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