Nature Podcast 11 May 2006

Introduction

This is a transcript of the 11 May edition of the weekly Nature Podcast. Audio files for the current show and archive episodes can be accessed from the Nature Podcast index page (http://www.nature.com/nature/podcast), which also contains details on how to subscribe to the Nature Podcast for FREE, and has troubleshooting top-tips. Send us your feedback to mailto:podcast@nature.com.

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Chris Smith: This week we'll be discovering how much seawater's rushing around in the Earth's mantle. We meet the first survivor of a large meteoric impact. We get tied up in RNA pseudoknots, and we'll be catching the spin about Saturn. Hello, I'm Chris Smith, and welcome to the 11th May edition of Nature's Podcast. First up this week, the perks of senior citizenship. Jeremy Field from University College, London, has been looking at why some members of a social species work much harder than others. Thankfully, it turns out that some things improve with age. (Nature 441, 214–217 (2006) ).

Jeremy Field: If you look at any, almost any social group, what you find is that some individuals seem to be working an awful lot harder than others. In the past it's tended to be assumed that that reflected a difference in how closely related they were to the individual they were helping, but recently it's been discovered that that's not the case. And what we've really shown is that a lot of that variation may really depend on what the individuals in the group stand to lose by working, by sort of wearing themselves out by working. In other words, the more you stand to lose, the less hard you'll be prepared to work.

Chris Smith: So how did you actually go about investigating this?

Jeremy Field: In lots of social animals, we can think of helpers as being effectively in a queue to inherit the position of queen. In about 2001 Mike Cant and I wrote a theoretical paper in which we suggested that how hard you work might be nothing to do with your relatedness, it might be do with a helper's chance of herself becoming the queen. So if your future is bright, if you like, you're near the front of the queue, you should take fewer risks. And the problem with testing that idea is how do we know each individual's position in the queue? Now luckily I had a PhD student who's a co-author on this paper, called Kathy Bridge, and she'd been looking at just that question in a species of wasp called the hairy faced hover wasp, okay? And what she'd found was really interesting. In nearly every group that she looked at, the queen was the oldest wasp and if you took the queen away, the next oldest wasp took over as queen. So the first thing we looked at was how hard do these different individuals work? And indeed we actually found that older individuals nearer to the front of the queue did work less hard. But that was inconclusive. An old wasp might work less hard just because they're old, for example. So what we needed to do was actually manipulate a female position in the queue. So, for example, if you image a group of four hover wasps on a nest, focus on the third oldest one, for example, the one third in the queue, what we did was, we took away the second-oldest wasp and the wasp that was third in the queue is then promoted.

Chris Smith: So when you do that experiment, what does happen to her? Does she fall into the lap of luxury?

Jeremy Field: Yeah. We found that what we predicted happened, so the third-ranked wasp went up to rank two and even though that wasp was still the same age, she started working less hard than before.

Chris Smith: Is this true for all social insects, because obviously one can think of examples where there are some in which you never have any prospect of giving birth to any young and therefore you can't immediately see how this would apply to those groups?

Jeremy Field: There are certainly a few social insects, like some of the ants, where the helpers really do have no chance of ever reproducing themselves, because they're morphologically specialised. They literally can't mate and they can't lay eggs. Then there are some other social insects where the helpers can still lay male eggs, they've still got some chance of reproducing, and then in a lot of wasps and bees, including the ones we've studied, every individual can potentially reproduce and potentially become a queen, and they are probably the most interesting ones to look at when you're looking at the evolutionary origin of eusocial behaviour because obviously they're a sort of example, we hope, of what the first kind of social species might have looked like.

Chris Smith: So the bottom line is that promotion makes you do less, although clearly that doesn't apply to scientists. Jeremy Field from University College, London.Now to a four and a half billion year old question. What's the composition of noble gasses in the Earth's mantle? And how much sea water is there washing around down there. This is a tricky one to answer because samples are readily contaminated on the way up. But Greg Holland from Manchester University has got around the problem by collecting gas samples from a carbon dioxide field. The results have produced a surprising finding that about ten percent of the world's oceans have been recycled through the mantle. (Nature 441, 186–191 (2006) ; Nature 441, 169–170 (2006) ).

Greg Holland: Initially what we tried to do was determine thermal gas composition of the mantle. Probably for the last thirty years, all the data has come from lava erupted from volcanoes so that's places like Hawaii or Iceland or mid-ocean ridges where the ocean floors are generated. But the problem with all this data is that it's contaminated with seawater or air, because the concentration of noble gasses in air and sea water is much, much higher than the rocks. But these samples are completely different, and we found out that actually there is seawater in the mantle and it's not just contamination.

Chris Smith: How did you do it? What was the method?

Greg Holland: Well, initially, I went out to New Mexico and I was armed with a set of stainless steel cylinders and I essentially used commercial carbon dioxide pipelines so in the same way that you have oil extracted from the crust, these companies in America would extract carbon dioxide so I would plug these same sealed cylinders onto the end of their wellheads and collect sample fairly contamination free.

Chris Smith: And then, how would you analyse them?

Greg Holland: After that we would then bring them back to Manchester and all these samples are almost pure carbon dioxide, so in our machines we have to remove all that carbon dioxide because we're looking at trace gasses which are parts per million, if that. So we would remove, by heating, these samples with a titanium sponge to crack down all the carbon dioxide and then just admit noble gasses into our spectrometer.

Chris Smith: And what was the real bottom line here? What was really surprising about what you found?

Greg Holland: Well, the interesting thing is that people always perhaps thought that we might be able to cycle water into the mantle, but no-one's ever been able to prove it. There's schools of thought that say this cannot happen, and there's schools of thought that say you can cycle tens of oceans' worth of water back into the mantle and have it coming out again, whereas with our data we can actually put a number on that and say it's about ten percent of the Earth's oceans have been seducted back into the deep mantle.

Chris Smith: Are you sure that the gas that's coming up, the carbon dioxide that's been collected and that you've sampled, is an accurate representation of what's genuinely down there? There's no artifact going on here?

Greg Holland: Oh yes. The interesting thing is that there's a type of sample called popping rock which is a very gas rich lava that has erupted from the ocean ridges. And people have always assumed that that is actually an uncontaminated sample representative mantle, but people have always been worried about fractionation as a magma body ascends, which it does beneath the ocean ridges. These types of samples are formed a completely different way. They're not a residue of the gassing in the same way that ocean ridge systems operate, but those popping rock relation ridge measurements are exactly the same as we have in these oil gasses, so the fact that two different types of eruption can provide you with the same data is fairly convincing evidence that there is no fractionation, and both are actually representative of the mantle.

Chris Smith: Greg Holland from the University of Manchester.On the way, meteorite impacts, the secret of pseudoknots, and the length of a day on Saturn. But first, we're going to look at some of this week's other major science news stories, including research in the Arctic, science in Qatar, and whether the US is prepared to handle a flu pandemic. Here's Nature's Alex Witze talking to Anna Lacey.

Alex Witze: We've got three stories on our radar for this week. The first one is a story about how meteorologists are upset that a lot of the weather stations up in the Arctic are closing. These are stations that record things like snowfall, river run off, data like that that's really important for understanding global climate change up at Northern latitudes. But a lot of them are shutting down and scientists aren't too happy about that. (Nature 441, 133 (2006) ).

Anna Lacey: Why are they closing them down?

Alex Witze: Well, as always, it's usually a question of cost. Many of these stations are manned, so there's people living there, going out fixing the equipment and helping gather the data. But it can cost $100,000 a year. So a lot of these stations are being replaced by ones that do it automatically. They only cost a couple of thousand dollars a year to run, but there's nobody to fix anything if it breaks, so if something goes down, you never know when someone might go out to fix it and get the data up and running again.

Anna Lacey: But how often do they actually break? I mean, in general, are they actually a good economy?

Alex Witze: It can depend. It varies on country to country and how much infrastructure they have in place basically to send people out to go and fix them. One of the problems with the automated stations is that they often under record things like snowfall. What will happen is the gauges will freeze up and they won't record how much snow is actually coming down, and that's the sort of critical information that's needed to get a handle on climate change.

Anna Lacey: Well, if that's the case, seeing as there's still people out there who don't even think climate change is happening, is this really the time to be skimping on data?

Alex Witze: That's an excellent question and polar researchers really want to get at that question. They're getting prepared for the International Polar Year which will be coming up in a year or two. And the Polar Year is basically gauged at getting the public involved, scientists involved, to get a whole broad swathe of data, put in new monitoring stations, fix ones that are broken, and scientists really hope that this whole new push in polar research will help get the data that they need to pin down some of the last remaining questions and convince some of the public that this is going on and it's really important to understand.

Anna Lacey: Well moving to a slightly happier tale now, it seems that science research in Qatar has struck oil? (Nature 441, 132 (2006) ).

Alex Witze: Yes, and this is a much more positive story, as you mention. What has happened is that the Emir of Qatar has designated that the money from one of the oil wells is going to go to scientific research and the country which, of course, is quite tiny on the Persian Gulf has been dedicating a fair amount of money to upping its higher education resources. They've built a whole sort of campus called Education City and have brought a number of western institutions to open branches there. And the Emir has again given this money, which combined with another foundation, means that they're going to have something like hundreds of millions of dollars each year for research. One of the things they want to set up is a diabetes genome centre. They may go head and try and genotype everybody in the entire population of Qatar, so there's a lot of societal outreach here, a lot of sort of bringing back to the community and to help answer some societal questions.

Anna Lacey: But is the scientific community as a whole going to take Qatar into the fold, especially with the problems we are having generally in the Middle East at the moment?

Alex Witze: That's a really good question. The Arab world is an area that a lot of scientists say could strengthen its scientific basis, and this initiative is one that could really help propel the Arab world towards the, not at the front, but at least, you know, up into the middle ranks of scientific powerhouses. This is an area where people really need to be doing work and there are a lot of Arab ex-pats who are very supportive of the project and say it can really bring recognition to a geographic region that is under-served and is under-serving the scientific community as a whole right now.

Anna Lacey: Well, let's go over to America now where they seem to be starting to have problems with bird flu? (Nature 441, 137–139 (2006) ).

Alex Witze: Yes. So we have a couple of stories in this week's issue. They talk about whether the Americans are prepared for bird flu to arrive on its shores. The US has a massive poultry industry and if birds start to get sick, it could have a great effect sort of economically on this hemisphere.

Anna Lacey: So what kind of safety plans have the US got in place to deal with any of these kinds of problems?

Alex Witze: Well, if you ask the Government, of course, they have all sorts of things in place. They have numerous websites. They have also these public information documents out there and floating around. But, in essence, what they're to do right now is figure out where the virus might come from and how, so the number one suspect would be birds migrating down from Alaska, across the Bering Straight from Russia. These are mostly sort of water fowl, shore birds, that kind of thing, and some of them might come up and breed, and then make their way down into North America, across Canada and into the US, and further South. Of course, there's lot of other ways they could get to the Americas, as it has spread throughout Europe and Asia. People smuggle birds all the time, fighting cocks, chicks that they might use for breeding, someone could bring in their pet rooster, who knows? And it could go from there.

Anna Lacey: So the Government at least is telling people in the US that they're prepared. Are the US really prepared though?

Alex Witze: That's an excellent question. We might have had an early look at that answer with what happened in New Jersey two weeks ago. There was a low pathogenic form of bird flu that barely makes birds sick, and certainly don't make humans sick. It was diagnosed in a New Jersey poultry market and it was sent to the all the appropriate labs to test and see if it was H5N1, that's the really nasty killer version. It turns out it wasn't, but it wasn't handled necessarily in the smoothest of manners, as you could say. When New Jersey tried to send the sample off to the national laboratory which is over in Iowa for testing, they didn't take the samples right and by the time they got there, they didn't have enough to test and so the national lab couldn't really confirm that it was not a dangerous form of bird flu. But you kind of wonder that they need to be taking samples better and making sure they have enough for testing, if in fact we do get the real H5N1 here at some point.

Chris Smith: With this week's news Alex Witze talking to Anna Lacey.This is the Nature Podcast from the 11th May edition of Nature with me, Chris Smith. As usual, all of the stories we're discussing this week are available from the Nature website at http://www.nature.com/nature. And there's also a full text transcript to accompany this programme at http://www.nature.com/podcast. You just need to follow the links to the programme that you'd like to read about.Now here's a discovery of quite literally meteoric proportions. Rolf Maier from the University of Quebec has been working at the Morokweng Impact Crater in South Africa. He's come across what looks like a piece of the meteorite itself amongst a sheet of melted material created by the intense heat of the collision. But conventional wisdom says it shouldn't exist. (Nature 441, 203–206 (2006) ).

Rolf Maier: What we've found is actually a meteorite in a melt sheet. Now I probably should start by saying that this was really an accidental discovery. We were exploring the Morokweng impact melt sheet in South Africa, which is an 800 metre melt sheet associated with a very large giant impact crater, a 70 km wide impact crater, for Sudbury-style nickel deposits. Now what one does in nickel-sulphide exploration, one looks for a crust of contaminant, particularly sulphide contaminants, so when we found in the melt sheet, in the Morokweng melt sheet, what looked like a 25-centimetre hornfels xenolith, a fine-grained xenolith with about five percent sulphide, we analysed it by XRF for major and trace elements, and when the results came back, the penny really dropped that we are looking here at something very unusual, at a meteorite in fact. You must remember that conventional wisdom suggested there cannot be preserved meteorites...

Chris Smith: Why is that, Rolf? Why don't you see meteorites preserved in this way?

Rolf Maier: Well, because large projectiles like the one responsible for Morokweng are not supposed to survive the impact because they impact the earth with such great speed and energy that they are supposed to be vaporised during impact.

Chris Smith: So that begs the obvious question, why did this one survive?

Rolf Maier: Exactly! So, you know, the problem is are the calculations incorrect or are we looking here at a fragment at the trailing edge of a meteorite? Whatever the case, this is, you know, something very unexpected.

Chris Smith: How do you know that it really is part of the meteorite?

Rolf Maier: Well, that is a good question. I guess it would be extremely unusual coincidence if that meteorite would have hit target rocks that contain the meteorite. Furthermore, the geochemical signatures of the meteorite are very similar to the impact signature of the melt sheet, particularly the [unclear] element ratios.

Chris Smith: Now if people have got the calculations wrong as you've said might be case, how are we going to put that right?

Rolf Maier: I guess that one has to look... you know, the calculations really are dependent on the input parameters and one possibility is that the speed, the velocity assumed in the calculations is too high. Perhaps Morokweng, the meteorite, the asteroid hit the earth at a much lower speed than is commonly assumed.

Chris Smith: The University of Quebec's Rolf Maier with the world's first survivor of a major meteorite impact.Now to Cambridge University and the concept of ribosomal frame-shifting, which is a clever way for agents like viruses to pack more information into their genomes. RNA sequences are read as a series of triplets, clusters of three genetic letters. Each of these triplets tells the ribosomes, the structures in cells where proteins are made, which amino acids to link together to make the desired protein. After each amino acid is added, the genetic message is moved along, or translocated, by three genetic letters, bringing the next triplet into the reading frame. But some RNA sequences are designed to make the ribosomes slip up, and instead of moving three letters along, it sometimes moves two. And this means that the same genetic sequence can now produce a totally different product. The process relies on a specialised RNA structure called a pseudoknot, and Ian Brierley and his colleagues have untangled how it works. (Nature 441, 244–247 (2006) ).

Ian Brierley: We've been looking at a process called ribosomal frameshifting and we've essentially discovered the mechanism. The ribosomal frameshift signal has two components, a slippery sequence, a homopolymeric stretch of nucleotides where the frame shift takes place, and an RNA structure which is essential for the process located nearby, called an RNA pseudoknot. To understand the basis of RNA structure, you have to remember that although RNA is single stranded, it has the capacity to form intramolecular base pairs. A pseudoknot is an elaboration of what's called a hairpin. A hairpin is just simply a reason why you have two regions base-paired and they're connected by a loop, a single stranded loop. A pseudoknot is an elaboration in which a region downstream of the hairpin can base pair back to part of the single-stranded loop. So you end up with, if you can imagine a knot, but in which the string is not passed through the hole, it just sticks to the outside.

Chris Smith: It sounds more like a tangle than a knot!

Ian Brierley: Well, if you pull them, they come apart in principle.

Chris Smith: But how does that affect the process of translation, turning RNA into a protein message?

Ian Brierley: Well, what we think happens is the ribosome has obviously evolved away to unwind RNA structure. Very recently in fact, it's been determined that three proteins near the entrance into the ribosome have a role in unwinding. They call this a helicase activity of the ribosome. And we suspect that most secondary structures are similar to hairpins and they probably unwind quite easily. Pseudoknots, however, have such a different structure that we feel that helicase probably struggles initially to unwind them, so the ribosome it then sticks at this point, and it's during this pause that the event takes place.

Chris Smith: And what were the key findings? And were there any surprises in what came to light?

Ian Brierley: The key findings were that the so-called pseudoknot stalled ribosomes were locked in a process of part of the elongation process called translocation. Now translocation is the step in elongation where the whole complex is moved physically through nucleotides. What we found was that at this point pseudoknot structure comes into play and it is largely unfolded, as far as we can tell, and jammed in the entry channel. And we think this creates quite a substantial amount of tension in the messenger RNA, so it's that when the ribosome tries to translocate the tRNA by three nucleotides it can only essentially go two.

Chris Smith: Cambridge University's Ian Brierley.Finally this week, we're taking a trip to Saturn to join the Jet Propulsion Laboratory's Giacomo Giampieri who showed in last week's edition of Nature how fast Saturn is turning. (Nature 441, 62–64 (2006) ; Nature 441, 34–35 (2006) )

Giacomo Giampieri: We measured for the first time the periodicity in the magnetic field close to the planet Saturn, and this is important because it may indicate the true rotational period of the planet.

Chris Smith: Why has that been a challenge for scientists to get a handle on previously?

Giacomo Giampieri: It is something which has eluded scientists for quite a long time. I remind people that Saturn was visited three times in the late 70s, early 80s by three space capsules, Pioneer 11 and Voyager 1 and 2. But in all these occasions it was not possible see any periodicity in the magnetic field, essentially because the magnetic field of Saturn is very peculiar. It's almost basically symmetric with respect to the rotation axis of the planet.

Chris Smith: So it's really difficult to work out how fast Saturn's turning?

Giacomo Giampieri: Exactly! What you see from the outside is something which doesn't seem to be spinning at all.

Chris Smith: So how have you got round the problem?

Giacomo Giampieri: Well, it's essentially a combination of two things. One is that Cassini has been in orbit around Saturn for almost two years now, and therefore we have many more data collected close the planet. These data were analysed using some very specific techniques to try to detect periodic signal and for the first time we were able to actually detect something very clearly, a period of about ten hours and forty seven minutes.

Chris Smith: So Saturn actually turns quite quickly?

Giacomo Giampieri: Yes. It's what is called a fast rotator, similar to Jupiter. And this has strong implications for the internal structure of the planet.

Chris Smith: So what sorts of things does it tell you about that?

Giacomo Giampieri: Well, the rotation of a planet is one of the main ingredients to try to determine the internal structure, because when you want to determine how the planet is constituted inside, you have to include the centrifugal force and the force which determines its shape. So knowing its rotational rate is one of the main ingredients to determine the internal structure of the planet in general.

Chris Smith: So why were you able to pick this up, but the three other attempts in the 80s missed it?

Giacomo Giampieri: Well essentially because the three other attempts were just flybys which lasted a few hours. And these periods of ten hours forty seven minutes requires many, many data to be picked up. So with just a single fly by or with just three fly bys like we had in the 70s, it was not possible to see it.

Chris Smith: Giacomo Giampieri who used measurements made by the Cassini probe orbiting Saturn to work out how fast the planet's spinning.Well, that's it for this week. Next week we'll be looking at social cheaters and also hunting for other planets a bit like the earth. But in the meantime, if you're in the mood for more science, this week's Naked Scientist podcast returns to the time of the dinosaurs and asks where they came from, how they evolved the power of flight and what wiped them out. That's the Naked Scientist podcast which is freely available from http://www.thenakedscientists.com.Production this week was by Derek Thorn and Anna Lacey in the Division of Urology at Cambridge University, and I'm Chris Smith.

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Recording and transcript (c) Nature Publishing Group 2006