Science Magazine Podcast

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Aug 24, 2012 - ... about supernova formation in a Report this week. You can read more about supernovas in a pair of Revi
Science Magazine Podcast Transcript, 24 August 2012 http://podcasts.aaas.org/science_podcast/SciencePodcast_120824.mp3

Music Host – Isabelle Boni Welcome to the Science Podcast for August 24th, 2012. I’m Isabelle Boni. Host – Kerry Klein And I’m Kerry Klein. This week: the origin of Indo-European languages, a project to track tropical fish, and a surprising study of the history of supernovas… Interviewee – Benjamin Dilday We’ve shown that the origins of supernovae—which, when we observe them, look very similar—might in fact be different. So there is a variety of ways in which Type-Ia supernovae can be formed. Host – Isabelle Boni Plus, a few stories from our online daily news site. Promo Support for the Science Podcast is provided by AAAS: the American Association for the Advancement of Science. Advancing Science, Engineering, and Innovation throughout the World for the Benefit of All People. AAAS—the Science Society—at www.aaas.org. Music ends Host – Kerry Klein Exploded stars, also known as supernovas, are key to studying the formation and evolution of the universe. But the origins of these explosions are not entirely understood: Type-Ia, a particular family of supernovas, arise when a white dwarf star explodes, but just how this white dwarf ignites in the first place has been debated. A study of the gas clouds surrounding a Type-Ia supernova known as PTF 11kx allowed Benjamin Dilday and colleagues to zero in on one particular way these explosions may occur. Dilday spoke to me about his surprising findings and their implications for cosmology. Interviewee – Benjamin Dilday Supernovae are the explosion of stars. Type-Ia is a particular type of supernova. What’s really interesting about the Type-Ia supernovae, one thing is that they’re very bright. And so we can see them across vast distances of the universe. But, more importantly, we know how bright they are, and so in astronomy we call them “standard candles”, which means that if we know how bright they are and we know how bright we observe them to be, then we also know the distance. And so we can use them to measure distances across the universe. And if we do that, we can study the expansion history of the universe, study

cosmology. And, in fact, Type-Ia supernovae were what were used to prove the existence of dark energy. Interviewer – Kerry Klein And so your particular study was all about the origins of supernovas, in particular TypeIa supernovas. So what are some popular theories right now for how supernovas are formed? Interviewee – Benjamin Dilday Right. So despite the fact that we use Type-Ia supernovae to study cosmology, we don’t really know in great detail what the progenitor systems are or, in other words, you know, what they were before they exploded as a supernova. So one thing that we do know is that it must have been a white dwarf star, and a white dwarf is what’s left over after a star like the Sun uses up all of its fuel so that the core is left behind, and we call that a white dwarf. But a white dwarf that is just sitting out there in space will never explode as a supernova. So we also know that in order for that to happen, the white dwarf must be somehow pulling matter from a companion star – so in other words a star that is in an orbit with the white dwarf. So what we really don’t know about Type-Ia supernovas is what is that companion? And so it could be a normal star, you know, something like the Sun. Or it could be what we call a red giant star, which is what happens to normal stars late in their life cycle, or it could be another white dwarf star. And in that case, the explosion would happen when they spiral into each other and collide and merge. So in our study, we show that for this particular case, the companion must have been a red giant star. And this is a surprising finding because recent evidence has really been pointing to white dwarf mergers as the primary way that Type-Ia supernovae are formed. And, you know, many people believe that this scenario could account for all Type-Ia supernovae, and maybe all Type-Ia supernovae are formed that way, but one of the things our study shows is that there’s a variety of ways to make a Type-Ia supernova. Interviewer – Kerry Klein So tell me about this particular case – this this supernova PTF 11kx that you mentioned. How is this different from other supernovas that we’ve studied, and how was it able to tell you how it formed? Interviewee – Benjamin Dilday So PTF 11kx was just a very interesting, very exciting supernova to discover. So right away when we took the first observation we knew that something interesting was happening. And so, what we could see is that there was gas in between us and the supernova. There’s a lot of gas, a lot of dust out in the universe and so supernova light traveling from a distant galaxy often just passes through gas on its way to it. But in this case, the gas had very unusual properties. And so we knew that the gas is probably left over from the progenitor system. And so, you know, we then went and got more and more observations with bigger telescopes, better instruments. And what we were able to see is that there was gas near the supernova and, in fact, there was multiple shells or multiple clouds of gas. We were also able to measure the velocity of the gas, which told us that, you know, it’s much, much, much slower than the material from the supernova

explosion, but at the same time faster than we expect from a red giant wind. And also we saw hydrogen. And so for anybody studying Type-Ia supernovae, seeing hydrogen is very, very exciting because hydrogen is, by far, the most common element in the universe, but it’s something that we don’t usually see in Type-Ia supernovae. You know, seeing hydrogen is a very strong indicator that it’s something like a red giant star, as opposed to a merger. And finally, about 60 days after the explosion, we saw the ejecta from the supernova – so, you know, the material that had been in the white dwarf, which is now exploding – we saw this running into the gas. And so it’s the first time that we were able to see the gas in the supernova system and then later on see the material from the supernova running into it. And so this – and also the fact that the gas that we saw in earlier observations was moving faster than a red giant wind – lead us to believe that there must have been a nova explosion maybe a few decades before the supernova. And just to clarify, a nova explosion is an explosion that’s much, much weaker than a supernova, and basically what happens is material accumulates on the surface of the white dwarf, and if it gets heated up enough, it can ignite and explode, but it’s not an explosion that destroys the white dwarf like a supernova does. But it’s just sort of the very outer layer, which explodes and flies off into space. And so if this happens, it can take the gas and clear out a big cavity, which we saw in the data, and also it can accelerate the material from the wind to the sorts of velocities that we saw. Interviewer – Kerry Klein Okay. So all of the materials sort of swimming around the supernova in the cosmos really had a lot of information to tell you about how it formed. And it all pointed you to this particular model involving a nova explosion between a white dwarf and a red giant. So can you just step back for a second and sum up the factors that led you to this particular progenitor model? Interviewee – Benjamin Dilday So first of all, there’s the outward moving gas that we see – so this is something that we’d expect from a red giant wind. There’s the material that we see the supernova ejecta running into, which is also something that could be put there by a red giant. The fact that we see multiple shells or clouds. And, so as I said, it was about 60 days before the supernova ran into the gas, which means there must have been a big cavity. And so this is something that could be explained by a nova explosion a couple of decades before the supernova. So these are the major lines of evidence that led us to believe that the progenitor was a red giant with a nova in the recent past. Interviewer – Kerry Klein So here’s a question on a bit more of a philosophical level. A lot of the cosmic bodies that we observe, we classify in terms of how they’re formed. So by zeroing in on a somewhat surprising mode of formation for this supernova, for PTF 11kx, would it be possible to say that it’s actually not a supernova at all and to completely reclassify it as something else? Interviewee – Benjamin Dilday

So I would say there’s no question at all that PTF 11kx is a supernova, and there’s no question that it’s the particular Type-Ia supernova. In fact, what’s interesting about our study is that we’ve shown that the origins of supernovae – which when we observe them look very similar – might, in fact, be different. So there is a variety of ways in which Type-Ia supernovae can be formed. And so the next step for us is to try to understand whether these different progenitor systems, in fact, do have subtle differences in the resulting supernovae explosions. Interviewer – Kerry Klein So as you said earlier, supernovas are really important in the study of cosmology. So does this study help to shed any light on the formation and evolution of the universe? Interviewee – Benjamin Dilday Yes, so this particular study is very important for our study of cosmology. So, you know, as I said before, we use Type-Ia supernovae to measure distances and study dark energy, the change of dark energy with time. And so any additional information we get about about the progenitor systems of Type-Ia supernovae can help us to use them more precisely to study cosmology. And so one example of that is that recently big supernovae surveys that are working with hundreds and hundreds of Type-Ia supernovae have shown that for supernovae in galaxies of different types, in fact, there are subtle differences between them. And so, you know, our study – which is related to the progenitor system for this supernova and which says that Type-Ia supernovae can come from a variety of progenitors – might be part of the explanation for that. And it’s also a framework for us to try to understand theoretically what differences there may be between the different progenitors. And all of that can help us to more precisely use Type-Ia supernovae to measure distances and to study cosmology and dark energy. Interviewer – Kerry Klein Great. Well, Benjamin Dilday, thank you so much. Interviewee – Benjamin Dilday Thank you. Host – Kerry Klein Benjamin Dilday and colleagues write about supernova formation in a Report this week. You can read more about supernovas in a pair of Reviews on luminosity and gamma-ray bursts, both online in today’s issue at www.sciencemag.org. Music Host – Isabelle Boni Mother. Madre. Mere. Mutter. These are all examples of cognates of the same word, their similar sound indicative of a common origin: in this case, the Indo-European language family. But where did this family itself come from? There are two competing candidates: the Pontic steppes approximately six thousand years ago, and the Anatolian peninsula eight to nine thousand years ago. Researchers such as Quentin Atkinson study

interdisciplinary sources such as historical evidence and modified epidemiological models, to determine the roots of Indo-European languages. Atkinson spoke to me about the team’s efforts, and starts off with a summary of the research. Interviewee – Quentin D. Atkinson So in this paper, we identified the homeland of the Indo-European language family by adapting what are called phylogeographic methods that were initially developed by epidemiologists to trace the origin of virus outbreaks. But instead of comparing viruses, we compare languages, and instead of DNA we looked for shared cognates – words that have a common origin, like the words “mother” in English and “madre” in Spanish indicate a common origin. And we compare these words across all the Indo-European languages. We used the cognates to infer a family tree of the languages. Combining that with information about the location of each language, we trace back through time to infer the location at the root of the tree, the origin of the Indo-Europeans. Interviewer – Isabelle Boni So before we get into the particulars of your study, could you tell me a little bit more about the Indo-European languages you looked at? Interviewee – Quentin D. Atkinson We took a sample of over 100 Indo-European languages, including 20 that are extinct, so they’re not spoken today. And we chose some of those because that allows us to reach back further in time by pegging our tree to these ancient languages. Some, like Hittite, were spoken over 3000 years ago. So we had over 200 meanings for each language. These were basic vocabulary terms, like words for mother, father, fire, water, or basic verbs, like run, walk. And in all, we looked at over 6000 cognates across these 200 meanings. And that was the data that we fed into the analysis to build the language trees. Interviewer – Isabelle Boni So we have this vast collection of languages, and you’re trying to find their origins in your paper. Can you tell me about the different hypotheses for how the Indo-European language family arose? Interviewee – Quentin D. Atkinson There are two competing theories for the origin of this family. The first theory was put forward by Maria Gimbutas and argues that the languages spread from the Russian steppe region, and that’s linked to archeological evidence for the spread of what’s called the Kurgan culture between 5 and 6000 years ago from that region. And the second theory, put forward by Lord Professor Renfrew, argues that in fact the languages spread much earlier, between 8 ½ and 9000 years ago, with the spread of agriculture from what is now Turkey, but Anatolia. And so these two theories have two different ages and two different homelands. And by tracing back in time using these methods to study viral outbreaks, we were able to test between the theories. And we found really strong support for the Anatolian theory – the spread with farming. Interviewer – Isabelle Boni

So going along with the Anatolian hypothesis, how does a language spread and evolve through farming? Interviewee – Quentin D. Atkinson So for languages, the spread across such a vast region – from Icelandic in the West to Sinhalese spoken on Sri Lanka in the East – we need to posit some fairly major powerful mechanism. And so one of the appeals of the agriculture expansion explanation is that it provides such a mechanism, that with the advent of agriculture, populations would have been growing, and as they grew, the next generation would have had to expand out a bit from the current range. And if that process went on generation after generation, it doesn’t take very long to cover a very large area. Of course, it’s also possible that if agriculture is spreading into an area that’s already been inhabited by hunter-gatherers it might be that the agricultural lifestyle looks fairly appealing to the hunter-gatherers and so they could also be adopting the agricultural technology and perhaps adopting their language as well. We find that this explanation fits nicely with the spread of IndoEuropean, but that doesn’t mean agriculture explains all language expansion, far from it. But it seems a good explanation in this case. Interviewer – Isabelle Boni Alright. So turning back to your main question on origin – Steppe or Anatolian – what was the methodology you used in answering this question? Interviewee – Quentin D. Atkinson First of all, we needed to reconstruct the family tree of the languages. That gives us insight into the history of the family. And to do that, we need information about the languages from which we can work out how they’re related. And so, by identifying cognate sets, we can group languages into subsets and subsets of those subsets and reconstruct the family tree. And by tracing along the branches of the tree and essentially accounting for how many gains or losses of these cognates we see, we can estimate how long the branches are and therefore how much time has elapsed. So we combine the cognate information with information about where the languages are spoken. And so we’ve modeled the gain and loss of cognates through time on a tree and try and identify the tree or set of best trees for explaining the data we see. We then want to put a time scale on the family trees. To do that, we have information about different events in IndoEuropean history. For example, we know the romance languages began to break up with the breakup of the Roman Empire, so we can put an age on that. And, in fact, we were able to find 14 different known divergence times on the tree, which we used to calibrate the rate of change. So that gives us the time scale. And then we have a model of spread of languages through time. So we know where the languages are spoken today. And we can trace back along the branches of the tree using what’s called a Brownian motion model for a relaxed random walk to identify the probability of different lineages being at certain locations as you go back in time. And if we repeat that process all the way down the tree, we can make some inference about the location at the root of the tree. Interviewer – Isabelle Boni

There are many possible convolutions and branchings for a language tree. So how did you find the best tree? Interviewee – Quentin D. Atkinson One of the challenges with this kind of statistical problem is that there’s a vast parameter space to explore. We looked at over 100 languages, and for that many languages, there are more ways of relating them to each other than there are atoms in the universe. So you can’t possibly evaluate all the alternatives. What you need is some clever statistical algorithm that allows you to search through the space of possible trees and get a kind of representative sample. And we used an approach called Markov chain Monte Carlo methods that sample from the space of possible trees. Essentially what they do is you propose a random starting tree – so just randomly connect the languages in a family tree – and then evaluate how well that tree explains your data given your model. And then you propose some change to that tree, and you ask whether it improves the fit to the data or whether it doesn’t. If it improves the fit, then you accept the tree. If it doesn’t, then you accept it in proportion to how much worse it makes the fit. This sounds like a weird thing to do, but it turns out that it’s based on some sound statistical principles, which mean that if you apply this algorithm, the sample of trees you get as you successively make these random changes approaches what’s called your posterior expectation, the posterior distribution for the parameters you’re interested in. So what that means is we have some prior beliefs about what the trees should look like. We have our data, which can then inform us further. And combining the data and our prior beliefs, we get some posterior beliefs about how likely different trees are. So that means we apply this method sampling from this vast space of trees and get an estimate for the range of language trees that best explain our data. So we want to look at all of the trees that it could plausibly be true. And that’s what we did in our analysis. So when we’re looking for the most likely origin – testing between the Anatolian origin and the Steppe origin – we’re sort of integrating out the uncertainty and exactly how the languages are related. Interviewer – Isabelle Boni So what are some future directions you would like to take your research? Interviewee – Quentin D. Atkinson Well, one of the novel developments in this paper was to remodeling expansion of languages across the landscape, but we also looked at rates of movement across land versus water, which might be different. You might be less likely, for example, in a population moving across the landscape as it expands to want to cross water. Or maybe you don’t mind crossing water but you do it very, very quickly. Anyway, we were able to differentiate between movement across water and across land. And what that highlights is that with these models we can look at movements across different types of landscapes. And so what we’d like to do in the future is incorporate more of that kind of information, perhaps looking at the effect of rivers or mountains and really trying to get at the detail of how the history of these cultures has played out over the last few thousand years. Interviewer – Isabelle Boni

Thank you, Quentin Atkinson. Interviewee – Quentin D. Atkinson Okay, thanks. Host – Isabelle Boni That was Quentin Atkinson on the origins of the Indo-European language family, the subject of a Report this week in Science. Music Host – Kerry Klein After its construction, the Square Kilometer Array, SKA for short, is going to be the largest scientific instrument in the world—and it’s going to be hosted almost entirely by Africa. Science’s Meghna Sachdev spoke with Roy Maartens of South Africa, the country with the largest share of the array, about what this means for science and technology on the African continent. Interviewee – Roy Maartens A big science project like this could provide a flagship for a government policy to draw more of the younger generation to science and technology. And in particular, of course, what we call here the disadvantaged community, those who have been disadvantaged under apartheid. Primarily, black Africans. I don’t know if you are aware of this, but one of the features of the apartheid system in South Africa was specifically to exclude black African school children from Science and Technology and in a sense to educate them for labor. And so that has left a devastating legacy, and one of the things this country has to do is turn that legacy around. Host – Kerry Klein Roy Maartens writes an editorial about the Square Kilometer Array in Africa in an Editorial this week. To hear more of his interview with Meghna Sachdev, find his article online in Science's August 24th issue -- it's free with a short site registration. Music Host – Isabelle Boni How does the evolution of a species affect a given ecosystem? This question has long gone unresolved because evolution was thought to occur too slowly for scientists to monitor the change. However, studies of animals with multiple reproductive cycles within a year are revealing that evolution is happening in observable timescales and that researchers can measure an effect on ecosystems. One such research program is the Guppy Project, which looks at the question of how the evolution of a small guppy impacts the environment in mountain streams. Science News Writer Elizabeth Pennisi traveled to Trinidad to see these guppies in person. Edward Hurme spoke with Pennisi about visiting the site and the work being done there.

Interviewee – Elizabeth Pennisi I arrived on a hot, steamy afternoon and was immediately picked up by Dave Reznick, the project leader. We drove in a dusty pickup with holes in the floorboard up into the mountains to a private house where the researchers were living and working. The mountains were very lush and green and beautiful; the house was very rustic but adequate. One day I watched them work in the lab, and the next day I went up into the streams with them. Interviewer – Edward Hurme So this doesn’t seem like the easiest place for your average scientist to get to. Can you describe the working conditions up in the streams? Interviewee – Elizabeth Pennisi Well they have to take these steep, windy roads up to get to the headwaters of the rivers that they’re studying. There are lots of potholes; there are even places where landslides have sort of eaten the edge of the road off. And then you come to the end of the road, and you start walking down a trail, and soon the trail ends, and you have to walk in the stream in order to get to the study sites. So it’s quite laborious. Sometimes you have to climb over waterfalls, and sometimes the water is chest deep. So it gets pretty, pretty interesting. Interviewer – Edward Hurme So they’re trying to keep track of wild fish in streams, which seems like a really daunting task. What was the methodology that they used for monitoring all these fish? Interviewee – Elizabeth Pennisi So one of the benefits of these river systems is they have sections of streams that don’t have any fish in them because they’re upstream of waterfalls, and the fish can’t reach them. So what these researchers did is they took a certain number of fish – actually 80 fish – from downriver in a place where there are a lot of predators and moved them to a place upstream where there were only killifish and no other predators. And they watched these fish grow. So before they put these fish in the streams, they mark them with two dots of plastic that they injected underneath the skin, and the plastic was color coded so that they could tell each fish from another. And every month they would go back in the stream and re-catch all the fish in the stream, see how many new ones had been born, and measure and photograph ones that they had caught before. By doing this, they could track what was happening to the fish as they were growing and as their population was expanding. Interviewer – Edward Hurme So what were they finding with monitoring all of these fish? What were their results? Interviewee – Elizabeth Pennisi So the first thing they saw was a population explosion. And the fish really increased in numbers so much so that they had trouble keeping up with their mark capture studies. Then what they’ve noticed over the couple of years that they’ve been doing the studies is

that the males are getting larger at maturity than they were before. And this makes sense because in streams where there are a lot predators, the fish have to grow up fast and reproduce in order to reproduce before they get eaten. But in this new environment, the fish don’t have to worry about getting eaten so much, and so they can take their time getting bigger. Interviewer – Edward Hurme So how are the researchers able to see the fish adapt to their environment over such a short time scale? Interviewee – Elizabeth Pennisi Well, their reproductive cycles are very short – they go through three or four generations a year. So in the three or four years that they’ve been studying these fish, they’ve been able to see a shift in the size and time and maturity of the males. Interviewer – Edward Hurme So are there any other researchers that have been using the same technique of looking at rapid evolution in animals? Interviewee – Elizabeth Pennisi Well there have been other examples of rapid evolution documented. One of the most notable was done down in the Galápagos Islands with Peter and Rosemary Grant, who every year go to the Galápagos and measure the body size and the beak size of the Darwin finches in one of the islands there. And what they were able to show is that beak size and body size responds to changes in seed availability, and the seed availability is determined by the weather. Interviewer – Edward Hurme So previously people thought that it was the ecology of an environment that shaped the evolution of a species. But is it the old “which came first, the chicken or the egg scenario?” – the ecology shaping the evolution or the evolution shaping the ecology? Interviewee – Elizabeth Pennisi Well what’s becoming clear is that evolution and ecology influence each other. The ecology influences how an organism will evolve. But then as an organism changes, it uses its environment in a different way and then changes the environment, and then those changes in the environment affect how the species will continue to evolve. Interviewer – Edward Hurme So going back to these streams in Trinidad, what are the future plans of these researchers to look at how the ecology and evolution of the streams are interrelated? Interviewee – Elizabeth Pennisi So what they are continuing to do is they not only monitor the fish and catch the fish every month, they also look at the characteristics of the ecosystem. So they do a census of the invertebrates there. They measure the primary productivity. They even look at

leaf litter to see how those parameters are changing as the guppies increase in number and change themselves. Interviewer – Edward Hurme Yeah, so it seems like the researchers have a full plate of research ahead. Is there enough money out there to do this kind of work? Interviewee – Elizabeth Pennisi Well the research has been going on thanks to a $5 million grant from the National Science Foundation, and that grant is over now. And so now the researchers have to find new money, which they haven’t quite gotten yet, in order to keep the program going. Interviewer – Edward Hurme Well it would be quite a shame if it all went to waste. Interviewee – Elizabeth Pennisi It would. Interviewer – Edward Hurme So you also wrote another article focusing on a similar phenomenon of evolution and ecology shaping each other. Could you talk a little about that? Interviewee – Elizabeth Pennisi Right. So that project involved alewives, which are a fish that live in eastern North America. And alewives are anadromous, where they live most of their life at sea, but every spring, they come up rivers and go into lakes to spawn, and then they come back again. And what happened was is 300 years ago, some dams were built creating landlocked populations of alewives. And those landlocked populations of alewives have affected the populations of the water flea, the Daphnia, that live there, and that effect on the Daphnia has had a ripple-down effect on the algae that live in the lake. And what these researchers have shown is that presence of the alewives causes a disappearance of the Daphnia, which leads to a change in how the algae, what algae are there and how they grow. In addition, the researchers have shown how another fish in these lakes – the chain pickerel, which eat alewives – has changed where it lives to take advantage of the landlocked alewives. Interviewer – Edward Hurme Wow. So it’s quite a complicated food web that’s continually evolving. Interviewee – Elizabeth Pennisi That’s right. Interviewer – Edward Hurme Well, Liz Pennisi, thanks for talking with me. Interviewee – Elizabeth Pennisi

Well thanks for having me. Science News Writer Elizabeth Pennisi writes about the Guppy Project in this week’s issue. Host – Isabelle Boni Music Interviewer – Sarah Crespi Finally today we have David Grimm, online news editor of Science. He’s here to give us a rundown of some of the recent stories from our online daily news site. I’m Sarah Crespi. So David, the first story we have today has made its circuit of the Internet. It’s about the effect of semen on ovulation, which sounds kind of mundane until you get into the details. Interviewee – David Grimm Right. Well, believe it or not, we actually don’t know – or until this study – we really didn’t know what the role of the fluid was in semen. Semen is primarily composed of sperm and the fluid that the sperm live in. And for a long time, scientists thought the fluid was basically just there to sort of keep the sperm happy and was sort of just a transport vehicle. But almost 30 years ago, actually, scientists began to wonder if there was some sort of factor in the sperm that induces ovulation. Now that’s not a concern for human women because human women are what’s called “spontaneous ovulators”. They ovulate on a regular cycle; they don’t need to be induced to ovulate. But there are a lot of animals that are called induced ovulators. Animals like camels and rabbits actually have to or, at least, scientists thought they had to have sex to sort of induce them to start ovulating and then basically have sex again. Interviewer – Sarah Crespi And how do they think that induced ovulation? Interviewee – David Grimm They thought that maybe just the physical stimulation of sex induced ovulation. But as I said, you know, as long as 30 years ago, scientists began to think, “Well maybe there’s actually something in the semen itself that’s inducing the ovulation; it’s not just the physical act of sex, but maybe when the male copulates with the female, he’s actually transferring something to the female that’s causing her to start ovulating.” This was a very controversial idea at the time and really hasn’t found support until now. Interviewer – Sarah Crespi Yeah, it’s really surprising that no one has gone through molecule by molecule and figured out what’s in semen.

Interviewee – David Grimm Exactly. And that’s exactly what the researchers did in this new study. They took llama and bull semen, and they spun it down just to get rid of the sperm and just to look at the fluid itself. And they did a lot of complex analysis to sort of try to separate it out molecule by molecule, and they actually injected some of these molecules into animals to see if they would induce ovulation. And after a lot of trial and error, they came up with a molecule called neural growth factor, or NGF. Interviewer – Sarah Crespi That sounds like something that we maybe have come across before. Interviewee – David Grimm Right. And that was…the scientists were a little disappointed. They thought they would find this mysterious new molecule that nobody knew about, but NGF is actually pretty well known. It’s actually already been linked to the development and survival of sensory neurons. So what the scientists found is not a new molecule but a new use for an old molecule. Interviewer – Sarah Crespi And so, you said this probably doesn’t have much use…this information probably doesn’t apply to humans, but it’s possible that it could have an effect. Interviewee – David Grimm In other experiments with cows, which are spontaneous ovulators like humans, the researchers found that NGF actually changed the timing and the development of eggbearing follicles. It also promoted the development and function of the corpus luteum, which is a temporary structure crucial to sustaining pregnancy. So even though NGF doesn’t appear to spark ovulation in humans, it may actually have other pregnancy boosting effects. Interviewer – Sarah Crespi But do the researchers know whether or not it’s actually present in human sperm? Interviewee – David Grimm Yeah. They actually have found it in human sperm, which suggested it it may be playing a function in our species as well. And that function may be to somehow promote pregnancy. And that could be really important for couples that are having trouble conceiving. Perhaps NGF could be a potential therapy. Interviewer – Sarah Crespi …or a test. Interviewee – David Grimm Exactly. Interviewer – Sarah Crespi

So this next story we have is about another problem that maybe surfacing from the overuse of antibiotics. Interviewee – David Grimm Right. Well, Sarah, antibiotics obviously are a “wonder drug”, and they’ve protected us from a lot of really nasty diseases. Farmers also use antibiotics to make cows, pigs, and turkeys gain weight faster. When these animals are on antibiotics, they tend to get a lot bigger, and that’s good for farmers because there’s more meat and more they can sell. This new study tackles the question, “If we gave antibiotics to people, would the same thing happen?” And that gets back to your original question, “Is there sort of a problem with us taking too many antibiotics?” Interviewer – Sarah Crespi Right. So how did they look at whether or not people were getting fat from the antibiotics? Interviewee – David Grimm Well what they did first was they actually looked at mice, and they added antibiotics to the drinking water of mice that had just been weaned. After seven weeks, the mice on antibiotics had significantly higher fat mass – they’re fatter basically – then a control group that was drinking just water. What they also looked at was the bacteria in the guts of these animals. Now, a lot of animals, including humans, have billions of microbial cells living in our guts, and they actually form these microbial communities, which we think are really important – or in the past few years have actually shown to be really important – for a variety of things: that they may help us break down nutrients, that they may be important for protecting us against certain diseases. This bacterial community is actually known as the microbiome. And one of the potential links between antibiotics and weight gain has been this idea that maybe antibiotics somehow muck around with these bugs in our gut, maybe they kill important bugs that would help us maybe digest nutrients more efficiently, or other processes that would be involved in metabolism, and by disrupting this you’re causing animals to gain weight. And indeed what they saw that in the mice that had gained weight, they still had the same number of microbes in their gut, but there was a difference in the composition of these microbes. Interviewer – Sarah Crespi So that’s mice. What about people? How can we test this in them? Interviewee – David Grimm Well, there was another study that actually also just came out which suggests that the link may hold in people as well. And this study looked at data from 11,000 children born in the U.K. in 1991 and 1992. And some of those children had been treated with antibiotics in the first six months of their lives and some of them hadn’t. And those who had been treated with antibiotics had a higher chance of being overweight at 10, 20, and 38 months of age. So this again suggests this correlation between the use of antibiotics and weight gain and this time in humans.

Interviewer – Sarah Crespi But there could be other explanations for this excessive weight in these children. Interviewee – David Grimm Exactly. This is just a correlation. Also, these changes in weight were really small. By the time these children reached six months and even seven years, there was no difference in weight between them and the children who didn’t get antibiotics. So this is a really controversial study. It’s a very intriguing idea, and both of these studies seem to give way to this idea that antibiotics can cause weight gain. And again, getting back to your original point, there’s a real overuse of antibiotics in the U.S. and in other countries, and this could be a potential side effect. But a lot of experts are saying these two studies are just way too preliminary; the data is not strong enough yet to firmly make a conclusion that antibiotic use leads to weight gain, at least in people. Interviewer – Sarah Crespi Gotta keep our eye out for that randomized study. Interviewee – David Grimm Right. Interviewer – Sarah Crespi Our last story is a new way to track deadly outbreaks. Interviewee – David Grimm Right. Sarah, this story has to do with a mysterious outbreak that happened at the National Institutes of Health in Bethesda, Maryland. In June of last year, a 43-year-old woman was admitted to the hospital, and she had a lung disease. Doctors knew she was carrying a highly resistant form of a deadly bacterium known as Klebsiella. But it didn’t make her sick, and they placed her in isolation, and they discharged her a little while later. No one else in the hospital seemed to have gotten infected with whatever she had. But a few weeks later, a bunch of other patients also came down with Klebsiella infections, and over the next three months 12 more patients contracted it, and six ended up dying as a result of these infections. And so there was this outbreak, and the doctors really weren’t sure what was going on because this woman didn’t have contact with any of these other people. But doctors really weren’t sure how this was spreading. This woman had no contact with these other patients that came down with it. Interviewer – Sarah Crespi We’re talking about a new way to track outbreaks. What did they do in this case? Interviewee – David Grimm Well what the researchers did was something that’s been called “genomic epidemiology”. And what that essentially means is they took a look at the genome of this Klebsiella bacterium. And what’s interesting about the genomes of bacteria is that when bacteria divide they accumulate mutations. And that means that when bacteria move from patient to patient or from person to person, they’re not exactly the same bacteria. There have

been small changes in the genetic code, which can help you distinguish one from the other. And that’s really useful for scientists because they can say, “Okay, this is the bacteria that was present in patient A, and these are the bacteria that are present in patient B.” Interviewer – Sarah Crespi So it’s like a puzzle where this patient has this set of changes, this other patient has those and more, and so you know who came after. Interviewee – David Grimm Exactly. And they can use that to sort of piece together the puzzle of how the bacteria moved from patient to patient. And when they did that, they found out that the female patient that was originally admitted to the hospital seemed to be the one that initiated this Klebsiella outbreak. But that the other three patients, they acquired her strain of the Klebsiella independently from each other, which is really weird. It wasn’t like she was…she passed it to one person, that person passed it to somebody else, and that person passed it to somebody else. Three other patients somehow got it from this woman even though they had no direct contact with her, and they all got it directly from the woman, they didn’t get it from each other. Interviewer – Sarah Crespi How did this bacteria jump from her to these other people without passing through anyone else? Interviewee – David Grimm Unfortunately, the doctors really aren’t sure how it got transmitted. What they do know is they had really strict hygiene regimens in place meaning that it should have been extremely unlikely for a person to pass the Klebsiella to another person or from this patient to pass it to a doctor who would have passed it onto another person. So what they think may have happened is Klebsiella is actually somehow living on the medical equipment that was being used with this patient, and that medical equipment got reused with these other patients. And that’s really surprising because Klebsiella wasn’t really thought to be able to survive in the environment; it was thought to be very sensitive and die very quickly. And so this research is not just telling us new things about how to track outbreaks but it’s telling us new things about this really dangerous bacterium, that it’s much heartier in the environment than we thought, and that could lead to new ways to combat it. Interviewer – Sarah Crespi And so this is a pretty new technology to, you know, sequence the whole genome of a bacteria and compare it with others. Is that a result of new technologies in sequencing? Interviewee – David Grimm Exactly. You know, sequencing is getting cheaper and cheaper. But even for this study, the scientists paid about $2000 per genome they sequenced. So this is a very expensive thing. It also took a long time. So if you’ve got a hospital that’s in the middle of an

outbreak, this sort of genomic CSI may sound like a good idea, but it’s going to be really expensive and take a really long time. Interviewer – Sarah Crespi All right. So what else do you have on the site week, Dave? Interviewee – David Grimm Well, Sarah, we’ve got a story about cell phone use and driving and why taking cell phones away from drivers may not prevent crashes. Also a story about singing apes on helium. So you just have to check out the site to read more about that. Interviewer – Sarah Crespi No audio? Interviewee – David Grimm No audio right now. And finally, for ScienceInsider, we’ve got a story about NIH cracking down on grant millionaires. Also a story about NASA’s plans to probe the interior of Mars. So be sure to check out all of these stories on the site. Interviewer – Sarah Crespi Thanks, Dave. Interviewee – David Grimm Thanks, Sarah. Interviewer – Sarah Crespi David Grimm is the online news editor for Science. You can check out the latest news and the policy blog, ScienceInsider, at news.sciencemag.org. Music Host – Isabelle Boni And that concludes the August 24th, 2012, edition of the Science Podcast. Host – Kerry Klein If you have any comments or suggestions for the show, please write us at [email protected]. Host – Isabelle Boni The show is a production of Science Magazine. Jeffrey Cook composed the music. I'm Isabelle Boni. Host – Kerry Klein And I’m Kerry Klein. On behalf of Science Magazine and its publisher, AAAS, thanks for joining us.

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