Why mutation is not as random as we thought

Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week, challenging the dogma of gene evolution…

Host: Shamini Bundell

And how chiral nanoparticles could give vaccines a boost. I’m Shamini Bundell.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

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Host: Shamini Bundell

First up on the show, reporter Charlotte Stoddart has been digging into a somewhat controversial finding that could rewrite the way geneticists think about evolution.

Interviewer: Charlotte Stoddart

We often think about mutations in the genome as a bad thing. Mutations can stop essential genes from working or cause cancer. But mutations are also a source of genetic variation, and this variation enables populations to adapt and survive.

Interviewee: Jianzhi Zhang

Every organism produces mutations and, simply put, mutations are errors that are made when DNA is copied.

Interviewer: Charlotte Stoddart

That’s Jianzhi Zhang, an evolutionary biologist at the University of Michigan. By looking at the DNA and counting mutations, biologists can work out the mutation rate – the frequency with which mutations occur.

Interviewee: Jianzhi Zhang

In the early twentieth century, people found that the rate that mutation is produced is independent of the consequence of the mutation. Regardless of whether this mutation is going to help you or is going to damage you, the mutation rate is independent of that.

Interviewer: Charlotte Stoddart

The mutation rate for each species, it seemed, was pretty stable. This insight won two scientists a Nobel Prize in 1969 and has been a tenet of evolutionary biology ever since. Here’s Michelle Trenkmann, a senior editor of biology at Nature.

Interviewee: Michelle Trenkmann

The general idea is that mutations accumulate across a genome randomly, and so we would expect that the acquisition of these mutations would happen at the same frequency everywhere in the genome.

Interviewer: Charlotte Stoddart

However, when we look at genomes, we see more mutations in some parts than others. This is because of selection. When mutations happen in parts of the genome that code for important genes, then very often those cells don’t survive. The harmful mutations are weeded out by selection, so we don’t see them.

Interviewee: Michelle Trenkmann

Most studies in molecular evolution rest on this assumption that the acquisition of mutations should be random across the genome, and the differences that we observe in populations are based on selection rather than differences in the mutation rate.

Interviewer: Charlotte Stoddart

Because mutation rates are assumed to be fairly constant over long time periods and fairly constant along the genome, researchers use the mutation rate to help work out how closely related two species are or how quickly a particular species or gene has evolved. You can imagine scientists’ surprise then when earlier this month a paper was published that questions these assumptions. The paper reports that the mutation rate in the plant Arabidopsis thaliana is not the same throughout the genome.

Interviewee: Detlef Weigel

The headline finding is relatively simple: more important genes mutate less.

Interviewer: Charlotte Stoddart

That’s Detlef Weigel, who led the research at the Max Planck Institute for Developmental Biology in Tübingen, Germany. His finding – that different parts of the genome mutate at different rates depending on how important they are – challenges a fundamental assumption in biology and suggests that mutation rate and natural selection are not two distinct evolutionary forces. The reality is more blurry. One of the first scientists to read the paper was Jianzhi Zhang.

Interviewee: Jianzhi Zhang

They said that the mutation rate is 58% lower inside the genes than right outside the genes. And it’s 37% lower in essential genes than in non-essential genes. These are quite big numbers.

Interviewer: Charlotte Stoddart

To get these numbers, Detlef’s team looked at data from mutation accumulation lines. Michelle Trenkmann, who handled the paper for Nature, explains what this means.

Interviewee: Michelle Trenkmann

These are basically organisms, so in this case these plants, these Arabidopsis lines, which propagate under reduced selection. So, basically, there are no selection pressures or very limited selection pressures on these plants, which allows them to measure just the mutation rate but not the effect of selection.

Interviewer: Charlotte Stoddart

The plant that the team studied has a mutation rate of roughly one mutation per genome, per generation. So, the team had to analyse many genomes over many generations to observe enough mutations to be able to pick out patterns in the data. Detlef says that they weren’t looking to overturn a well-established principle about mutation rates.

Interviewee: Detlef Weigel

Much of what we do in science, you have some intuition from observing the natural world. Based on that intuition, you formulate a formal hypothesis. Then you conduct experiments to test that hypothesis. In this case, it would have been a really outlandish hypothesis, I think, for us to say, ‘Well, wouldn’t it be great if conserved genes or important genes mutated less.’ Everybody would have said, ‘You are completely out of your mind!’

Interviewer: Charlotte Stoddart

First author Grey Monroe was actually looking for gene knockouts – genes which have lost their function because of mutation. He was exploring the data…

Interviewee: Detlef Weigel

And then he observed this curious pattern, that when he looked at genes, that as you approached the gene, if you will, you could see mutation rate was relatively high, and then inside genes it was much lower. And then, when you got again into the region that was not genic, mutation rates were higher again. So, he saw this pattern and was scratching his head a little bit, and then it was really a wonderful story of chance, of the prepared mind. He was sitting next to a doctoral researcher, Thanvi Srikant, and Thanvi was looking at this pattern and she said, ‘You know what, this pattern that you see there looks really similar with what I see some of the chromatin marks that I’m interested in.’

Interviewer: Charlotte Stoddart

Chromatin is the genome – the DNA – plus the proteins, such as histones that help to organise and package the genome. Grey found that the mutation rate was correlated with certain chromatin features or modifications.

Interviewee: Detlef Weigel

Then he went back to the literature and he saw, yeah, there’s actually all this biochemical literature that says that chromatin modification is important for DNA repair.

Interviewer: Charlotte Stoddart

This finding was important because it suggested a mechanism – a possible explanation for why mutation rates might vary across the genome. Cells have machinery that can repair damage to DNA, reducing the number of mutations. Chromatin modifications affect DNA repair, and DNA repair affects the mutation rate. The team knew that suggesting a plausible mechanism might convince other scientists that their finding was real. In 2012, a paper was published in Nature that also found lower mutation rates in important genes. In this case, the work was done in bacteria, in E. coli, and the researchers couldn’t explain their findings. Detlef recalls the reaction.

Interviewee: Detlef Weigel

This was such an amazing observation that, right away, the smartest minds in evolutionary biology started to pluck this apart. They made very good arguments why this could never evolve. They said a single gene mutates so few times, for that single gene to mutate even fewer times is just not possible.

Interviewer: Charlotte Stoddart

That’s because for a gene to mutate less, the lower mutation rate needs to give the offspring a big enough advantage that it’s selected for, that it can evolve. But for a single gene, mutations are so rare that this just doesn’t happen.

Interviewee: Detlef Weigel

This is where our discovery comes in. We noticed that important genes, as a class in the genome through chromatin modification, they are marked in a different way. And so, hundreds or even thousands of important genes then behave sort of as a unit. And because it’s this large unit, then selection is possible, and we show in the paper some calculations that this would work. So, this is, in a way, the insight that the selection is not on the individual gene but on all these important genes as one coherently behaving class.

Interviewer: Charlotte Stoddart

Detlef and his team now had a plausible mechanism. But they were still not confident enough in their finding to publish.

Interviewee: Detlef Weigel

So, because we knew this would be so controversial, we were really, really worried that we had somewhere made a mistake and just too much groupthink. So, one of the first things we thought was, ‘Okay, who could be the harshest critics of our work?’ So, we sent them our paper and I said, ‘Please, before we go live with this, please let us know.’ And we got quite harsh criticisms from our colleagues, and we took these criticisms on board.

Interviewer: Charlotte Stoddart

They also posted their results in a Google Doc and invited comments via Twitter.

Interviewee: Detlef Weigel

So, after we had gone through this sort of pre-peer review, if you will, only then did we actually send it for publication.

Interviewer: Charlotte Stoddart

This is when Jianzhi Zhang saw the paper.

Interviewee: Jianzhi Zhang

I didn’t believe it in the beginning. I reviewed this paper for multiple rounds. In the first round, I think the analysis was not very straightforward, but I suggested a more straightforward way of analysis, which the authors took, and also they enlarged their data, so it became more and more convincing.

Interviewer: Charlotte Stoddart

Detlef and Jianzhi are looking forward to seeing what other researchers do next. For example, to test if Detlef’s findings hold true in other organisms as well.

Interviewee: Jianzhi ZhangBased on the mechanisms that this paper proposed, this phenomena should also exist in other organisms. There’s no reason that it only exists in Arabidopsis. So, I’m very curious whether this is also true in other organisms.

Interviewer: Charlotte Stoddart

If it does turn out that mutations rates vary across the genome in other organisms too, as Jianzhi anticipates, it will be a big deal for the field.

Interviewee: Jianzhi Zhang

This will change fundamentally how we view mutation, selection and evolution because our current view is that mutation is completely random, right. When you observe something – for example, you observe a particular gene evolves faster than another gene – our assumption is that the mutation rate is the same. So, if the evolution rate is different, it must be because the selection is different on these two genes. But their data suggests it may not be entirely due to selection, although selection may still be at work, but a large part of this variation is actually due to mutation rate variation. So, our explanation of a lot of phenomena would be changed.

Interviewer: Charlotte Stoddart

Will Jianzhi need to re-evaluate some of his own work?

Interviewee: Jianzhi Zhang

Yes, definitely. I think not just me. Probably half of the evolutionary biologists will have to re-examine their previous papers to see whether the interpretation is correct.

Host: Shamini Bundell

That was Jianzhi Zhang from the University of Michigan in the US. Before him, you heard from Detlef Weigel from the Max Planck Institute for Developmental Biology in Tübingen, Germany, and Michelle Trenkmann, the senior editor here at Nature who handled the paper. If you want to read more, we’ll put a link in the show notes.

Host: Benjamin Thompson

Coming up, we’ll be finding out about how the handedness of a nanoparticle can affect its action on the immune system. Right now, though, it’s time for the Research Highlights, read by Dan Fox.

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Dan Fox

Centuries-old plant remains might have revealed the key to political power in the ancient Andes – beer spiked with hallucinogens. From AD 600 to 1000, the Wari people ruled large swathes of the Andean highlands. Now, researchers have analysed parts of plants found at a ninth-century Wari outpost in modern Peru, identifying seeds from the vilca tree and large quantities of fruits from the Schinus molle tree. The Wari used the fruit to brew a beer-like beverage known as chicha. They probably added the vilca seeds, which are hallucinogenic, to the beer and consumed the brew at a feast. The communal use of vilca-laced beer is thought to have strengthened social ties. Throwing big boozy parties would thus have helped the Wari leaders to reinforce the empire’s political control. The authors suggest that because obtaining the vilca seeds and preparing the drink was difficult, the Wari elite further cemented their authority by offering memorable feasts that could not be replicated anywhere else. Feast on that research in full in Antiquity.

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Dan Fox

An enormous breeding colony of fish over twice the size of Paris has been discovered in icy waters near Antarctica. The Jonah’s icefish lives in Antarctic waters, where it excavates a shallow nest in the sea floor for its eggs, which are then usually guarded by the male until they hatch. Researchers surveying an area in the Weddell Sea called the Filchner Trough found a vast region packed with icefish nests, with some 60 million active nests covering an area of at least 240 square kilometres. The breeding colony probably supports a food web that includes everything from starfish to Weddell seals. The researchers have called for this unexpected abundance of life – the largest known uninterrupted colony of breeding fish on Earth – to be protected. Read that research in full in Current Biology.

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Interviewer: Benjamin Thompson

The shape of a molecule is often fundamentally important to how it interacts with the world around it. And it’s not just which bits are sticking out at which angles. In many cases, it’s whether a molecule is left- or right-handed that determines its action. This ‘handedness’ is known as chirality, and we’ll explain more about that in a moment, because this week in Nature, a team have published a paper looking at the role chirality might play in activating the immune system and how it might be used to help boost the actions of vaccines. I wanted to find out more about the paper, so I gave Bryden Le Bailly, a senior editor here at Nature, a call. Bryden, how are you doing? Hello, welcome to the show.

Interviewee: Bryden Le Bailly

Yeah, thanks for having me. I’m doing well. How are you?

Interviewer: Benjamin Thompson

Yeah, I’m doing okay. So, long-time listeners to the podcast will recognise your voice, Bryden, but you haven’t been on for a little while so, for the benefit of those who don’t know you, what do you do here at Nature?

Interviewee: Bryden Le Bailly

Yeah, sure. I’m one of the senior editors on the manuscript editor team at Nature, and I handle papers on the interface between chemistry and biology, so basically how do we make molecules and then how can we use them to interrogate biology or to make drugs. And then on the other side, what does biology do in sort of chemical terms, so how does a drug bind its target, and what does that do. So, that’s the kind of thing that I’m interested in.

Interviewer: Benjamin Thompson

Well, that’s why I wanted to reach out to you as well because we’ve got a paper in Nature this week that’s kind of related to many of those things, and specifically it’s looking at chirality, and that’s maybe a word that’s familiar to people from maybe school. What is chirality when we’re talking about sort of chemistry and biology?

Interviewee: Bryden Le Bailly

Yeah, sure, so chirality is all about the arrangements of atoms in a molecule. So, most organic molecules are made up on carbon – that’s why they’re organic molecules – so we’re mainly made up of carbon. And when you think about a carbon atom, it can have four other different groups that are connected to it. And if we think about those four different groups – so let’s say A, B, C, D – if you stick them on those groups, you could have them, for example, in a clockwise direction or you could have them in a counter-clockwise direction. And you then have the same molecule but two forms of it that are effectively mirror images, and they are what’s called enantiomers.

Interviewer: Benjamin Thompson

And I guess you can think about these mirror-image molecules like your left hand and your right hand.

Interviewee: Bryden Le Bailly

Exactly. We always use the sort of left and right hand analogy as the perfect way, and so, yeah, your hands are sort of macro-scale enantiomers basically.

Interviewer: Benjamin Thompson

And this has been quite key to a lot of drug discovery – how these different sort of left and right hand mirror images work.

Interviewee: Bryden Le Bailly

Absolutely, so biology is inherently chiral. For example, your famous DNA double helix – that’s right-handed. And similarly, the amino acids that make up your proteins, they’re all what we call left-handed amino acids. And so, when we think about drug discovery, we then also need to think about making molecules that are chiral. It’s really important we get that because if you have the wrong enantiomer, so the opposite mirror image, you can have different effects. One example of that recently is with ketamine, where we knew that mixture of the two enantiomers was commonly used as a horse tranquilizer or anaesthetic, but recent efforts have shown that it actually works as an anti-depressant. But the left- and right-handed forms of ketamine, which is a chiral compound, do different things and they have different anti-depressant effects. So, now we understand that we actually want to have one of those hands and not the other, and that’s the same when you’re making drugs generally.

Interviewer: Benjamin Thompson

And you’ve talked a lot about sort of organic molecules there, but in this work they’re looking at chiral nanoparticles made of gold. And to try and get a bit of a sense of scale then, how big is a gold nanoparticle?

Interviewee: Bryden Le Bailly

One really interesting thing here is that actually they’re very big compared to a lot of biology. Proteins are on the order of maybe one or a few nanometres in size. The nanoparticles we’re talking about here are 120 nanometres, so it’s 100 times bigger than the sort of things that you would expect to interact with in biology. For example, the receptors you would get in biology we’d want to typically target for drug discovery. So, we don’t really know if they would interact with biology in the same way. And so, what the paper here does is they basically say, ‘Right, we’re going to prepare these left- and these right-handed chiral gold nanoparticles, and we’re going to see if they elicit different responses,’ and they’re specifically looking at immune responses. And they find that actually they do. They do actually have different immune responses and that’s down to their inherent chirality.

Interviewer: Benjamin Thompson

Why have they done that? Is there previous work showing that these nanoparticles could induce an immune response or something like that?

Interviewee: Bryden Le Bailly

There’s not really that much out there because it’s really a difficult question. The immune system is very complicated. I mean, in the era of COVID, we’re currently understanding immune responses to viruses, for example, and immune responses to nanoparticles are going to be very complicated, and so this paper goes a long way to unpicking how that might work. And so, what they show here is that you can take a left-handed nanoparticle, in this case, and actually it’s going to give you a stronger immune response than the right-handed nanoparticle. And what’s really important about this paper is they don’t just stop there. They actually then look at how that works. And this understanding is, for me, what is really interesting here because it’s guiding people towards how, for example, you can develop chiral nanoparticles for a range of biomedical applications.

Interviewer: Benjamin Thompson

And one of the things that the team look at in this work, Bryden, is how these nanoparticles, which seem to be inducing an immune response, could be used to maybe boost how vaccines work.

Interviewee: Bryden Le Bailly

Yeah, absolutely. So, often with a vaccine, you’ll have what’s called an adjuvant, which is an additive to enhance the immune response to that vaccine itself. And here they show with mice that if you add these nanoparticles to a flu vaccine, you actually get more antibody production with the left-handed nanoparticles than you do with the right-handed nanoparticles. So, this paper basically shows that we can have a role of chirality in adjuvants.

Interviewer: Benjamin Thompson

And Bryden, as an editor, you often look at these kind of interfaces, as you say, between chemistry and biology. Where do you see this maybe going, do you think?

Interviewee: Bryden Le Bailly

There’s been a lot of proof-of-principle stuff done with nanoparticles in general in, for example, drug delivery. That’s been a really big area of nanomedicine. But I think this paper is interesting because to me it starts a research question. It actually says, ‘What else can be done now we understand that there is a difference in response between these two nanoparticle left- and right-handed forms? The fact that this then signals to other researchers that this can be useful in a variety of different fields, that’s the long-lasting impact. That’s why we really like the paper.

Interviewer: Benjamin Thompson

Obviously, we need some words of caution – this is early work that was done in mice.

Interviewee: Bryden Le Bailly

Absolutely. There’s lots more research to be done, and that’s why I say it’s exciting. I’ll be very interested to see what more comes out of this avenue of research in the next 5-10 years.

Interviewer: Benjamin Thompson

That was Nature’s Bryden Le Bailly there. Look out for a link to the paper by Xu et al. and a News and Views article in this week’s show notes.

Host: Shamini Bundell

Finally on the show, it’s time for the Briefing chat, where we talk about some of the stories from the Nature Briefing. So, Ben, what have you been reading about this week?

Host: Benjamin Thompson

Shamini, this is a story that I read about in Cosmos. Now, we heard earlier in the podcast about a finding which is maybe challenging existing views on evolution, and this is, I guess, kind of along similar lines. But in this case, instead of sort of thinking about evolution, it’s thinking about scavenging and in particular it revolves around the Australian marsupial the Tasmanian devil.

Host: Shamini Bundell

Ah, so the Tasmanian devil famously doesn’t spin round and round very fast like in the cartoon. I know that. But is it a scavenger?

Host: Benjamin Thompson

So, it is a scavenger, Shamini, and the Tasmanian devil is a carnivorous marsupial, about the size of a small dog, and it has a reputation for being quite grumpy. And what’s interesting about this work is that scavengers are kind of expected to eat whatever they can find, right? That’s kind of the nature of what it is. If there’s some food there, you best have it, you best scavenge it, I suppose, because you don’t know where your next meal is coming from. And this article looks at a research paper that says that’s not necessarily the case for the Tasmanian devil. It seems that they can be potentially quite picky, selective eaters.

Host: Shamini Bundell

Oh, because, yeah, the definite stereotype would be eat any old thing I could find lying about. How are the researchers basically checking out what’s on the menu for these Tasmanian devils?

Host: Benjamin Thompson

Well, in this case, Shamini, what’s happened is they’ve analysed the eating habits of 71 Tasmanian devils across 7 sites. Now, these were caught in the wild and a whisker was taken from them, and then they were released. And this whisker carries kind of imprints of the animal’s diet over time. And it’s something we’ve talked about before – kind of looking at isotopes to get a sense of what’s going on. And one of the quotes from the researchers is ‘these animals have broken the laws of scavenging,’ which is kind of neat. So, what they’ve found is that only 1 in 10 appeared to kind of eat everything and anything that was about, but the rest of them seem to favour things that they kind of liked, like maybe wallabies or possums and so forth. And this varied from animal to animal, so it’s kind of a new way of thinking about scavenging behaviour.

Host: Shamini Bundell

Oh, wow, so you can tell that they’re clearly not just eating at random. And I love that they have different individual tastes. That’s wonderful.

Host: Benjamin Thompson

And from what I understand, this kind of behaviour isn’t shown in other scavengers, and the question as to why, I suppose, is an interesting one too. I mean, it’s thought that maybe they can afford to be picky because they’re not competing where they live with any other scavengers, so they can take a bit of time to choose what they eat maybe.

Host: Shamini Bundell

So, it sounds like Tasmanian devils are living a pretty good life. Is this research going to be able to benefit them?

Host: Benjamin Thompson

Yeah, I mean you say living a pretty good life, Shamini. Actually, the story of the Tasmanian devil is quite a sad one. They’re under threat. Numbers have dropped hugely for a variety of reasons, but not least because of this contagious cancer that’s called Devil Facial Tumour Disease, which has absolutely ripped through populations of these animals, and so some populations have been kept in captivity until it’s safe to release them. So, knowing that they have potentially a dietary preference could be utilised to make sure they’re being fed appropriate diets and what have you to help care for them until they can be let out back into the wild.

Host: Shamini Bundell

Oh, brilliant. Anything that’s helping out the Tasmanian devils is looking great. So, I have also got a story this week mentioned in the Briefing. It’s an article in The Observer. It’s very excitingly titled ‘Archaeology’s sexual revolution’. It’s a really exciting look at how in archaeology and bioanthropology the way that you tell the sex of skeletons has changed, and skeletons that people have always maybe assumed are a man might actually have been a woman, and sort of vice versa.

Host: Benjamin Thompson

Right, so you said the way it was done has changed then. I imagine there must be some sort of technological breakthrough maybe which has enabled this to happen?

Host: Shamini Bundell

Yeah, exactly. Well, I mean, quite a few different technological ways that you can do this. So, one way that they would traditionally try to sort of sex skeletons, sometimes you can tell from the bones, like hip bones, but sometimes you can’t or those bones are missing. They would often look at what’s called like grave goods, so what are these people buried with, especially if it’s sort of fancy people being buried with their possessions. And a lot of the time, they would find men buried with swords and weapons and things, and women more likely to be buried in jewellery. But there’s one particular famous example where, once they got the ability to do DNA testing, they had this sort of famous Viking warrior that they’d found, and they did some DNA testing and were like, ‘Ah, actually, this was a woman and not a man,’ which sort of made them stop and sort of re-think everything. And another example mentioned in the article was this find of a cemetery in Italy where they had sort of several graves, and one of the graves had two skeletons in it who were holding hands. And everyone was like, ‘Ah, it’s so beautiful, this man and this woman who will be in love forever,’ and they used a really cool technique, a sort of really recent technique actually, to figure out that both of these skeletons were male, and so then that raises questions of whether it was a romantic relationship and all sorts of debate about that.

Host: Benjamin Thompson

So, it seems like maybe a two-pronged thing here then, Shamini, so re-evaluating things technically but also re-evaluating things societally as well.

Host: Shamini Bundell

Yeah, exactly. So, some researchers very much think that, well, inevitably, archaeologists have put our sort of modern biases onto what was happening in the past. Of course, all of these are very blunt tools, so a lot of them, what they’re really telling you is whether this individual had an X or a Y chromosome, but that’s obviously sometimes not entirely clear cut. So, there was one example of a medieval skeleton from Finland which they were able to do more of a DNA analysis on, and they found that this individual had XXY chromosomes, which is Klinefelter syndrome, which would mean that they would have appeared male, but this individual was buried in female clothing but also with swords. So, it’s more clues as to how these people lived even though we can never be really sure. And there’s a lot of times when this kind of stuff is going to be really useful. A new technology in particular, so for example, if you’ve got prepubescent, really hard to look at the bones and look at the sex. If you’ve got sort of like ancient hominins, like Lucy was mentioned, like Australopithecus and Neanderthals and all that, they might not have the same sort of bone structure as us, so these new techniques are really useful. And one particularly cool technique was then the DNA is too damaged, they found a technique to look at the proteins in tooth enamel, which is much better preserved, and they can look at the protein, and it’s a particular protein that’s sort of influenced by a gene that’s either on the X chromosome or the Y chromosome, so again, you can tell something about the genetics of that individual.

Host: Benjamin Thompson

So, do you think this will lead to maybe a wholesale re-evaluation of skeletons that have been uncovered from throughout antiquity?

Host: Shamini Bundell

Yeah, so people are sort of going back and looking and sort of, yeah, re-assessing. In particular, I think there is some interest in these rare occasions where skeletons are sort of buried together, so like double graves, in going back and checking those, especially if they’ve all been assumed to be male-female pairs based on the fact that they’re double graves.

Host: Benjamin Thompson

Well, thank you for bringing that one, Shamini. And listeners, if you’d like to read either of these stories, we’ll put links to them in the show notes, alongside a link on where you can sign up for the Nature Briefing, to get more stories like this delivered directly to your inbox.

Host: Shamini Bundell

That’s all for this week. As always, you can keep in touch with us via Twitter – we’re @NaturePodcast – or send us an email – we’re podcast@nature.com. I’m Shamini Bundell.

Host: Benjamin Thompson

And I’m Benjamin Thompson. Thanks for listening.