Amazing animals: bats on treadmills, and showering elephants
In this animal-themed edition of the news: What prompted scientists to put vampire bats on a treadmill? Also ahead: why medicinal leeches are returning to the UK’s waterways. Plus, the spiders that know what kind of food will satisfy their dietary needs.
In this episode
00:58 - Why scientists put vampire bats on treadmills
Why scientists put vampire bats on treadmills
Ken Welch, University of Toronto
It might sound like something from a popular horror novel, but vampire bats running on treadmills is a serious research piece that aims to gain a better understanding of a mystery that has surrounded vampire bats; what is going on with their metabolism that lets them keep up such an active lifestyle, on a diet so heavily propped up by blood? Ken Welch at the University of Toronto explains…
Ken - Blood is very rich in proteins. Think of all the haemoglobin that's floating around in our red blood cells and all of the albumin and the other proteins that make up part of the plasma in our blood. But the other components of the diet that we think about other than proteins are carbohydrates, sugars, and starches, and then fats. And in a traditional mammalian diet or a typical mammalian diet, it is a diet that's relatively well-rounded, having lots of carbohydrates in it, some fats and some proteins, some amino acids. So their diet is just kind of really lacking almost all of the carbohydrate and lipid components and has this excess of protein and an excess of iron because a lot of that protein is the haemoglobin that has the iron in it.
Will - So something must be going on for them to still be able to run so efficiently and quickly. How does that go from you theorising that, to a bat ending up on a treadmill?
Ken - <laugh> Yeah. Well, if we wanted to investigate the metabolism of flying things like bats and hummingbirds and other birds, for most of those animals, you need to let them fly in a wind tunnel. But it's really hard to study the physiology of an animal that's flying around freely. And it's very difficult to get access to a large flight tunnel where you can really interrogate these things. But with vampire bats, they don't hover. But we knew that they were actually pretty good on the treadmill. And it was in conversation with those scientists in Belize in between other experiments that I kind of became convinced that it would be really quite possible to get them to run on the treadmill for extended periods of time so that we could actually measure their metabolism while they were doing this.
Will - So by analysing what comes out when they respire, you're able to see what they're using as fuel for this running.
Ken - So the oxygen that you and I are taking in from the environment around us, and we're breathing out CO2, other animals are doing that as well. And so just like we can put a human on an exercise bike or on a treadmill so that we can capture their exhaled breath. Well, we can't necessarily convince a vampire bat to wear a mask, but if we make the treadmill small enough, we can stick it inside of a chamber and we can measure the air coming out of the backside of that chamber where that bat is running, which includes some of its breath.
Will - So what did you find out?
Ken - First and foremost, we found out that they're oxidising chemicals, that they're producing energy, to sustain running at a very high rate. But in addition to that, we wanted to actually say what fuel source are they burning? And for that we needed a way to kind of label something and look for it to be produced. And what we're looking for in this case is a certain, if you will, flavour of carbon dioxide, carbon dioxide that has a carbon-13 molecule in it rather than a carbon-12 molecule. These are isotopes of carbon. Your audience might be familiar with carbon-14. That's the radioactive form of carbon that's used in radiocarbon dating. Well, carbon-13 is not radioactive, so we don't need extra permits to work with it. But if we can buy certain chemicals, be they sugars or lipids or amino acids that are very, very enriched in this rare form of carbon, we can use a special laser technique to measure that and tell the difference between those two forms of carbon. So we gave the bats a blood meal just prior to running them on the treadmill, to which we had added a small amount of the amino acid glycine or the amino acid leucine that was enriched with this carbon-13 molecule. And if the bats started to use those amino acids as well as the amino acids in their blood meal as their fuel, then when they're oxidising those things in their muscle mitochondria, that's what's becoming the CO2 that's being breathed out. So we look for the signature of that special heavy form of carbon dioxide coming out in their breath. And we saw that very, very rapidly. That signature went very high, as high as 60%, meaning 60% of the CO2 molecules that they were breathing out had the signature consistent with the amino acids in the meal we'd just given them. It looked like they were relying mostly or exclusively even on the amino acids, the building blocks of the proteins that were there in that blood meal. So not only were they, yes, seeming to power their running essentially exclusively with protein oxidation, but they were doing so using amino acids that they'd ingested just moments before. So they were bringing these into their system and using them extremely quickly.
Will - Do we have any idea how they might be doing this?
Ken - So what we think is going on is that in their cells, in their muscle cells especially, the biochemical pathways that utilise carbohydrates or that utilise lipids to burn them for energy, are expressed at lower levels potentially. And they've really ramped up the biochemical pathways that do break down amino acids and have just sort of supercharged those. That said, we want to understand if the way that vampire bats metabolism has been supercharged to use amino acids, is it exactly the same as the way that, for example, the tsetse fly or a female mosquito that feeds on a blood meal, is it the same way that their pathways are enhanced or are there differences? Are all amino acids equally good as fuel if you're a vampire bat? Lots of those questions are still left to be explored and reasons to go down to Belize the next time around and study them again.
Will - And just one last question. And not that I'm worried about it at all, but I feel compelled to ask how quickly can they run, just out of interest?
Ken - Well we were pushing them to 30 metres per minute, that's almost a hundred feet per minute. Now, you and I can probably outrun that, but we didn't get them to their maximum. They can potentially go faster. We didn't have time to test it. And back in 2005, the treadmill that Dan Riskin and John Hermanson used was run with a drill to make the rotor spin and they couldn't get it to go any faster than the maximum that they hit. So these guys still have some surprises up their sleeves as it were.
07:45 - Why medicinal leeches are making a return
Why medicinal leeches are making a return
Naomi Ewald, Freshwater Habitats Trust & Aaron Harvey, London Zoo
It has been announced that medicinal leeches are successfully breeding at London Zoo. The largest native leech species in the UK used to be abundant, but their number went into decline when they began to be used less readily in medicine, and their natural habitats - such as wetlands - were drained. But these segmented worms seem to be back in vogue. James Tytko took a trip to London Zoo to find out why…
Naomi - Hi there. My name's Dr. Naomi Ewald from Freshwater Habitats Trust and I'm part of the project looking at leeches and their conservation in the UK. Medicinal leeches are one of the largest leeches we have in the UK. They can grow up to about 10 centimetres, sometimes bigger for really large adults. Not only are they big, but they're also really patterned. So they have this lovely red and yellow stripe down their bodies that looks sort of like a running stitch and on their bellies they're yellow and black patterned. And we'll look later but you can actually tell individuals apart based on the patterns on their bellies. So these are big leeches. They're blood sucking leeches and they're the only leech in the UK that can do that.
James - In terms of their role in fresh waters around the UK, what do they eat and what eats them? Apart from human blood, of course <laugh>.
Naomi - So medicinal leeches are really important as part of when we are thinking about conservation of ponds in the UK. So we have about 500,000 ponds in the UK. Unfortunately, most of them are polluted to some extent, normally because of surrounding land use change, agricultural runoff, or because they're no longer grazed by grazing animals. And so where we find leeches in the UK is because they're still within important freshwater areas. So these are the best of the best ponds that we have. And out of those 500,000, there are only about 150 ponds left in the wild in the UK that support medicinal leech.
James - Let's move to the medical history then, if you would.
Naomi - Yeah, so we've known that medicinal leaches have been used for what you might have in inverted commas called 'medicine' really since ancient Egyptian times. And there was something like a leech mania around the 17th and 18th century through into the 19th century, particularly in Europe. And essentially if you were feeling a bit under the weather, they thought that they could rebalance you by sticking a leech on you. So we know that St. Bartholomew's hospital in London was using up to 90,000 leeches a year, and in France they were importing 60 million leeches a year at the height of this leech craze. And you know, it's questionable whether actually that did any good or not because back in the days some of those practices were probably not very clean and they were probably taking leech from one person and sticking it onto another. So the risk of dying from infection and gangrene was probably as much as it was a cure.
James - Fortunately, bloodletting by leeches has been discredited as a medical practice for quite some time. So why the kind of conservation push now? Is it the other pressures to their environment that you mentioned?
Naomi - Yeah, that's right because we know that leeches are now only found in those very best of the best places. The first step is to try and see if we can rebuild those populations naturally. So obviously we're advising landowners that they have the leeches and what sort of management they could undertake to improve it, and we're trying to create new ponds adjacent to those important freshwater areas. So building out and creating a sort of a network of clean freshwater ponds across the landscape. If that doesn't happen, we then want to think about whether we can look at sites where they've been historically, but are now missing and work out whether we can recover them to those places as really a signal that the habitats are improving and that if they can support a healthy population of leeches, they're probably supporting a lot of other good stuff as well.
James - Indeed. What about this renewed medical interest in leeches and particularly their venom?
Naomi - So medicinal leeches have a really clever saliva that's designed to help them feed, and that essentially is a component made up of anticoagulants so that the blood will flow freely once they've bitten in. So they have three jaws with serrated teeth and they'll puncture a hole in their victim and then the blood will start flowing because of their saliva. They also have an antihistamine which stops the swelling and opens the blood vessels so that it flows even more. And then there's something of a sort of an antiseptic and also a way that will stop you feeling them even biting you. So essentially if a leech latches onto you, you don't know about it and you bleed for a really long time. And in the 1970s they realised that actually there was a whole new world of medicine that could benefit from what you could learn from leeches, particularly around the sort of cosmetics and also reattachment of limbs because one of the key things is to keep the new tissue alive. And if you've got blood being drawn through that by this saliva and it's very hard to recreate that synthetically. So the best bets are to find a leech, stick it on you, and then that works really well. But then we discovered that the leeches they've been using are Mediterranean medicinal leech and not our lovely native UK leech. And so really we wanted to see, well, can we use some of the techniques that they learned from the medicine trade to actually see if we could breed them in this country? And this is when we turn to London Zoo for their advice because obviously they have all the experience in the world of helping set up these breeding programs.
James - Without further ado, I think it's time to see the fruits of that labour.
Aaron - I'm Aaron Harvey. I am the aquarist here at ZSL London Zoo. I am the head of looking after the leeches here at ZSL.
James - Terrific. Well that makes you very well placed to talk me through what I'm looking at here. I've got three boxes full of leeches of kind of incrementally increasing size, I think it would be fair to say. So tell me about these first ones.
Aaron - So the first box we have here, so these are our smallest leeches. These are just coming up to about three months of age. They can live as adults for up to about 20 years.
James - Okay. So these are really at the start of their journey.
Aaron - Very start of their life. And then with our second box...
James - A little bit more placid, probably fair to say.
Aaron - So these are slightly older. So these are just over three months or about three months of age. They've had a fair few feeds now. So they're starting to chill and calm down a lot more. They're very sensitive to movement and body temperature. So this is generally the activity we'll see when we're working with them
James - He's looking at me as a potential meal.
Aaron - Maybe, these leeches again, these are older, so these are actually four months of age.
James - Tell me a bit about the kind of techniques Naomi was talking about that have translated from the renewed medical interest in leeches and how that's been applied here at London.
Aaron - We've taken a lot of evidence from wild caught data. We've looked at temperature fluctuations through seasonality, and we've tried to bring that here to London. So we control water temperature very closely, especially around this time of year, we start to drop their water temperature. Eventually when it gets to December, January time, we actually get to about 10 degrees. So the leeches can hit their winter dormancy and then when it comes back into spring and summer, their water temperature will hit straight back up into the 25s to even sometimes 30 degrees. And that encourages their breeding process.
James - When we talk about reintroducing species into the world, you know, people often like to think of eagles or bison and maybe the less glamorous leech gets a little bit less attention. But it's no less important, is it?
Aaron - They're very important. They're very good ecological indicators. They're a great sign of a healthy ecosystem and they're animals we desperately need in our native wildlife.
James - So Naomi, tell me, when might we start putting these creatures back in UK fresh waters?
Naomi - Well, over the next couple of years we're hoping to start the wild surveys, and then after that we'll start to think about whether we can reintroduce any. So check back in with me in five years time and we'll give you an update. And obviously, you're welcome to come out and see when we've got to that point. If we are reintroducing them, that will be when we'll be doing it.
16:54 - Spiders choose their most nutritious next meal
Spiders choose their most nutritious next meal
Jordan Cuff, Newcastle University
We’ve all been stood in a supermarket aisle peering at the packaging and wondering whether the food contained within includes the nutrients needed to sustain us. Well, it turns out that humans might not be alone in this. Some species of spider have been seen indulging in what has been described as ‘nutrient specific foraging’ - which means they know what kind of meal to go after in order to fulfil their dietary needs. Newcastle University’s Jordan Cuff explains more…
Jordan - Animals much like us, have to balance their nutrient intake. So they have to eat a nice balance of carbohydrates, lipids, and proteins to ensure that they live nice, long, happy lives. So there's a lot of evidence for this phenomenon. Invertebrates and even in invertebrates as well, but mostly from, from lab studies. So my aim with this work was to try and show that nutrients are important in these foraging choices, particularly in spiders in the field as well.
Will - Were the nutrients differing depending on the age or sex of the spiders involved?
Jordan - Yeah, absolutely. So one of the main things we wanted to look at was how the different prey and the nutrients within those prey differed between different groups of spiders. So we looked at different spider species and we found that some of them, the money spiders particularly, which sit on these beautiful sheet webs and just wait for prey to come to them, they ate particularly carbohydrate rich prey compared to the wolf spiders, which are much more active and run around on the ground. And they tended to eat much more lipid and protein rich prey. And then when we compare between life stages, we start to see some really interesting patterns. So the adult spiders are eating more carbohydrate-rich prey. So this is likely because they're a lot more mobile, running around trying to find a mate and doing quite a bit of hunting as well. Whereas the juvenile spiders tended to prefer more protein-rich prey, which aligns with the fact that they're developing and they're still growing. And similarly, we noticed differences between sexes as well. So male spiders, similar to a lot of the adults, preferred that that carbohydrate rich prey, perhaps again because they're seeking the mates, whereas the female spiders that tend to wait for the males to come to them, but instead have to invest more resources in developing little eggs to form the next generation of spider lings. They were investing more of their time in finding protein and lipid-rich prey.
Will - I mean, that all makes perfect sense in terms of why they would want to eat those sorts of things. But I struggle to understand my necessary nutrient intake when food is spelled out for me on the back of a packet. How on Earth do the spiders know what to go for?
Jordan - Sadly their prey doesn't come in convenient packaging. So instead they have to try and perceive the nutrients within the prey. And there's not much known about how they might do that yet. It'll vary quite markedly between different predators and different animals. Generally a lot of animals depend quite heavily on a sense of smell, for example. And it might be that some nutrients give off a particular scent. And some of our preliminary analyses in that direction seem to indicate that that's likely to be the case. But spiders have a particularly bad sense of smell most of the time. And instead they rely on things like vibrational cues to identify their prey. So in that case, there's likely to be an aspect of learning. So much like some of the recent work on bumblebee showing that they can learn to problem solve. I think these spiders are likely to be learning which nutrients are associated with which prey groups, and that's likely to be an imperfect system, but at least one way to start to identify which nutrients they need next.
Will - Could we therefore introduce spiders of a certain age or sex or species into say a field to take care of certain crop pests?
Jordan - Essentially the main rationale behind this research was to identify ways that we could manipulate this nutrient specific foraging behaviour to get spiders to eat more crop pests. And what we found is many of the pests are really rich in lipids and carbohydrates, particularly because they're sucking all the juices out of these crop plants. But essentially with that richness in lipids, it's likely to be really beneficial to the spiders because as you go up these trophic levels, there's evidence that shows that there's less and less lipid. And carbohydrates as well are mostly prominent in plants, and spiders don't tend to have much access to plants as a resource. So again, carbohydrates are likely to be a really important part of their diet. So we could, using research like this, begin to identify spiders that preferentially target prey rich in those lipids and carbohydrates and promote those spiders by managing our farms and our habitats in a particular way to try and get more of those spiders eating crop pests.
21:45 - Asian elephant stuns scientists with self-showering
Asian elephant stuns scientists with self-showering
Lena Kaufmann, Humboldt University of Berlin
An Asian elephant at Berlin Zoo has gained notoriety by working out how to use a hose to take morning showers. The elephant in question is named Mary, and her antics were so unusual that they have been featured in the journal Current Biology. Elephants have been described as using tools for many years now, but these incidences were mostly anecdotal. Now, however, comes an opportunity to perform a long term study on what makes an elephant’s tool brain tick. Lena Kaufmann at the Humboldt University of Berlin has been telling my colleague Chris Smith all about it…
Lena - So it was kind of a lucky finding for me. I've been working at the zoo for over three years now doing behavioural experiments and observations with the elephants there. And I was there in the morning tagging along with the morning routine that the elephant caretakers have with the elephants. And they shower the elephants every morning. It's important for their skincare as well. There was this one keeper who sometimes just hands this one female elephant Mary the water hose when he's done with showering her a little bit, and he just lets her basically shower herself with it. And I just saw her really, it seemed like, very aimfully showering herself. And I immediately recognised that that was something very, very interesting and special.
Chris - Effectively, the hose is becoming a tool in her, I won't say hands, but in her trunk. She's using a tool in order to affect an outcome, which is getting a wash, which is something she wants.
Lena - Exactly, yes. So their trunks are very, very dextrous. So their trunk tip is often compared to a human hand. As to the goal, I would say it's body care definitely, but probably also partially comfort behaviour. Elephants love to spray themselves with water as well, so that's an important part of their behavioural repertoire.
Chris - We knew that elephants used tools though, didn't we? We already knew that they were quite familiar with using their trunk to pick things up, manipulating things, and then doing things with the things they pick up. So what does this add to our understanding?
Lena - Our study would be the first, or one of the first cases, of really like a long-term empirical study on elephant tool use and in addition with also the specialty of the type of tool she's using. I think it's a very fascinating new finding that we made. Also, we have this suggestion that of course it's speculation that maybe water hoses might be tools that elephants can understand intuitively in a way because they're kind of similar to the trunks, right? And they use their trunks to shower themselves and to spray water.
Chris - How do you think she would've learned to do this in the first place? Can they watch other individuals? Because we know that many animals socially learn, they watch another animal do something and that's how they pick it up. So would she have watched the keeper and then thought, 'well, I could do that'. Is that what you think the steps probably were?
Lena - It might be a possibility that just the basic understanding of you can use a water hose, you can hold it and use it for something might have come from humans, but it would require very specific cognitive abilities and a very high understanding of another individual, of another species, right? From an elephant's perspective to understand what a human is doing. So we would have to look into it more.
Chris - Nevertheless. You do also go on to say in the paper about the fact that another elephant, I want to say, gets the hump <laugh> and seems to intervene. So they're, they're obviously watching what each other are doing because the other elephant that comes in tries to stop Mary having a shower.
Lena - Exactly. Yeah. So the younger female that's standing next to Mary, she, at some point she started intervening with the showering. And we're not sure of what exactly her goal, the aim of these interventions was. But one idea would be that she's actually maybe trying to stop the water flow potentially. So at some point, she was able to reach the water hose that was going to the showering Mary, and she started pulling it towards her and then actually clamping it in a way with her trunk, like really changing her grip and then just pressing it. And that as a result of this, the water flow to Mary stops sometimes actually.
Chris - Was this to elicit a reaction on the part of Mary to get the other elephant's attention? Or was it to provoke? Or was it because the elephant is genuinely intrigued about how the hose works and by squeezing it and seeing the water stopping, that is actually part of the learning process?
Lena - So we're not sure if she really was trying to get a reaction or to stop the water flow to Mary. It's also possible that she was playing with the hose. One theory that the elephant caretakers at the zoo have is that it feels good to grab the water hose because of the vibrations that the water pressure inside is creating. So when you clamp the water hose basically and you stop water flow, there must be strong vibrations and elephant trunks are highly sensitive, especially to touch, basically. So it might also be just an interesting behaviour that might be some play behaviour involved there, but it's a possibility that she was trying to stop the waterfall.
Chris - Having made these observations and got this lovely footage on your phone and published the findings in the journal, what are the take home messages?
Lena - I would say that we definitely need more long-term empirical studies on elephant cognition and behaviour such as this one. And then also that this is an exceptional case due to the complexity of the tool that Mary's using. And also the way she's applying it, it's an exceptional case of elephant tool use.
27:43 - Why are boat and plane propellers in different places?
Why are boat and plane propellers in different places?
Thanks to Andy Wheeler for the answer!
Will - As it turns out, there are a fair few answers to this question in which physics and practicality go hand in hand. Some aircraft have their propellers closer to the front because goods are often loaded on and off at the back. And putting humans near spinning blades isn't always a sensible idea. It's also common for boats to have propellers at the back to avoid them bonking into things. Halc on the forum also points out: ‘A small boat tends to lift its bow out to the water at high speeds. Not a good thing then if the propulsion is there’, which is a very fair point. But there are also good physics reasons for these respective propeller placements as well. And here to explain is the University of Cambridge's, Andy Wheeler.
Andy - The big difference between water and air is that water is very much more dense than air. So if you take a metre cubed of air, it weighs about a kilogram and a metre cubed of water weighs about a ton, so a thousand times more. So that means that propellers for aircraft need to be much bigger. And that's because the thrust you get from a propeller is related to the amount of the mass flow that passes through the propeller and the speed with which the propeller can push that backwards. And so that can affect practically where you could put propellers on an aircraft. You couldn't have a propeller that was too close to the ground that might then hit the ground or towards the back of an aircraft that might affect how the aircraft could land. Because the propeller is also attached to an engine and the engine tends to be heavy. And the distribution of weight on an aircraft is very important. So if you have too much weight towards the back of an aircraft, that will affect how the aircraft can be controlled in flight.
Will - And is there a case of there needing to be the right sort of air flowing through an engine?
Andy - That's right. So quite important to the performance of a propeller is how the flow is entering the propeller if you were to put a propeller behind something. And so the flow coming into the propeller is very distorted. That would affect the prop performance of the propeller. The propeller on the boat, because the water is a thousand times more dense than air, it's much smaller and you tend to mount that at the back of a boat. And I think that's more to do with where you'd want to mount the engine. So for instance, on a small boat, you might want that boat to pitch up a little bit so the weight of the engine can help with that so that the boat can then move more smoothly through the waves. So the viscosity isn't really the main thing that affects these big decisions on where you put the engine and the propeller and how you distribute the weight, for instance, in each case.
Will - I did anticipate this being far more a physics question, but it does seem to be more one of a practical applicational question.
Andy - One thing I'd like to say is that actually there isn't really any physical principle that tells us we can't put an aircraft propeller at the back. I mean, you'll see some aircraft do have propellers at the back or have jet engines at the back of the aeroplane. And as we move towards more futuristic proportion systems, we might start to see more electrically-driven propellers and those can be made much smaller and they can be distributed over the aeroplane. And that gives us a much bigger degree of flexibility in the design of the aeroplane. So we could have small propellers mounted on the wings, for instance, and that can help to blow air over the wing to improve the performance of the wing.
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