪ INTRO].

Theft in nature isn’t exactly a novel idea. I mean, animals steal stuff  from each other all the time.

Squirrels steal food.  Burrowing owls steal burrows. Emperor penguins will even  take each other's chicks. But some of nature’s most extreme  thieves might be the toxin-stealers.

Taking another creature’s poison is a little  harder than just nabbing a nut or a nest. To do it without hurting yourself,  you need serious biological tricks. But thanks to some clever adaptations, animals have managed to steal all  kinds of toxins — including these five.

First up are pore-forming toxins. These are mostly produced by certain bacteria, but they’re also used by cnidarians, a group that includes sea anemones and jellyfish. If you’ve ever been stung by a jellyfish, you’ve experienced a dose of pore-forming toxin.

As the name implies, these toxins  form pores in cell membranes, making the membrane permeable. In other words, the toxin puts  holes in the target cells, which can cause them to  rupture. And when that happens, the cell loses critical nutrients.

Even worse, those pores also  give other toxins a way in. So, even if the pores themselves  don’t cause a cell to die, some other substance might. What’s weird, though, is that  despite being super dangerous, cnidarian toxins are also found in  certain kinds of worm-like species, including nudibranchs, flatworms,  and at least one true worm.

And these worms don’t produce  the toxins themselves:. They take them from cnidarians and  use them for their own defense. Take aeolid nudibranchs, for example.

Commonly called sea slugs, these  animals are some of the few that can successfully wrangle a stinging  cnidarian, like a coral or an anemone. After they catch their prey, the  nudibranchs eat the animal's tentacles, including the nematocysts, the  part that delivers the venom. Somehow, they do this without  getting stung themselves.

But that’s still not the most impressive part. Once the slug has ingested the nematocysts, they travel through its digestive  system to special glands in its cerata, which are short, tentacle-like structures  on the outside of the slug's body. Then, when it's threatened, the slug  can deliver its venomous payload by detaching the cerata.

And this might be a sort of  multi-purpose defense mechanism:. The detached cerata could sting the predator, but could also just distract it  while the slug makes its escape. Next up, we’ve got cyanogenic glucosides, which are toxins produced  by plants for self-defense.

Chewing or digesting a cyanogenic  glucoside releases hydrogen cyanide, a compound just as deadly in  real life as it is in the movies. Hydrogen cyanide deprives cells of oxygen,  and that can ultimately cause cell death. Except, these glucosides are  also found in some plants that are regularly eaten by herbivores.

So in many cases, like for the birds-foot  trefoil, these compounds don’t protect them from large animals. Like, cows can  pretty happily munch on this stuff. But the glucosides do provide protection against smaller predators like snails and insects.

That is, except for the six-spot burnet, a moth that depends on birds-foot  trefoil as a larval host. Like cows, the burnet’s larvae can eat  trefoil all day without suffering ill effects, despite being much, much  smaller than our bovine friends. And to pull this off, the  larvae have a few tricks.

For one, they eat fast, which  limits the amount of time they’re in contact with the cyanogenic glucosides. But most importantly, the environment in their gut just doesn’t break down those compounds. In an acidic gut like ours, those  molecules would be digested and release hydrogen cyanide, but the burnet larva  has a gut that’s more basic than acidic.

The burnet isn’t the only member  of the moth and butterfly family that doesn’t digest these molecules, but  what happens next is the special part. See, the burnet larvae don’t  just leave the glucosides alone. Instead, they move them into their own tissues.

Scientists don’t know much about  how they do this, but they know that once the glucosides are in place, they  act as a powerful defense mechanism. In fact, the intact molecules  remain in the insect’s tissues even after it turns into a moth. The moth keeps the glucosides in “defense  droplets” inside cavities in its skin.

And then, when the moth tangles with  a predator, it releases the droplets. In small doses, this means the moth tastes bad. But in large doses, it might be deadly.

Most predators never find out, though, because they know better than  to bother a six-spot burnet. Up next are the cardenolides. These are cardiac-active steroids, which  broadly means they mess with the heart.

Once inside your body, they  block the sodium-potassium pump, a structure responsible for transporting  those elements across cell membranes. Blocking them can cause an irregular  heartbeat, and if it’s severe enough, can lead to heart blockage or even cardiac arrest. Cardenolides are found in  plants all over the world, including the African Acokanthera  tree, which has a cardenolide called ouabain in its bark and roots.

Indigenous Somalis use this  toxin to poison their arrow tips and make it easier to bring  down big game like elephants. And the usefulness of ouabain hasn’t been  lost on the African crested rat, either. It deliberately steals the tree’s  toxin by chewing its roots and bark, mixing it up with its saliva.

Then, the creature applies this mixture to  the specialized guard hairs that cover its body, kind of like how you might slather  on a conditioner or a styling gel. The guard hairs absorb the  toxin and then deliver it to any predator that’s foolish  enough to bite the rat. What’s especially wild is that cardenolides  are the same toxins used in rat poison, yet they don’t seem to harm  this particular rodent.

Scientists don’t really know why, but it  might be because their salivary glands are unusually large and may produce secretions  that can somehow process the toxin. Now, like cardenolides,  bufadienolides are steroidal toxins. And they also affect sodium-potassium pumps.

They cause an increase in sodium and  a decrease in potassium in the cell, which prevents the cell  from conducting electricity. That can lead to a heartbeat  that’s too fast or too slow. And again, in severe cases,  it can cause cardiac arrest.

But don’t tell that to the tiger keelback. This snake keeps bufadienolides in special  glands on its neck called nuchal glands. But again, it doesn’t make these toxins itself.

This time, it gets them  from the toads that it eats. Luckily for the snake, it’s  resistant to bufadienolides. In fact, a lot of snakes have a  natural resistance to these toxins, including ones that don’t even eat toads.

Studies have found that these  snakes seem to get their immunity from unique amino acids on the part  of the pump that binds to the toxin. But the tiger keelback goes  beyond mere protection:. It puts the toxin to work for its own defense.

When a predator damages the  snake’s nuchal gland tissue, it gets rewarded with a mouthful  of stinky, yellow toxin. As for how the toxin gets  there, a 2007 study found that the tiger keelback’s nuchal glands are full  of tiny blood vessels called capillaries, suggesting that the toxins are  transported there in blood plasma. And when the snake doesn’t eat toads, it also doesn’t have bufadienolides  in its glands at all.

Instead, they fill up with really benign  stuff, like water, lipids, and carbohydrates. So toad-eating isn’t just about food:  It’s also important for self-defense. And as a nice bonus, mother  snakes can pass the toxin along to their offspring, as well.

And finally, batrachotoxins are  poisons that affect the nervous system. These toxins affect the sodium  channels in nerves and muscles, changing their sensitivity  to voltage and their ability to choose which ions to transfer across membranes. The result is that nerves that can  no longer send signals to muscles, which is pretty bad news,  especially for the heart.

Humans famously steal batrachotoxins  from poison dart frogs, so-named because the toxin can be used  to make darts a whole lot more lethal. But other animals steal these toxins,  too, though not necessarily from frogs. New Guinean passerine birds get batrachotoxins from the melyrid beetles that they eat.

Like poison-dart frogs, the birds aren’t  affected by the toxins, possibly because they have special sodium channels that  have evolved resistance to them. Regardless, somewhere along the evolutionary road, the birds developed the  ability to store these toxins and secrete them in their feathers and skin. Instead of, you know, just digesting them.

Scientists aren’t completely sure how  they do this, but the result is clear:. The birds themselves become toxic. See, feathers in general act as a barrier  between a predator and a bird’s flesh.

For most birds, it isn’t a super effective barrier because the predator can  just pluck out the feathers. But if you’re a passerine, predators  that mess with your feathers will get a nasty surprise. The toxin dose isn’t usually large enough to kill, but it can cause respiratory  irritation and other unpleasantries.

The toxin also seems to help the  passerine ward off parasites, like lice. In fact, a 1999 study found that  lice seem to deliberately avoid the feathers of toxic birds. Lice that do come into contact with  the toxin also had shorter lifespans.

So, fewer lice to start with, and a shorter  irritation from those that do attach! Some studies also suggest that the passerine  may be able to transfer batrachotoxins from their feathers to their eggs, potentially  protecting the eggs from nest robbers. So, whether it’s something they do deliberately, or bit of a happy accident, nature’s  thieves can be pretty crafty!

Also, toxin-stealing is still  an active area of research, so it’s probably a lot more common  than scientists even realize. Still, there’s a lot to appreciate  about what we do understand. How these animals sequester and use  toxins can teach us important things about how structures in their bodies  evolved and how species interact.

Just, you know, make sure you handle with care. If all of these toxin-stealing  animals have got you pumped up about the wonders of the world, you might want to  check out Music for Scientists after this. It’s an album that was inspired  by the beauty of science.

The songs were written and  recorded by Patrick Olsen, and the whole project is an  homage to people of science. If you want to check it out, we recommend  starting with Aristarchus in the Rain, which is a bit of a bop. You can start streaming at  the link in the description. [♪ OUTRO].