Octopuses Use Suckers To ‘Taste’ Harmful Microbes

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

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

NICHOLAS BELLONO: 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.

FLORA LICHTMAN: Put on your party hat and wetsuit because it’s cephalopod week, our annual celebration of all things octopuses, squid, and cuttlefish. 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 Bellono, professor of molecular and cellular biology at Harvard University in Cambridge, Massachusetts. Nick, welcome back to Science Friday.

NICHOLAS BELLONO: Thank you.

FLORA LICHTMAN: Tell me what you found.

NICHOLAS BELLONO: 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 chemotactic 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 the water that maybe a fish uses to track down prey at a distance.

But the octopus is exploring by touch. So that’s where we started with this whole exploration of the arms. And that was a surprising discovery, and that’s the story that we had. But we actually didn’t what they sense in their environment.

FLORA LICHTMAN: Like what are those insoluble molecules?

NICHOLAS BELLONO: Exactly. What are the molecules, and how is the octopus distinguishing its prey from let’s say rocks along the seafloor?

FLORA LICHTMAN: So I know you looked at crab shells, which octopus eat, to figure out what they’re sensing.

NICHOLAS BELLONO: 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, were covered in microbes. Everything the act was 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. 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 in cleaning the eggs is very gentle, very delicate, very different than if you see it go capture a crab.

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. 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 this one’s bad. I’m going to get rid of this one so that I don’t contaminate this entire clutch and not allow these eggs to develop. And so through seeing that, we really wanted to explore this idea.

FLORA LICHTMAN: 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?

NICHOLAS BELLONO: Exactly. 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 what it’s tasting. We actually don’t what information that relays to the octopus, but you’d be surprised that these behavioral experiments which are silly in the end are really challenging to figure out because the octopus just does whatever it wants.

So we always have to figure out some kind of– I don’t know– a relatively simple approach to ask what it will do with a new stimulus. And so the experiment that we came up with 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 this overly intelligent animal, and it would the difference– but actually it doesn’t. It tries to eat the fake crab.

FLORA LICHTMAN: A lot of us eat fake crab, Nick. So just to say.

NICHOLAS BELLONO: So, yeah. Anyway, the octopus would go for the fake crab, and 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 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.

FLORA LICHTMAN: So it’s like– that’s like, oh, stinky rotten molecule.

NICHOLAS BELLONO: It may be equivalent to stinky rotten molecule. Exactly. And we don’t know– to us, that’s what we could imagine for stinky, rotten food. I don’t know what that means for the octopus tasting by touch. Might be a very different kind of sensation. It’s hard to imagine.

But I think that would be the analogous scenario is that it realizes, oh, this crab is actually really gross because it has 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.

FLORA LICHTMAN: Does the stinky molecule only get produced? Do those microbes only exist in large abundance when the crab is dead?

NICHOLAS BELLONO: 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.

FLORA LICHTMAN: Did you find the delicious– if we’re going to stay with the analogy. Did you find the delicious, yummy molecule?

NICHOLAS BELLONO: The delicious molecule? 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.

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FLORA 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 ways that octopuses mate.

NICHOLAS BELLONO: 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.

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FLORA LICHTMAN: Are you enjoying the cephalopod week deep dive? Well, we’ve only just dipped a toe in. We’ll have more cephalus 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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How does your work reframe how we think about these octopus arms? Should I be thinking about them as giant tongues or a sensory body that is actually– that is totally foreign to us?

NICHOLAS BELLONO: 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 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 capture something dangerous.

And this is what I thought for a while, that these arms are detectors of harm, but 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 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.

FLORA LICHTMAN: That’s wild. Just need to pause to say that’s–

NICHOLAS BELLONO: Exactly.

FLORA LICHTMAN: That’s wild. Go on.

NICHOLAS BELLONO: So how could this arm, 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 queue. And so we look to see is this arm specialized, and actually what we’ve been finding is that the male hectocotylus does have 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 and context of food but also to take care of their eggs and to find mates and so on because this is a very chemosensory driven animal.

FLORA LICHTMAN: How are their other senses? How’s their vision?

NICHOLAS BELLONO: Their vision is exceptionally good. They have a huge visual system. A big part of their brain, the optic lobe, 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?

FLORA LICHTMAN: Yeah, that’s mysterious.

NICHOLAS BELLONO: 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 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.

FLORA LICHTMAN: Do you think they can see color?

NICHOLAS BELLONO: I don’t know. I would say that all 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 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 training people to learn how to do science, too.

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

NICHOLAS BELLONO: I don’t know. I would say no. We have– my lab has had over 100 different species of animals. We have lots of stuff in here that we’re studying. We also have protists, plants, fungi. We study lots of different organisms, and we try to compare different evolutionary novelties like what we’re talking about in octopus to see what are broad principles, what are extremes.

So I would say scientifically no, but then again, I don’t know. 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 creatures, and even if I remove myself from being a scientist, they really do inspire wonder in the natural world, which is why we do science. And so in that way, they’ve always been an attractive model.

FLORA LICHTMAN: Attractive model isn’t making my heart sing. Exactly. You have over 100 species in your lab. What animal is really capturing your heart right now?

NICHOLAS BELLONO: Maybe my favorite animal of all time– and I don’t want to say– 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 chloroplasts. And they retain them in their own bodies to do photosynthesis, which–

FLORA LICHTMAN: What?

NICHOLAS BELLONO: 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 organelle it makes that takes up the chloroplast like a endosymbiosis like how 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.

FLORA LICHTMAN: I’m sold. We can have two weeks– cephalopod week, which we’re giving our full heart and love and attention to right now, but I see sea slug week on the horizon.

NICHOLAS BELLONO: Sounds good.

FLORA LICHTMAN: Thanks, Nick.

NICHOLAS BELLONO: All right. Thank you.

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FLORA LICHTMAN: Dr. Nicholas Bellono, 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 octo moms care for their babies, and, yes, obviously we have baby octopus pics. You can also find cephalopod themed games and hands on educational activities all at sciencefriday.com.

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 Shoshannah Buxbaum. I’m Flora Lichtman. Thanks for listening.