In this episode of Tiny Show and Tell Us, we talk about the Ampullae of Lorenzini that allow sharks to detect the electrochemical signals coming from prey. We also cover the fascinating science behind cyanide-filled clovers. Did you know cyanide is actually a very popular poison in the plant kingdom?
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Transcript of this Episode
Sam Jones: Welcome to Tiny Show and Tell Us, the bonus series where you write in with your favorite science story, fact or piece of news, and we read your email aloud and then dive deeper. I'm Sam Jones, I'm the exec producer of Tiny Matters, and I want to give a big thank you to science writer and chemist Anne Hilden for doing the research for this episode. Today I'm here again with science communicator, George Zaidan, who you can also hear on Tiny Show and Tell Us episodes six and seven. Hey, George.
George Zaidan: Hey, Sam, it's great to be here. Before we get into things, just a reminder that Tiny Matters is always looking for you to write in because that's what makes future episodes possible. You can email tinymatters@acs.org or you can also click the Google form link that we put in the episode description. So I think I went last time, you want to go first this time?
Sam Jones: Absolutely. Okay, so I have a very fun one for you today, George.
George Zaidan: Excellent.
Sam Jones: This is from listener Ian, and Ian writes, "Maybe this is an esoteric and subjective fact, but one of the best named parts of animal anatomy are the ampullae of Lorenzini." Tell me that's not fun to say.
George Zaidan: That's great. Ampullae of Lorenzini named by Italian scientist Guillermo del
Lorenzini.
Sam Jones: You're close, I will get into it.
George Zaidan: Oh, really?
Sam Jones: No. I mean, the fact that it's an Italian scientist meaning you're close, yeah, that was it, that was it really. Ian continues, "These are the pits in the snout of a shark that are an important part of their electrical field sensory system. Bonus fact, these electrosensitive organs were mostly lost during teleost fish evolution, but a few lineages independently re-evolved their spidey senses. Bonus, bonus fact..." Ian, I love these, "The ampullae cells are developmentally related to the fluid sensing hair cells found in fish lateral lines and human ears. And one of the genes that's important for both hair cell development and ampullary organ development, and may be involved in evolutionary loss gain of these organs but the details are still TBD and messy, is the same gene that controls how curved your ribs are."
George Zaidan: What?
Sam Jones: Evolution's crazy.
George Zaidan: It is wild.
Sam Jones: Ian didn't say that last part, but I think he would agree. Okay, so thank you, Ian. I'm excited to talk about this.
George Zaidan: Great set of facts, Ian.
Sam Jones: Yeah, really, really excellent. So Anne did a lot of the research for this, and she said that when she first typed ampullae into her search bar, the first word ampulla came up. And apparently in ancient Rome an ampulla was a small round vessel for storing liquid. So it makes sense that as an anatomical term, ampullae refers to tiny fluid filled chambers. So let's talk about the ampullae of Lorenzini, they're named after the physician and ichthyologist... That word. Physician and ichthyologist, aka fish researcher, Stefano Lorenzini.
George Zaidan: Love it.
Sam Jones: Not Guillermo, Stefano.
George Zaidan: I was so close.
Sam Jones: So close. Who gave them an exact description, but he had no idea what their purpose was. So he's like, "It's these things, they do this thing, let's name it after me. Slap my name on it, let's go." And that was in I think the 1600s, took a while but fortunately now we know what they do. So these are electrosensory organs that contain specialized cells that can detect small changes in environmental voltage gradients using ion channels that are molecularly different from those that you see in mammals. So these are very unique. And so they form a series of tube-like structures just beneath the skin, and I've also seen them referred to as jelly-filled canals.
George Zaidan: Oh, gross.
Sam Jones: And one of the... Oh, this is so bad. And one of the scientific book chapters that I perused said, quote, "Squeeze the snout, thick fluid emerges from the ampullae through pores in the skin." I'm like, "Leave that shark alone." Anyway, that's lovely. So these special organs may help sharks find prey since living creatures generate tiny electrical fields.
George Zaidan: I see, I was going to ask, yeah.
Sam Jones: They're able to sense these electrical fields coming off of different things that they want to eat.
George Zaidan: Interesting.
Sam Jones: So the ampullae of Lorenzini have been found not just in sharks, but rays, sturgeons, aquatic salamanders, and a bunch of other species. So researchers have found that electroreceptor systems were present in a variety of ancient fish early on in their evolutionary history. So it seems like some of the groups of fish lost their ability to sense electric fields as they evolved, so this is the more ancient state is having this capacity. So specifically the loss happened when teleosts, which are a subclass of bony fish, branched off from sturgeons and paddlefishes. And so most of the fish that we know today are teleosts. And then similarly, the precursors to mammals actually lost their ampullae of Lorenzini when terrestrial tetrapods branched off from amphibians.
George Zaidan: Interesting.
Sam Jones: Man, can't believe we lost those.
George Zaidan: What if people who have sixth sense really just have the ampullae de Lorenzini?
Sam Jones: Oh, I see a new movie in the works.
George Zaidan: I see dead people. No, really, I'm just sensing electrical...
Sam Jones: They're just growing up, and they're just like, "You don't have these jelly-filled canals like I do?"
George Zaidan: Oh, that's actually a good premise for a horror movie. Can you imagine a small child ghost with jelly coming out right under her eyes? Ooh, awful.
Sam Jones: And then she turns into a shark and it's like Sharknado the Sharknadoing or something.
George Zaidan: Tonight's dreams brought to you by Sam Jones.
Sam Jones: Oh, my gosh. Okay, so where was I? All right, so sharks and rays on the other hand, they're cartilaginous fish, and they all have ampullae. But both bony and cartilaginous fish of all types have a related system for sensing pressure changes in their environment, and this is called the lateral line system. Which I think a lot of people have heard of, have you heard about this?
George Zaidan: Never, I have never heard of this.
Sam Jones: Okay, I'm a dork. Okay, so it consists of a line of pores that run down either side of the fish's spine, and then they have more pores around their face. The sensory cells at the bottom of these pores have cilia or hair-like structures that create neural signals according to the movement of fluid in the canal, it's really cool. I would say generally aquatic creatures have all of these really cool adaptations for sensing their environment we do not have.
George Zaidan: No, we don't. They live in 3D, we live in 2D basically, right?
Sam Jones: Yeah, that's a good point.
George Zaidan: We can't go up when we feel like it, we have to take the stairs or something.
Sam Jones: Yeah. No, that's true. So in this paper that Anne found, which side note was actually published by scientists that I worked with over a decade ago before I started my PhD, because science is so, so small.
George Zaidan: Oh, wow. That's cool.
Sam Jones: Yeah. So it says that in fish that have electro-sensing cells, those cells develop from lateral line cells while the fish are embryos. So it also says that electro-reception has independently evolved at least twice within teleosts, although electro-receptors in teleosts are shaped really differently and may have more active uses like communicating with members of the same species. So pretty cool.
George Zaidan: Super cool.
Sam Jones: Fish are great, mammals, we've got some work to do. Humans, really I'm talking about humans, yeah, yeah.
George Zaidan: Some mammals are awesome, dogs are great.
Sam Jones: That's true, we already established that a couple episodes ago, so dogs are great.
George Zaidan: Yeah, that might be my favorite one so far, is that dogs love you. But of course it would be.
Sam Jones: Yeah, we're biased.
George Zaidan: We're biased. So I have a fact about clovers from Clover. So we checked on this, it's a listener named Clover. Hi, Clover.
Sam Jones: Hi, Clover.
George Zaidan: And Clover writes in a fact about white clovers, and they write, "White clovers, Trifolium repens, are easily identifiable by white stripes on their leaves. Those stripes contain cyanide in them that the clovers release when the leaves are damaged as a defense mechanism." And Clover ends with an exclamation mark, which I think is very appropriate given the awesomeness of that short but sweet fun fact.
So I want to start with the obvious fact that four leaf clovers are scientifically proven to confer luck on people, so I don't know why this is still disputed, it's obviously true. And just moving on from there. But seriously though, when you think of a four leaf clover, you are probably thinking of this exact species, white clovers. If you go on Wikipedia and find the page for a four leaf clover, you will see a Trifolium repens four leaf clover. Okay, now to the real meat of the fact, which is plants make cyanide, which is fascinating, and it's not just white clovers, 2,000 plus species of plants produce cyanide.
Sam Jones: Whoa. Okay, that's shocking to me. And I love talking about poisons, I don't know if you remember that.
George Zaidan: I have been a Tiny Matters listener for a while, so I am aware.
Sam Jones: How did I miss this? Okay, all right, please continue.
George Zaidan: So as you probably know, cyanide is toxic because what it does is it interferes with cellular respiration. And to make a really long story short, it prevents your cells from using oxygen, even if you are breathing in all the oxygen that you theoretically would need. And the analogy I like to make here is that it's as if you are dying of thirst in a pool, there's water all around you but you cannot drink it so you die of thirst.
Cyanide is very toxic. So I weigh about 170 pounds, half a gram of cyanide is plenty, more than enough to kill me. So two questions. One, why do plants produce cyanide? And two, the more interesting question is, how do they produce it without also poisoning themselves? So we'll start with the why and then we'll get to the how. So the ‘why’ is that... We're not 100% sure because we can't ask a plant, but most scientists think that they do it as a defense mechanism. And the reason is that plants can't run away, if something's trying to eat a plant, it has two options, it can do a mechanical defense like a thorn or it can do a chemical defense like cyanide.
Another reason they produce cyanide in particular, we think, is because metabolically it's pretty cheap, it's a carbon triple bonded to a nitrogen, and that moiety can either be bonded to a hydrogen or something like sodium or potassium. So it's three atoms, it's easy for a plant to produce, and it is toxic to a wide range of living things. So you produce this one poison and you're likely to hit most of the things that would try and come by and eat you.
Okay, so now the ‘how,’ how do they make this poison without also poisoning themselves? And this is totally genius. So what they do is they do not produce cyanide by itself, because if they were to they would poison their own mitochondria. What they do is they attach the cyanide to something harmless, like a sugar. So now you have a sugar that is covalently bonded to a cyanide molecule. And this combo molecule, which is called a cyanogenic glycoside, is totally non-toxic because the sugar is so big that it prevents the cyanide from doing what it would otherwise do. And they're bonded together, so that's it, that bond is not going anywhere.
Sam Jones: So can I ask a question, and maybe you're going to go into this?
George Zaidan: Please.
Sam Jones: So if I ate clover, would I experience cyanide poisoning?
George Zaidan: What a great question, and the perfect segue into the next... So yes, you would, and here's why. Because the clover and all the plants that make cyanide also make an enzyme that cleaves the bond between the cyanide and the sugar. Cuts that bond, that releases the cyanide, and at that point that cyanide can be poisonous and is poisonous. And so when a clover is just sitting around the enzyme and the cyanogenic glycoside don't ever come into contact with each other, but if you were to chew it, breaking up the cells, smashing all the vesicles inside, mixing all the components, they do come together. And that's when the enzyme breaks the bond, cyanide is released. And by that point it's in your stomach, it's in your intestine, it's inside you, it's going to be toxic. So that is total genius.
Sam Jones: There must be so many fictional novels back from the 1800s where these... I want to say women, because I feel it's a little bit more stealth, smarter some might say. And so I wonder how many stories there are of some female character collecting clovers to poison her terrible husband or whatever.
George Zaidan: So actually that's a great point. I didn't look into how much cyanide clovers particularly produce, but there are definitely plants that produce enough where if you eat it as a human it's going to be toxic to you. There are some species of yucca, I think it's yucca, that produce enough cyanide that you have to process the thing before you eat it. Again, the way that you would do that is by simulating chewing. So what people do is that they grate... I think that's cassava actually. They grate the cassava and that causes the cyanogenic glycoside to mix with the enzyme, and then they just leave it out to dry, cyanide all evaporates away. Or they wash it with water, or maybe they do both. And at that point you have a safe to eat food that has been rid of most of the cyanide.
And what I really found interesting about this is that I think we've heard often that evolution is this sort of cat and mouse game, and this is a perfect example of this. There are some animals that have evolved anti cyanide defenses, so they can eat basically as much cyanide containing plants as they want. And this leads to what ecologists call the Red Queen hypothesis, which is the idea that species need to constantly evolve defenses, and counter defenses, and counter counter defenses just to avoid going extinct. And the reason it's called the Red Queen hypothesis is that it's from Lewis Carroll's Through the Looking-Glass. So the Red Queen says to Alice, "Here you see it takes all the running you can do to keep in the same place." So you evolve these defenses, and counter defenses, and counter defenses, and counter, counter, counter defenses, and the reward you get for that is just surviving.
Sam Jones: Not dying.
George Zaidan: Yeah, exactly. So I thought that was awesome, thank you, Clover, for sending in a fact very appropriately about clovers.
Sam Jones: Yeah, I love that. Also, when you were talking about the cassava and people grating it, leaving it out, you have the cyanide that actually just vaporizes. It made me think a lot about the number of people that died just trying to eat something, and then they're like, "Well, we can't do it like that, what about if we roast it? Nope, that person still died." And the cassava's like, "Got them, just keep going." And it's like, "All right, we found a thing." And everyone's like, "Do we have to try a new food?" "Yes, we have to try a new food, who's up for it?"
George Zaidan: Yeah. And I mean, the really interesting thing about the cassava thing is that you'd think, well, why do people even grow this? What's the point of growing a toxic food? The answer is that you can grow it, leave it in the ground, animals can't steal it from you because it's toxic. And then if you ever have a famine or you're short on food one week you can harvest some, and boom, you can process it, and eat it, and it's a safety food. That's one way that people use it.
Sam Jones: Oh, that's really cool, didn't know that, interesting. You learn so much in a Tiny Show and Tell Us.
George Zaidan: You do.
Sam Jones: It's really the gift that keeps giving.
George Zaidan: It is, and we learn so much. How much of this did we not know before we started?
Sam Jones: Almost all.
George Zaidan: Yes.
Sam Jones: I knew what a lateral line was.
George Zaidan: I didn't.
Sam Jones: All right, so all.
George Zaidan: All right. Well, thank you for tuning into Tiny Show and Tell Us, a bonus episode from Tiny Matters, a production of the American Chemical Society.
Sam Jones: To be featured in a future episode, send us an email with your Tiny Show and Tell at tinymatters@acs.org, or click the Google form link in this episode's description. We'll see you next time.
- Molecular basis of ancestral vertebrate electroreception
- How sharks and other animals evolved electroreception to find their prey
- Distribution, morphology, and cytology of ampullae of Lorenzini in the Oman shark, Iago omanensis (Triakidae), from the Gulf of Aqaba, Red Sea
- Lateral line system
- The evolution and development of vertebrate lateral line electroreceptors
- Cyanide fact sheet
- Factors affecting the hydrogen cyanide potential of white clover (Trifolium repens L.)
- Cyanogenesis potential and iodine concentration in white clover (Trifolium repens L.) cultivars