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Class Supplement, Nature Podcast Digest Feb 18 2012

2012年3月21日

The original script of this podcast: http://www.nature.com/nature/podcast/v482/n7385/nature-2012-02-16.html
The audio file of this podcast: http://www.nature.com/nature/podcast/archive.html

種の絶滅加速の原因は、環境の変化により新種ができやすくかつ育ちにくくなる点にもある。環境がすぐに元通りになれば元の種に戻る。
Jeffrey S. McKinnon: Right. So in the 20th century, we saw an influx of nutrients into freshwater aquatic systems and this resulted in Eutrophication, where algae numbers go up dramatically. What you end up with is a reduction in oxygen levels and that influences the white fish quite directly, in that some parts of the lake might become difficult to inhabit, but more significantly their eggs don’t survive and hatch, because they’re deposited on the sediment and that tends to be an area, which is really affected in terms of the oxygen. The remaining fish are obliged to spawn shallower and that is likely to result in more hybridization with other shallow spawning white fish and then in addition the Eutrophication affects the prey distributions so the food available changes dramatically as well.
Geoff Marsh: And so this is coined in the literature as reversal of speciation. It seems to be the absolute correlate of how species come into being.
Geoff Marsh: And they mentioned in the paper that in some of those lakes that Eutrophication problem that nutritious pollution has been eliminated or greatly reduced. Can we expect a re-speciation of the previously extinct species?
Jeffrey S. McKinnon: Yeah that’s a really interesting question, isn’t it? So some recent theoretical models suggest that if the disruption is brief, you might get something of a re-speciation and have something like the original species re-emerged. They’re not going to be exactly the same, so it’s going to be a good deal of genetic exchange. But if the niches re-emerge then you might expect something like that to happen. What the time frame would be is harder to say and exactly at which point it becomes impossible for that happen is also more difficult to say at this point.

19世紀半ばの天体爆発の反射光を観測して爆発原因を探る。
Armin Rest: Eta Carinae is a star that has a great eruption, is one of the most massive stars in our galaxy and in 1838, it had an eruption and that eruption brightened the star, so it got about two to three times brighter than it was before and that was actually observed by astronomers in South Africa.
Geoff Brumfiel: And what I think is really neat about this paper is even though this happened over a hundred years ago, you guys have been able to see some light from the explosion, right?
Armin Rest: Yes. So, the big thing was eruptions like that happen not very often. So in the Milky Way galaxy, in our galaxy, there are only two known in the last few hundred years and unfortunately at the time, there was no modern instrumentation yet, so nobody could take images or pictures of this eruption and so you don’t know much about the eruption itself. And what we have been able to do is look at light, the most conflicted by dust and because it was conflicted, so it took a longer light path. It reached us 140 years after it actually reached the first time. So now we’re actually able to look at this great eruption with modern instrumentation.
Geoff Brumfiel: So what you’re saying is the light from the eruption went out and bounced off a cloud and came back to earth and the extra time it took to go out and be reflected was 140 years, so that you could still see an echo, you call it, of the original eruption.
Armin Rest: Because we can take a spectra, we kind of like get the fingerprint of this explosion, so we can figure out what was the temperature of the explosion and some of the other information. And one of the really surprising things that we found was that the explosion itself it is actually – or the eruption – is actually much cooler than we thought it will be. There have been other objects like this great eruption, observed in other galaxies and all of these other so called super novae impostors, they have much hotter temperatures and the great eruption of Eta Carinae was thought to be a prototype of this kind of eruptions and so now it turns out that the prototype is different than what it was a prototype for.
Geoff Brumfiel: So what do you think is actually going on with Eta Carinae?
Armin Rest: That’s actually still debatable. Nobody really knows what happened. Eta Carinae is a binary star and we know that the companion star, which is much, much smaller than Eta Carinae has some kind of impact on Eta Carinae. It has a very elliptical orbit, and whenever it is close to Eta Carinae, it’s so close that it actually disturbs Eta Carinae and one of the possibilities is that one of these encounters that happens every five years or so triggered something that caused this kind of outbursts. But what exactly happened, we don’t know yet, but now we’re actually able to get spectra from different times of this great eruption and so in a couple of years, I hope that we have solved this problem.

海に陸地ほど多くの種が存在しない原因は過去の大量絶滅らしい。
Geoff Marsh: And we’re sticking with fish for our first highlight. Contrary to the popular saying, there are not plenty of fish in the sea, but why. Marine environments cover about 70% of the earth’s surface, but contain only 15 to 25% of all estimated species. To find out why, a team from New York Stony Brook University studied ray-finned fish in marine and fresh water environments. This group represents 96% of all fish and half of all vertebrate species. Even though the marine environment is much larger and has more algae fuelling its food chain, they found that both environments had about the same number of species. They also discovered that all living ray-fins descend from a fresh water ancestor, suggesting that ancient extinctions have robbed the seas of their species. Nature liked this paper because it highlights the stark contrast in diversity between the land and the sea and it starts to explain why.

温暖化の結果、アメリカ合衆国の猛暑日の数が増加中。
Summer temperatures once considered exceptionally high have become more frequent across the United States in recent decades as a result of anthropogenic climate change. A US based team compared summer temperature extremes from 1950 to 1999 with simulations derived from 16 global climate models. Their models suggest that US summer temperatures will continue to rise as the century progresses. Even in the regions that have warmed relatively little so far, the chances of extreme temperatures will be at least 70% in any given year by the middle of this century.

ヒトの狂牛病の原因でイースト菌にもあるたんぱく質は自ら変形し自己複製するので、突然変異の鍵でもある。
Kerri Smith: Prion proteins are the Jekyll and Hyde of biology. They’ve long been associated with incurable degenerative diseases like Creutzfeldt–Jakob disease in humans and BSE in cattle, but they just might have a beneficial side too. A team led Susan Lindquist: In the popular imagination they are famous for causing a very bizarre and terrible human disease Creutzfeldt–Jakob disease and the basic idea was that you could have a protein that was one of your own brain’s protein and it would change shape and when it did that it could self-perpetuate that shape and then that could get passed onto another individual and it will all start all over again and you’d actually have an infectious disease that was caused by a protein rather than being caused by an exogenous nucleic acid point vector.
Kerri Smith: But they’re not all bad, are they. Prions in yeast at least might have a useful job to do.
Susan Lindquist: That’s exactly what our work is trying to show that prions, these proteins that can change shape and then self-perpetuate that change and shape and get another protein of the same type to change shape. It was actually perfectly normal and reasonable biological mechanism for doing some interesting things and back when I first started thinking about this actually I remember thinking, gee! This is such a great mechanism, why isn’t it used biologically?
Kerri Smith: Here in this paper then you’re providing some new evidence for the idea that these shape-shifting proteins, these prion proteins have something to do with evolution, have an evolutionary function.
Susan Lindquist: Yeah, they have something to do, we believe, with providing a survival advantage in the wild; we call it a bet-hedging strategy. So, basically when the protein shifts into this prioned shape, it changes the function and this decoding function and so the cell starts to make some proteins slightly differently used to make them and that can have all kinds of new biological traits. And you know, a lot of the times that they do that is very good but quite a few of the time they can do amazing things with these changes, what they couldn’t have done otherwise.
Kerri Smith: So, normally changes like this, you know, new biological traits arise because of mutations in genes, are you suggesting that prions can introduce changes too, and this isn’t a totally new hypothesis, but why is it so controversial?
Kerri Smith: Now let me see if I have got this straight then. So there are a very small proportion of these prion proteins that might have this function, but they are basically acting as little valves that just let natural variation out.
Susan Lindquist: Yeah, and then once it happens, what’s great about it is that it self-perpetuates so it actually becomes mechanism to inherit a new set of trait and then of course the whole things acts in reverse too, cells can lose the prionic state and they continue to grow and replicate. They can lose the prion.

アメリカ合衆国2013年度予算案の科学関連予算では疾病管理センター、環境保護庁、NASAへの割り当てが大幅にカットされたが全体的には思ったほど大ナタではないとのこと。
Ivan Semeniuk: I would say some areas that have been hit the hardest are places like the Centre for Disease Control and Prevention. They had a fairly large hit; also the Environmental Protection Agency has been on a steady decline. There is an effort there to preserve sort of core programs but it’s definitely losing money. NASA, NASA science in particular was hit hard this time around and you know one of the more visible manifestations of that is NASA has pulled out of the ExoMars project basically leaving ESA to go it alone , these would have been a pair of missions to Mars in 2016 and 2018 So NASA’s basically concentrating now on getting the James Webb space telescope into orbit and planetary science is taking a back seat as a consequence.
Ivan Semeniuk: I think most researchers are saying it’s better than it could have been, of course they would have preferred steadier gains but given the fiscal reality I think most agencies are feeling, they’ve done as well as they could.

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