Marcus Byrne: The dance of the dung beetle

マーカス・バーン: フンコロガシの踊り

Translator: Joseph Geni Reviewer: Morton Bast

翻訳: Chiaki Takeuchi 校正: Misaki Sato

This is poo,

これはフンです

and what I want to do today is share my passion

今日はフンに懸ける私の思いを

for poo with you,

共感して頂きたいと思います

which might be quite difficult,

できなくても構いません

but I think what you might find more fascinating

しかしこの小さな生物と フンの関係には

is the way these small animals deal with poo.

興味を持てるのでは ないでしょうか

So this animal here has got a brain

この生物の脳は

about the size of a grain of rice, and yet it can do things

米粒ほどの大きさです しかし人間なら

that you and I couldn't possibly entertain the idea of doing.

試みることもないことを 彼らはするのです

And basically it's all evolved to handle its food source,

つまり彼らの食糧源である

which is dung.

フンの扱い方です

So the question is, where do we start this story?

さて何から話しましょう?

And it seems appropriate to start at the end,

やはりここはお尻からが いいでしょう

because this is a waste product that comes out

これは他の動物が出す 排泄物ですが

of other animals, but it still contains nutrients

まだ栄養が残っています

and there are sufficient nutrients in there

フンコロガシが生きていくのに

for dung beetles basically to make a living,

十分な量の栄養素です

and so dung beetles eat dung, and their larvae

彼らはフンを餌とし その幼虫も

are also dung-feeders.

またフンを食べます

They are grown completely in a ball of dung.

フンだけを餌にして 成長するのです

Within South Africa, we've got about 800 species of dung beetles,

南アフリカには800種の フンコロガシがいます

in Africa we've got 2,000 species of dung beetles,

アフリカ全体では2000種

and in the world we have about 6,000 species of dung beetles.

世界では6000種です

So, according to dung beetles, dung is pretty good.

彼らにとってフンは 相当のごちそうです

Unless you're prepared to get dung under your fingernails

指でフンをほじくれなければ

and root through the dung itself, you'll never see

フンコロガシ種の9割は

90 percent of the dung beetle species,

お目にかかれません

because they go directly into the dung,

彼らはフンの奥に

straight down below it, and then they shuttle back and forth

入り込み 地上のフンと

between the dung at the soil surface

地中の巣との間を

and a nest they make underground.

何度も往復するからです

So the question is, how do they deal with this material?

では 彼らはフンを どう扱うのでしょう?

And most dung beetles actually wrap it into a package of some sort.

大半は何かしらの形にまとめます

Ten percent of the species actually make a ball,

1割方は フンをボールのようにして

and this ball they roll away from the dung source,

元のフンから離れた 場所へと転がし

usually bury it at a remote place away from the dung source,

地中に埋めます

and they have a very particular behavior

彼らは独特の行動を取りますが

by which they are able to roll their balls.

その行動によってフンが転がせるのです

So this is a very proud owner of a beautiful dung ball.

ここに自慢げなフンの持ち主がいます

You can see it's a male

オスです

because he's got a little hair on the back of his legs there,

足の後ろに毛が生えていますからね

and he's clearly very pleased about what he's sitting on there.

彼はこの美しいフンの玉に ご満悦のようです

And then he's about to become a victim

ところが悲劇です

of a vicious smash-and-grab. (Laughter)

卑劣な強盗の 犠牲者となりました

And this is a clear indication

この行為はフンが貴重な

that this is a valuable resource.

食糧源であることの表れです

And so valuable resources have to be looked after

貴重な食糧源は特別な方法で

and guarded in a particular way, and we think

守る必要があります だからフンを遠くに

the reason they roll the balls away is because of this,

転がすのではないでしょうか?

because of the competition that is involved

フン獲得の競争が

in getting hold of that dung.

激しいからです

So this dung pat was actually -- well, it was a dung pat

このフンの塊--もはや過去形ですね

15 minutes before this photograph was taken,

この写真を撮影する15分前は塊でした

and we think it's the intense competition

この激しい競争こそフンコロガシが

that makes the beetles so well-adapted

フンを転がすに至った

to rolling balls of dung.

理由ではないかと思うのです

So what you've got to imagine here is this animal here

ではこの生物がアフリカの

moving across the African veld.

草原を横切る姿を想像して下さい

Its head is down. It's walking backwards.

頭を下に 後ろ向きに歩いています

It's the most bizarre way to actually transport your food in any particular direction,

食糧の運び方として これ以上ないほど突飛です

and at the same time it's got to deal with the heat.

しかも熱との戦いもあります

This is Africa. It's hot.

アフリカは暑いです

So what I want to share with you now

ではここで私と同僚が行った

are some of the experiments that myself and my colleagues

実験についてお話します

have used to investigate how dung beetles

フンコロガシは運搬と熱に

deal with these problems.

どう対処しているのでしょう

So watch this beetle,

このフンコロガシを見てください

and there's two things that I would like you to be aware of.

二つの点に注目して下さい 一つは

The first is how it deals with this obstacle

置かれた障害物に対する

that we've put in its way. See, look, it does a little dance,

対処法です ちょっと踊りましたね

and then it carries on in exactly the same direction

そして最初に向かっていた方向と

that it took in the first place.

全く同じ方向に歩いていきます

A little dance, and then heads off in a particular direction.

一瞬踊ってから 目的の方向へと進みます

So clearly this animal knows where it's going

彼らは行き先が 分かっているのです

and it knows where it wants to go,

行きたいところがわかっています

and that's a very, very important thing,

これは非常に重要なことです

because if you think about it, you're at the dung pile,

例えば自分が大きなフンの塊の中にいて

you've got this great big pie that you want to get away from everybody else,

ご馳走を独り占めしたい 遠くに運びたいわけです

and the quickest way to do it is in a straight line.

直進するのが 一番手っ取り早いですよね

So we gave them some more tasks to deal with,

そこで私達はこの子に 更に課題を与えました

and what we did here is we turned the world

彼の足元を回転させたのです

under their feet. And watch its response.

彼の反応に注目して下さい

So this animal has actually had the whole world

彼の世界は足元で今回転しました

turned under its feet. It's turned by 90 degrees.

90度回転したのです

But it doesn't flinch. It knows exactly where it wants to go,

しかし全く動じません 行きたい方向に

and it heads off in that particular direction.

再び向かっていきます

So our next question then was,

ではどうやって彼らは

how are they doing this?

行き先を認識しているのか?

What are they doing? And there was a cue that was available to us.

何をしているのか?　 私達は気がつきました

It was that every now and then they'd climb on top of the ball

彼らは時々ボールの上に登るのです

and they'd take a look at the world around them.

そして辺りを見回します

And what do you think they could be looking at

ボールの頂上に登って

as they climb on top of the ball?

彼らは一体何を見ているのでしょう?

What are the obvious cues that this animal could use

動物が利用できる手掛かりは

to direct its movement? And the most obvious one

何でしょう? 一番分かりやすいのは

is to look at the sky, and so we thought,

空でしょう では空の何を

now what could they be looking at in the sky?

見ているのでしょう?

And the obvious thing to look at is the sun.

空と言えば太陽です

So a classic experiment here,

そこで典型的な実験をしました

in that what we did was we moved the sun.

太陽を動かしたのです

What we're going to do now is shade the sun with a board

板を使って太陽を遮ります

and then move the sun with a mirror

そして鏡を使って全く違う

to a completely different position.

位置に太陽を動かします

And look at what the beetle does.

フンコロガシの反応を見てください

It does a little double dance,

少し踊って

and then it heads back in exactly the same direction

元の方向と全く同じ方向へ

it went in the first place.

歩いていきます

What happens now? So clearly they're looking at the sun.

彼らが太陽を見ていることが 明らかになりました

The sun is a very important cue in the sky for them.

彼らにとって太陽は 重要な手掛かりなのです

The thing is the sun is not always available to you,

でもいつも太陽があるとは限りません

because at sunset it disappears below the horizon.

日没後は水平線の下に 隠れてしまいます

What is happening in the sky here

空には私達には見えない

is that there's a great big pattern of polarized light in the sky

偏光の大きなパターンがあります

that you and I can't see. It's the way our eyes are built.

人間の目では感知できません

But the sun is at the horizon over here

しかし太陽は 水平線上にあります

and we know that when the sun is at the horizon,

太陽が水平線上にある時は--

say it's over on this side,

例えばこちら側にあるとすると

there is a north-south, a huge pathway across the sky

南北に大きな帯状の

of polarized light that we can't see

偏光パタ―ンができます 人間には見えません

that the beetles can see.

でもフンコロガシには 見えるのです

So how do we test that? Well, that's easy.

ではそれを証明しましょう

What we do is we get a great big polarization filter,

大きな偏光フィルターを用意します

pop the beetle underneath it, and the filter is at right angles

その下にフンコロガシを入れます フィルターは

to the polarization pattern of the sky.

空の偏光パターンの向きと 直角に置きます

The beetle comes out from underneath the filter

フンコロガシは フィルターの下から

and it does a right-hand turn,

出てきて 右に曲がります

because it comes back under the sky

元々の向きのパターンの

that it was originally orientated to

空の下に戻ったので

and then reorientates itself back

元々の方角へと

to the direction it was originally going in.

体の向きを変えたのです

So obviously beetles can see polarized light.

彼らには光の偏光が わかるのです

Okay, so what we've got so far is,

ここまでのおさらいをすると

what are beetles doing? They're rolling balls.

フンコロガシはボールを転がします

How are they doing it? Well, they're rolling them in a straight line.

しかも直線で転がします

How are they maintaining it in a particular straight line?

何故曲がらずに 移動できるのか?

Well, they're looking at celestial cues in the sky,

それは私達の目には見えない

some of which you and I can't see.

天空の手掛かりを 使っているからです

But how do they pick up those celestial cues?

ではその手掛かりは どう感知するのか？

That was what was of interest to us next.

それがまさに次の疑問でした

And it was this particular little behavior, the dance,

そしてこの踊りこそが 重要なのではないかと

that we thought was important, because look,

考えたのです 何故なら

it takes a pause every now and then,

このように時々休憩しています

and then heads off in the direction that it wants to go in.

そして再び行きたい方角へと 向かいます

So what are they doing when they do this dance?

この踊りが持つ意味は何なのか?

How far can we push them before they will reorientate themselves?

何が起こると彼らは向きを 変えるのでしょう?

And in this experiment here, what we did was we forced them

こちらの実験では まず無理矢理彼を

into a channel, and you can see he wasn't

この溝に誘導します 良く見ると特に

particularly forced into this particular channel,

無理強いはされていませんね

and we gradually displaced the beetle by 180 degrees

そして徐々に 180度ずらしていき

until this individual ends up going in exactly the opposite direction

最終的に元の方向とは

that it wanted to go in, in the first place.

逆方向へと向かわせます

And let's see what his reaction is

彼の反応を見てみましょう

as he's headed through 90 degrees here,

90度の場所を通り過ぎ

and now he's going to -- when he ends up down here,

歩き続け 最終的には

he's going to be 180 degrees in the wrong direction.

元の方向とは 180度反対方向を向きます

And see what his response is.

彼の反応を見てみると

He does a little dance, he turns around,

少し踊って 回転して

and heads back in this. He knows exactly where he's going.

再び溝の中を進みます

He knows exactly what the problem is,

彼は何が問題なのか理解し

and he knows exactly how to deal with it,

かつ対処法も心得ているのです

and the dance is this transition behavior

そしてこの踊りを転機に

that allows them to reorientate themselves.

彼らは正しい方向に 向き直るのです

So that's the dance, but after spending many years

以上が踊りについてです しかし灼熱のアフリカで

sitting in the African bush watching dung beetles on nice hot days,

何年もフンコロガシを 観察しているうちに

we noticed that there was another behavior

踊りに関連するもう一つの

associated with the dance behavior.

ある行動に気がついたのです

Every now and then, when they climb on top of the ball,

ボールに登ると彼らは時たま

they wipe their face.

顔を拭くのです

And you see him do it again.

またやりましたね

Now we thought, now what could be going on here?

これは一体どういうことなのでしょう?

Clearly the ground is very hot, and when the ground is hot,

明らかに地面は熱いです 地面が熱いと

they dance more often, and when they do this particular dance,

踊る回数が増えます そして踊ると

they wipe the bottom of their face.

顔の下の方を拭くのです

And we thought that it could be a thermoregulatory behavior.

これは温度調節をしているのではないか

We thought that maybe what they're doing is trying to

熱い砂を払い 顔に唾をかけて

get off the hot soil and also spitting onto their face

頭を冷やしているのではないかと

to cool their head down.

私達は考えたのです

So what we did was design a couple of arenas.

そこで二つの舞台を作りました

one was hot, one was cold.

一つは熱く 一つは涼しい状態です

We shaded this one. We left that one hot.

こちらは日陰に もう一つは日向に置きました

And then what we did was we filmed them with a thermal camera.

そして熱探知カメラで 撮影しました

So what you're looking at here is a heat image

今映っているのは 熱を映像化したものです

of the system, and what you can see here emerging

そしてフンの中から低温の

from the poo is a cool dung ball.

フンコロガシが出てきました

So the truth is, if you look at the temperature over here,

フンコロガシは低温 つまりクール

dung is cool. (Laughter)

かっこいい奴なのです(笑)

So all we're interested in here is comparing the temperature

私達の関心はフンコロガシと

of the beetle against the background.

周囲との温度差です

So the background here is around about 50 degrees centigrade.

周囲はおよそ５０℃です

The beetle itself and the ball are probably around about

フンコロガシとボールはおよそ

30 to 35 degrees centigrade,

30℃から35℃くらいでしょう

so this is a great big ball of ice cream

例えるなら 大きな アイスクリームの塊を

that this beetle is now transporting across the hot veld.

熱い草原の上を転がしていく ようなものです

It isn't climbing. It isn't dancing, because

まだ登っていません 踊っていません

its body temperature is actually relatively low.

体温が比較的低いからです

It's about the same as yours and mine.

私達の体温とほぼ同じです

And what's of interest here is that little brain is quite cool.

そして小さな脳みそも かなり低温です

But if we contrast now what happens in a hot environment,

ところが周りが熱くなると

look at the temperature of the soil.

地面の温度を見てください

It's up around 55 to 60 degrees centigrade.

55℃から60℃です

Watch how often the beetle dances.

頻繁に踊り始めましたね

And look at its front legs. They're roaringly hot.

前足を見てください 相当熱そうです

So the ball leaves a little thermal shadow,

ボールは熱の影を残しています

and the beetle climbs on top of the ball

そしてフンコロガシは ボールに登ります

and wipes its face, and all the time it's trying to cool itself down,

顔を拭き 常に体温を下げ 熱い砂を

we think, and avoid the hot sand that it's walking across.

避けようとしていると考えられます

And what we did then was put little boots on these legs,

そこで靴を履かせてみました

because this was a way to test if the legs

地面の温度を足で知覚するのか

were involved in sensing the temperature of the soil.

確認するためです

And if you look over here, with boots they climb onto the ball

ここを見て下さい 靴を履くとボールに登る

far less often when they had no boots on.

回数が格段に少なくなります

So we described these as cool boots.

クールブーツと命名しました

It was a dental compound that we used to make these boots.

靴は歯科治療用の 材料で作りました

And we also cooled down the dung ball, so we were able

またフンのボールも冷やしました

to put the ball in the fridge, gave them a nice cool dung ball,

冷蔵庫で冷やしたフンを与えたのです

and they climbed onto that ball far less often

するとボールが熱い時と比べて

than when they had a hot ball.

登る回数がかなり減りました

So this is called stilting. It's a thermal behavior

「高床歩き」です 人間も熱い砂浜を

that you and I do if we cross the beach,

歩くときにします

we jump onto a towel, somebody has this towel --

他人のタオルに飛び乗り

"Sorry, I've jumped onto your towel." --

「失礼 踏んでしまいました」 と言って

and then you scuttle across onto somebody else's towel,

別の人のタオルに 飛び移る

and that way you don't burn your feet.

足を火傷せずに済みます

And that's exactly what the beetles are doing here.

フンコロガシの行為も全く同じことです

However, there's one more story I'd like to share with you,

もう一つお話をしたいと思います

and that's this particular species.

それはこの種についてです

It's from a genus called Pachysoma.

パキソーマ亜属と呼ばれ

There are 13 species in the genus, and they have

13種が存在します 彼らには

a particular behavior that I think you will find interesting.

興味深い習性があります

This is a dung beetle. Watch what he's doing.

これはフンコロガシです 見てください

Can you spot the difference?

違いが分かりますか?

They don't normally go this slowly. It's in slow motion.

この映像は通常の 速度ではありませんが

but it's walking forwards,

ポイントは前向きに 歩いている点です

and it's actually taking a pellet of dry dung with it.

しかも乾燥した 小さなフンを運んでいます

This is a different species in the same genus

同じ属の違う種ですが

but exactly the same foraging behavior.

全く同じ採食行動を取っています

There's one more interesting aspect of this

もう一つ興味深いことがあります

dung beetle's behavior that we found quite fascinating,

何とフンコロガシは餌を探し

and that's that it forages and provisions a nest.

巣に持ち帰るのです

So watch this individual here, and what he's trying to do

この子を見てください

is set up a nest.

巣作りをしています

And he doesn't like this first position,

最初の位置は気に入らなかったのか

but he comes up with a second position,

二つ目の位置に巣を構えます

and about 50 minutes later, that nest is finished,

50分後 巣が完成し

and he heads off to forage and provision

食糧調達へと出かけます

at a pile of dry dung pellets.

乾燥したフンの粒達を目がけます

And what I want you to notice is the outward path

注目してもらいたいのは

compared to the homeward path, and compare the two.

往路と復路の違いです

And by and large, you'll see that the homeward path

復路のほうが往路より

is far more direct than the outward path.

遥かに真っすぐです

On the outward path, he's always on the lookout

往路では常に新しいフンが

for a new blob of dung.

周囲にないか探しています

On the way home, he knows where home is,

復路は自分の巣を目指して

and he wants to go straight to it.

真っすぐ帰るのです

The important thing here is that this is not a one-way trip,

重要なのは 普通のフンコロガシと違って

as in most dung beetles. The trip here is repeated

餌場と巣の間を何度も

back and forth between a provisioning site and a nest site.

往復していることです

And watch, you're going to see

そして南アフリカの犯罪が

another South African crime taking place right now. (Laughter)

繰り返されます

And his neighbor steals one of his dung pellets.

お隣が彼のフンを盗みました

So what we're looking at here

ここで目にしているのは

is a behavior called path integration.

経路積分と呼ばれる行為です

And what's taking place is that the beetle

フンコロガシには本拠地があります

has got a home spot, it goes out on a convoluted path

食糧を求めて外に出るときは

looking for food, and then when it finds food,

複雑な経路をたどり 食糧を見つけると

it heads straight home. It knows exactly where its home is.

真っすぐ帰宅します 場所が分かっているからです

Now there's two ways it could be doing that,

二つの可能性が浮上します それを確かめるために

and we can test that by displacing the beetle

餌場にいるフンコロガシを

to a new position when it's at the foraging site.

別の場所に移します

If it's using landmarks, it will find its home.

地上の何かを目印にしているなら 家に帰れます

If it is using something called path integration,

一方 経路積分を利用しているなら

it will not find its home. It will arrive at the wrong spot,

巣を見つけることはできません

and what it's doing here if it's using path integration

経路積分を 利用するということは

is it's counting its steps or measuring the distance out in this direction.

この方向に向かって 歩数 距離を測っているということです

It knows the bearing home, and it knows it should be in that direction.

基準となる巣がどの方角に あるべきか把握しているのです

If you displace it, it ends up in the wrong place.

位置をずらすと場所を間違えます

So let's see what happens when we put this beetle

ではこのフンコロガシを使って

to the test with a similar experiment.

実験してみましょう

So here's our cunning experimenter.

ここに狡猾な実験者がいます

He displaces the beetle,

フンコロガシを移動します

and now we have to see what is going to take place.

どうなるか見てみましょう

What we've got is a burrow. That's where the forage was.

ここに巣があります あそこにあった餌場は

The forage has been displaced to a new position.

新しい場所に移しました

If he's using landmark orientation,

目印を使っているなら

he should be able to find the burrow,

巣を見つけられるはずです

because he'll be able to recognize the landmarks around it.

巣の周りの目印が 認識できるからです

If he's using path integration,

経路積分を使っているなら

then it should end up in the wrong spot over here.

こちらの間違った場所に 到着します

So let's watch what happens

実験にかけられた フンコロガシが

when we put the beetle through the whole test.

どうなるか見てみましょう

So there he is there.

ここにいますね

He's about to head home, and look what happens.

家に帰ろうとしています どうなるか

Shame.

残念です

It hasn't a clue.

全く分かっていません

It starts to search for its house in the right distance

餌場から 正しい距離にあるはずの家を

away from the food, but it is clearly completely lost.

探していますが 完全に迷子になりました

So we know now that this animal uses path integration

つまり彼らは経路積分を使って

to find its way around, and the callous experimenter

移動しているのです 無慈悲な実験者は

leads it top left and leaves it. (Laughter)

左上に誘導して そのまま去ります

So what we're looking at here are a group of animals

ここに描かれているのは太陽を

that use a compass, and they use the sun as a compass

コンパスにして移動する

to find their way around,

生物です

and they have some sort of system

彼らは何かしらの仕組みで

for measuring that distance,

この距離が測れるのです

and we know that these species here actually

これらの種は 歩数を数えることが分かっています

count the steps. That's what they use as an odometer,

その仕組みを 距離計のように利用して

a step-counting system, to find their way back home.

巣に戻るのです しかしフンコロガシが何を

We don't know yet what dung beetles use.

利用しているのかは 解明されていません

So what have we learned from these animals

米粒ほどの大きさの脳を持つ

with a brain that's the size of a grain of rice?

この生物から 学んだことは何でしょう?

Well, we know that they can roll balls in a straight line

彼らが天空の手掛かりを使って

using celestial cues.

ボールを真っすぐに 転がせることが分かりました

We know that the dance behavior is an orientation behavior

踊るのは方角を決めるのと

and it's also a thermoregulation behavior,

温度調節のためだ ということも学びました

and we also know that they use a path integration system

そして巣に戻るときは 経路積分を

for finding their way home.

利用することも知りました

So for a small animal dealing with a fairly revolting substance

不快な物体を扱う こんな小さな生物からでも

we can actually learn an awful lot from these things

人間なら絶対しない彼らの行為を見て

doing behaviors that you and I couldn't possibly do.

学べることは多いのです

Thank you. (Applause)

ありがとうございます