Nature Podcast

This is a transcript of the 24th July 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 podcast@nature.com.

Advertisement

The Nature Podcast brought to you by Bio-Rad's new ProteoMiner Protein Enrichment Kit, a novel sample prep tool kit that enriches and detects low abundance proteins. Learn more at http://www.bio-rad.com/.

End Advertisement

Kerri Smith: This week the rise and rise of China and the ensuing energy demands.

Jeff Tollefson: The scale is pretty huge. The numbers are actually almost hard to believe and still going up.

Adam Rutherford: We discover what it means when parasites are actually much bigger in ecosystems than predators.

Armand Kuris: Just as predation is a critically important ecological process, infectious diseases are probably a comparably important force.

Kerri Smith: And a plea to make population control a priority.

John Cleland: It's difficult to envisage a reasonable future for Niger and similar countries, unless rapid progress towards population stabilization is made.

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

Adam Rutherford: And I'm Adam Rutherford. China and Africa are already on our radars this week, but we start off in Cambodia, where scientists have been tracking arsenic contaminated ground water. Here's Geoff Brumfiel.

Geoff Brumfiel: Arsenic is a major contaminant in low-lying Asian countries such as Bangladesh. The toxic metal is found in high concentrations in underground aquifer and threatens the health of millions. Geologists know that arsenic comes from the Himalayas, but exactly how it makes its way into the water supply is a mystery. Now, one group has followed arsenic's movements through the Mekong Delta in Cambodia. I spoke to Scott Fendorf of Stanford University to learn about their findings and how they might help limit future exposure to the deadly element. Nature 454, 505–508 (24 July 2008)

Scott Fendorf: It turns out that the arsenic doesn't come from some type of industrial source, but it's actually native to the Himalayas and washed down in the sediment level to the big river systems and deposits in the low lying areas and then as the sediments get buried and it turns out that there are these processes that cause the arsenic to come out of sediments and get into the water.

Geoff Brumfiel: I guess, we don't really understand where or how this is happening, is that right? We don't understand how the arsenic is moving out of the sediment and into the actual reservoirs.

Scott Fendorf: Right that's been the question over the last 10 to 15 years now. We've have been trying to figure out why the arsenic is actually coming off the sediment and the exact processes as well as, where they are occurring within the sedimentary profile.

Geoff Brumfiel: And so your research is a step forward in this from what I can tell. You're looking at the Mekong Delta of Cambodia and you've been able to look at how arsenic has travelled through the delta there, is that right?

Scott Fendorf: Yeah, that's correct. We came up with a hypothesis that the arsenic was probably being displaced from the sediment starting early in the burial process. So in other words it would be up near the surface and that might continue as the sediments are buried deep down.

Geoff Brumfiel: So, how were you able to actually track the flow of water and I guess, by a proxy arsenic then.

Scott Fendorf: We went in and we had to put in what we call a large field array of wells and each of these wells has multiple depths at which we're sampling from and we, set to substitute a transect that would go from the Mekong River itself and then perpendicular to the Mekong out into what are called the peripheral wetland areas and so we set this transect of wells then that would allow us to track the water levels underground and then we could track the water levels above ground as well and once we have done that for a period of time, we could then translate that in to the ability to model which way the water was moving.

Geoff Brumfiel: So, I understand that one of the most interesting things you found here is that this is all actually rather sensitive to human interference that when people are doing irrigation and digging wells, they actually have a big influence on how arsenic flows into these deltas, is that right?

Scott Fendorf: Yeah that's correct, we knew from Bangladesh that the irrigation wells there had basically a dominant impact on which direction the water flows. So then moving into the Mekong Delta, we're able to establish that with these much simpler conditions and otherwise in the absence of irrigation wells, that the water has much simpler flow and then from that we're able to derive then how the system is disturbed by different land use changes, irrigation being a big one; that is you start to dig a lots of wells and pump lots of water out in these fairly flat regions that ends up being a huge, huge factor in terms of dictating which way the water actually moves and how fast it moves.

Geoff Brumfiel: So, I mean, can you use this information then to may be control how much arsenic is getting into people's actual homes and drinking water? Is there anything that they can do differently?

Scott Fendorf: It doesn't necessarily allow us to go in and clean it up but it certainly does allow us to promote land use changes that are going to possibly over the long term help the arsenic situation in the ground water. Typically all these areas are very low lying and have massive flooding every year; and so they are always looking for a fill material and the villages are usually built up on some type of, kind of, an island almost and so in places like Cambodia where we watched the excavation take place, there are multiple ways that they excavate. In some cases they skim off the surface, just you know, few feet from a large area and then pile that up and in other cases they dig down quite deep from an isolated area and build that up. And it turns out that those small differences just in how they excavate, can actually make a fairly big difference in terms that the way the water flows back into the ground water and it changes how much arsenic is actually then moving back to the system. In the case where they dig a fewer number of pits, but much deeper, it turns out that you're getting most of the arsenic overburden out off way and eventually that should lead to possibly cleaner water than a few just skim off the surface. So that's an example of how you can do small changes to have an impact on the arsenic and the groundwater.

Adam Rutherford: Stanford University's Scott Fendorf talking to Geoff.

Kerri Smith: The News and Opinion section of the mag this week is looking East; China is rapidly becoming a scientific force to be reckoned with. Nature's commissioning editor Sara Abdulla has joined us in the studio to give us a run down. Sara, what was the impetus behind this collection of articles.

Sara Abdulla: As all eyes turn to China with the start in a couple of weeks of the Beijing Olympics, we want to explore the scientific challenges that this fascinating nation is facing internally and the challenges that it poses to the rest of the scientific world.

Kerri Smith: Scientifically then it is clear that China has some challenges to overcome, but some big ambitions. Give us an idea of how it compares to the science super powers that we're familiar with; with the US and Europe.

Sara Abdulla: Well, one in five people on the planet are in China. China publishes the second most scientific papers in the world after the US. It produces the most science and engineering graduates in the world and you can basically pick any measure and there's some jaw dropping statistic. For example, there are some indications that China may use 42% of the world's cement.

Kerri Smith: Wow, that is impressive along with the scientific stats; the cement stat is also an impressive one. Another article in the collection takes off the roads into suspect somewhat and asks can China really meet this self-imposed scientific targets that it has been setting. So in which arena is it right on track and in which is it falling behind?

Sara Abdulla: In space there's has been a lot of talk, of sort of, big ambitions and China really wanting to be a global player and it seems to be a bit of, sort of, Tortoise and the Hare situation, where it has obviously not got the sort of budgets and breadth that someone like the US has, but it certainly put up some really important Earth-monitoring satellites in recent years. On the health front, there is impressive disease surveillance policies now in place after the SARS outbreak of 2003, although still much work to go on and access to treatment for HIV and Aids which is a growing and alarming problem in China. The research culture obviously there is massive funds going into scientific research notably areas like structural biology, palaeontology, nanotech where China has decided that it wants to be a real research juggernaut but there is still work to be done on the kinds of education it's currently a little bit rote, management skills are a bit of shortage there and also the regulatory and innovation culture needs some shifts too. And then the environment obviously much bigger push is needed on the air quality, water quality, conservation, the economic juggernaut is just putting immense pressure on land and biodiversity.

Kerri Smith: The environmental issue that you just mentioned is one that reports of Jeff Tollefson has been finding out more about. He was dispatched to Beijing to investigate where the country is finding the energy to power its industry and its population of 1.3 billion people. Earlier in the week, I called Jeff in Washington to find out more. Published online 23 July 2008, Nature 454, 388–392 (2008)

Jeff Tollefson: Beijing is booming and buildings are going up all over the place everywhere you look, you see a new skyscraper going on, the downside of this is you've got some pollution issues, massive air pollution. At time these skyscrapers just tend to appear out of nowhere and there is smog as you are driving down the roads in Beijing. Further out about an hour outside of Beijing, I went and visited ENN, which is a company that is now getting into underground coal gasification, and solar, and wind and biofuels. This is a company that has built a six-story office building, new headquarters, a R&D centre. They are currently clearing ground for three new research labs and they are also building a solar panel manufacturing plant there. And all this has happened in the past year.

Kerri Smith: Give us an idea then of this scale of coal use in China. How much is being burnt, how many new power stations are opening weekly, monthly?

Jeff Tollefson: The scale is pretty huge. The numbers are actually almost hard to believe. Trend is going to something like two and a half billion metric tons of coal each year at this point and the numbers are still going up. In terms of coal plants, the common statistic is that, you know, one or two is going up each week. China built about a 170 Giga watts of capacity in 2006 and 2007 and just for perspective that is more than all of the United Kingdom over the last century.

Kerri Smith: And is this predominantly, sort of, old school dirty coal technology that they are using?

Jeff Tollefson: This is the thing, it is predominantly old school coal, conventional coal, but it is advanced conventional coal. So China has made a decision that they want to make their coal resources go as far as they can and they are now putting in, you know, state-of-the-art super critical conventional coal burning power plants and turning down a lot of the older ones. So it's not the old power plants that we think of when we talk about you know the dirty coal-fired power plants. These are good ones, but they are still conventional plants.

Kerri Smith: So, they are really going forward in terms of the energy efficiency here and I believe from your feature that the government is really encouraging that. But is there anything to suggest this is a more climate friendly way of getting your energy?

Jeff Tollefson: Well that's the question. Right now in China as within the United States and other parts of the world, I mean, they don't have an economic reason to cut carbon dioxide emissions. They are going at this from an energy security standpoint right now. Climate is a different story. They are developing greater gasification combined cycle plants and they are in the race for the first integrated coal-fired power plant that would capture and store carbon dioxide emissions underground. So there are some promising developments there. The question is whether they can drive the cost down for these advanced technologies.

Kerri Smith: What might help China to do that faster, what will encourage them and is it just a question of just throwing money at the problem?

Jeff Tollefson: One question is money, I mean these technologies are more expensive and the Chinese government has to make a decision right now. They're trying to alleviate poverty and develop the economy and they had been very successful at that right now, but if you want to put in more expensive technologies that means you've got less money for poverty development and energy bills go up. Who's going to pay is a classic question and the Chinese don't feel that they're obliged right now to pay to develop the latest climate technologies. They see the West is having some responsibility to help bare those costs, now if they decide to move forward and if you can get out, you know some kind of, an agreement in terms of who's going to pay then it is quite possible that the Chinese can drive down these costs faster than anybody in the world and they might be able to deploy them faster than anybody in the world. But the question, who pays, will always be there?

Kerri Smith: Sara turning back to you, the growing and increasingly wealthy population of China means that energy efficiency is, as Jeff just has been telling us as a key concern, meanwhile another facet of China's population is causing sensual problems. So what's going on there?

Sara Abdulla: In 1979, China's population was mushrooming and Deng Xiaoping put in place the infamous one-child policy, basically meaning that married couples could more or less only have one child or face financial, social, economic penalties such as losing jobs and so on. And the result of this at the turn of the millennium, there are 117 male births for every 100 female births and this is a gender disparity that's basically unprecedented in world history. Indeed in some parts of China, the gulf is as much as 150 to 100, which essentially means that there is a couple of generations and who are going to find it very, very hard to get married and settled down and there is some concern that this could an increase in social unrest and organized crime, female trafficking, even though now the one child policy is very much offended and could be going away, it will take sometime to turn that trend around.

Kerri Smith: And there is more on that in a special report that Phil Ball has written for the News section of Nature this week. In another article that forms part of this package as well, there is a commentary that looks at how other aspects of China's social and political milieu might be affecting research.

Sara Abdulla: Yeah, so the commentary talks about the tensions that are arising between China's ambitions to be a world player on the scientific stage and its focusing on to the fashionable topics such as structural biology, nanotech, and so on. And they are in turning on needs, they are crying out for research such as healthcare, energy generation, food and water security and we also have some vox pop from researchers who have stayed in China, left or returned and they pick up on issues such as the difficulties of getting hold of reagents, the challenges of building a lab with post docs from the spoiled 'Little King Generation', which is what they call the one-child generation, the difficulties of forging increased international collaboration against the backdrop of China's human rights record and also its reputation for regulatory laxity, the need for flexible funding, the importance of altering the culture to allow failure. But happily as one of our book reviews this week points out, scientific policy making has come a long way in the past few decades and there is a real political and public engagement with science in China.

Kerri Smith: Alright, many thanks Sara. That collection of features and opinion articles is available as always from http://www.nature.com/nature.

Adam Rutherford: China's infamous one-child policy is one of the more extreme population control measures the world has ever seen and is one reason why measures like these have become a touchy subject. Demographer John Cleland from the London School of Hygiene and Tropical Medicine wants to see population control back on the agenda.

John Cleland: Population control has fallen from fashion as an international priority. One reason is the spectacular declines in birth rates that have characterized most of Asia or Latin America. Much of the credit should go to vigorous promotion of modern contraception by governments, with the generous financial support from donors. One key lesson of past decades is that poor families do not necessarily want or need large numbers of children. Another important lesson is that rapid declines in fertility can be achieved without a cause to coercion as in China's one-child policy, but there remains one region where the transition to smaller family sizes has barely begun. In sub-Saharan Africa women have five births on average. Over the next 40 years, the populations of most countries in that region are expected to double or even triple in size. Over one-third of the projected total world population increase, over that period, will come from Africa. These figures are a cause for serious concern. For the past 30 years, the population growth in Africa is outstripped food production. The region imports 20 billion US dollars worth of food per year, equivalent the total amount of overseas aid that Africa receives and that figures predates the steep rise in food prices. To prevent recurrent famines and widespread malnutrition, the modernization of agriculture must be a top priority. Of equal urgency is the need to moderate the increasing number of mouths to be fed. The future for some countries is potentially catastrophic. Take Niger for example, it has lost half its arable land to the encroaching Sahara desert. Two years ago, a serious famine was averted only by international food aid. Fertility remains at about 7 births per woman, when it is levelled to half in the next 40 years as the United Nation expects, Niger's population would nevertheless grow from 16 million today to 50 million by 2050. It's difficult to envisage a reasonable future for the Niger and similar countries, unless rapid progress towards population stabilization is made. Even where countries have food security, high fertility still makes escape from poverty much more difficult. A well-educated and skilled able force is one of the pathways to economic success. How can education improve when the number of school-aged children doubles every generation? Most African governments have policies to reduce birth rates through the promotion of family planning, but they have been receiving precious little support from the World Bank and the international community to implement these policies. The time has come to revitalize the family planning agenda. Unless this happens, the prospects for achieving decent living standards in Africa will be greatly diminished.

Adam Rutherford: John Cleland from the London School of Hygiene and Tropical Medicine.

Jingle



Adam Rutherford: This is Nature Podcast. Coming up in just a moment, we've dealt already with possible famine, the burgeoning science wars between east and west and lethal levels of arsenic. We await only the fourth horsemen of the apocalypse, Pestilence, more on that from me in just a moment.

Kerri Smith: But first here is Charlotte Stoddart with news on how flies know where to fly.

Charlotte Stoddart: Many animals including birds, mammals, fish and insects used the earth's weak magnetic field for orientation and navigation. But the precise mechanisms underlying this internal compass have eluded researchers. One possibility is that the magnetic fields are sensed by a chemical reaction in special receptor cells in the eye and in May of this year, we talked to a team from the University of Oxford, who successfully tested a model system in their lab. Now researchers from the University of Massachusetts Medical School have gone one step further, showing for the first time, the molecular basis of a chemical compass in an animal, as Steven Reppert explained to me. Nature advance online publication (20 July 2008)

Steven M. Reppert: Well we've done with the chemical based system has made a substantial advance in terms of really identifying a molecule that others have proposed could function as a light sensitive magnetoreceptor and that is the cryptochromes.

Charlotte Stoddart: This molecule called the cryptochrome is a blue light sensitive receptor in the eye and you've shown that it plays a central role in magnetic sensing in fruit flies. What was your experimental set up?

Steven M. Reppert: It is an apparatus that was constructed that's called a T-maze and each arm of the T is essentially a plastic tube and so a current could be passed through this coil that is on either end of the two arms and depending on the direction of the current, we generate a magnetic field on one end and not on the other end. So what we then did was to first train flies to associate the magnetic field with a sugar reward and then after taking flies that were trained in that way and now putting them in the T-maze, they very, very consistently went towards the magnet.

Charlotte Stoddart: Once you trained flies then to prefer the side of the maze with the magnetic field, how did you then demonstrate that this blue light sensitive receptor that is enabling them to sense the magnetic field.

Steven M. Reppert: Well one of the first things we did was to look at the part of the light environment that was critical for this magneto-sensitive response and what we used was a variety of filters to, sort of, cut off different parts of the spectrum of light that the flies would normally see and what we very clearly showed is that the flies required short wavelength light for this response. Then the second thing that we did was we looked at two different mutations and in both instances where a Cry is non-functional, we abolished the magneto-sensitive response. So this was really the first demonstration in a living animal that cryptochrome is really necessary for magneto-sensitive response.

Charlotte Stoddart: You did two things then, to show that this cryptochrome is necessary. You, first of all you blocked the wavelengths that this receptor protein is sensitive to and showed that when they were blocked the flies lost their magnetic sense and you also showed that when the cryptochrome didn't function properly in mutant flies then also they lost their magnetic sense, how can cells that are light-sensitive tell an animal its position in relation to a magnetic field.

Steven M. Reppert: That's a good question? We don't know the answer to that but we think that we have now an animal system in which we can begin to sort of tease a part both the cells that are used and in the fly, where the cryptochrome is expressed and we even in the fly will be able to perhaps mutate protein in ways that would predictably cause changes in the protein and allow it no longer to act as a light sensor. And again this has been predicted by more biochemical and biophysical studies that had been done in vitro situations. So we can pick up on those results and use them to try to design experiments in all animals.

Charlotte Stoddart: And one of those in vitro studies in fact, we reported in the Nature Podcast in May and that was a group at the University of Oxford who showed that light sensitive chemical reactions when tested in the lab could detect the direction of a magnetic field and now you've demonstrated that this kind of mechanism works in Drosophila and that this blue light sensitive receptor is necessary and so what are your next steps?

Steven M. Reppert: Well in fact it's interesting you say that because I just contacted the senior office of that paper, made them aware of our work and we both now decided, we need to get together and talk, because we would like to be able to in some way provide them with a cryptochrome protein, so that they could test in their assay system. Because they chemically synthesized a molecule that underwent, sort of, changes that a molecule would need to and showed that it could sense the geomagnetic field and they speculated that cryptochrome would be a good candidate, so it's really great because their finding buttressed with ours so, well, lets get together and see if we can do this with fly cryptochrome.

Kerri Smith: That was Steven Reppert talking to Charlotte.

Adam Rutherford: Finally this week, if famine, war and death haven't got at you yet, a dose of Pestilence showed, finish you off. You probably and correctly think of parasites as being tiny, tiny creatures compared to their hosts, but a team based at UC, Santa Barbara has looked at a different measure of size; biomass, which the total amount of tissue in an ecosystem. They found in this week's Nature that the total biomass of parasites in the ecosystem can exceed that of its top predators. I spoke to lead author Armand Kuris and began by asking him why biomass is such an important concept. Nature 454, 515–518 (24 July 2008)

Armand M. Kuris: It's important because it's the most direct measure of productivity when you add to the actual standing amount of tissue in a system, the amount produced during reproduction; you have productivity in an ecosystem.

Adam Rutherford: Okay and you've been looking at the impact of parasites on biomass in ecosystems. Until your paper what were the previous estimates of parasite biomass?

Armand M. Kuris: Really there were none and what our paper does is solve a sort of hidden paradox. If parasites and infectious agents are very, very small, why do they have such a large effect and being invisible, being inside their hosts they are actually perceived throughout the history of science as having negligible or irrelevant mass. We've shown that their mass and their productivity is quite substantial and this implies that it is a major driver of ecological processes and that this energy drain is probably a major part of the disease process in hosts including humans.

Adam Rutherford: And you've shown that the biomass of some of these parasites is equal or even more than some of the top predators in food systems. How did you go about sampling these parasitic biomass?

Armand M. Kuris: With a tremendous amount of effort, we created an enormous data set by going to three different estuaries on the California and the Baja California coast and carefully quantifying the distribution and abundance and all living things from little almost microscopic copepods up to the top predators, birds, sharks and on top of that we then, with equal care dissected all of those species almost 200 species for all the infectious agents that we could detect and quantify their abundance and their mass.

Adam Rutherford: Okay, and what sort of parasites are we talking about here. I mean, looking at your paper and I'm particularly troubled by the ones which you call parasitic castrators.

Armand M. Kuris: No aren't they troubling. It turns out that this is a fairly common parasitic strategy. Now all parasites other than parasitic castrators in a sense degrade their habitat, the host, every bit of energy that they take, every bit of damage that they do degrades or shortens the life of the host potentially and when the host dies, so do the parasitic castrators are like body snatchers, they only take energy from reproduction; they cause the blockage of reproduction in the host and they don't affect the viability of that host. So they go on without damaging the long term lifespan of their hosts. And in our system, the flukes the major group of parasitic worms all start of their lives in some long-lived snails and in those snails these worms are parasitic castrators, we had I think 24 species of them and all of them are parasitic castrators in the snail or the bivalve hosts. They live in those hosts for 10 to 20 years.

Adam Rutherford: So all in all a pretty successful and unpleasant strategy for survival. Now what is the overall significance of this? It seems that we've grossly underestimated the significance of parasites on ecological systems.

Armand M. Kuris: The overall significance is that this study, I think for the first time, provides a general reason why infectious processes are likely very important in most ecosystems. The second and more speculative aspect is that this also suggests that the actual drain of energy is a major part of the disease process in animals including humans. When you add to the direct energy that is moved from host to parasite, through the parasite into whatever size it is, you add to that the conversion energetic loss, you add to that the repair of damaged tissues every time malaria destroys some blood cells, the host must make more, one for one, and the defensive caused to reduce or eliminate the infectious agents. It looks like as an energetic driver in ecosystem; infectious disease must generally be important and in the health of organisms including humans that this may be a suggestion that there is a strategy for disease management that has not been recognized that this may be the primary cause of disease and they could be addressed with some newly conceived sophisticated strategies.

Adam Rutherford: Armand Kuris from UC Santa Barbara. That's all from us for this week. Join us next time for among other things snake fangs and how to predict eclipses. I'm Adam Rutherford.

Kerri Smith: And I'm Kerri Smith. Thanks for listening and have a good week.

Advertisement

The Nature Podcast brought to you by Bio-Rad's new ProteoMiner Protein Enrichment Kit, a novel sample prep tool kit that enriches and detects low abundance proteins. On the web at http://discover.bio-rad.com.

End Advertisement