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Class Supplement, Nature Podcast Digest, Review Homework Worksheet 1

2012年6月1日

The audio file of this podcast: http://www.nature.com/nature/podcast/archive.html

The original script of this podcast: http://www.nature.com/nature/podcast/v484/n7393/nature-2012-04-12.html

☆Read the following part of Nature Podcast Digest 2012/04/12, and do the following tasks.

Matthew C. Fisher: Well, here we have a large box full of newts (イモリ) which are just coming back into the water after being hibernated over winter(冬眠後) and what’s common with all of these newts here is that they’re infected (感染している)by a very highly virulent lineage of the fungus(毒性の高い種類の菌), Batrachochytrium dendrobatidis which has been spreading like wild fire around the world, causing a number of species extinctions (種の絶滅)that we’re seeing. The Mallorcan midwife toads on the other hand have got a very similar lineage of the fungus, but it doesn’t kill, at least not in the level that we see with the strain that’s infecting these newts. So it seems that not only we’re moving these very highly aggressive forms of fungi (菌たち)around, but we’re also moving other less aggressive forms around and what really kind of comes together is that we’re actually just doing a lot of moving around with absolutely everything. There’s just this whole global rearrangement going on (世界規模で(生物の)再配置が起こっている), not only in fungi but also in bacteria(バクテリア), viruses(ウイルス), vertebrates(脊椎動物), pretty much anything you care to mention.

Geoff Marsh: So would you say that all these recent outbreaks(病気の大流行) in the wild animal populations are down to human activity?

Matthew C. Fisher: Yes, all of these disease emergences are symptomatic, essentially of globalization. (主にグローバル化による症状)

Geoff Marsh: And so your research in this lab, working on this one particular pathogen (病原体), fits into a wider global picture of the impacts, fungal pathogens are having on wild animal species.

Matthew C. Fisher: Yes, it does. So, we now know there are probably more than three and half million species of fungi out there. Only a handful of which are known to cause serious disease in vertebrates, but importantly that number is increasing year on year. So scientists at the United States are finding that this new species of fungus Geomyces is causing the destruction (壊滅)of the North American bats and they’re seeing fungi that were previously thought to be non-virulent (無毒)causing decline in coral (サンゴ礁)in the Caribbean (カリブ海)and it goes on and on. So, yes, there’s a lot of fungal biodiversity (菌の生物としての多様性)out there, and we’re finding out that more and more that has this rather nasty characteristic.

Matthew C. Fisher: Well initially, theory shows that as the host becomes rarer, as pathogens dry, the density(密度) is down, then the pathogen itself tends to go extinct before the host (宿主)does and then the host bounces back (復活する)and this is the normal density dependent cycle that you see with the host and its pathogen. However, fungi have this set of characteristics that enable them to wade (切り抜ける)these limiting mechanisms, so particularly what fungi are very good at doing is persisting(しぶとく生き続ける) in the environment or infecting many, many species that are generally parasites. So that means that when you’ve driven your susceptible (影響を受けやすい)species down to very low levels, the chances are that you’re also holding out (持ちこたえる)in another tolerant (耐性がある)species that you keep on releasing infected stages into the environment (感染状態で環境内に放出し続ける)and eventually overwhelm (圧倒する)that susceptible species and bang it’s gone.

Matthew C. Fisher: Well, as you rightly point out, there’s a huge industry that goes into protecting crops against fungal pathogens, but you just can’t do that, in natural wild life populations. It really is an incredibly difficult problem. Certainly on the island of Mallorcan where we have these beautiful Mallorcan midwife toad tadpoles, we’ve actually gone there and we’ve caught every animal in the valley and treated it with an antifungal drug (殺菌薬で治療し)and we’ve kept it in a bio-secure facility (無菌設備)until we hope that the fungus has disappeared from the environment and then we put them back. So, essentially, we’ve tried this environmental mitigation (緩和)and it really just hasn’t worked(うまくいっていない). So, yes, we have to be very creative in solutions that we use against these pathogens in the future, but essentially, the bottom line is just don’t introduce them in the first place.(要するに、そもそも菌を環境に持ち込むなということです。)

Geoff Marsh: I mean, it’s very obvious to put a value on crop species that might be being infected by fungal pathogens, how do you put a value on these wild populations of frogs and newts etcetera?

Matthew C. Fisher: Well, this is of course a very difficult problem. We don’t really understand the wider value of the ecosystem services (生態系がしている仕事)that these species produce. Some scientists in America have attempted to do this and they’ve costed out the services that the bats do every year by eating pests (コウモリが毎年害虫を食べることによってなす仕事を換算した)and this turns out to be a very big number, three and a half billion dollars per year, perhaps more, and similarly, you know, these frogs are going to be providing services which are essential to us; however, we’ve never actually put a number to this and this is really important these days because to actually recognize the value of these species and the loss owing to these new diseases that accrue (これらの種の価値と結果として生じる新しい病気による損失を実際に認識する為には)we really need to understand the actual financial cost that they provide to us.

Tasks

1. Answer the following question in English. Why do more species go extinct by fungus infection compared to infections with other pathogens? Use your own words. In other words, make it short and simple.

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2. Summarize other points in the digest in English. Say it aloud, and write it down here.

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You could use the following Japanese summery to do these tasks.

物の病原体となる菌がグローバル化と共に世界中に広がっている。通常の病原体の場合、宿主(菌が寄生する生物)の数が減ると病原体も消失し、宿主の種は復活する。しかし菌類の場合、多種多様の宿主に付いているため、消失することはなく、弱い宿主は絶滅する。植物と違い、除菌はうまくゆかない。菌の移動阻止が最も有効な対策。全てを見積もることは不可能だが、菌によって失われる生態系が果たしている役割をお金に換算すると相当な額になることは確か。

☆他の記事の使い方: 1) プリント1ページ上のURLで音源をタウンロードして聞く。(スクリプトもダウンロード可能)2) プリントの英文で内容確認。3) 要約を言って書いてみる。4) プリントの和文要約を見て確認。

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