Science Friday - Why Do Cephalopods Make Ink?

Episode Date: June 18, 2024

The most wonderful time of the year has arrived: Cephalopod Week, Science Friday’s annual tradition of spotlighting all things octopus, squid, and cuttlefish.One of the many things that make cephalopods special is their ink. What’s it made of? Why do they shoot it at their predators? And why did they evolve this incredible skill?To talk all about inking, guest host Annie Minoff is joined by Dr. Lauren Simonitis, research and biological imaging specialist at Florida Atlantic University.Learn more about how to get involved in Cephalopod Week!Transcript for this segment will be available after the show airs on sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

This week is our annual celebration of all things, octopus, squid, and cuttlefish, and we're talking all about inking. So if they have a ton of mucus in the ink, they can make these ink ropes. Think about if you pick up slime and you pull it for a really, really long time. It's Tuesday, June 18th, and this is Cephalopod Week on Science Friday. I'm sci-fi producer Shoshana Bucksbaum. What started as a response to Shark Week about a decade ago has now become a beloved Science Friday tradition. And one of the many things that make Sothelopods special is their ink. So why do they shoot ink at their predators anyway? What's that ink made of? And why did they evolve this

incredible skill? Here is guest host Annie Minoff with more. Joining me to talk all about inking is my guest. Dr. Lauren Simonitis is a research in biological imaging specialist at Florida Atlantic University based in Boca Raton, Florida. Welcome. Thanks so much for having me. So let's start with the basics. What do cephalopods use their ink for? So cephalopods use their ink for a variety of different reasons, but they all have to do with social activities mostly. So one of the biggest ones is anti-preditor. So during a predation event, an ink response is a great way to get out of that situation

because ink is really dark in color, so it has a good visual response. Ink also has a lot of chemicals that smell really strongly or really badly. So it's a chemical response, but it's also a physical response because it's really gloopy and it can stick all over them, though it's this physical, chemical, visual trifecta of a predator weapon. I did not think of ink as gloopy. Yes. So ink is produced by the ink gland in. In. cephalopods, but there's also the funnel organ, which produces mucus. And together, they release secretions from the ink gland and the mucus or funnel organ at the same time. And that produces this like gloopy, black, smelly substance. Okay. So you mentioned predation, which is I think the thing most people are aware of that cephalopods might use their ink to avoid getting eaten. But what else might they use it for? Yeah. So there is some evidence that.

that they can use it between animals of the same species. They can do different forms of ink. And that is also modulated by the amount of mucus they put in the ink. So if they have like a ton of mucus in the ink, they can make these ink ropes where like think about like if you pick up slime and you pull it for a really, really long time, it creates like a nice thin line. They do the same thing with their ink. And some papers have tied the behaviors that they do with the type of ink responses that they have.

They can be used in mating displays. And some in like the deep ocean where light is limited, they can use it for this fluorescent type display where they can't normally see each other too well. And you were talking earlier about kind of shooting out this inky mucous combination to block maybe a predator's view. But I also understand that sometimes they can use it to fool a predator. Yeah, it is a really cool thing. They make what's called a pseudomorph. And basically, again, they put a good amount of mucus into it. One of the coolest things about them is their chromatophores,

which allow them to change what they look like on the outside, so the color that they are. And what they can do is they'll change to a really dark black color. And then they'll ink this little black or dark brown ink mass. And then they change to a light color and like jet away. No way. And that little ink mass stays. So from the Predators view, they saw a black squid.

Now they see this same black squid like blob. So they're going to go and attack that blob and get a mouthful of ink instead of a mouthful of squid. That is wild. So it's like, don't look at me. I'm going to jet off over here. The actual cephalopod is this inky stuff over here. Yeah. They're very Houdini-like in that way.

Wow. Okay. So we talked a little bit about what the ink actually is. I know there's this mucus involved. but what else is actually in this stuff? Yeah, so there are a lot of really strong chemicals. So there's a good amount of free amino acids. But one of the main things is melanin.

And melanin is the same thing, you know, that gives our skin color, our hair color, our irises color. And the melanin is what gives it that really dark black color. Melanin is a big molecule. It's like photo reflective. So that's why it has that really dense coloring. And how do they make the ink? So within their inkland, that's where they generate it. So inside they have a bunch of different layers of tissue and they go through this process that have a lot of precursors of melanin. So some of those are dopamine is one of them. U melanin is a form of melanin that they also make a precursor to melanin. So they have these building blocks that they slowly make into melanin in their inkland. And then the ink gland is a little pouch off of their digestive system. And so, So whenever they are threatened or whenever they want to expel ink, that's how they do it.

They push it out from their inkland. Because they're so closely related, the inkland in their gut, it's thought that inking evolved as a way to make that excretory pathway more powerful. Because if you've ever picked up a frog or if you pick up like a little dog and it's really excited or really scared, it's really often for animals to release waste as a form of a defense. It's just a little poo when they're just a little too excited. Exactly. So it's pretty common. And we see it a lot in the animal kingdom of animals just essentially flinging their waste products at predators. But then cephalopods, they've kind of given it a little extra oomph. We kind of

think that they added ink into their extratory pathway. And then it became its own expratory pathway through evolutionary history. The other great thing about melanin is since it's so big, a lot of chemicals can bind to it, such as heavy metals. So it's thought that a lot of the extratory pathway that the ink started as was to detoxify the body because all of the heavy metals were sticking to the melanin. If they can jet off all of that melanin, they can detoxify their body. So it's kind of like a cleanse. Exactly. Yeah. An ink cleanse. Got it. And you mentioned earlier that this ink can have a smell. Like could I smell it? And what does it smell like? Yeah. So it's kind of of hard when we think about smelling in the aquatic environment versus the terrestrial environment.

We both live in fluids, right? They live in water. We live in air. And the chemicals that we smell are transported on that fluid. So it's a little hard to think about the parallels between smelling it and water and smelling in an air. But I can say from experience working with this, just opening up my vats of ink. It is so pungent that a lot of those odors do aerosolize and to become smellable in the air. But I think one of the ways that we can really think about what it smells like and what that chemical cue is like is when we think about eating paella or squitting pasta. So as humans, we really like that bitter taste that squid ink has, which is why it's incorporated

in so many different cuisines in the world. And I don't usually think about that like squitting pasta being smelly, though. Like when you open the vats of ink, can you describe what it smells like? Actually, so I get some of my supplies of my ink specifically for cuttlefish. I get them from food suppliers that sell giant vats of ink for squid ink pasta and that kind of stuff. And it kind of smells fishy. It kind of just smells really, really pungent. It's just like an overwhelming kind of unpleasant smell.

But then when you cook it and once it's diluted, right? because I have essentially a giant vat versus the little teaspoon that you put in just to add a flavor. I mean, not to make this a pasta conversation, but how do they get that ink that they then put in the pasta? Yeah, so unfortunately, it is not very animal friendly. I was worried you might say this. Yeah, as far as I know with my research, I can't say I can speak too much on the culinary side for it or the farming side, but I do know that they do have to kill the animals and harvest the ink glands. Because, like I said, if you're just inking the animal, like, you know, I always thought that

they had them in like little inking pens and then they went in and collected their ink every day. But when you do that, they also have that mucus. And the mucus is not delicious. Ideal for like what you want. Okay. So some cephalopods may have been harmed in the making of your squid ink pasta. Yeah. Unfortunately.

So everyone associates octopuses and squid with ink, but cuttlefish also use ink. So I understand there's at least one species of cuttlefish that uses its ink kind of for a dramatic flourish. This is, of course, the male Andrea Cuddlefish. And as I understand it, he shoots out this big plume of ink and then kind of pops through it to impress his mate. Like, ta-da, here I am. Yeah, it is really adorable. I have seen videos of it, and I think it's super fascinating. And the thing about these type of behaviors is they are so, like you have to be serendipitously

seeing these behaviors because these are behaviors that normally happen in the wild and don't always happen when we have these animals in a managed care facility, like an aquarium. So a lot of what we know about the ties between ink behavior and ink, what it looks like, happen from, you know, divers taking videos. or fishermen seeing something happening out there and taking a video of it. And I'm sure that there are plenty of other cool inking behaviors that we just haven't recorded and haven't been lucky enough to see yet. And do other cuttlefish use ink in that way too or just the Andrea?

As far as I know that's the only one I've heard of, another really cool way that some cephalopods use ink is it also acts as an antimicrobial agent. So there's a lot of chemicals in it that stop microbial growth. And something in the ocean environment that is really prone to microbial growth is laying your eggs, right? Yeah, you don't want any microbes near those eggs. Right. And you're laying them like on the substrate or like on the seafloor, on sea grasses. And they're just kind of sitting there and waiting to develop.

And you can kind of defend them, but keeping them from getting all those microbes and all that growth on them, all that biofowling is hard. But since ink has antimicrobial components, and it also has this predator defense chemicals in it, it's a really good thing to inject that into your eggs. So there are some species of cephalopods, which their eggs are filled with ink. And what is special about the cuttlefish, their ink? So honestly, there's not terrible amounts of differences between different cephalopod inks that have been studied. While we do know a lot about cephalopod ink compared to other

inking animals, we still don't have a very wide variety of ink samples from these guys. You just said other inking animals. What other animals ink? So one of the other kind of more well-studied inking animals are these sea slugs. They all belong to the same genus Aplegia. And they actually eat red algae. And they take the red algal pigment. They modify. They modify. it in their body, and then they create some defensive chemicals in their body, and they mix them together and put them out into the environment as this inking response. And it's this red, purply, really beautiful ink. Red and purple? Is that common? What kind of colors of ink are out there? So if you think about cephalopods, those are kind of more of a black ink, ranging to like

a bluish ink. Sometimes cuttlefishing can be a little bit more brown. Applesia, they make ink that is red or like reddish purple. It really depends on the color of algae that they're eating, which interesting about a pleasia too is that like if you feed them green algae or even if you feed them like lettuce, they will still produce the defensive chemicals and they'll still like produce something out of their ink gland. It just won't be colored anymore. So the color really depends on the algae that they eat. Now all of these animals that we talked about that produce ink, did they all evolve from a common ancestor? Yeah. So no. We do not have any common inking ancestor. So even though aplegia, the sea slugs and cephalopods, they're both

gastropods, they don't all descend from some common inking ancestor. Their inkland production sites are not homologous, which means they're not passed down through evolution. But then we also get even more out of the box when we think about the other inking animals. So there's a tinafore that inks that has been discovered recently by one of my colleagues. There are crestfish, which are this type of fish that, to my knowledge, we don't, we have no records of them like inking, like nobody has seen them inked, but in necropsies, they have found ink glands within the crestfish. Interesting.

So fish with ink glands. Yes. And then even weirder, if I can top that, is there are two species of whales, pygmy and dwarf sperm whales that ink as a predator response. Interesting. Inking whales. Yes. So is it that all these species evolved this inking capability separately? Yeah, that is what initially really got me excited about this project. This was kind of the focus of my dissertation, was I joined my PhD lab under Dr. Christopher Marshall, and he had this collection of pygmy sperm oil ink.

He was like, do you want to figure out how does this work as a predator defense? I was like, that sounds like the best project, absolutely. So I started doing research and we have this really, really unusual ink. And I wanted to compare it to these other kind of well-studied inks, inks that we know more about. That's why I picked an apleasia species, Appalachian Californica, the California Sea here, and the common cuttlefish. And then I approached it from a lens of convergent evolution, which is exactly what you were just talking about, where different species, different animal groups evolve the same solution. to a problem through different pathways. They all had the same good idea. Exactly, yeah.

And so you're comparing all of these different inks. I think you mentioned the pygmy sperm whale, cephalopods. What did you find in that comparison? So the first thing we did was look at the chemistry. And while that work had already been done on the cuttlefish and the aplegia, it hadn't been done yet on cogia, which is the pygmy sperm oils. So we were looking across the board what their chemical composition was like, and there wasn't really like a cocktail that every single inking organism has selected

for them. And like, this is what works. But what we found is if we grouped together the invertebrate inks. So if we look at the C-SLC ink and the Cuddlefish ink, they have a lot of torrine, which is a really strong amino acid. And then if we look at the Cuddlefish and the pygmy sperm whale ink, they both have melanin-based ink. So we see comparison. and some similarities, but there's not like one formula that they all share. What is the biggest mystery out there about inking that you would like to solve? You know, we have these two theories about how it evolved through this extratory pathway, through this antimicrobial pathway.

I would just love to find out how this evolved. And unfortunately, it's a little hard. We do have some good fossil records of cephalopods. Yes, there is fossilized egg. Wow. And it's been pretty consistent. We see those precursors to melanin in that ink. We see e-melanin. So we do know that it's been pretty well conserved with encephalopods, but we don't really know that much about the other organisms.

So I think really uncovering the evolutionary history of inking across the taxa are really interesting. Well, I wish you the best of luck uncovering that mystery. That is all the time we have. I would like to thank my guest, Dr. Lauren Simonitis, research and biological imaging. specialist at Florida Atlantic University based in Boko-Raton, Florida. Thanks so much for having me. I had a great time. Me too. Science Friday has been celebrating Cephalopod week for over 10 years. And in that time, we've learned that sci-fi listeners love cephalopods as much as we do. If you visit our website, you'll find lots of other great cephalopod content, including a way that you can sponsor a virtual cephalopod. If you go to

ScienceFriiday.com, you can help us choose the most popular cephalopod in our sea of support. The last three years it's been the common octopus. We're hoping that this year, another octopus finally gets their moment in the spotlight. That's all the time we have for today. Lots of folks help make the show happen, including Santiago Flores. Emma Gomez. Diana Plasker. Tomorrow, are we nearing the singularity? A melding of human and machine. We'll talk with Ray Kurzweil about his new book. I'm SciFri producer Shoshana Bucksbaum. Catch you next time.