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Interviewer: Shamini Bundell
Welcome back to the Nature Podcast. This week we’re looking at a mystery that’s emerged from a red supergiant star.
Interviewer: Adam Levy
We’re also looking at the bloom of algae and how clinicians are stopping genetic diseases from being passed on. This is the Nature Podcastfor August the 17th2017. I’m Adam Levy.
Interviewer: Shamini Bundell
And I’m Shamini Bundell.
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Interviewer: Shamini Bundell
Nearly everything living in the oceans today – from the tiniest shrimp to the mightiest whale – is there thanks to algae. Algae are tiny organisms that carry out photosynthesis and form the base of the food web in the ocean. Although they’re microscopic, algae are eukaryotes – more complex and much larger than bacteria and their rise to dominance in the oceans may have set the scene for even more complex life to emerge. In a Naturepaper this week, scientists have determined a new timeline for this transition. Anand Jagatia spoke to palaeo-bio-geochemist, Jochen Brocks, from the Australian National University and started by asking him what the oceans were like before algae conquered them.
Interviewee: Jochen Brocks
For most of Earth’s history, the organisms that were converting sunlight to energy and carbon dioxide to carbon were microscopic bacteria called cyanobacteria – the green coloured bacteria. Conversely, algae are much more complex organisms that have cell volume up to a thousand times larger and they are a composite of so-called protest eukaryotic complex organisms that swallowed the cyanobacterium about 1.6 or 1.7 billion years ago and became light-using photo-tropic organisms themselves.
Interviewer: Anand Jagatia
Why was that shift such a profound shift? What did it change? What were the impacts of that?
Interviewee: Jochen Brocks
When it comes to ocean ecology, size really matters, and bacteria are just very, very small and you cannot create complex ecosystems based on very small very creatures at the bottom of the food chain because the transfer of energy and carbon to high levels is very inefficient and so the transition from the world of bacteria to the world of much larger algae is probably one of the most profound transitions in Earth’s history. But the thing is, no-one really knew when that happened, so based on molecular clocks – plus, minus one billion years, we don’t know – fossils are extremely rare and they just do not tell us when this transition happened.
Interviewer: Anand Jagatia
And that’s what you were trying to work out in this paper. You were using molecular fossils. Can you explain what they are and how they work?
Interviewee: Jochen Brocks
The cell membrane contains molecules that are called sterols and when an organism dies, these molecules will be transferred to the bottom of the sea and turn into a hydrocarbon fossil, and in this way we can determine the relative concentration of molecules derived from algae and bacteria. And this gives us a measure of the importance of these groups of organisms. And what we did is we took sedimentary rocks from the time from about one billion years to the present and determined when algae became important, based on those molecules.
Interviewer: Anand Jagatia
So what did you find out then, when you reconstructed this timeline of the rise of algae using these molecular fossils?
Interviewee: Jochen Brocks
The timeline was extremely exciting. About 50 billion years before algae molecules become really abundant, it was the greatest climatic catastrophe in Earth’s history – so-called snowball earth event – which started 770 million years ago. At this point Earth froze over entirely, probably all the way to the equator and the even oceans were frozen 2 kilometres deep. The Earth – this snowball Earth – remained in this freezing state for 50 million years. And after it melted, we get a beautiful signal of biomarkers and rocks sitting directly above these melting blocks and there’s only bacteria. And then, a few million years later, the algae kick in. The concentration of algae molecules goes up by the effect of one thousand and from a very simple assemblage of molecules; we get full complicated diversity of those algae molecules that we still have today. So it’s really a black and white signal: it’s a signal from a completely bacterial world to a eukaryotic wold.
Interviewer: Anand Jagatia
Do you think then that snowball Earth was somehow responsible for causing this shift or triggering this shift?
Interviewee: Jochen Brocks
Yeah it’s very tempting to make that connection of course and this is all we can do in geology – to call out events that happened more or less at the same time but yes, there’s a very beautiful hypothesis: how this snowball is related to the rise of algae. In ecology, in ocean ecology, size really matters. For example, if phosphate is very low, cyanobacteria will win against the much larger algae and that’s pure physics because small creatures have a very large surface to volume ratio and by pure diffusion are more capable of taking up trace nutrients. The snowball – the melting snowball – might simply have provided a huge burst of nutrients into the ocean and tipped the scale towards some of the more complex creatures.
Interviewer: Anand Jagatia
What would be some of the alternative hypotheses from this data?
Interviewee: Jochen Brocks
There will be ecologists – marine ecologists – that say wow, if phosphate levels go up I would expect actually cyanobacteria to win the race. I believe it would be nitrogen levels or other nutrients that are more important. The second thing that might be controversial is the consequences. My idea is we get large creatures at the base of the food web that we are feeding the energy, that provided the food, for larger and larger organisms to appear, you get an escalatory arms race, escalatory evolution towards larger and larger size.
Interviewer: Anand Jagatia
So, if this is correct then we really have algae to thank for the whole ecosystems and animals that we have today?
Interviewee: Jochen Brocks
There is a very easy to understand analogy: if there was no plants going on land, there would also be no animals. It’s the same in the ocean. If we didn’t have the algae, we would not have any animals in the ocean. I wish I could show you a picture of the scale of the cyanobacterium next to an alga. It is really a mouse and an elephant. If you see this picture you can really appreciate what this change at the base of the food web actually did. A cyanobacterium is nothing you can feed on. It is tiny; it doesn’t provide too much energy, so algae at the base of the food web, next trophic level, are creatures like foraminifera or radiolarians: they are already enormous in comparison. They’re gigantic; they are the T-rex’s of the Precambrian age.
Interviewer: Shamini Bundell
That was Jochen Brocks speaking with Anand Jagatia. Jochen’s paper is available now at nature.com/nature.
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Interviewer: Adam Levy
Naturereporter, David Cyranoski, has written a feature this week looking at an approach to stop genetic diseases from being passed on. And this topic is incredibly close to home for David.
Interviewee: David Cyranoski
We have a genetic defect in my family which I’ve seen the effects of first hand over generations and it’s a polycystic kidney disease and kicks in when you’re 40 or 50 and destroys the kidneys. So I’ve seen the kind of damage that it can do. The money and the suffering that goes into all of this is amazing.
Interviewer: Adam Levy
There’s a lot of talk about the promise of gene-editing in treating conditions like this. You may remember that just 2 weeks ago we discussed a study that used CRISPR to gene-edit human embryos and rid them of a genetic mutation. These techniques still have to overcome many ethical and technical hurdles before they could help families like David’s. But there’s an approach that’s already an approach that’s available now: pre-implantation genetic diagnosis and screening. The idea is simply to use IVF and check embryos for the genetic disease before implanting one in the womb. It completely side-steps many of the issues of gene-editing and David is already thinking about the impact it could have on his family.
Interviewee: David Cyranoski
It could only be 10 people or something like that and they could have this disease out of the family forever.
Interviewer: Adam Levy
Pre-implantation genetic diagnosis (PGD) is already being used around the world, including in the UK and the US. David reports from China and his feature looks at the rapid uptake of PDG that has taken place across this huge country.
Interviewee: David Cyranoski
It’s really growing quickly. There were only four clinics in China that were proved licensed to do it in 2004 and now there are 40 clinics that can do it and these clinics are huge.
Interviewer: Adam Levy
In part, this rapid boom has been made possible by researchers like Sunney Xie. He’s a chemist at Harvard and has worked on a technique for reliable genome sequencing that is now used for some PDG in China. He told me about the first disease that his technique was used to screen.
Interviewee: Sunney Xie
It is a disease that gave rise to bone tumours. So, starting from age 2, this person in this case would have tumours removed every 2 years.
Interviewer: Adam Levy
If the parents were to conceive a child the conventional way, there would be a 50/50 chance that this debilitating disease would be passed on from the father to the child. But Sunney and his collaborators were able to make sure that the embryo that was implanted didn’t have the mutation and a few months later, on the 19thSeptember 2014…
Interviewee: Sunney Xie
The baby girl, she was perfect and when we went to feed her she was smiling at us. She didn’t even cry so she was a perfect baby.
Interviewer: Adam Levy
For Sunney, this baby girl brings home just why PDG is so important in combatting these inherited conditions. His genome sequencing technique has helped more than 200 families in China and Sunney is hopeful that PGD could one day achieve even more.
Interviewee: Sunney Xie
If you continue to do this, you will eliminate these major diseases after several decades. And I think people want to do that. They admit it’s necessary to do that and it’s not controversial.
Interviewer: Adam Levy
Screening embryos may be less controversial than gene-editing but there’s still ethical concerns. In the west, there’s deep anxiety that approaches like this could one day lead to eugenics where society permits designer babies which are chosen for their desirable traits, not just their absence of disease. But David explains that there are big differences in how this is spoken about in China.
Interviewee: David Cyranoski
In China the word ‘eugenics’, the word they use to translate the nineteenth century concept of improving the gene pool actually means healthy birth, so it’s a completely untainted word.
Interviewer: Adam Levy
David thinks this has a big influence on reducing the stigma surrounding the approach. But Sunney doesn’t think this is what has driven the growth in PDG. Last year China ended its policy of one child per family. This created a huge group of older women who are suddenly allowed to have a second child but needed fertility treatment to fall pregnant. This gave them the option to screen embryos before implantation.
Interviewee: Sunney Xie
It’s not like people are insensitive about the classical issues. It’s just that there are more people that want babies free of these genetic disorders. There’s a real need.
Interviewer: Adam Levy
David agrees that China isn’t adopting these techniques thoughtlessly. In some ways it seems China is actually more restrictive than certain western countries.
Interviewee: David Cyranoski
I think people are going into this very carefully which might not be the image that you have from outside of China. One interesting example is sex selection in China. That’s something that in the US is completely fine to do and if you go on chat rooms in the US you can hear a lot of people just very nonchalantly… yeah, I have one son so next time I want to have a girl and I’m going to use embryo selection for it. But that’s something in China that would be ethically, they think it’s wrong and it’s also illegal.
Interviewer: Adam Levy
As PDG continues to grow, what’s legal and what’s socially acceptable may change. But Sunney already feels that PDG is an invaluable weapon in the battle against genetic diseases.
Interviewee: Sunney Xie
I feel like this is the most useful thing I’ve ever done. I never even imagined that the technique that we developed for fundamental research was able to help people so quickly.
Interviewer: Adam Levy
That was Sunney Xie and reporter David Cyranoski. To find out more about pre-implantation genetic diagnosis in China, head over to nature.com/news where you’ll find David’s feature.
Interviewer: Shamini Bundell
Still to come, Californian climate research and a battle over bones. That’s in the News Chat but now we’re joined by Charlotte Stoddart reading this week’s Research Highlights.
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Interviewer: Charlotte Stoddart
We’re doomed. The mutant ants are coming. Okay, we’re not doomed but two teams have independently created the first gene-edited ants: terrifying. Both groups used CRISPR technology to edit the gene behind the industrious insect’s sense of smell. Both sets of mutants lost their ability to smell as may have been anticipated. This meant they could no longer use pheromones to communicate. How antisocial. No, seriously. Both studies did find the new colonies to be less social. Take a nosey at those two papers over at cell.
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Interviewer: Charlotte Stoddart
Some people chew gum to stave of smelly breath and some people chew to stop themselves chomping on chocolate. But how about chewing gum to detect dental disease? That’s right, clinical candy. Scientists have made a biosensor to detect peri-implant disease. That is an inflammation of the gums cause by dental implants. Saliva from patients causes the gum to release a strong, bitter taste – yuck. This not so tasty tool could one day be used anywhere, anytime, reducing the cost and complexity of diagnosis – sweet. Get your teeth stuck into the full story at Nature Communications.
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Interviewer: Adam Levy
Across America people are preparing for Monday’s total solar eclipse. Not wanting to miss out on the eclipse mania, this week we are publishing an animated film on what scientists have learnt from studying eclipses throughout history.
Interviewer: Shamini Bundell
I think it’s fair to say that the biggest star in science this week is the sun but it’s not the only one making headlines. Scientists from Chile and Germany have been taking a close up look at a much more distant star: Antares – the brightest star in the constellation of Scorpius. Antares is 800 times larger than our sun. It’s what’s known as a red supergiant, a group which includes the biggest stars in the universe by volume. And it formed when a heavy star burnt through its fuel and collapsed, causing an enormous surge of heat that inflated its volume and gave it a cooler, redder outer layer. Red supergiants are constantly losing mass, seeding their environments with elements for the next generation of stars and planets. What drives this mass loss is a puzzle and one that feeds into a bigger mystery about when a star will end its life in a giant supernova explosion. Understanding what’s going on at its surface could provide some clues. Now, for the first time, astronomers have mapped out the movements of the hot gas on Antares’ surface but the results aren’t quite what they expected. To find out how they managed to study the surface of this distant red supergiant, reporter Lizzie Gibney spoke to astronomer Keiichi Ohnaka.
Interviewee: Keiichi Ohnaka
Although red supergiants are the biggest stars in the universe, even with the biggest telescope in the world at the moment, they look like just a mere bright light source or light point.
Interviewer: Lizzie Gibney
And so you wanted to get an actual picture of this star’s surface. So, how did you go about doing that?
Interviewee: Keiichi Ohnaka
We are combining multiple telescopes, in our case 3 telescopes, to form a virtual patched-up gigantic telescope – as large as 82 metres. And with this gigantic telescope we can achieve a very high sharpness. We can take a very sharp photo of the surface of stars.
Interviewer: Lizzie Gibney
And it’s not exactly a photo that you’re taking is it? What is it that you are able to determine about the surface from your map?
Interviewee: Keiichi Ohnaka
What’s new in our work is in addition to just taking a photo of the surface of stars, we managed to measure the motions over the surface of stars, so in other words, the velocity of the gas at each position on the surface of the supergiant.
Interviewer: Lizzie Gibney
And what did this motional velocity of the map show us then about the surface of Antares?
Interviewee: Keiichi Ohnaka
It looks very chaotic or turbulent. This means we can recognise a number of very large blobs or bubbles or cells, and as large as the radius of the star itself and these bubbles are moving in a very turbulent manner with up to 20 kilometres per second. So, some bubbles are upwelling and some bubbles are downdrafting.
Interviewer: Lizzie Gibney
And is there a good explanation for this kind of frantic bubbling that we see?
Interviewee: Keiichi Ohnaka
At the moment no, because the bubbling motions are reminiscent of convection, the ones we see, for example, in boiling water. We compared the observations to the latest convection selection for red supergiants and we found out the current theoretical simulation cannot explain the motions in the bubbles and the atmosphere – the size of the atmosphere that we observed. So what we can say at the moment is convection alone cannot explain the turbulence.
Interviewer: Lizzie Gibney
Okay, so it’s a bit of a mystery. Are there any good ideas about what might be causing this turbulence then?
Interviewee: Keiichi Ohnaka
So one idea is, for example, it might be related to magnetic fields, for example, as we see on the surface of the sun and the magnetic fields are actually detected in every supergiant but there is no theoretical simulation or reliable theoretical simulation that can be compared with the observations. So at the moment it might be but we can’t say magnetic fields. And another idea is, for example, radiation heating molecules in the atmosphere might cause such turbulent motions but again this is still just an idea and somebody has to make a model, a theoretical model, based on this idea.
Interviewer: Lizzie Gibney
And are there any observations you can do to help clear up this mystery and figure out what’s causing the turbulence?
Interviewee: Keiichi Ohnaka
Yes, so the one idea is to do some three dimensional diagnostics throughout the atmosphere, so what we did this time is to have the map of the motions of the material in the upper atmosphere of Antares but we can’t do the same thing at a different height within the atmosphere. So, for example, closer to the surface, and further away from the surface of the star. In this way we can have a three dimensional idea of how the materials move within the atmosphere from very close to the surface of the star and at great distances from the star. Then we might have a better idea what is really causing these turbulent motions
Interviewer: Shamini Bundell
Interviewer: Adam Levy
Time now, as always, for the News Chat and Dan Cressey has joined us in the studio. Hi Dan.
Interviewee: Dan Cressey
Hello.
Interviewer: Adam Levy
So it’s no secret that it has become a little bit harder to be a climate scientist in America in recent months but California is looking to actually do something about this.
Interviewee: Dan Cressey
Yes, once again California is going out on its own in certain ways. And this time round they’re looking at or at least considering setting up a California Climate Science and Solutions Institute which would be a new mega funding institute to give lots of money to climate scientists.
Interviewer: Adam Levy
It sounds like a noble idea. Is it on the verge of being built? How close actually are we?
Interviewee: Dan Cressey
It’s very much in the early stages of development. This idea is being floated around. It’s got some pretty impressive backers, notably a whole bunch universities based in California whose names would be very familiar to any of our listeners, but yeah, at the moment it’s not entirely clear that this is going to happen.
Interviewer: Adam Levy
So, early days, but is there talk of where the money to actually fund this would come from?
Interviewee: Dan Cressey
Yes, people who are supporting this are talking about millions of dollars per year flowing through this new institute and there are suggestions that this could come from California’s cap and trade system which is, of course, another example of the state just deciding it’s going to get on and do things about climate change off its own back without waiting for the rest of the US and some cases the rest of the world to catch up.
Interviewer: Adam Levy
Are there particular types of research that they’re going to be funding? Would it be solutions or understanding the climate system?
Interviewee: Dan Cressey
Yeah, as the name ‘Science and Solutions Institute’ implies, they’re kind of trying to cover the spectrum here. So, although, again we’re at very, very early days, the suggestion is that this would be both basic and applied research projects.
Interviewer: Adam Levy
Is it just California that’s taking these steps to protect climate science or are there other parts of the US which are also making moves like this.
Interviewee: Dan Cressey
It’s not just California. On the other side of the country in New York, there is a similar, albeit it seems slightly smaller initiative doing this, which is Columbia University – the science team – is also looking for an alliance of universities and people to come together and support research and they already have what you could consider a kind of trial project under way with a centre for climate and life science at Columbia which currently has raised a much smaller sum than they’re talking about in Columbia – about 8 million dollars – but yeah, that’s already going on out there.
Interviewer: Adam Levy
You mention at the beginning that this isn’t the first time California has gone out on its own relative to the rest of the country. What other examples are there of California going rogue?
Interviewee: Dan Cressey
Well there’s the cap and trade system that I already mentioned. I think the other really good example in comparison to what they’re doing here would be its stem cell research institute which was kind of brought in at a time when the rest of the country was looking a little bit leery about stem cell research, California just said no, we’re going to do this. And they set up an institute that distributed millions of dollars to stem cell researchers.
Interviewer: Adam Levy
Let’s move on now to our second story. It won’t come as a surprise to many of our listeners that there’s lots of work going on to sequence DNA from ancient humans and ancient animal bones but it’s actually become very competitive to do this.
Interviewee: Dan Cressey
Yes, and we say in our story that this has become a game of bones and obviously you can’t do this science if you don’t have the bones. You can’t get DNA out of them and analyse that DNA and make all of these amazing findings which have been reported in Natureand elsewhere about who these people were and where they might have come from and where they might have gone to and the cultures they carried around. The first thing you need to do this work is a bone. And that means, if you’ve got that bone, you might want to keep it to yourself and get to do the cool science yourself.
Interviewer: Adam Levy
So some institutions actually seem to be hoarding bones?
Interviewee: Dan Cressey
That’s certainly what’s being suggested by three archaeologists who’ve written a letter to Naturethis week and they say there needs to be better co-ordination and fairer access to these samples to ensure, firstly that everyone gets a shot and secondly that there is enough left to go around and people can do the kind of replication studies and ensure that we have samples for future advances in technology that might allow us to do more.
Interviewer: Adam Levy
When we say we need to make sure there are bones left for future advances, is that because the bones are damaged in some way when they’re tested?
Interviewee: Dan Cressey
Yeah, this is destructive testing. A lot of science you can do by just looking at a bone, maybe scanning it, but in this case you need to basically crunch it, take a piece of it, and do your analysis on that. So if everyone in the whole world got to do all of the analysis they wanted on all of these ancient bones, there would be no ancient bones left.
Interviewer: Adam Levy
Are there any institutions which are being good examples to the rest of the community and are actually sharing their bones?
Interviewee: Dan Cressey
It’s important to say that a lot of researchers already do share their samples around and are very generous sending things to other research groups. One of the places that we sight in this story is a centre in Israel that’s a kind of clearing house for animal bones in ancient DNA studies and if you dig up a bone in Israel you can send it to this central facility and they will deal with a lot of these questions.
Interviewer: Adam Levy
Is this something that is actually likely to change at all in the future because it seems like all the incentives are to keep hoarding bones because as you say, if you have the bones, you have the power.
Interviewee: Dan Cressey
So this happens in a lot of scientific fields but the issue here is that ancient DNA is a really, really hot subject at the moment and people want to sort this problem out so they can get on with doing the science and getting all those papers which are going to end up probably in the pages of Natureand wherever.
Interviewer: Adam Levy
Dan, thanks a lot for joining us. For more on those ancient bones and for this California initiative on climate, head to nature.com/news.
Interviewer: Shamini Bundell
That’s all we’ve got time for this week but if you’re excited about the upcoming eclipse in America then make sure to check out our YouTube channel, youtube.com/NatureVideoChannel. We’re looking at the lessons we’ve learnt from eclipses over the years.
Interviewer: Adam Levy
See you next week. I’m Adam Levy.
Interviewer: Shamini Bundell
And I’m Shamini Bundell.
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