Does a hot mint still taste cold?

US scientists have unlocked the secret of how the nervous system senses low temperatures, discovering in the process why sucking a mint makes your mouth feel cold.

Writing in Nature, David Julius, from the University of California San Francisco, found that mice lacking a gene called TRPM8 ceased to react to low temperatures. When offered a choice of a warm or cold surface, the TRPM8-deficient mice would spend significantly longer sitting in the cold than normal control animals. 

The missing gene encodes a pore which sits in the membrane of a specific class of cold-sensitive nerve fibres. When the nerve is cooled down the pore changes shape, triggering the production of excitatory nerve impulses that are relayed to the brain. The pore is also activated by menthol, which provokes the pore to change shape at much higher temperatures than it would normally, explaining why sucking a mint makes your breath feel cold against the back of your mouth.

But "Polos" making your mouth cold isn't the "hole" story because the mice weren't entirely cold-insensitive. Taking the temperature down below 10 degrees C resulted in an increase in nerve activity again suggesting that there might be a further "extreme cold" receptor waiting to be discovered, or that at these low temperatures the physical damage done to tissue is enough to trigger other pain pathways.  Either way, researchers hope that by understanding the workings of these sensory nerve pathways they will be able to design better drugs to block pain syndromes including those triggered by exposure to the cold.

3rd Jun 2007

Trees taught us to walk

Have you ever wondered why humans walk on two legs, while pretty much all other animals prefer four?  Most human evolution researchers think we started to walk upright through a process beginning with “knuckle walking” on land – the way that chimps and gorillas (and maybe some of the Naked Scientists team!) walk today.

This change was thought to have happened when our ancestors left the forests of East Africa and moved onto the grasslands. But researchers from the University of Liverpool have come up with some evidence to suggest that we actually learned to walk upright by foraging in treetops for food, in a paper published in the journal Science.

Their studies of Sumatran orang-utans have led them to the conclusion that knuckle walking is quite a recent development for chimps, and that the ancient great apes actually spent more time on two legs in trees, holding onto branches for support.  So us humans may never have gone through a knuckle dragging stage at all, and skipped straight from tree living to two feet on the ground.

One of the researchers, Professor Robin Crompton explains that “Walking upright on two legs, gripping branches with the feet and balancing themselves by holding or touching higher branches with their hands is actually a very effective way of moving on smaller branches. It helps to explain how early human ancestors learnt to walk upright whilst living in the trees and how they would have used this way of movement when they left the trees for a life on the ground.”

3rd Jun 2007

Gotta Lotta Bottle

Diet-conscious New Zealanders may soon be able to tuck into naturally "skimmed" milk thanks to a programme set up to breed a herd of cows that produce milk containing less than a third of the nomal levels of fat.

Scientists from a Biotech company called Vialactia discovered a Fresian cow, christened "Marge", that carries a mutant gene.  As a result she produces milk containing only 1% fat, compared with the 3.5% fat normally found in whole milk.  Her offspring also produce naturaly low-fat milk, indicating that the trait, which the scientists have yet to identify, is dominant.  Another bonus is that the milk also contains high levels of omega-3 fatty acids and makes butter than spreads as easily as margarine even when it's cold.  According the Vialactia chief scientist Russell Snell, the company expects to have the first commercial herd of cows supplying naturally low-fat milk and "ready-spready" butter by 2011.

3rd Jun 2007

Cigs spoil sperm

We’ve known for a long time that tobacco smoking can cause a range of cancers – in fact, it’s believed to be responsible for more than a quarter of all cancer deaths in the UK.  And there’s plenty of evidence to show that pregnant women who smoke can harm their unborn babies.

But now scientists in Canada have discovered that fathers who smoke could be passing on genetic damage to their kids.  The team found that male mice who were exposed to cigarette smoke had changes in the DNA within their sperm. Such changes could increase the risk of cancer, or other diseases in their kids.

The researchers tested mice who had been exposed to similar relative levels of smoke of an average human smoker, and looked at the sequence of a certain stretch of DNA.  They found that the rates of DNA mistakes, or mutations, was 1.4 times higher after 6 weeks and 1.7 times higher after 12 weeks, compared to non-smoking animals.

Based on previous studies, the researchers think that their results could be extrapolated to the rest of the genome.  Although this work has only been done in mice, it does provide more evidence that men who want to become dads should quit smoking while trying to conceive.  Because men constantly generate new sperm, the DNA-damaging effects of smoking are unlikely be so long-lived.

3rd Jun 2007

Imitation is the highest form of flattery, and may even save your life

US researchers have found that canny moths impersonate the sounds made by their bad-tasting relatives to ward of bat-attacks.

Writing in this week's PNAS, Jessie Barber, from Wake Forest University, trained two species of bats to hunt for moths within sight of two infra-red enabled video cameras. At the same time he recorded the sounds produced by moth prey and the hunting bats. In response to hearing the sonar emitted by bats to locate their meals, some unpalatable tiger moths use a pair of structures called tymbals to broadcast ultrasonic clicks of their own, which are designed to warn the hunter that they taste bad. The bats then duly avoid them. But other tastier moths appear to have muscled in on the trick to avoid being eaten and mimic the bat-repelling sounds with good effect: "we found that bats do not eat the good-tasting moths that make the similar sounds," said Barber. Moths that exercised the right to remain silent, on the other hand, fared less well and were instantly gobbled up.

3rd Jun 2007

Science Update - Planets

Bob - Hey, Naked Scientists! We were inspired by your last show to talk about planets this week. I’m going to tell you how scientists are using diamonds and lasers to simulate the intense pressures inside large planets. But first, Chelsea has this for us from the Acoustical Society of America meeting that just finished up in Salt Lake City, Utah.

Chelsea - Do you recognize this, Bob? [music]

Bob - Sure. It’s the opening riff from Smoke on the Water.

Chelsea - Yeah. And haven’t you wondered what it would sound like on Mars?

Bob - Yeah. In fact I wonder that on a daily basis.

Chelsea - Well, you have something in common with physicist Andi Petculescu of the University of Louisiana-Lafayette.

Andi Petculescu (University of Louisiana-Lafayette): It’s one of my all-time favorite songs.

Chelsea - He’s come up with a new way of simulating sound on different planetary bodies. Here’s Venus:

[Smoke on the Water riff on Venus]

Chelsea - It’s chock-full of carbon dioxide, which steals energy from the riff’s high-frequency tones. Here’s Saturn’s moon Titan:

[Smoke on the Water riff on Titan]

Chelsea - Titan’s atmosphere is a lot like Earth, but it’s colder and under more pressure, so the sound travels farther and the music sounds louder. But what about Mars?

Andi Petculescu: Mars would sound like this. [silence] So basically no sound.

Chelsea - Making it not such a great place for the next inter-planetary rock festival.

Bob - Yeah, I guess not. Thanks, Chelsea. Well, pairing gem-quality diamonds with lasers sounds like fashion design, but it’s actually a new scientific technique for simulating high-pressure environments. Geophysicist Raymond Jeanloz of the University of California-Berkeley says you first compress a small amount of the material you’re studying between two diamonds. Then you send shockwaves through the material using powerful new lasers.

Raymond Jeanloz (University of California-Berkeley):  With these very high-powered lasers, it’s possible to get to very, very high pressures that previously were effectively accessible only next to nuclear explosions.

Bob -   At these high pressures, chemicals behave completely differently; for instance, water becomes metallic. Jeanloz says that outside of labs, these conditions would be found at the cores of supergiant planets beyond our solar system.

Chelsea - Thanks, Bob. Next time, we’ll be back to tell you how television watching and moving in with a partner can affect your weight. Until then, I’m Chelsea Wald...

Bob - ...and I’m Bob Hirshon, for AAAS, The Science Society. Back to you, Naked Scientists!

June 2007

Jamming Rice

Find out how to pick up a jar of rice without touching the jar, and what it has to do with holes in the road.

What you need

What to Do

Fill the jar with rice

Put the knife into the jar and wiggle it gently for a while, then take the knife out, push it in again jiggle it some more.

You will have to keep topping up the jar with rice, and it will take a few minutes.

At some point you will find something strange happens when you take the knife out.

What may Happen

As you jiggle the knife you will notice that the level of the rice drops, and it slowly gets harder to move the knife.

Eventually when you try and take the knife out it stays stuck in the jar.

What is going on?

When you pour rice into the jar the rice grains will be disorganised. 

When you shake the grains gently with the knife the grains fall down into the gaps between the other grains filling up most of the spaces.

If you look closely in the jar you will notice that the grains tend to line up, this is because they take up less space this way.

 Because there is very little space for the grains to move into when you push the knife into them, so they have to bend and distort to allow the knife to get in - just like a piece of wood would have to.  This takes a lot of force to do so the rice will push back and grip the knife, allowing you to pick up the jar with the knife.

What has this got to do with holes in the road?

When the road is dug up it is normally mended so the repair is flat, but after a couple of years it normally turns into a dent.  This is because the stones that were used to fill the hole are vibrated slightly by traffic going over the top.  This means that they pack together better, take up less space and create a dent.

Written by Dave Ansell

Clever Birds - How Scrub Jays Plan for the Future

Chris - I'm very pleased to welcome Nicky Clayton from Cambridge University. Now Nicky you work on scrub jays, I understand that's a kind of bird, but perhaps you could kick off by telling us first of all what actually is a scrub jay and why would you want to work on it?

Nicky - Well, I work on a number of birds which are part of the crow family. This includes ravens and magpies and jays, and the ones that I work on are jays, rooks and jackdaws.

Chris - But why are you particularly interested in this family of animals?

Nicky - Well, these birds are particularly clever. We think of them as the feathered Einsteins or the feathered apes of the bird world. They have huge brains for their body size and there are all kinds of examples of just how clever they are.

Chris - One of the things you did recently was to see how good they were at planning for a rainy day, so tell us about that.

Nicky - Well, these birds hide food for the future. We call this caching behaviour, from the French word to hide. What we were interested in was the extent to which they could plan, because obviously other animals hide food, like squirrels, and many animals hibernate or migrate which means they have a forward looking behaviour. But there is a difference between a simple forward looking behaviour that might be triggered by a seasonal cue which will be entirely inborn and actually planning which would require some sort of thinking or forethought.

Chris - So how do you know they're actually doing that?

Nicky - So what we did was we asked whether they could plan for tomorrow's breakfast, and this is an experiment that was actually done by two of my Ph.D. students. It was led by Caroline Raby with help from Dean Alexis, and a member of my department Tony Dickinson, so credit must go to them as well as to me. What we did was to ask whether they could plan for tomorrow’s breakfast, so we taught them that there were a suite of room that they could visit during the day.

Chris - Like a bird motel or something?

Nicky - That’s right, a bird motel with a suite of three rooms and in the evening they went to sleep in the dark just as all birds do and when they woke up in the morning, they found themselves in one of two motel rooms. On some days they found themselves in motel room 1, they woke up hungry and breakfast was served, so no problem. On other days however, they found themselves in motel room 2, which was unlucky because when they woke up hungry as usual, there was no breakfast. But then all of a sudden, we gave them an unexpected test, which was to give them the opportunity to hide food as well as eat it in the evening and all the birds put the vast majority of the food, in motel room 2, where breakfast wasn’t served.

Chris - So they knew that they had been hungry there in the past so they were relying on this past experience to plan for tomorrow because they may be in motel room 2 and have no food.

Nicky - Exactly, but they hadn’t been trained to hide food in either of these rooms, and they used their past experience about which rooms served breakfast in the morning and which didn’t to solve a potential problem. They didn’t know where they’d be in the morning, so just in case, they’d put the food in the room where breakfast isn’t served.

Chris - Why do they have this trait, you can see why we might do that because we are a bit more complex than they are, but what benefit does it serve this family of birds to have this ability?

Nicky - Well, that’s a very interesting question from a number of levels; my husband, Dr. Nathan Emery and I have suggested that intelligence has evolved independently in two very different groups of animals: Apes, which obviously includes us, and members of the crow family. We think that this is because in the wild they have similar problems to solve, and they evolved around the same time as apes (around 5 million years ago), they are also highly social. One of the major theories formulated by Nicholas Humphrey is that the reason why we and other apes are so intelligent is because we live complex social lives. This is not just about living in a big group, but having to keep track of who does what to you and being able to network and do politics. The argument is that, those are exactly the type of problems that the members of the crow family solve.

Chris - I saw this piece in the Daily Telegraph this week, it says: “A quick smoke is good for the wings. Birds are picking up discarded cigarette butts and using their smoke to fumigate their wings of parasites, experts have suggested. Rooks have been spotted swooping onto the tracks at Exeter St. David’s railway station in Devon and then placing their wings over the smoke to collect the fumes. One commuter said: I noticed the rooks because they are not usually found in towns. They were generally flapping about when a chap flicked a cigarette butt onto the track. It was still alight, and one of the rooks swooped down, picked the butt up with its beak and they flew around and landed on the platform dancing around with a cigarette butt in its beak. It looked quite comical, but then it dropped the butt onto the platform, placed its wings over it, collecting the smoke. It seemed as though it was using it to get rid of something, like an ant or a parasite or something.” And then they got a quote from someone at the RCPB who said they’ve never heard about it but perhaps they’d learn to use the cigarette smoke to kill off parasites.

Nicky - How very clever, I’ve got to go and see them. I’ve never seen that but of course rooks are renowned for doing a number of very innovative and seemingly clever things. One of the most famous examples is that a couple of years ago they won the award for BBC’s cleverest animal. This was rooks on one of the M4 motorway service stations, and what the birds were doing was finding a very innovative way of getting food that was at the bottom of the rubbish bins on the service station. So two birds would sit in tandem on the opposite ends of the rubbish bin, and slowly pull up the bin-liner under their feet. They would do it in tandem so that all the food would go to the middle where it’s within beak's reach and then one bird would start tossing the food over the side while the other bird popped down onto the pavement to guard the food so it couldn’t be stolen by others.

Chris - And because no one has ever shown them how to do that, they’ve had to work that out for themselves and then teach each other, so one has had to look at what the other one is doing to work out how to do it?

Nicky - Well I guess the million dollar question is whether each individual bird works it out for themselves and it just so happens that lots of them do it, or whether they are actually learning from one another. That’s very interesting and it’s one of the kinds of experiments that we are starting to do at Cambridge University; to look at whether the rooks will learn from one another and whether you could actually get mini cultures depending of which individual bird is learning to do things in a particular way.

Kat - I think one of the most fascinating things that have come out of bird research recently is that they use tools, because you can associate humans or Chimps with using tools, but birds have beaks so why do they need to use tools? So tell us a bit about tool usage in birds.

Nicky - Well, your beak can only go so far, just in the same way that if there is a small hole, you can’t get your hand in there, it may also be that the hole is sufficiently small or deep that the food is out of beak’s reach and that’s when you’d need a tool. There are a number of species of birds that use tools, but the most remarkable thing is that one member of the crow family, the New Caledonia crow actually makes tools. So this sort of puts in on par with chimpanzees; they don’t just use tools, they actually manufacture them, and they make different types of tools for different purposes.

Chris - Is there any clue given to us if you look at the animal’s brains as to why these birds have these spectacular abilities compared with other animal that don’t perform like this?

Nicky - Well if you look at the relative brain size, then obviously we have the biggest relative brain, but if you look at the next ones down it’s the dolphins, but it’s also the apes within the mammals and in the birds there are two groups, the crows and the parrots. If you look at where the enlargement is in the brain, just as in apes the enlargement is in the neocortex the same is true for the crows, the enlargement is in the avian neocortical area. So the same part of the brain is enlarged.

Chris - Thanks Nicky. That’s Nicky Clayton from Cambridge University who works on Scrub jays and trying to use them to get insight into how they plan for the future and perhaps how our brains work too.

June 2007

Meerkats - Happy Families?

Now to the Kalahari Desert and the study of the most co-operative mammals of all, the Meerkats.But what's the basis of their society and how is it organised? We spoke to Professor Tim Clutton-Brock from Cambridge University about his work with the Kalahari Meerkat Project.

Tim - I've worked on Meerkats now for 13 years and we've managed to tame up, habituate, 14 different groups of Meerkats so we have about 300 animals in the Kalahari which is where we work, and each of those groups, the groups of somewhere between 10 and 40 animals in each group, each has a separate territory of about somewhere between five and ten square kilometres. And we can recognise all those individuals and we have got them so tame that they'll actually climb onto electronic balances at request, so we've trained the Meerkats for crumbs of hardboiled egg to get onto the balances.

Chris - What are you ultimately hoping to find out by doing this?

Tim - I think the single focus of the study is why they're so co-operative, so the Meerkats are arguably the most co-operative mammal, perhaps it's a near-run thing between them and naked mole rats but Meerkats are very, very co-operative. One female in each group breeds and everyone else in the group helps to rear her pups, males and female group members, fully mature individuals, fully mature males, baby-sit the pups. They help to get food for the pups, they guard the pups, they go on guard in turn so the group is breeding as a unit not unlike an insect society.

Chris - How do they decide who is the dominant female?

Tim - When you remove a dominant female, all the potential other females compete like fury, they fight commonly, and then one finally emerges and she suppresses the others, she commonly evicts the main challengers over the next few months, and then she turns in and produces children over, oh, it can be five to ten years, so the group gradually becomes a dominant female and the male she's mated to and her children.

Chris - So how do they persuade all of their other members of their colony to rear their own, well, the children of the animal that's breeding at the expense of breeding themselves?

Tim - Well, that's a very good question. They stop the other females breeding so the presence of the dominant female actually suppresses their fertility so the others can't breed. If they do breed, and they do occasionally, the dominant female commonly kills and sometimes eats their pups.

Chris - So that's a pheromonal suppression, is it?

Tim - It's probably a pheromonal suppression. It may also be partly through direct interaction because the dominant females are aggressive towards the other females. The other way they help to suppress is that when at particular stages of the breeding cycle, they throw the oldest female subordinates out of the group so one way of getting your daughter to help in Meerkats society is to sling her out into the outside world so she sees just how tough that is and then when she comes back in she's prepared to do the washing up.

Chris - I know a few humans who can benefit from that strategy, but quite complicated behaviour. Where do they get it from?

Tim - I think the co-operation is associated with desert living and with diurnality, with the fact that they're active during the daytime and if you live in an open desert and you're active during the day, you're very, very susceptible to predators and you've got to come up with some way of combating predators and groups defend each other against predators, they put on guards to keep an eye out, they keep a huge network of burrows as escape systems from predators, so the group is very, very important in keeping predators out.

June 2007

A Primates Eyes

Dr Andrew Smith works with Tamarin monkeys in South America and the endangered Buton macaque with Operation Wallacea in Indonesia.

Chris - Tell us about this work on how monkeys use colour, and why this is relevant to us.

Andrew - Certainly, I’ve been researching on primate colour vision. It’s an interesting topic because primates unlike the majority of animals have got three cone colour vision, which means they can see the same range of colours, more or less, as we can. Non-primate mammals such as dogs and cats see the world in a reduced set of colours, and we weren’t entirely sure why this was the case.

Chris - People often say that dogs see the world in black and white, but that’s not true. A dog sees the world in colour, but probably akin to how a colour blind human would see.

Andrew - Exactly, if you imagine a dulux colour chart, it’s just a reduced set of those colours, not being able to distinguish certain combinations of those, rather than simply seeing the world in black and white or ‘an other colour’ and white.

Chris - So how was it first discovered that monkeys and other primates did have this ability, it wasn’t just us?

Andrew - What they were doing was looking at colour vision capabilities by giving them more or less the same tests that they were giving humans; basically asking them to discriminate between different coloured shapes. If they could tell the difference between the colours then obviously they can tell that those are separate and distinct colours.

Chris - So it’s set up so that there’s no way they could do that by having two colour- they had to have three colour vision to do that.

Andrew - Yes.

Chris - So what’s your view on the reason why they have got that ability?

Andrew - I think the main reason is probably due to foraging ability, so being able to detect fruit against a background of leaves. Leaves are invariably green, but many fruits when they’re ripe – which is when plants want animals to eat them and also when they will contain the most amounts of sugars and nutrients, are often orange, yellow or reddish. The ability to distinguish ripe fruits from a background of leaves, which obviously if you are human and colour blind its likely that you have distinct problems telling the difference between red and green, if you cant do this it will be difficult for you to pick out red fruits against a green background. Evolving good three cone or trichromatic colour vision is going to enable primates to choose the ripe fruits against a green background of leaves.

Chris - Is that what we have to thank for the fact that we have such good colour vision?

Andrew - We think so. That’s probably the leading theory although there are alternatives that maybe it has evolved to enable you to pick out very young leaves. Young leaves are much more nutritious, they’ve got less noxious secondary compounds in them than old leaves. For folivorous, leaf eating, monkeys such as howler monkeys or gorillas, and maybe our human ancestors, the ability to pick out the newest, youngest, tenderest leaves may have been a selective advantage for the evolution of three cone colour vision.

Chris - We’re not herbivorous, we’re omnivorous so we eat some meat but you would have thought that other animals, that actually spend their entire life eating leaves, are dependant on eating plants all the time just to survive. It would be even more important to them, wouldn’t it? So why don’t cows and sheep and goats have that ability?

Andrew - It’s possible that cows and sheep simply haven’t had the chance mutation to develop three cone colour vision, and also, being much larger animals they have to graze and consume much larger quantities. Also it really depends on the type of leaf you’re talking about. The leaves in terms of primate colour vision are from tropical forests where predation pressure on the leaves is quite high, and interestingly they do flush through a kind of pinkish-red when they’re new leaves. However in grasses, the new leaves are basically the same as, or very similar to the adult leaves.

Chris - Is it just fruit that they use this enhanced colour appreciation for or could there be other spin-offs?

Andrew - There could be other spin-offs; it may help to detect predators. If you think about the coats of many cats in rainforests, such as ocelots, margays, jaguars, or indeed leopards, the yellowish hues in their coats may be more easily distinguished if you’ve got good three cone colour vision.

Kat - Another thing that’s important as well as being able to spot predators is to actually find somewhere safe top sleep when you’re trying to avoid predators. How do monkeys cope with that when they’re living in the wild?

Andrew - It certainly seems for the small monkeys, the tamarins from the Amazon that I’ve been looking at that, predation is probably one of the most important aspects of their ecology. What they do is try to find the most secure sites, usually high up in trees, often hidden by dense tangles of vegetation and lianas. Also the monkeys really use the sites very infrequently; they change their sleeping site almost every night. The longest I’ve ever known them to sleep in the same site for is three consecutive nights. This is probably to stop any predators in the area building up a search image and maybe smelling a distinct monkey scent from a particular tree that they’ve been sleeping in a lot. By changing their sleeping sites very frequently they’re hoping to avoid predators.

June 2007