振動

Good Vibrations—Key to Insect Communication

（Soundbite of 1）Treehoppers Chirping）

David Greene （Host）： What you’re hearing are treehoppers. These are insects that communicate with each other by making leaf stems vibrate.

（Soundbite of Crickets Chirping）

Greene： And what you’re hearing now are crickets， whose chirps contain encoded messages that convey life or death information. Scientists discovered this vibrational world of insects through close listening. That’s what we’re calling our project on decoding nature through sound. Today， NPR’s Christopher Joyce and audio producer Bill McQuay of the Cornell Lab of 2）Ornithology profile two scientists who reveal how these insects manage their complex social lives with sound.

Christopher Joyce （Byline）： Lots of animals， including ourselves， can feel sound as well as hear it. Elephants， for example， can communicate by 3）rumbling at low frequencies we can’t hear—whales too.

Bill McQuay （Byline）： But you don’t have to weigh a ton to rumble.

Joyce： No， in fact， you

don’t have to be bigger

than a pea， like a

treehopper， a curious

little sap-sucking insect

that lives on the stems

of leaves. Biologist Rex

Cocroft is a researcher at

the University of Missouri

who studies treehoppers.

In 1999， a team from

NPR’s Radio Expeditions

program 4）rendezvoused

with him at a 5）locust tree in a backyard in Virginia.

McQuay： He was pressing a phonograph needle up against the stem of a leaf.

Rex Cocroft： I’m just trying to get a good contact here between the 6）stylus on the phono 7）cartridge and part of the plant. Mind you， this is not in the manufacturer’s instructions for these phono cartridges.

McQuay： There’s no guidebook for listening to treehoppers. Cocroft created his own. He knew that needles in those cartridges are exquisitely sensitive to vibration. So he connected a wire from the cartridge through an amplifier and to his headphone.

Joyce： And this is what he heard.

（Soundbite of Treehoppers Chirping）

Cocroft： All the signals we’re hearing are signals produced by males.

Joyce： They’re vibrating their 8）abdomens at incredibly highspeed to make an assortment of bizarre sounds. Some are

for attracting females. And some are aimed at other males.

（Soundbite of Treehoppers Chirping）

Cocroft： We’re hearing that the kind of purring （imitating treehopper sounds） sound—are sounds that males give either when two males meet each other or when they’re mate-searching on a branch.

McQuay： Normally， we can’t hear any of this. The sound travels inside the stem.

Joyce： So how did such a weird insect telegraph evolve？ Well， Rex says treehoppers， like many insects， have very sensitive legs. And they stand around on stems， which are good at transmitting vibrations. So they used what nature gave them. It gave them a way to communicate. And as social animals， that’s what they need to thrive.

Cocroft： They have so many different forms of social behavior and grouping. And once you have animals living in groups， then you have all sorts of interesting possibilities for communication.

（Soundbite of Treehoppers Chirping）

Joyce： Such as scouts tapping out a signal to others that there’s a predator nearby.

McQuay： Technology revealed this hidden vibrational world， things like phonograph needles and devices called accelerometers that measure vibration. And that ushered in a new generation of insect 9）eavesdroppers.

Laurel Symes： So I’m here tonight in Fort Worth， Texas.

Joyce： Like Laurel Symes， a biologist at Dartmouth College. Symes tunes into vibrations we can hear made by crickets.

Symes： So now we’re looking at a male tree cricket. So the way that the cricket makes sound is to use its wings. And if you look closely at one of the wings， it has a whole bunch of little tiny teeth on it. And that rubs against a vein on the other wing and it causes the whole wing to vibrate sort of like a drum head would.

Joyce： Crickets don’t have a big vocabulary like treehoppers. What they do have is a remarkable ability to discriminate tiny differences in sound frequency， a skill worthy of a concert violinist. It’s the females that can do this. And the reason—Bill， you want to explain that？

McQuay： So you go out in the woods and you hear crickets chirping. They’re males of several species all saying come and get me. To us， they sound pretty much the same， but they aren’t. The speed at which they rub their wings together， the pulse rate， varies from species to species. And Laurel discovered that females know that.

Symes： And they’ve evolved to be very， very good at recognizing the exact thing that they’re looking for.

Joyce： Which is the pulse rate of a potential mate from their own species？ And there’s a good reason to be very picky.

Symes： If you don’t get it right， you lose. Joyce： You lose if you pick the wrong species of male to mate with. You won’t make little crickets.

McQuay： Laurel actually rigged up a clever experiment to test how good the females were. She 10）synthesized the chirps of various male crickets on a computer. They were identical to the real sound and she played them for two species of females through a speaker. Here’s one chirp， a male at 43 pulses per second.

（Soundbite of Crickets Chirping）

McQuay： The females of one species immediately hustled over to the loudspeaker. The other females—not interested. Then Laurel used this chirp at 51 pulses per second.

Joyce： Just eight pulses a second faster than the first one.

（Soundbite of Crickets Chirping）

Joyce： And the females of the other species， the one that ignored the first sound， they got all romantic with the speaker. So what’s happening is that each species of cricket， there are about a hundred and forty in North America， has divided up the sound 11）spectrum into sonic niches. Each species identifies with its own frequency like a radio station. And they do it with a brain the size of a pin head.

Symes： And that’s one of the things that makes them cool is they have really simple sensory systems and still they 12）parse this really complex world.

Joyce： Symes spent years recording crickets to figure all this out. She goes wherever they are like up a tree on the Mexican border where border patrol agents wondered just what the heck she was doing.

Symes： You’re part way up a tree and， you know， the vehicle pulls up and stops and they flip on their light， you know—what you doing out here tonight， ma’am？ Oh， I’m just collecting crickets. They believed me； that’s what amazed me.

Joyce： Now she’s so tuned into the cricket world she thinks and sounds like them.

Symes： （Imitating cricket） That’s about 60.

McQuay： Yes， Laurel can do 60 pulses a second herself. She says it’s a lot like a humming refrigerator.

Joyce： In fact， she’s always listening to vibrations； crickets， fans， air-conditioners.

Symes： We think that we really know what’s going on out there and we’re getting this tiny slice of all of the sound in the world.

Joyce： As for Rex Cocroft， he says most of this sonic world still remains to be discovered.

Cocroft： It’s a very intense world and so little of it really still has ever been listened to that it is very possible for anyone to go out into a weedy field or roadside and tap into those plants and hear very interesting sounds that no one has ever heard before.

Joyce： Sounds shaped by millions of years of evolution and the struggle to survive.

（角蟬鳴叫的片段）

戴維·格林尼（主持人）：你們聽到的是角蟬的叫聲。這些昆蟲是通過使葉莖振動來相互交流的。

（蟋蟀鳴叫的片段）

格林尼：你們現在聽到的是蟋蟀聲，它的叫聲包含著傳遞生與死訊息的編碼信息。科學家通過近距離的探聽發現了昆蟲的振動世界。我們把這個項目稱為通過聲音解碼自然。今天，國家公共電臺的克里斯托弗·喬伊斯和科內爾鳥類實驗室音頻制作人比爾·麥奎伊將講述兩位科學家揭秘這些昆蟲是如何通過聲音來應付他們復雜的社交生活的故事。

克里斯托弗·喬伊斯（撰稿人）：很多動物，包括我們自己，都可以在聽到聲音的同時感受到聲音。比如，大象可以通過發出我們聽不到的低頻率的低沉聲音進行交流，鯨魚也是如此。

比爾·麥奎伊（撰稿人）：但是你的重量不需要達到一噸才能發出低沉的聲音。

喬伊斯：不必，實際上，你只要和豌豆一般大小就可以了，比如角蟬——一種奇異的以葉莖為食的吸汁小昆蟲。生物學家雷克斯·寇克勞福特是密蘇里大學的研究員，角蟬是他的研究對象。1999年，國家公共電臺的《電臺探索》節目的一組工作人員與他在弗吉尼亞州一個后院的槐樹下會面。

麥奎伊：他將一根唱針壓在一片葉子的莖上。

雷克斯·寇克勞福特：我只是想盡量讓留聲機拾音器的唱針和這株植物的一部分有較好的接觸。注意，這并不在這些留聲機拾音器制造商的操作指南之列。

麥奎伊：沒有任何聽取角蟬叫聲的指南手冊。寇克勞福特創造了自己的方式。他知道留聲機拾音器上的唱針對振動異常的敏感。所以，他將拾音器的擴音器與耳機用電線相連。

喬伊斯：這就是他聽到的聲音。

（角蟬鳴叫的片段）

寇克勞福特：我們所聽到的所有信號都是雄性角蟬發出的。

喬伊斯：他們以難以置信的高速度振動他們的腹腔，發出各種奇特的聲音。一些聲音是為了吸引異性，而另一些則針對其他同性。

（角蟬鳴叫的片段）

寇克勞福特：我們聽到那種低沉的聲音（模仿角蟬的叫聲），是兩只雄性角蟬見面時或者他們在樹枝上尋找配偶時傳遞出來的。

麥奎伊：通常我們聽不到這些聲音。這些聲音在葉莖里傳播。

喬伊斯：那么，這些奇異的昆蟲是怎樣發出訊息的呢？呃，雷克斯說，和很多昆蟲一樣，角蟬有非常靈敏的腿。它們站在葉莖的周圍，莖是傳播振動聲音的優質媒介。所以，它們使用的是大自然的饋贈。自然給予了它們一種交流的方式。作為一種社交型的動物，這是它們繁榮昌盛所必需的條件。

寇克勞福特：它們有很多不同形式的社交行為和種群。一旦你發現群居生活的動物，你就會發現各種各樣有趣的交流方式的可能性。

（角蟬鳴叫的片段）

喬伊斯：像這樣偵查時敲擊出傳遞給其他人的信號表示附近有捕食者。

麥奎伊：科技展示了這個隱秘的振動世界，像留聲機唱針以及叫加速計的這類儀器可以測量振動。這令昆蟲探聽邁入了一個新的時代。

勞雷爾·賽姆斯：所以，我今晚待在德克薩斯州的沃思堡。

喬伊斯：勞雷爾·賽姆斯是達特茅斯學院的一名生物學家。賽姆斯將蟋蟀發出的振動頻率調整為我們能聽到的頻率。

賽姆斯：所以，現在我們看到的是一只雄性樹蟋。這只蟋蟀是通過它的翅膀發出聲音的。假如你靠近觀察這些翅膀的其中一只，你就會看到它的翅膀上有一整組極小的齒狀物。摩擦另一只翅膀上的翅脈，可以使整只翅膀像鼓面一樣地振動。

喬伊斯：蟋蟀不像角蟬那樣有那么大的詞匯量。它們擁有一種卓越的能力，那就是可以分辨聲頻中細微的差別，這種能力是音樂會的小提琴演奏家應有的。只有雌性蟋蟀才有這種能力。為什么？比爾，你可以解釋一下嗎？

麥奎伊：這樣，你走進森林里，聽到蟋蟀的叫聲。那是幾種雄性蟋蟀，都在叫你來抓它。對于我們來說，它們聽上去幾乎一樣，但是它們并非一樣。它們摩擦翅膀的速度，即脈率，不同種群是有所不同的。勞雷爾發現雌性知道這些。

賽姆斯：它們也非常擅于識別它們正在尋找的東西。

喬伊斯：哪種脈率是它們同一種群的潛在配偶發出的？這里有一個吹毛求疵的好理由。

賽姆斯：如果你無法判斷正確，那你就會錯過。

喬伊斯：如果你選了不同種類的雄性進行交配，你就會失敗。你就配不出小蟋蟀的種。

麥奎伊：實際上，勞雷爾做了一個巧妙的實驗，來測試雌性蟋蟀的辨別能力有多強。她在電腦上合成了很多雄性蟋蟀的叫聲。它們和真實的聲音一模一樣，她通過揚聲器將這些聲音傳給兩種種類的雌性蟋蟀。這是一種雄性蟋蟀的叫聲，脈沖數為每秒4 3次。

（蟋蟀聲的片段）

麥奎伊：一種類別的雌性蟋蟀立刻擠到揚聲器上，另一種的雌性一點興趣都沒有。然后勞雷爾播放脈沖數為每秒51次的叫聲。

喬伊斯：只是比第一種每秒快了8次而已。

（蟋蟀聲的片段）

喬伊斯：另一類忽略第一種叫聲的雌性，全都和揚聲器談情說愛起來。而事實是，在北美，有大約140種蟋蟀，每種都將聲譜細分為若干個波段。每一個種群就像電臺一樣識別它們自己的頻率。它們是用針頭般大小的腦子做到的。

賽姆斯：它們令人覺得很酷的一點是，實際上它們只有很簡單的感覺系統，但是它們分析著這個非常復雜的世界。

喬伊斯：賽姆斯花了很多年的時間來記錄蟋蟀的情況，才發現了這些。她跟蹤它們到它們去的任何地方，比如墨西哥邊境的樹上，邊境巡邏員想知道她到底在搞什么鬼。

賽姆斯：你爬到一棵樹上，你知道，巡邏車開過來，停下，然后他們打開燈，問道：“夫人，今晚你在這里做什么？”“噢，我只是在收集蟋蟀。”我回答。他們竟然相信了我，那令我驚詫不已。

喬伊斯：現在，她已經完全適應了蟋蟀的世界，想的、說的都和它們一樣。

賽姆斯：（模仿蟋蟀）這是大概60次的。

麥奎伊：沒錯，勞雷爾自己可以做每秒60次。她說，就像冰箱發出嗡嗡聲一樣。

喬伊斯：事實上，她總是在傾聽蟋蟀、風扇以及空調的振動聲。

賽姆斯：我們以為我們真的知道那里有什么在發生，然而我們獲得的只是世界上所有聲音中極小的一部分。

喬伊斯：對于雷克斯·寇克勞福特來說，他認為這個聲音世界的絕大多數東西還有待去探索。

寇克勞福特：這是一個非常熱情的世界，但是我們已經聽到的聲音實在是太少了，所以每個人都可以去到一片雜草叢生的地面或路邊，通過那些植物聽到以前從未聽過的非常有趣的聲音。

喬伊斯：經過數百萬年演變以及為生存而拼搏形成的聲音。