Nature Podcast

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Adam Rutherford: Coming up, we solve the reproductive riddle of a potentially painful ancient tryst.

John A. Long: The thing about placoderms is that they have these very strange bony clasps in the male and for the life of it sometimes could have inserted them into the female without tearing them apart literally. You know, reproduction would have seemingly been a very painful affair.

Kerri Smith: And we explain the mystery of a mid-century blip in sea surface temperatures.

David W. J. Thompson: The US ships were recording temperatures using engine room measurements and the British ships were recording temperatures using the bucket measurements and at the end of the war, the US ships they went home and this would cause temperatures to spuriously drop.

Kerri Smith: This is the Nature Podcast. I'm Kerri Smith

Adam Rutherford: And I am Adam Rutherford. We are kicking off this week with an amazing fossil fish from Western Australia. The Gogo Reef formation is a rich source of incredibly well preserved sea creatures from the Devonian Period, which ended 360 million years ago. A team from Museum Victoria has discovered a new species of placoderm, that's a large group of extinct, armour-plated fish that dominated the seas at the time. Now there are over 300 species known, but this new one is special. The specimen is so well preserved that John Long and his team have identified an embryo complete with umbilical cord contained within the mother - proof that like modern sharks, placoderms gave birth to live baby fish. I spoke to John and started by asking him to describe what the Earth looked like when this fish was alive. Nature 453, 650–652 (29 May 2008)

John A. Long: Well, the Devonian was an interesting time of the planet because the lands were covered with just small plants at the beginning of the Devonian. Oxygen levels dipped to quite low periods of 12% rising up to about, you know, 20% towards the end and the world was ruled by fishes. They were the most dominant and advanced form of vertebrates on the planet.

Adam Rutherford: And it's the placoderms that you've been looking at as the dominant fish in the sea, what are their distinguishing features?

John A. Long: Well, placoderms are like the Devonian dinosaurs really, they are group of an extinct vertebrate that basically they were fish covered in armour plates, very shark-like in their general appearance, but they didn't have teeth that were developed in rows; they just had these bony jaws that had teeth developed as cusps along the bony plates. There were about 200 to 300 different species of placoderms in the Devonian. They were the dominant life in the planet for something like 70 million years.

Adam Rutherford: And the controversy about placoderms, it concerns how they reproduce but with your new paper your new discovery, you seemed to have completely solved this problem.

John A. Long: Yes, well way back in the 1930s, a very famous British palaeontologist called Professor D.M.S Watson described a group called the ptyctodonts and these were a strange group of placoderms with crushing tooth plates. They clearly ate, you know, clans or hard shells of certain animals and ptyctodonts were the only group of the seven different orders of placoderms that were found to be clearly sexually dimorphic, in other words, the males had these clasping organs around the pelvic fins, long bony sheets with spikes sticking on them and females had a smooth pelvic basal plate area and this is a bit like the sharks and stingrays and chimaeras of today, in which the males have soft clasping organs and the females don't have them and the males obviously insert them into the females for reproduction. The thing about the placoderms is that they have these very strange bony clasps in the male and for the life of it sometimes they could have inserted them into the female without tearing them apart literally, you know would have been, reproduction would have seemingly been a very painful affair. So there are different theories where the males may have grabbed the female and used the clasps to get close to them and then simply, you know, put the sperm in the water near the cloaca of the female, but we never actually had any firm evidence or proof that there was internal fertilization going on until this specimen was found and this specimen with an embryo inside it and clear proof that the embryo was also fed by an umbilical structure, means that they must have had internal fertilization.

Adam Rutherford: To the inexpert, it seems so astonishing that you can get preservation of things, tissue as delicate as umbilical cord, what are the conditions that are needed to make such an incredible find?

John A. Long: Well let me just explain basically about Gogo. Gogo is an amazing site in Kimberley in the Northwest of Australia. So, David Attenborough filmed there in 1979 for his series 'Life on Earth', when he wanted to demonstrate one site on the planet to demonstrate fish evolution, because the Devonian fish from Gogo was 3-dimensional and perfectly preserved. The fish are found in limestone nodules and the limestone slowly dissolves away in weak acetic acid and the bones come out in 3-dimensions like as if the fish died yesterday, you can still open and close the mouth of some of them, so we are starting off with the truly exceptional fossil site and secondly Gogo has recently produced some amazing preservation of soft tissues in these fishes. We were preparing this Gogo fish and just started and all the boring of placoderms that you know we would rather paper all this anyway and we put it in the acid one more time to prepare up the vertebrae and then we saw the embryo. We just couldn't believe it. This is the first time in any fossil, found anywhere in the world that we have an actual soft tissue related to an umbilical feeding structure from the mother to the young.

Adam Rutherford: So you mentioned that David Attenborough had filmed on in Gogo and as a result of that, in honour of that you've named this new species after him.

John A. Long: Yes, I was very impressed with 'Life on Earth', the series and when David Attenborough went to Gogo and he picked up this skull of an ancient lung fish and he showed the world what an important site it was and it was really the first time attention was drawn to the significance of this site. So we named the fish Materpiscis attenboroughi in honour of Mr. David and in a letter I got from him recently I found out that he was absolutely thrilled. He was over the moon to have this honour bestowed upon him.

Kerri Smith: John Long from Western Australia's Museum Victoria. His book, 'Swimming in Stone, the Amazing Gogo Fossils of the Kimberley' is out now. The Devonian period may well have been the heyday of placoderms, but I am pretty sure if you have my university professors were around them too, on the podium this week, Peter Lawrence at the University of Cambridge in UK argues that in academia age shouldn't matter.

Peter Lawrence: In the United States unlike in Europe, everyone has the right by law to be considered for work independent of their age. All age discrimination became illegal in the US in 1986. This initiative and others like it in Australia and Canada have resulted in a scientific exodus from Europe and Japan where mandatory retirement policies condone an institutionalized discrimination. The contributions of scientists well beyond the six decades indicate that many of the assumptions on which these prejudicial policies are based are incorrect. Drosophila pioneer Seymour Benzer was asking razor-sharp questions well into his mid 80s. E.B Wilson wrote the wonderful third edition of his textbook in his late 60s. Some older scientists are great role models and mentors. Some augment the international reputation of their institutes, teach or administrate freeing younger scientists. More importantly, they can provide a deeper perspective on scientific strategy. Retirement turns able academics into lame ducks several years beforehand. They cannot take on graduate students and they lose their negotiating power, because they cannot seek new posts and it drives gender disparity. In 2007, in the UK, 85% of men reaching retirement age qualified for a full pension having worked for 40 years, but only 35 % of women did so. That said, not every aging scientist earns his or her keep, the problem of selection has to be faced. The traditional alternative to throw everyone out at a certain age regardless of their wishes or their usefulness simply because of the voiced difficulties of management is indefensible. Researchers should be evaluated and made to leave whenever performance no longer justifies their space or costs. Their entire contribution including teaching, mentoring, and administration should be judged in an open minded and tolerant way. Not just by counting papers, grants or by undergraduate ratings on teaching. If following this assessment old or even young are fairly judged to be incompetent, inactive, disruptive or wasteful, they should leave or have their space reduced to an appropriate level. The second difficulty is financial. It is said that older scientists can be so expensive that insufficient funds remain to hire new personnel, so we must restructure salary so that they can fall as well as rise. If scientists take on fewer duties, let us reduce their rewards, further many scientists have built up pensions, they should be started on time and the salary reduced partially or completely. If the individual is of particular use to an institute, it may wish to reward his/her contributions with some supplement. We also have to be realistic and admit that offering secure tenure with a salary of 30 or 40 years regardless of whether there is any useful contribution to the employing institute is wasteful and unfair. Indefinite tenure has already been abandoned by government research institutions. Scrapping mandatory retirement may require significant retooling of academic employment structures, but I think the gains will be well worth the pain.

Adam Rutherford: Peter Lawrence, who until the age of 65 worked at the Medical Research Council and now, continues his work on the fruit fly development at the University of Cambridge. Now from older scientists to an old theory on how to achieve the perfect balance of sons and daughters, which receives a new support this week. Here's Charlotte Stoddart.

Charlotte Stoddart: A team at the University of Edinburgh have found that female malaria parasites are able to adjust the sex ratio of their offspring in response to the genetic makeup of their population. It's the first time that such sophisticated reproductive behaviour has been demonstrated in a parasite, and it may help scientists develop a vaccine or drugs to combat malaria. The finding also supports a long-standing theory about sex allocation, which was developed by evolutionary biologist, William Donald Hamilton in the mid 1960s. Since then, the theory has been well demonstrated in complex animals, such as mammals, birds, and insects, but until now it is not well understood in parasites. Here's lead author, Sarah Reece with more on that theory. Nature 453, 609–614 (29 May 2008)

Sarah E. Reece: Hamilton's theory simply explains why it's a sensible strategy for mothers to adjust the sex ratio of their offspring in line with how much competition their sons are going to experience to mate. So, for example, if you imagine a situation in which a mother comes alone and is laying a brood of her offspring, and if it's the case that when her offspring mature and they are ready to mate, if the mating group consist entirely of siblings, brothers and sisters that have come from the same family, that mother would have been best off by minimizing her production of sons and maximizing her production of daughters, because this does two things. First of all, it reduces the amount of competition that her sons are going to be experiencing to mate and by producing more female, it provides her sons with more females to mate with.

Charlotte Stoddart: In populations then with lots of closely related males, the best strategy for a mother is to have a heavily female biased breed of offspring and this kind of behaviour is well understood in multicellular animals, but until your new study, parasite sex allocation was a bit of a mystery, wasn't it?

Sarah E. Reece: Yeah! That's right. This area of local mate competition is probably the most well understood area of sex allocation because like you say, we know so much about it from insects and we thought for a long while that parasites like malaria parasites, might be producing female biased sex ratios for this very reason, but its only very recently that we've had the technology to be able to do the experiments, to actually test whether this is what they are doing.

Charlotte Stoddart: What did you do then?

Sarah E. Reece: Well, we were able to create infections that consisted of clonal relatives, so all the parasites in those infections were genetically identical and other infections that were more genetically diverse, so mating groups would be consisting of a mixture of relatives and non-relatives and we were able to track the males and females produced by the different parasites in our infections and show that when parasites find themselves in infections with non-relatives, they increase their production of males in line with the predictions of theory.

Charlotte Stoddart: Your findings then match Hamilton's theory of local mate competition and also what we see in other animals.

Sarah E. Reece: They do and they don't. At the beginning of infections, they match perfectly with what Hamilton's theory predict, but as infections of malaria parasites progress, things seem to get a lot more complicated for the parasites and they seem to be evaluating, sort of more complex information about the environment that they are in and making more subtle sex allocation decisions.

Charlotte Stoddart: Now, in order to alter their sex ratio in response to the genetic diversity of males in the group, these parasites must have some way of recognizing their kin for evaluating that genetic diversity, do we know how they do that?

Sarah E. Reece: Well! That's absolutely right and this is the first time that we've been able to show that parasites do actually have some way of evaluating whether they are in an infection with clonal relatives or non-relatives and so we have absolutely no idea what information they are going to be using. There's two potential ways they could go about this. One is that they could be using some information that the environment is giving them and say for example, if they can evaluate something about the immune response that's being mounted, that might tell them whether they are in an infection of relatives or genetically diverse infection, or the alternative is that that they're somehow interacting with one another and that helps able to directly recognize other parasites and establish whether they are genetically identical or different to one another.

Charlotte Stoddart: Your findings give more support to this evolutionary theory of sex allocation and you say in your paper that it supports the power of a Darwinian approach, but I'm wondering if it also has medical applications, can this help us to prevent and treat malaria?

Sarah E. Reece: I hope so. When considering organisms like malaria parasites, we understand a lot more about the disease-causing parasites than we do about the sexually-reproducing parasites, but you know these parasites can't transmit new infections unless they reproduce sexually. So my feeling is that we really need to be able to understand the basic biology of their sex lives in order to be able to control them properly in the longer term.

Kerri Smith: Edinburgh University's Sarah Reece. The malaria parasite is most certainly an unwanted visitor in humans, but we host numerous other microbes that don't harm and sometimes even benefit our bodies. Interactions like these taking place in the guts, are the subject of a package of articles in Nature this week. You can catch up on the latest research and news on symbiosis and microbiology at
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Adam Rutherford: Okay science fans, coming up in just a moment a brain-machine interface that enables monkeys to feed themselves using a robotic arm, but before that Geoff Brumfiel looks into a mysterious blip in sea surface temperature recorded half a century ago.

Geoff Brumfiel: Science is supposed to be self-correcting and it usually is, but some mistakes take longer to catch than others. In 1945, global sea surface temperatures appeared to take a mysterious dive. The drop has really puzzled David Thompson of the Colorado State University. So, when he went on Sabbatical this year, he started to think about it. This week he and his colleagues describe how the apparent cooling was likely due to a measurement mix up. I called him to learn how he figured it out. Nature 453, 646–649 (29 May 2008)

David W. J. Thompson: So, when I am on a Sabbatical and then it gives you a lot of time for doing research and daydreaming and noodling and whatever. So, I revisited a problem I've been looking at, almost a decade ago of trying to pick apart the global mean temperature record and pulling out patterns or processes that impact global mean temperatures. So somehow if you have some time series of the global mean temperatures and you say, I know El Nino impacts that. So we had a simple way of pulling down El Nino out of that record and then we said, "okay we know that random weather variability impacts that record, so let's pull that out". We just kept pulling things out and then you see what's you are left with. And what you are left with is this large drop in global mean temperatures at the end of the World War II that doesn't correspond with a volcanic eruption or any known climate phenomenon.

Geoff Brumfiel: And in terms of global mean temperature, may I imagine another thing that affects is global warming or climate change, is that right. I mean, do you see an increase due to human activity.

David W. J. Thompson: That's right. You can see that in the paper, the second figure shows the original global mean record and in the one below that is the record that has been cleaned up and by cleaning it up it clarifies this warming over the last few decades and just how, you know, robust that is, but it does highlight that and in the middle part of the century there was a drop of about 0.3 Celsius or so and so the context for that is that the warming over the century is about 3 quarters of a degree Celsius or so.

Geoff Brumfiel: How did you figure out what was going on?

David W. J. Thompson: I actually started the work funny enough when I was a graduate student and so I contacted my old thesis advisor and we bounced ideas back and forth for a week or so and then we eventually came to the realization that the drop is probably not physical and the reason for that is because it is very pronounced in the ocean data and not clear in the land data.

Geoff Brumfiel: So what does the data tell you?

David W. J. Thompson: So, it's pretty clear I think that where you put your thermometer and how you measure temperature will have, though each have biases relative to what the actual temperature is. What became clear when we looked more at the data is that at the end of the war, the U.S ships were recording temperatures using engine room measurements and the British ships were recording temperatures using the bucket measurements and at the end of the war, the US ships, they went home. They no longer provided sea surface temperature measurements and so suddenly it went from a mix of measurements where you had lots of engine room and just a few buckets to having a lot of buckets and very few engine room measurements and this would cause temperatures to spuriously drop suddenly.

Geoff Brumfiel: Is there any way to correct for this problem in the data?

David W. J. Thompson: That's what they are doing and they've done this in the past. The corrections are I guess will be substantial right after the wars in my understanding and were dropped to near zero by the mid 1960s. So it will just impact the middle part of the century.

Geoff Brumfiel: I've got to say that I am a little surprised that nobody has caught this in almost you know, what's up in now over 50 years since this data was taken. Are there any lessons here for people doing these sorts of climate measurements or any sorts of climate measurements? I mean, there is a lot of data coming in from different places, right.

David W. J. Thompson: The key and I think the key for listeners to get from this is that the sea surface temperature and the land data are measured and they are completely independent measurements and so whatever is shared in both of those records is extremely robust, so this drop only appears in the ocean part of the record and so that's one reason that flags it as being not right, but the warming of the last 30 years is very robust in both data sets.

Kerri Smith: Finally in this show, an arm that can move by the power of thought alone. Scientists know quite a bit about the brain signals that control the movements of our limbs and for a while they've been exploring the possibility of reading out these signals and using them to control prosthetic arms, in people with paralysis or amputation. A study in Nature this week, by Andrew Schwartz and his team from the University of Pittsburgh, brings the reality a step closer. We are joined in the pod by Mike Hopkin, who has been looking at this report. Hi Mike. Nature advance online publication (28 May 2008)

Michael Hopkin: Hello.

Kerri Smith: Now tell us first of all, why are people trying to make these devices and how do they work?

Michael Hopkin: Well, people are trying to help people who are paralyzed to try and have, if you like, so to get body, some way of grabbing things in their environment and may be taking a drink from a cup or eating some food or just controlling some tools, may be one day even a pen, without having to ask for help all the time and so one way they are looking at doing this is by implanting networks of electrodes into the part of the brain that controls movement, the motor cortex, and once they figured out exactly how to get these devices to work, they'll actually be able to read the signals that your brain is generating and interpret those and use a prosthetic device to make the movements that your body would otherwise have made if you weren't suffering from paralysis.

Kerri Smith: Now in the past, these experiments have very much been in the virtual realm, haven't they? They've been moving cursors on a screen or that kind of thing, and this new study builds on that by actually enabling the monkeys they use to interact with their environment.

Michael Hopkin: Yeah! And that's quite an important point because obviously when these things are ultimately used by people, they'll be needing to grab things in the real world means one thing to control a computer game or you know a virtual reality environment, but that's not going to help you and what they've done with these monkeys is develop a device that can actually control a real robot arm in a real laboratory grabbing a real item.

Kerri Smith: And how did the monkeys do?

Michael Hopkin: Well they did quite remarkably well, considering what a complex task it actually is for their brains to do. There were two monkeys in the study and monkey A, as it was called actually managed to grab a piece of food in 61% of the trials that was given and the other monkey, monkey B was even better and she scored 78%.

Kerri Smith: Now, you can probably tell us a little bit about how difficult this kind of task actually is, because they do the same thing on humans and you've been, let's say, human M, yourself in an experiment, tell us a bit about that?

Michael Hopkin: Yeah, this was a similar technology that I tried once, it was using an electrode catheter fixed on to my head and read brain signals in my own brain to try and control a cursor to simply moving from left to right which is obviously a very virtual world thing and it is not as easy as it looks, so these monkeys would have had to do a bit of training before the more complex device could be made to work for them.

Kerri Smith: So after that training then, what could the monkeys actually do?

Michael Hopkin: Well, the idea was that they use this prosthetic arm to grab pieces of food that's obviously something very important to monkeys, these were macaque monkeys and they trained first of all by using a joy stock to control their prosthetic arm and the arm was mounted just next to their shoulder so it was in a fairly natural position and the arm worked pretty much like a normal human or monkey arm and it sort of could move with a fair amount of freedom in the shoulder and then just pretty much in one direction at the elbow and then a simple claw pincer mechanism on the end to simulate a hand, so it has got a realistic structure. Once the monkeys had learned to control these using the joystick and grab some nuggets of food off the end of the peg then their arms were placed in some tubes so that they couldn't move their real arms around anymore and then it was all down to their thought processes and then the food was quite tempting monkey food, it was either halves of grapes or little piece of marshmallow.

Kerri Smith: So they even use this setup for some quite new behaviours that the authors were bit struck by.

Michael Hopkin: Well, they were surprised by how naturalistic the movements looked, you might expect it to be quite jerky, but of course the implant in the monkey's brain was taking a reading every 30 milliseconds. So really it was a quite fluid smooth movement, you couldn't tell you know the individual stages of the movements; it wasn't jerky and when they put obstacles in the way, the monkeys could stay the arms around them and they realized that the marshmallows in particular were quite sticky so they could open the claw just before it got to their mouth and kind of lick the marshmallow off the end and also the performance of the arm wasn't affected by, you know, any movements that might distract the monkeys or anything that might go into their visual cortex, background noises and things like that. So it shows that it is taking brain readings that are quite robust and not susceptible to any other signals that might be buzzing around their brains.

Kerri Smith: And there are some videos of the experiments alongside that paper online at That's it for this week's show. Next week, we'll be finding out what makes Saturn's rings lumpy. This is the Nature Podcast, I'm Kerri Smith.

Adam Rutherford: And I'm Adam Rutherford. Thanks for listening.


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