These tiny fish combine electric pulses to probe the environment

Nick Petrić Howe

Welcome back to the Nature Podcast, this week: the puzzle solving bees showing a uniquely human trait…

Benjamin Thompson

…and fish that connect together to electrically sense the environment. I’m Benjamin Thompson.

Nick Petrić Howe

and I'm Nick Pétric Howe.

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Nick Petrić Howe

What makes us human?

Is it walking upright? Well, plenty of animals do that. Well, what about tool use? Again, take a look at some of our close cousins, or even birds and octopuses and you’ll see that’s not the case. Well then… what about culture? You know the sort of nebulous thing that means that we collectively are able to build cities, make art and create the infrastructure necessary to listen to podcasts like this one. Well maybe…

But even that is debatable, by some definitions several animals show culture, such as Japanese macaques that wash sweet potatoes before eating. They don’t need to, but one macaque figured it out and then they learnt from one another, and the behaviour spread throughout their society and has persisted for decades.

One thing, though, that people have still thought of as uniquely human, is the ability to do something that you couldn’t come up with on your own. Like building the atomic bomb. That is to say something which, no matter how hard you tried, would be impossible to achieve without standing on the shoulders of many generations of scientists before you.

And yet now, new research is suggesting that even that may not be solely a human trait. And the team behind the work have made the argument using the humble bumblebee. Now I worked with bees for my PhD, although admittedly my research was nothing to do with culture, but when I found out that this research was carried out just down the road from Nature towers at Queen Mary University of London, I couldn’t resist hopping on the tube, curious about culture, to chat to one of the researchers involved.

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Alice Bridges

I'm Dr. Alice Bridges. Currently on a postdoc at University of Sheffield, but I did my PhD at Queen Mary and that's the work that's included in this paper.

Nick Petrić Howe

And you know, why did you decide to work on bumblebees, what is about bumblebees that caught your interest?

Alice Bridges

Bumblebees are really really useful model organisms for any experiments on social learning, especially experiments where we're trying to get them to learn a really complicated behaviour, because they're really easy to train. Other animals, when you're training them, you're probably giving them a reward in exchange for doing the target behaviour. But once they've had a certain number of awards, they're full, and they don't want to take part anymore for a bit. But with the bumblebees, they have this infinite stomach in a way because they will take the reward that they get back to the colony, leave it there for the others and then come back to collect more. So even when they're not hungry themselves, they'll still be coming out and wanting to try again. So you can keep training them for really extended periods. So it's quite efficient compared to another species. And as for why bumblebees and not honeybees, you get about 150 maximum bumblebees in the hives that we order. Honeybees, you're looking at 10s of 1000s. So in the event of a great escape, it's a little bit easier to deal with the bumblebees.

Nick Petrić Howe

Yeah 1000s of honeybees sounds quite like a different sort of scenario.

Alice Bridges

Yeah.

Nick Petrić Howe

And I want to talk to you today because there's a paper coming out in Nature that you've been writing, and it has a couple of different things that it tackles. So it has social learning, and it also has culture. Now people may have a vague notion of what these things are, but would you be able to do a couple of definitions for us? What do we mean by social learning? And how does that differ from something like culture?

Alice Bridges

So as humans, it's sort of difficult, I think, to kind of define culture because it does just permeate every aspect of our lives. When we talk about culture, especially in non-human animals, we refer to behaviours that are socially learned. So that's behaviours that you learn from someone else. So you're not developing that behaviour by yourself. If you're observing another person or being taught potentially as humans by that person, and this behaviour then has to remain in society, even, you know, group of friends or subculture for a period of time, so over multiple generations of learners. So in short, all culture is socially learned. But social learning and socially learned information and behaviours aren't necessarily cultural, they have to persist.

Nick Petrić Howe

And, you know, you mentioned humans there. But this isn't just a human thing, right?

Alice Bridges

No, so people originally thought it was exclusive to humans. Only relatively recently, did people even conceive of the idea that animals might have a form of culture of their own, we found behaviours that meet the definition of culture in a huge range of species. So chimpanzees, dolphins and other whales, birds as well, so birdsong and the tool design in New Caledonian crows. So we're increasingly understanding that culture is really relevant to animals, we sort of do understand now that it's a second form of inheritance, so complementary to genetic inheritance.

Nick Petrić Howe

And so, you know, you work on bumblebees, and this idea of culture was something you're quite interested at looking at. So, can you tell me what you were trying exactly to figure out? And how you're trying to figure it out as well?

Alice Bridges

So, we already know that bumblebees are sort of capable of sustaining cultural variation trends in their behaviour as a form of culture if they're given the chance. People know that animals are capable of culture. But it's still thought that human’s ability to learn behaviours that are so complex that we can't possibly re-innovate them ourselves in isolation, is what makes us unique and is responsible for our success as a species, I suppose. So what we wanted to find out was whether a tiny bee was capable of the same thing.

Nick Petrić Howe

So what is your thing then that is so complicated that the bees can never figure out on their own, but they could potentially socially learn from one another?

Alice Bridges

So we created this puzzle box, the box contains a reward. But in order to get it, the bees have to perform two actions. First, they have to push a blue tab out of the way, so that they can then push a red tab, expose the reward beneath and the sort of the key point of this is that the first step, so moving the blue tab, they don't get any reward for doing that, they have to wait until they've then moved the red tab and get the reward at the end. This is really not trivial for bees. People like to think I think of bees as very industrious and hardworking – I prefer to call them efficient. Depending on how well they do in the experiment – I call them lazy. They really don't like doing things that aren't obviously connected to getting a reward. I mean, they learn via association so if there's no reward, there's no punishment, there's nothing to associate with whatever behaviour they've done. How can they learn it? In general, if they can't get a reward, their behaviour isn't being productive, they will stop. So with this puzzle box, we were actually asking the bees not just to do something that they weren't getting a reward for, we will also want them to move away from the location of the reward first, before they can get it. And yeah, it might seem pretty simple to humans. But for a bee this is, this is really, really difficult. And we saw that when we were trying to train them to do it.

Nick Petrić Howe

So the first step was you were training the bees to learn this, how many sort of learnt how to do this? And I guess how many were then able to transmit this learning via social interaction?

Alice Bridges

So actually trying to develop the training protocol was really hard. Because essentially, we found we couldn’t do it, we could not train them to do something that is unrewarded. They just they weren't having it. We started initially by training them backwards from opening the red tab. And once they could do that, we tried to move the blue tab progressively further, and they just would not push it. And we tried everything.

In the end, the only thing that worked to get them to even try to push it so they have a chance to figure out that they can was to put a temporary reward underneath the blue tab so they’d do the first behaviour, get that reward, then do the second behaviour, get that reward, and then take away that reward after they'd learned both. Which, again, they absolutely hated. When they, I guess, when they opened the first blue tab, and they would find that there was no longer a reward. Often you would get a response from them something akin to a tantrum, they start flying erratically, you might hear them smacking the number tag against the top of the arena, they might storm off back to the hive and not want to come out. You have to really sort of persuade them, please try again, here's an easy one.

So we were having to very slowly remove this reward from one in every four and one in every three boxes and every other box, then increase– increase the reward at the end. And then finally, they sort of accepted this was how it was going to be. This took a while. We finally got a successful bee and we were obviously going crazy in that video of that bee doing it so that audio cannot be shared with the wider public. But after that, we were able to use this protocol on several bee's. I think in total, we must have trained about 12–13 bees manually like this. And then we paired those bees with naive observers. So these were bees that had never seen the box before and they'd certainly never experienced getting a reward for pushing the blue tab. And then we basically let those pairs of bees forage together on these puzzle boxes. And after 30 sessions, we gave the observer bee a test by itself. So we gave them a box and they had 15 minutes in order to open it and of 15 observers who were paired with our demonstrators, 5 of them, were in fact able to pass this learning test. So this was a really crazy result for us. They had never had a reward for pushing blue, but they were still able to learn the complete behaviour.

Nick Petrić Howe

And so what do you think this means then that these bees were able to learn this behaviour that will never be able to come up with on their own, and then other bees will able to observe and then do the same behaviour.

Alice Bridges

I guess it opens up a huge range of possibilities. First of all, it seems that bees are capable of learning things from each other that are more complicated, more difficult than we ever really imagined. They are the first animal ever shown to do this. In fact, I think the fact that a bee can do it must sort of prompt a reassessment of the capabilities of other animals. It does suggest that perhaps our sort of ability to learn such behaviours isn't something that is setting us apart from animals and other species. Rather, the differences are more quantitative rather than qualitative. So, you know, perhaps these capacities are very evolutionarily basal? Perhaps they're not actually that difficult, or perhaps the bees have super efficient tiny brains that allow them to basically come up with a more efficient solution, then perhaps, our much bigger brains. So I think it definitely raises a huge number of questions.

Nick Petrić Howe

I guess one thing I was wondering as well like, the sort of the way that these bumblebees are like, you have the queen, and you have the workers and everything. The workers may learn something, and they learn this behaviour, but then they will, you know, go to the great colony in the sky, and they may not pass it on, because the next colony will be made by a new queen. So, is this sort of like a sustained thing? Are they able to sustain this into the future?

Alice Bridges

Well this is, I think, the truly fascinating thing. There's that whole sort of unfortunate, early 2000s, we only use 10% of our brains that has led to some very unfortunate movies. Literally we use all of our brains, obviously, we use all of our brain tissue, it's very metabolically expansive. If we didn't use it, we wouldn't have it. It is expensive to do these kinds of cognitive feats. So, if it's not necessarily going to be useful to a species, you might not expect them to do it. You're right, the colonies once the year ends, especially these Bombus terrestris in the UK, the colony collapses. So, it's survived only by the newly mated queens who, as you've said, will not really have picked up any foraging techniques from the other workers – they go off and found their own colony. So, it's likely with our bumblebees that any culture that maybe they were able to come up with during their time would be lost at that point and they'd have to sort of start again from zero. There are other social insects and bees. So, honeybee colonies persist consistently over many years. There are some tropical bumblebees that do the same, stingless bees. And here, I think you'd be more likely to find this sort of long-term sustained culture than in the bumblebees, but they were still able to do it, which does suggest that maybe it's not that cognitively difficult to achieve.

Nick Petrić Howe

And so what do you think then, is the future of this research? What do you need to find out next? And what would you like to find out next?

Alice Bridges

I think sort of the long-term goal would be to see whether things such as the nest design behaviours such as the leafcutter, ants farming, even the honeybee dance language, which I think there was a science paper suggesting that elements of that are socially acquired, as well, it's not purely innate. I think quite a lot of these behaviours, these supposedly innate behaviours, even if they are now perhaps they weren't always I mean, there are mechanisms through which selection can act on either general cognitive ability or behavioural biases. And in this way, it's possible that learnt traits might become increasingly innate over time. I would love to know whether this is what in fact has happened whether maybe when we looked at these animals, we didn't see culture because we were looking too late.

Nick Petrić Howe

That was Alice Bridges, formerly of Queen Mary University of London and who’s now at the University of Sheffield, here in the UK. For more on bumblebees, check out the show notes for some links.

Benjamin Thompson

Coming up, how tiny fish can use each other to extend their electrical sense. Right now, though, it’s the Research Highlights, with Dan Fox.

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Dan Fox

In the immediate aftermath of the 1883 eruption of Krakatau volcano in Indonesia, sunsets around the world turned an eerie green. Now, scientists have linked these uncanny colours to the size and spread of volcanic particles. Big volcanic eruptions often create redder-than-normal sunsets, because there are more particles in the atmosphere to scatter the sun's dying light. But many observers reported unusual green skies after the 1883 event. A team of researchers modelled the atmospheric conditions that could lead to green sunsets and found that if the Krakatau tower eruption sent a large number of 500 to 700 nanometre particles into the upper atmosphere, and sunlight scattered off those particles could have created green twilights. The authors say that studying records of volcanic skies can help researchers to better understand the power of past eruptions. Read that research in full in Atmospheric Chemistry and Physics.

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Dan Fox

Some stars are messy eaters, and that has allowed researchers an insight into their dining habits. White dwarfs are dense, Earth-sized embers of dying stars. Any planetary body that teeters over the cusp of a white dwarf’s gravity faces a violent death: as it falls into the star, its material is vaporised into particles. Normally, metallic particles from a shredded planet are deposited uniformly across the star’s surface. But researchers examining the light from a white dwarf named WD 0816-310 saw variations in wavelength as the star rotated suggesting that patches of planetary metals are concentrated around the magnetic pole. They hypothesise that the stars radiation and magnetic field might have helped to give the metallic particles an electric charge before magnetic fields on the star accumulated these crumbs near the poles. And these leftovers allow the astronomers to infer that the devoured body was similar in size to Vesta, the second largest asteroid in our solar system. If that has whet your appetite, you can find the research in full in The Astrophysical Journal Letters.

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Benjamin Thompson

You’ve likely heard of echolocation, but what about electrolocation? It’s a similar idea but instead of sound, certain animals living in water can use electrical pulses to sense their environment.

Research published this week in Nature shows that a small African fish, called the elephantnose fish, may do this in a remarkable way — by using the pulses of other fish, to “see” the same scene from different perspectives.

Reporter Anand Jagatia spoke to author Nate Sawtell about the study, and started by asking him how this electric sense actually works.

Nate Sawtell

This is an animal that can actually not only sense, but also generate electricity. As the fish is swimming around emitting these fields, objects underwater conduct electricity differently than the water. So a rock, for example, would be an insulator, it conducts less well than the surrounding water. Another animal like prey or another fish, you know, its insides are full of salt so it's more conductive than the surrounding water. So this electric sense allows animals to sense objects nearby them that conduct electricity differently than the water. So this is, in that sense, like echolocation, you have made a sound that causes echoes that come back to you. Here, you emit an electrical field and objects in the environment cause more or less current to flow through your skin, casting what we call electrical images on the body of the animal that then the brain can decode in order to localise, detect and characterise objects.

Anand Jagatia

A potential issue that fish like this one might encounter when they're going around sensing their environment is interference from other fish who might be sending out their own electrical signals. But in this paper, you're looking at a different sort of phenomenon, which is actually that some of these fish might be able to use signals from other fish to their advantage.

Nate Sawtell

Yeah, that's right. What we found is that the fish can benefit greatly we think from the pulses of other fish and we showed a couple of different ways that this could be the case. So one, he's listening to his own pulses but then he also can get a perspective, a different perspective about the nearby environment by listening in on the pulses of other fish that are nearby. Another aspect is the fish could get more samples of– of the world. So if he's discharging his own pulse, say, 5 times, or 10 times per second, he's getting that information stream but if he can use the pulses of other fish, he can double that or triple that, or quadruple that. Another thing we found that's quite interesting is that the pulse of another fish can allow these animals to see further than they could otherwise.

Anand Jagatia

So can you talk us through how you went about investigating this? So what are some of the experiments that you did? And what did you find when you did them?

Nate Sawtell

There is a certain part of the brain of the fish that receives the input from the electrode receptors on the skin. So this is like the retina, but for the electrosense. So we know where to look, we put our electrodes in that brain region. And we saw directly that the signals related to electro location coming not just from the fish's own field, but from the field of a friend actually existed in the brain. So it's one thing to find a signal in the brain. But of course, you know, critically, we want to show the fish actually uses the signals to guide behaviour and we had an array of 32 objects that we can turn off or on whenever we want. And whenever the fish notice one of these things turning on it would issue something called the novelty response. So they changed discharge rate and we can measure that. So we did that under normal conditions, and we could figure out how far away the fish could effectively see. And then the trick of the experiment now was to add in pulses of other fish. So we didn't use real fish in this experiment. But to keep tighter control, we made artificial pulses of other fish. And using this approach, we could see that indeed, as we predicted, that the fish could see further when these other pulses were on. And furthermore, that the direction and the extent of that extension of range matched the predictions of our electrical field model.

Anand Jagatia

And why is it that using another fish’s signals can help the first fish to see further?

Nate Sawtell

So, the energy that the fish uses to sense dissipates very steeply or drops steeply as a function of distance. So, if the fish emits an electrical field it falls steeply as it moves into the world, interacts with an object, and then it dissipates again as it returns to the fish. So, there's this two-way loss of energy. But what we found is that in the case of two fish, with an object say in between, now the energy from the neighbour, from the friend, just has to travel once from the neighbour, through the object and to the fish's skin. That one-way instead of two-way travelling of energy, allows the fish to maybe see twice as far or even three times as far as he could otherwise.

Anand Jagatia

And it's like free information that's out there, right that they can tap into. And so, it makes sense that they would do that.

Nate Sawtell

That's exactly right. The information is there, and it seems that they use it. And the other experiment we did was to train the fish to discriminate between two objects. And these objects were identical visually, they only differed in their electrical properties. But then the trick we played in this experiment was to require the fish to do the same discrimination but only based on the pulses of another fish. And again, we're using an artificial pulse because we can control it. Then we were able to change the electrical properties of the objects only at the time when the pulse of the other fish was provided. So, in this way, the fish had no access to information about these two objects based on its own pulse, but only based on the pulse of the other fish.

Anand Jagatia

Can I just check that I've understood it right. So, it's almost like as if you have a human and you put something over their eyes, and then you change something about the world when their eyes are closed. And then if I can tell you what changed, when my eyes were closed, then I'm getting information from somewhere else and that's the analogy with– with the fish?

Nate Sawtell

Yeah, that's right. So, this is a very similar idea and they kind of transpose that idea onto the electric fish.

Anand Jagatia

So, what are the implications of this, then? Is this the first time that this way of collectively sensing the environment has been demonstrated in an electric animal?

Nate Sawtell

Definitely the first time in an electric animal. And we think it's one of the clearest examples that an active sensing animal can work in this collective mode. So, there's many forms of collective sensing that we know. So, in schools of fish or flocks of birds, or antelope herds, there's collective sensing in the sense that the sight of a predator will impact one animal and that an animal will begin to escape, and then other animals react. So that's kind of a very typical form of collective sensing. This form that we've described is kind of unique and interesting, because all of the animals in the group are instantly sharing the information. So, the electrical field travels at the speed of light to all of the members of the group. So, this is kind of a very rapid, intimate, and cost free way to share information and build up a better perception of the environment. So, we think it's quite, quite remarkable.

Anand Jagatia

Elephant nose fish really seem like such amazing animals, and they may even be my new favourite animal. What else are you hoping to study about them in the future now that you've made this discovery?

Nate Sawtell

These fish actually have bigger brain to body mass ratios than humans. So, we've always wondered what are the animals doing with these large brains. So, this new capacity that we found, this collective sensing, raises interesting opportunities for us to try to understand whether the enormous brains of these animals may be devoted, in part or maybe in large part to processing these complex streams of information that the fish are receiving in groups, and also perhaps, to organising their collective behaviour in a way that would promote this kind of collective sensing. One thing you could imagine is that to make maximal use of this ability, you might need to have a very good idea, a very good model, if you will, of your neighbours and your friends. Exactly where are they in space? How are they moving? So, the idea that these animals have social models or social internal models in their brains is one that we'd like to pursue, and there could be lots of interesting opportunities along those lines.

Benjamin Thompson

That was Anand Jagatia talking to Nate Sawtell from Columbia University in the US. If that story has electrified your interest… well you can find a link to the paper in the show notes.

Nick Petrić Howe

Finally on the show, it’s time for the Briefing Chat, where we discuss a couple of articles from the Nature Briefing. So, Ben, what have you been looking at this week?

Benjamin Thompson

Well I've been reading a story in Nature, and it's about a new method to grow organoids using cells collected from amniotic fluid and it's based on a paper in Nature Medicine.

Nick Petrić Howe

And this is something I always get a little bit confused about: what is an organoid? Is it just like a bunch of cells? Or is it like a small organ? What is an organoid?

Benjamin Thompson

A little bit of both actually, I think it's fair to say. So, organoids are organ-like groups of cells, okay. And they're grown in a lab, and they resemble whole organs but in miniature, right. We talked about brains on the show before some people call them mini brains, but they are lab grown structures. Now it's worth saying that these aren't the easiest thing in the world to grow right, they can take quite– quite a long time. And typically, organoids are grown from mature cells taken from biopsies, okay. And– and then they're programmed to become something called an induced pluripotent stem cell, right. And these can differentiate into other types of cell and eventually into these little organoids. They've been used to learn more about development and how diseases progress, that sort of thing, okay. But this paper specifically is looking at modelling foetal tissue, okay. And this can be quite challenging as researchers can have limited access to the necessary cells for ethical and practical reasons.

Nick Petrić Howe

So, you said that they're doing this using amniotic fluid I guess this presents different challenges from other ways of doing this. So how did they manage this in this particular case?

Benjamin Thompson

Well, what's happened here is the team have collected cells from within amniotic fluid and this fluid was collected from people who were having it removed as part of a standard prenatal care like an amniocentesis for example. And what the researchers have done is they've taken some of this amniotic fluid and they've isolated individual cells within it, okay. And these are, these are stem cells, right, that are associated with the epithelial layer of different tissues. And so, what they've done is they've used these cells to grow tiny organoids of the intestine, of the kidneys and of the lungs. And what's more, these cells already have their own identity, right. They don't need to be reprogrammed, they are destined to develop into these sorts of tissue, right. And so, it shows that amniotic fluid could be used as a source of living cells as they’re shed into the fluid. It supports and surrounds the growing foetus.

Nick Petrić Howe

And so, what do the researchers hope to do with these particular organoids, then?

Benjamin Thompson

Well, this is kind of early days, of course, this technique isn't ready for the clinic just yet. But the advantage that it has is that these organoids can be grown quite quickly, right in four to six weeks. And so, this means that they could be used to screen for treatments, or they could be used to learn more about congenital disorders and what have you, but– but it's only a start, right? There's obviously a bunch of caveats here. So far, only three types of organoids have been grown based on these epithelial cells. And some conditions, you know, involve multiple different layers of cell, for example, and some organs don't shed cells into the amniotic fluid, right, the heart or the brain, for example. So– so it can be really hard to use this technique to study congenital heart defects, for example. But as I say, this is a start, and a lot more tests need to be done to work out, you know, are these organoids reflective of the organs that they are being used to model for example, all these sorts of things, but certainly some interesting research.

Nick Petrić Howe

Well, it certainly sounds intriguing. And I'm sure it's a technique that we'll be keeping an eye on as it matures. But for my story this week, I want to ask you, do you remember a story from the end of last year, about an ancient whale that researchers thought might be the heaviest animal to ever have existed?

Benjamin Thompson

Right, yes, I do. But I think a word might is doing an awful lot of lifting there, heavy lifting I suppose you might say. But yeah, continuing our animal theme for this week show, Nick. So, what's going on with this one?

Nick Petrić Howe

So, to back up a little bit, just to give everyone the context. This is about an ancient whale that researchers named Perucetus colossus and this was described in a paper in Nature in August last year, and the researchers at the time suggested that this could be the heaviest animal to ever existed. Now, the difficulty with that is it's really hard to work out how heavy an ancient animal is. And it's actually really hard to figure out how heavy some animals that exist now are. And so, what this story is about — and I was reading about this in The New York Times — is some other researchers have sort of been a bit sceptical about this claim. And they've said that actually, the analysis that the original research did was wrong, and it would be much, much lighter, according to their work.

Benjamin Thompson

I mean, I guess it's hard to measure mass from a very, very long time ago, right? Because I suppose a lot of that's held in muscle and fat and what have you, which, as we spoke about many times doesn't really exist in the fossil record. So I guess, all you've got is some bones or a fraction of a skeleton, and people are trying to work things out from that.

Nick Petrić Howe

Yeah you know it’s really, really difficult. So, in the original research, the researchers figured that this ancient whale probably weighed around 180 metric tonnes, so 180,000 kilogrammes—

Benjamin Thompson

—wow—

—and the way that they figured that was because its bones were very dense. And they reckon that the dense bones allowed it to be on the bottom of the ocean, where most of the food would have been at that time, at a time, when the whale would have had to still have air in its lungs. Whales these days can store oxygen in their tissues and stuff. So they don't have to have like a big bubble of air in their lungs. So, they thought that the bones were sort of weighing it down to an extent. And so, they used a comparison with modern day manatees that also have dense bones for a similar reason. So, in this new research, what they've done is they've reanalysed the blue whale and they've used data from Japanese whaling ships to do this. And they've created a 3D model of the blue whale to figure out its mass. And doing this they've given the blue whale a bigger mass, but then when they put the ancient whale into this model, they find that it's much much lighter than the original research suggested. So, they think that it was actually only around 50 metric tonnes.

Benjamin Thompson

Right so the heavyweight belt then has passed back to the blue whale, according to this research?

Nick Petrić Howe

Yes, but, there's a but, which is that ancient whales and also the blue whale itself, like a living animal are very, very difficult to weigh. And so it's really hard to figure out how much mass even living things may have had, nevermind these sort of ancient, non-existent anymore whales. And the original researchers disagree with this analysis, and they say that they found more evidence that the ancient whale was manatee-like and so would have these very dense, heavy bones. But as you sort of alluded to, it's really hard to figure out because there's a lot of stuff other than bones that go into the mass of something. So, it could be something that we may never know. But it seems that at the moment, different researchers are coming at this from different angles and coming up with different answers. So, what was the heaviest animal is a bit of a question mark for now.

Benjamin Thompson

So, we've got a new team of researchers weighing in on this, then. Is this an important question to answer? Or is it just everyone likes to know who's top of the tree kind of thing?

Nick Petrić Howe

It depends how you define important, I guess. But these researchers behind the new research were sceptical of the original research when it first came out. So, I think they've taken that scepticism and done some science to back up their scepticism. And yeah, I mean, it's interesting, because these sort of debates and discussions can help build a picture and help build a scientific consensus of what these ancient animals may be like. But is possible that it’s an unknowable question as well. So perhaps this will just ping pong, back and forth forever.

Benjamin Thompson

Well as with so many of these stories, you're right, I'm sure this one is going to run and run and we'll be there to cover it when the next instalment hits. But let's leave it there for the time being for this week's Briefing Chat. But listeners, for more on these stories and where you can sign up to Nature Briefing to get even more of them delivered directly to your inbox, check out the show notes for some links.

Nick Petrić Howe

That's all for this week. But if you've enjoyed the stories on the show, let us know. Send an email to podcast@nature.com or you can tweet at us @naturepodcast. We may even read them out in the next show. I'm Nick Petrić Howe.

Benjamin Thompson

And I'm Benjamin Thompson. Thanks for listening.