Octopuses Use Suckers To ‘Taste’ Harmful Microbes

Researchers found that octopuses can use their arms to detect harmful microbes on the surface of objects like crab shells or their own eggs.

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• 1:09Flora Lichtman?

  Hey, this is Flora Lichtman, and you are listening to Science Friday.

• 1:15Flora Lichtman?

  Today on the show, the mysterious ways that octopuses use their arms to sense the world around them.

• 1:23Speaker 04

  Could it be that certain arms are specialized for certain functions? Maybe it's not that they're all tongues, as you said. Maybe they're all doing different things.

• 1:35Flora Lichtman?

  Put on your party hat and wet suit because it's cephalopod week, our annual celebration of all things octopuses, squid, and kettlefish. And to kick things off, we are bringing you an ode to the octopus arm, which I learned is not called a tentacle. Believe it, it's an arm. You may have heard that octopuses can use their arms to taste their surroundings. But how exactly does that work? New research provides some clues. Here to tell us more is Dr. Nicholas Bologna, professor of molecular and cellular biology at Harvard University in Cambridge, Massachusetts. Nick, welcome back to Science Friday.

• 2:15Speaker 04

  Thank you.

• 2:15Flora Lichtman?

  OK, tell me what you've found.

• 2:18Speaker 04

  So years ago now, we found that octopuses actually have receptors in the suckers of their arms, which are proteins that bind molecules from the environment to inform an animal about its surroundings, similar to how we taste or smell. And so we came up with this story, basically, which was that if the octopus is exploring its environment using this chemotactile sense, or this taste by touch sense, then it would make a lot of sense that the animal would be detecting these relatively insoluble molecules that would adhere to surfaces. And that would be different than, let's say, a soluble molecule that would diffuse through

• 3:03Speaker 04

  the water that maybe, you know, a fish uses to track down prey at a distance. But the octopus is exploring by touch. So that's kind of where we started with this whole exploration of the arms. And that was a surprising discovery. And that's sort of the story that we had. But we actually didn't know what they sense in their environment.

• 3:25Flora Lichtman?

  Like, what are those insoluble molecules?

• 3:27Speaker 04

  Exactly. What are the molecules? And how is the octopus distinguishing its prey from, let's say, rocks along the seafloor?

• 3:37Flora Lichtman?

  Okay, so I know you looked at crab shells, which octopus eat, to figure out what they're sensing.

• 3:44Speaker 04

  That's right. And the crab shell turns out not to be so interesting upon first inspection. But what we noticed is that there's actually a lot of things growing on the crab. And that got us thinking, maybe what's different about these surfaces isn't necessarily the surface itself, but it's the community of microbes that lives on the surface. Because almost all surfaces are covered in microbes. We're covered in microbes. Everything the octopus is touching is covered in microbes. And so could it be that the diversity in these different communities is actually what's informing the octopus about what it's exploring? And the one thing I'll say that really convinced me early on was looking at the eggs.

• 4:28Speaker 04

  So we did some microscopy just to look at the surface of eggs. And octopuses do this interesting thing when they're taking care of their eggs. So the mom will guard her clutch and clean and aerate her clutch until her death. So she won't leave to eat. She won't do anything. She really guards those eggs and she's constantly cleaning them. And you can see that the behavior of the arms and cleaning the eggs is very gentle, very delicate, very different than if you see it go capture a crab, right? And so there seems to be some different signal that the animal has from the eggs. In addition to taking care of the eggs very closely, the octopus will actually reject every so often a couple of eggs from the clutch.

• 5:12Speaker 04

  And so we looked at the eggs and what was really surprising was that the eggs did have microbes on them, but the microbial community was very different once the eggs weren't in the clutch. We wondered, could it be that the animal can clean, aerate the eggs and then sense, okay, this one's bad, I'm going to get rid of this one so that I don't contaminate this entire clutch and, and not allow these eggs to develop. And so through seeing that, we, we really, you know, wanted to explore this idea.

• 5:44Flora Lichtman?

  Okay. So to explore this idea, this hypothesis that the octopus is sensing microbes with its arms, you do all this fancy biology footwork. You figure out which molecules the sensors are responding to from the crabs. You start making these crab microbe molecules in large quantities. And then what? And then you expose the octopus to them?

• 6:03Speaker 04

  Exactly. And, and this allowed us to ask questions about animal behavior because now we had, again, true molecules from the environment and we could ask, what do they tell the octopus? Or what does the octopus do when it senses these molecules? Because as you mentioned, you might have heard about how the octopus can taste with its arms, but we actually don't know what it's tasting. We actually don't know what information that relays to the octopus. But you'd be surprised that these behavioral experiments, which are like kind of silly in the end, are really challenging to figure out because the octopus just does whatever it wants. And so we always have to figure out some kind of.

• 6:44Speaker 04

  I don't know, a relatively simple approach to ask what it will do with, you know, a new stimulus. And so the experiment that we came up with was, was to coat crabs with this molecule. And because crabs themselves are pretty complicated, they move around, they also have their own molecular composition. We decided to use some fake plastic crabs that we then coated with agar. And we could either give them the fake crab. And you might think that the octopus is, you know, this overly intelligent animal never know the difference. But actually, it doesn't. It tries to eat the fake crab.

• 7:21Flora Lichtman?

  A lot of us eat fake crab, Nick.

• 7:22Speaker 04

  Yeah.

• 7:24Flora Lichtman?

  So just to say, you know.

• 7:27Speaker 04

  So yeah, anyway, the octopus would go for the fake crab and it, it will, it'll actually try to eat it. We can even find little piercings of its beak. But if we give it a fake crab coated in this, this microbial derived cue, it actually avoids the crab. And we later learned that this microbe is greatly enriched in crabs as they decay. And so actually, what this molecule that's produced by microbes is informing the animal of, is of crabs becoming basically foul. So crabs that the octopus shouldn't eat.

• 8:02Flora Lichtman?

  So it's like, that's like, oh, stinky rotten molecule.

• 8:07Speaker 04

  It may be equivalent to stinky rotten molecule, exactly. And we don't know, you know, to us, that's sort of what we can imagine for stinky rotten food. I don't know what that means for the octopus, you know, tasting by touch might be a very different kind of sensation. It's hard to imagine. But I think that that would be sort of the analogous scenario is that it realizes, oh, this crab is actually really gross because it has, you know, a lot of this particular microbe on it. And the microbe is really what is informing the octopus of this difference and of what it should and what it should not consume.

• 8:43Flora Lichtman?

  Does the stinky molecule only get produced, you know, do those microbes only exist in, in large abundance when?

• 8:51Flora Lichtman?

  The crab is dead?

• 8:53Speaker 04

  Yeah, so the microbe can be found on live crabs or recently deceased crabs. But it grows and it starts to make up the majority of the microbiome or contributes to the most of the diversity of the microbiome as the crab decays over time.

• 9:11Flora Lichtman?

  Did you find the delicious, you know, if we're going to stay with the analogy, did you find the delicious yummy molecule?

• 9:20Speaker 04

  We haven't yet. We are trying to figure that out and we actually have some experiments in the lab now, not only looking at the arms for taste, but we actually find that there's another sense organ that surrounds the octopus's beak. So it's actually traditionally called the lip, I guess lip equivalent for an octopus. And it seems that this sensor actually might be the one that detects the delicious molecule, but more to come.

• 9:56Flora Lichtman?

  Please do not go away because you're not going to want to miss this. Our ode to octopus arms continues with details on the absolutely mind boggling waves that octopuses mate.

• 10:10Speaker 04

  The male will find the female and then it uses the hectocotylus by inserting the hectocotylus into the female mantle and it searches around in the mantle for the ovaries.

• 10:28Flora Lichtman?

  Are you enjoying the cephalopod week deep dive? Well, we've only just dipped a toe in. We'll have more cephalo stories all week, plus hands on family activities like building your own octopus den. You can also join our sea of support with a small contribution to keep programming like this happening all year long. Swim over to sciencefriday.com to see it all.

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• 12:43Flora Lichtman?

  How does your work reframe how we think about these octopus arms? Like, should I be thinking about them as giant tongues or like a sensory body that is actually, that is totally foreign to us?

• 12:58Speaker 04

  Yeah, I'm not really sure. We've been thinking about this from some of the behavioral experiments I just mentioned, and we used to think that the arms were basically used to warn the octopus. And so the octopus is constantly probing its environment. It's feeling around, it's looking for stuff all the time. And we thought, maybe it's the case that it uses its arms to explore cracks and crevices, and a prey moves, it grabs it. Unless the prey is gross, like we just talked about, in which case it would expel it so that it wouldn't, you know, capture something dangerous. And this is sort of what I thought for a while, that these arms are sort of the, you know, detectors of

• 13:38Speaker 04

  harm. But I don't know if this is true anymore, because we just had this pretty surprising finding, which is not published yet, where we were trying to figure out, could it be that certain arms are specialized for certain functions? Maybe it's not that they're all tongues, as you said, maybe they're all doing different things, I don't know. And so we looked at the various arms, and we paid close attention to the specialized arm of the male octopus called the hectocotylus. And the hectocotylus is used specifically for mating. And so how octopuses mate is the male finds the female, they're not very social creatures

• 14:20Speaker 04

  generally. And so upon rare encounter, the male will find the female, and then it uses the hectocotylus by inserting the hectocotylus into the female mantle, and it searches around in the mantle for the ovaries. And once it detects the ovaries, the two animals pause, and then the male will transfer a spermatophore, which is a packet of sperm, from its mantle down the length of its arm to the tip where the ovary is. And this is how they mate.

• 14:50Flora Lichtman?

  That's wild. Just need to pause to say, that's

• 14:53Speaker 04

  Exactly.

• 14:54Flora Lichtman?

  That's wild. Okay, go on.

• 14:55Speaker 04

  So how, how could this arm, this, this one specialized arm, find the female one? And then how could it find the ovary amongst the other organs when it has no other cue, right? And so we looked to see, is this arm specialized? And actually, what we've been finding is that the male hectocotylus does have

• 15:20Speaker 04

  The same sensory receptors that we find in the other arms, it has a couple that are particularly enriched. And these sensory receptors also bind metabolites that are secreted by the female ovary. And so this is telling us that, in fact, these receptors are specialized to bind lots of stuff and probably to facilitate a vast array of behaviors beyond how we're thinking of taste by touch in context of food, but also to take care of their eggs and to find mates and so on, because this is a very, you know, chemosensory-driven animal.

• 16:01Flora Lichtman?

  How are their other senses? How's their vision?

• 16:03Speaker 04

  Their vision is exceptionally good. They have a huge visual system. A big part of their brain, the optic globe, is devoted to vision. Vision is another puzzling aspect of the cephalopod, one in which we're also actively exploring right now. So cephalopods are traditionally thought to be colorblind, yet they can do, as you probably know, very complicated camouflage displays of all different kinds of colors. So how is it that they can color match if they can't see color?

• 16:40Flora Lichtman?

  Yeah, that's mysterious.

• 16:41Speaker 04

  The reason that they're thought to be colorblind is they have only one opsin, which is the protein that's used to detect light. And so we have several different opsins which absorb several different wavelengths, and that's why we can see color. So if the octopus only has one, how can it see color? And so this is something that we're exploring, which is how can this this opsin function in this context? Does it truly absorb in one wavelength? Are there many? Are there other light signals that contribute? This is a very puzzling area of cephalopod behavior.

• 17:18Flora Lichtman?

  Do you think they can see color?

• 17:20Speaker 04

  I don't know.

• 17:23Speaker 04

  I would say that all the the the evidence in literature suggests that they can't. What I'll say is, pretty much every time that we've went into studying these animals, we end up finding something unexpected and different than what we imagined. And I think that that's, you know, fascinating for learning about cephalopods, learning about octopuses, but it's really also a nice reminder as a scientist to be open minded and to let biology guide you to something different. And that's something that the cephalopod to us has been great for, you know, training people to learn how to do science, too.

• 18:05Flora Lichtman?

  That's a lovely thought. Have you always been an octopus freak? Has this been a lifelong dream to work with cephalopods?

• 18:12Speaker 04

  Um, I don't know. I would say no. Um, we have, my lab has had over a hundred different species of animals. We have lots of stuff in here that we're studying. We also have protists, plants, fungi. Um, we study lots of different organisms and we try to compare different evolutionary novelties like what we're talking about in octopus to see, you know, what are broad principles, what are extremes? So I would say scientifically, no. But then again, um, I don't know, like, I, I didn't plan to study octopus even when I came here, but if you go and visit one in an aquarium, they're just such striking

• 18:55Speaker 04

  creatures and, you know, even if I remove myself from being a scientist, they really do inspire, you know, wonder in the natural world, which is why we do science. And so in that way, um, they've always been a attractive model.

• 19:10Flora Lichtman?

  Attractive model isn't, um, isn't making my heart sing exactly. You have over a hundred species in your lab. What animal is really capturing your heart right now?

• 19:20Speaker 04

  Maybe my favorite animal of all time, and I don't want to say, I mean, we have a lot of great projects. I like everyone's stuff. But maybe my personal favorite animal is the so-called photosynthetic sea slug, which I think is just totally nuts. They eat algae and then they suck out the chloroplast and they retain them in their own bodies to do photosynthesis, which

• 19:45Flora Lichtman?

  What?

• 19:46Speaker 04

  is very weird. And then they'll eventually digest these chloroplasts once they're severely starved, and then they can resist starvation for an incredibly long period. It's something that we've just published a new study about and how they do this. How can they retain these chloroplasts? Because the question is, if the chloroplast is removed from its natural habitat, which is the algal or plant cell, how does it get new proteins? How does it keep functioning? How does the slug do that because it's now in a slug cell? And what we found is that the slug actually has this, this organelle

• 20:28Speaker 04

  it makes that takes up the chloroplast, sort of like endosymbiosis, like how, you know, mitochondria are mitochondria formed a really long time ago from an ancient prokaryotic cell. But the slug managed to do this in one lifetime. It takes in the chloroplast, it houses it in this organelle, it sustains it to do photosynthesis. And then, once it's really hungry, it digests the chloroplast and gets an extra boost of energy.

• 20:55Flora Lichtman?

  Okay, I'm sold. We can have two weeks. Saphapod Week, which we're giving our full heart and love and attention to right now, but I see Sea Slug Week on the horizon.

• 21:07Speaker 04

  Sounds good.

• 21:09Flora Lichtman?

  Thanks, Nick.

• 21:10Speaker 04

  All right. Thank you.

• 21:12Flora Lichtman?

  Dr. Nicholas Bologna, professor of molecular and cellular biology at Harvard University in Cambridge, Massachusetts. Are you hungry for more octopus stories? Head over to sciencefriday.com to read about an octopus garden discovered in Canada. This is an underwater nursery where a group of octomoms care for their babies. And yes, obviously, we have baby octopus pics. You can also find Saphapod-themed games and hands-on educational activities all at sciencefriday.com.

• 21:47Flora Lichtman?

  Thanks for listening. Don't forget to rate and review us wherever you listen. It really does help us get the word out and get the show in front of new listeners. Today's episode was produced by Shoshana Buxbaum. I'm Flora Lichtman. Thanks for listening.