Nick Petrić Howe
Welcome back to the Nature Podcast, this week: how octopuses taste with their arms...
Benjamin Thompson
...and the latest from the Nature Briefing. I'm Benjamin Thompson.
Nick Petrić Howe
And I'm Nick Petrić Howe.
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Nick Petrić Howe
First up on the show, octopuses have fascinated researchers for years, but it's still been a bit of a mystery as to how they actually sense the world. Now, though, new research is revealing some of the key receptors and how evolutionary differences at a molecular level could be reflected in some very different behaviours. Reporter Dan Fox is here with the story.
Dan Fox
Octopuses, or octopodes, or even octopi — depending on your disposition — are quite different from humans. Other than the obvious differences, they also experienced the world very differently from us.
Corey Allard
Certainly, there are some things that are familiar. We know that octopus are visual animals, and they'll use their eyes.
Dan Fox
This is cell biologist, Corey Allard from Harvard University in the United States.
Corey Allard
But what's really striking about them is the way they use those sort of enigmatic eight arms that they have. And they're using those to really reach into cracks in the seafloor to probe around, into surfaces or areas that aren't accessible to things like their eyes that maybe they can't see into.
Dan Fox
In fact, octopuses are able to accept or reject potential prey using only their arms. And this behaviour has long inspired researchers to investigate their sensory capabilities.
Corey Allard
There were some very early studies from the 1960s that showed what looked like sensory cells in the sucker cups. And that was one of the things that got us curious in the first place. That, yeah, it seems like maybe there's a bonafide sensory system housed within the arms in the sucker cups. But we don't know anything about how it works.
Dan Fox
But science has come a long way since the 1960s. And publication of the first octopus genome has opened the door for new avenues of research. So this week in Nature, there are a pair of papers from Corey and his colleagues on octopuses that are unpicking how these eight-limbed creatures sense things, and how they use those sensory abilities.
Corey Allard
Our strategy was to start with bioinformatics. So we take samples from different organs in the octopus, and we look at gene expression profiles. And the rationale here is that the sensory receptors we're looking for, should be more abundant in the rims of the sucker cups versus other places in the octopus. And what was really striking to us was that instead of a single receptor or a couple receptors, we identified an entire family of these chemotactile receptors,
Dan Fox
But the receptors they identified, which they call chemotactile receptors, or CRs, didn't look like the kinds of receptors usually seen in sensory systems.
Corey Allard
They didn't resemble known sensory receptors. Instead, they're they're most closely related to a family of receptors called nicotinic acetylcholine receptors.
Dan Fox
These nicotinic acetylcholine receptors are found throughout the nervous systems of many different animals. But usually, they detect neurotransmitters within the body and are involved with things like controlling muscle contractions. In humans they're the focus of research into treatments for everything from Parkinson's disease to nicotine addiction, but they are not sensory receptors, or so researchers thought.
Corey Allard
In the course of their evolution octopus have converted these ancestral nicotinic acetylcholine receptors into sensory receptors — they look almost identical at first glance. And it wasn't until we look closer that we started to appreciate some of the structural regions that are mediating these functional differences.
Dan Fox
The team imaged the octopus receptors using cryo-electron microscopy, and compare the structure they found with the nicotinic receptors found commonly in other animals. And they found a subtle but very important difference in an area called the ligand binding site. This is where the receptor binds with its chemical partner. In nicotinic receptors this is a cage-like structure that binds with neurotransmitters, like acetylcholine, causing its ion channel to open and transmit signals. But the octopuses' receptors are different. Instead of a cage, they've evolved to have a shallow groove and that allows for a wider range of materials to bind. In particular, materials that don't mix well with water, like the kinds of greasy residues left on the seafloor by potential prey. A useful tool in a hunt.
Corey Allard
We describe this as being a chemotactile sense, which basically combines chemosensation, sensation of chemicals, with tactile sensation or touch. The types of chemicals that they're actually able to sense are very hydrophobic molecules, things that you would not expect to find in the water column in a marine environment and things that instead you would expect to find on the surfaces in a marine environment, so it makes sense that they would have to physically touch them.
Dan Fox
This clarified picture of the molecular mechanism behind taste-by-touch helps explain some of the octopuses’ unique behaviours, especially when compared to the structure of the same types of receptor in related animals, like squid, as Guipeun Kang, another author of the research, explains.
Guipeun Kang
Octopuses use their chemotactile receptors for their exploratory predation behaviour. Interestingly, octopus and squid have different predatory strategies. Instead of using its arm for exploration, rather squid, ambush predator, hide, strike and pull their potential prey and then decide to eat or reject it.
Dan Fox
This behavioural difference, the researchers say, can be explained by their different receptors.
Guipeun Kang
The squid chemotactic receptor binding site is not sticky at all. So this receptor is not responding to greasy molecules. Instead, in response to bitter tastants that are soluble and easily diffusive in water. It explains squids' strikingly different predatory behaviour.
Dan Fox
Evolutionary differences at a molecular level align with strikingly different abilities and behaviours. And this is far from the end of the story.
Guipeun Kang
Oh yeah, there are a lot of things we don't understand. Here we just started looking at one of each receptor from octopus and squid, there are more octopus and squid chemotactile receptors with different properties may pursue different function in sensory system.
Dan Fox
For example, there is evidence that some octopus receptors can also detect voltage, but how this ability fits into their broader sensory system is still unknown. Even within the world of the chemotactile receptors already studied, there's much more to learn. Here's Corey again.
Corey Allard
You know, we initially got into this study thinking that we would be studying a sensory system that's used for predation — for finding prey. And while we still think that's the case, so far, most of what we've discovered relates to aversive stimuli or things that the octopus doesn't like. And so, we're really interested to find if somewhere in this diversity of CRs, there are receptors that mediate what we would call appetitive sensation, or, you know, food things that the octopus maybe wants to eat. Or if the octopus maybe just eats anything, unless it has a signal that says no, don't eat this.
Nick Petrić Howe
That was Corey Allard from Harvard University in the US. You also heard from Guipeun Kang from UT Southwestern Medical Center, also in the US. To find out more you can find links to a pair of papers in this week show notes. And if you want to see those octopus arms in action, we also have a video on our YouTube channel. And we'll put a link to that in the show notes.
Benjamin Thompson
Coming up, we'll be chatting about some stories from the Nature Briefing, including how soil samples can be returned from Mars, what ancient eclipses reveal about climate change, and a question for the makers of the next dinosaur movie blockbuster: should a T-Rex have lips? Right now, though, it's time for the research highlights with Noah Baker.
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Noah Baker
A glacier's catastrophic collapse has been linked to global warming. As temperatures rise with climate change, a melting glacier in the Italian Alps triggered a devastating avalanche on July 3rd 2022. Around 64,000 tons of water, ice and rock broke away from Marmolada glacier in northeastern Italy. The collapse led to a massive ice avalanche that charged more than two kilometres down the steep northern slope, killing 11 mountaineers. To tease apart the root cause of the disaster, an Italian team of researchers analysed satellite and aerial images of the glacier that had been captured before and after the event. During the late spring and early summer months of 2022, temperatures in the region were 3.5 degrees higher on average than they had been during the previous three decades. The temperature spike resulted in the accumulation of huge volumes of melt water in deep cracks in the glacier, leading it to break apart and collapse. The researchers concluded that next generation monitoring should be developed to deliver early warnings to tourists in glaciated areas. You can read more on that study in Geomorph.
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Noah Baker
Hair found in a cave on the Mediterranean island of Menorca has provided rare direct evidence that people in prehistoric Europe consumed hallucinogenic plants. The strands of hair, which were properly cut from dead individuals as part of a funerary ritual, were found inside a wooden container hidden in a small subterranean chamber. The chamber had been sealed from around 800 BC until it was discovered in 1995. A Spanish team analyzed the hair and within it they found three mind altering substances, the hallucinogens atropine and scopolamine, and the stimulant ephedrine. The substances are found in native plants in Menorca, such as the thornapple, henbane, mandrake and joint pine, the individuals could have consumed these plants up to one year before their death. Remains of psychoactive plants and artistic depictions of drug plants have offered hints in the past that ancient Europeans used drugs, but these hair locks provide rare direct evidence of the practice. You can read more in Scientific Reports.
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Benjamin Thompson
Finally on the show, it's time for the Briefing Chat, where we discuss a few articles that have been highlighted in the Nature Briefing. And this week, we've actually got a triumvirate of chat and Nick, you and I are joined by none other than Shamini Bundell. Shamini, hello.
Shamini Bundell
You know I can't stay away from the Briefing Chat, and I've got an awesome story for you this week.
Benjamin Thompson
Well go ahead, why don't you go first then, what have you got for us?
Shamini Bundell
Okay, so did you know that the colour of the moon during a lunar eclipse can actually tell you something about the state of the atmosphere at the time of the eclipse.
Nick Petrić Howe
I mean, the first thing I thought about eclipses, and the colour of them is surely there's not much because it's all dark. So how are we seeing colours of eclipses.
Shamini Bundell
So a lunar eclipse, as opposed to a solar eclipse is when the earth blocks the light from the sun. And the moon, as you say, goes dark, but it is often still visible. But there's sort of variations on that. Sometimes it can be really dark, sometimes it can be lighter, sometimes it can be a sort of reddish color. And the colors that you can see in the eclipse, are often linked to particles in the atmosphere that can be caused by volcanic eruptions. And different kinds of volcanic eruptions, and different timings, can cause different colours. So reddish eclipses suggest an eruption that injected aerosols into a sort of lower layer of the atmosphere. And a particularly dark eclipse would indicate a huge eruption that pushed volcanic aerosols high up into the stratosphere. And scientists have been using ancient descriptions that people have written about eclipses and what they look like in order to get information about ancient volcanic eruptions.
Benjamin Thompson
So ancient descriptions in which I guess are few and far between?
Shamini Bundell
Yes, so this is the sort of history side of this and this story — which I've been reading in Nature, and it's based on the Nature paper — is kind of interesting in the way it brings together, you know, what you would usually consider history, reading sort of old manuscripts, with climate science and things about solar geoengineering, things like that. So these researchers have gone back and taken examples of texts from around the period 1100 to 1300. So in Europe, that would have been the kind of medieval period so they've got texts from monks and sort of ancient scholars and all over the world as well, you know, a poet in Japan who wrote a description, and where these people have got descriptions of the Moon's colouration and how dark it was during the eclipse, they can use that to estimate okay, how much of this volcanic haze, these particles, would have been present? And where? And then also, to some extent, okay, when would the eruption likely have taken place sort of compared to the timing of the eclipse, and they basically match the dates that they found with the data from things like ice cores and tree rings. So in a way, it's not brand new data. It's not eruption that we didn't know what happening. But you know, let's say you find a layer of dust in an ice core. And then you can time that to this particular poet in Japan was looking up and seeing a beautiful lunar eclipse and writing a description of it.
Nick Petrić Howe
I mean, this sounds really interesting that people are able to do this, but these were eclipses that happen, you know, almost 1000 years ago. What can it sort of tell researchers about the climate and volcanic eruptions?
Shamini Bundell
So the important thing here is that these volcanic eruptions, especially big ones, potentially have worldwide climate impacts. And this period they were looking at, 1100 to 1300, is the sort of run up to what's known as the Little Ice Age. So this was a sort of unusually cold period, it's kind of debated whether it was a sort of globally cold period. But there were definitely notable very cold winters during that period. So, you might be familiar with paintings of people ice skating on the frozen Thames River, in London, they used to hold fairs on the river. At one point New York Harbour was frozen over. So it's of interest, how did climatic changes and volcanic eruptions impact those kinds of temperature changes in different parts of the earth. And the other thing that it might be relevant to is this idea of solar geoengineering. So, this is the idea that some people have put forward to say, climate change is a problem, temperatures increasing, can we put something in the atmosphere that will reflect light back out and stop the earth heating up? So, for example, like sea water or different kinds of gas released by balloons, and this is a really big, untested idea. That's very controversial. But it's possible that volcanic eruptions are kind of the only sort of similar thing that we have that we could possibly compare it to, to get an idea of what might happen if we put various things up in our atmosphere to try and stop global warming.
Benjamin Thompson
I mean, it's always interesting when we kind of get that interface between history and the modern scientific enterprise. What are the researchers saying about this work?
Shamini Bundell
Yeah, so one of the researchers notes that these kind of medieval manuscripts and things have been used by historians for a long time to look at social trends, political trends, and he says, if they're able to provide such an accurate record about social and political events, why not about natural events?
Benjamin Thompson
Neat! Well, let's move on then, in this week's Briefing Chat, and why don't I go next? And I've got a story that I read about in Nature. And it's something that we've all talked about over the past few years. And it's about efforts to return samples of soil and rock and atmosphere back from Mars to Earth. And this story has been looking at kind of the latest goings on in that area.
Nick Petrić Howe
Right? So, this is following on from the Perseverance mission, where it's finding some samples that are eventually to be returned to Earth. So, I'm guessing now, we've figured out a way to actually get them back to Earth?
Benjamin Thompson
Maybe, in fairness, and Nick you're absolutely right. So Perseverance has been rolling around the Jezero crater on Mars for a little while now, collecting these kind of cigar shaped tubes... and this got off to a bit of a rocky start... I think, Shamini, it was you and I who talked about this a while back. But it's been doing a pretty good job now. And it's collected a bunch of these things. And what's weird about this is... actually sending the Perseverance rover to Mars, and successfully having a drive around the surface and drilling samples of rock, almost seems like the easy part to be honest with you. And for a few years, NASA and the European Space Agency, the ESA had been planning this kind of daring mission to get these little cigar shaped tubes back and it seems like sending spacecraft no earlier than 2027 is the plan. But technological and financial hurdles could really derail this. And last month, NASA said that he wants to allocate around a billion US dollars to Mars sample-return in the upcoming fiscal year. And this is of course, a huge sum of money. That means they might have to dip into other parts of their science budgets and other missions could lose out, for example.
Benjamin Thompson
I do remember thinking at the time that it was sort of bold to collect all the samples and just say like, "hopefully, we can get them back in the future." But there are budgetary limitations, do they think it's very likely to happen? Obviously, they must think it's pretty important to sort of spend so much of their budget on it.
Benjamin Thompson
Yeah, no, you're absolutely right. And in the coming months, NASA and the ESA will have to make some crucial decisions on what this mission might look like. And I think I can give a vague overview of the plan, right? And the basic idea is this: so the ESA would fly a spacecraft to Mars, and that would orbit the planet, right? And then the following year, NASA would send another spacecraft to land on the surface to pick up the samples, and then blast off, okay, back into orbit attached to the ESA craft and that would then fire the samples back to Earth, right? And that would arrive back no earlier than 2033. Easy, right? Fairly straightforward.
Nick Petrić Howe
If you say so!
Shamini Bundell
I'm not so sure about that!
Benjamin Thompson
Well, right, and a lot of things need to be invented, right? So like the rocket that takes off from the Martian surface. But the sorts of things at a much more granular level is what needs to be considered, right? So Perseverance has been collecting these samples, it's been roving around, it's actually taken two sets, right? One set is in its belly and the plan is that those samples will be delivered to the NASA rocket, which would then take them up which would then blah, blah, blah and all the rest of it. But if that doesn't work, there's a backup plan. And Perseverance has actually been dropping some samples behind it over the past little while, right? So, it's dropped 10 samples and it's kind of a zigzag pattern a few meters apart, and if you can't deliver the samples directly, the plan is the next mission will actually also contain two helicopters that will take off with little sort of pincer arms and pick up the samples from the surface and they're kind of the backup. And the plan was to have two helicopters, but these budget constraints are really kicking in now, they might only be one helicopter. And I mean, there's lots of moving parts here, right? Both in an engineering sense, and in a kind of behind the scenes sense as well.
Nick Petrić Howe
So I guess there's a lot that they need to figure out to make this actually happen. But if it does, what then?
Benjamin Thompson
Well, scientists are absolutely itching to get their hands on these samples, as you might imagine, right? Because they're from a bunch of different parts of this Jezero crater, okay. Some of these rock samples are igneous rocks, okay, so they're formed from from molten rock, and been able to get hold of these will allow researchers to actually accurately date parts of Mars, which, up until this point has been really, really hard to do, right? Because you can't actually get hold of it and have a look at it, right? And other samples are very different sorts of rocks. And some of them are form of fine-grained sediment that appears to have interacted with water, okay. So, the Jezero crater once held a lake. And if there's any life to be found — and that if doing a lot of work — they think that maybe somewhere in this kind of sedimentary samples, that could be the bio signatures of ancient organisms. Obviously, we don't know the answer to that, of course. But if you're going to have a look, this seems like the place to look. But of course, this is a monumentally difficult mission. So many moving parts, as I say, but the next few months is when we'll get really quite a detailed look at what the plan could be and how much it could cost. So hopefully, the next time we talk about this, the wheels will very much be in motion.
Nick Petrić Howe
Well, if you can't wait until 2027, I've got a story that will keep you sort of sated in the meantime. So I've been reading a news story in Nature. And it's about the T-Rex and you know, T-Rex are quite famous for having big teeth, but they may have also had lips to cover them.
Benjamin Thompson
When I saw we were going to cover this story on the show. I spent a lot of time — and admittedly this is not ideal for a podcast — just playing on my lips, over my teeth and sort of baring my teeth and wondering what a T-Rex might look like. And I must confess this isn't a question I've even considered. Why is this something that researchers are interested to know more about?
Nick Petrić Howe
Well, it has actually been a debate for a long time whether or not they had lips. So, lips are actually really quite useful for protecting your teeth. So if you have enamel in your teeth, you need to keep it moist in order to stop it cracking. And so if you have big teeth — and especially if you're a T-Rex, and it takes you two years to grow a new one — you don't want to be losing teeth because of that. But it's been hard to figure out whether or not this is the case, because we don't have any good fossils that have all that soft tissue that would tell us straight off, intact for the T-Rex. So, some researchers have been looking at a skull of a related species and skulls of some other animals as well to try and figure out whether or not they had lips.
Shamini Bundell
So I'm trying to sort of picture this and trying not to picture cartoon human lips, but on T-Rex — which is definitely my first thought — but basically, the idea is that if a T-Rex or another animal has its mouth closed, if it's got lips, you wouldn't be able to see the teeth. They wouldn't just be sort of sticking out all jaggedy — they'd be covered. Are there any modern sort of examples you can give us?
Nick Petrić Howe
Yes. So, there are a couple of different modern examples. And maybe I can start by doing a comparison. So, in the past, the idea we've heard about T-Rex's teeth and their lips, or lack thereof, has been much like crocodiles. So, when crocodiles have their mouth closed, all their teeth are sticking out, and the reason that this has been thought to be similar to the T-Rex, is because crocodiles — other than birds — are the closest living relative of dinosaurs as a whole, so the idea was that maybe they're similar. However, the reason that crocodiles are able to have their teeth like this is they spend most of their time in the water, and that actually acts to protect… And also they can go through a heck of a lot of teeth with no particular problem. So, the researchers have been investigating different skulls and they actually found that one of the things that is closest to the T-Rex skull is that of the Komodo dragon. And the Komodo dragon does have lips — not like our lips, they're more sort of solid, scaly things — but they just cover their teeth. So, when their mouth is closed, you can't see any teeth. And it seems like their skulls are a lot closer to the T-Rex skulls than a crocodile skull is. So, if you look at a Komodo dragon skull, and you look like up into its mouth to see the roof of the mouth, you'll see just holes above where the teeth are. And these are for blood vessels and nerves and things. Whereas in a crocodile, there are a lot of holes everywhere, which is part of how they sense things in their mouth. But it seems like the T Rex just have the same holes above their teeth. So, it seems to resemble the Komodo dragon skull much more than it does the crocodile skull even though the Komodo dragon is much more distantly related to the T-Rex.
Benjamin Thompson
And obviously T-Rex is an iconic extinct creature. And there are lots of things we don't know about it. And this question now gets added to the pile, I suppose. Is there a way that it'd be possible to answer it? Because as you say, like actually getting fossils of soft tissue is pretty hard to do.
Nick Petrić Howe
The fossil of the soft tissue would be the way to do it. It is still quite debatable. So one of the other things that they did in this study is they looked at a tooth from Daspletosaurus, which is a tyrannosaurid, not a T-Rex, but related to it. And they looked at the sort of wear of these teeth, and they had kind of even wear all around the teeth. Whereas in something like a crocodile, they have much more wear on the outside of their teeth, where they're sort of being exposed. So, this sort of suggests that there was something protecting the dinosaurs' teeth, like lips. So, this is another line of evidence that they looked at. But then some of her palaeontologists have said, well, actually, it's the dentin, not the enamel that's more important — and dentin there's another component of teeth, which T-Rex had a lot of — and it may have protected the teeth and they're also much larger... So, there's a lot of sort of debate going back and forth and I don't think it will necessarily be solved until we find like the soft tissue. But one researcher who was interviewed for this story said that this, they believe, is the single strongest case for lippy Tyrannosaurus yet.
Shamini Bundell
Well, I'm always glad to be on the Briefing Chat and have a dinosaur story. So that's great. And listeners, if you want to find out about any of these three stories that we've chatted about today, you can find the links to them in the show notes, and of course, a link to where you can sign up to the Nature Briefing, which will send you regular emails with more stories like these.
Nick Petrić Howe
That's all for this week. But just before we go, a little bit of good news, a couple of our shows have been nominated for Webby Awards, as well as the main categories were also up for a People's Voice Award voted for by listeners.
Benjamin Thompson
Yeah, that's right. So, if you've got a couple of minutes spare and want to cast your vote for us, look out for a link on where to do so in the show notes. And as always, you can keep in touch with us on Twitter, we're @naturepodcast, or you can send an email to podcast@nature.com. I'm Benjamin Thompson.
Shamini Bundell
I'm Shamini Bundell.
Nick Petrić Howe
And I'm Nick Petrić Howe. Thanks for listening.