Greg Gage: If I asked you to think of a ferocious killer animal, you'd probably think of a lion, and for all the wonderful predatory skills that a lion has, it still only has about a 20 percent success rate at catching a meal. Now, one of the most successful hunters in the entire animal kingdom is surprising: the dragonfly. Now, dragonflies are killer flies, and when they see a smaller fly, they have about a 97 percent chance of catching it for a meal. And this is in mid-flight. But how can such a small insect be so precise? In this episode, we're going to see how the dragonfly's brain is highly specialized to be a deadly killer.
葛列格·蓋奇 (GG):如果讓 你想像兇猛的捕食動物, 你可能會想到獅子, 但即使獅子捕食技巧出色, 牠捕食的成功率也只有兩成。 要說動物王國中最成功的捕食者, 答案可能會讓你大吃一驚, 是蜻蜓。 蜻蜓是飛行獵手, 當牠們看到比自身體型小的飛蟲, 有 97% 的概率能捕捉到作為食物。 而整個過程可以在飛行中完成。 一隻如此小的昆蟲 為何有如此高的精準度? 在這一集中,我們將會看到 蜻蜓的大腦如何讓牠成為致命殺手。
[DIY Neuroscience]
[DIY 神經科學]
So what makes the dragonfly one of the most successful predators in the animal kingdom? One, it's the eyes. It has near 360-degree vision. Two, the wings. With individual control of its wings, the dragonfly can move precisely in any direction. But the real secret to the dragonfly's success is how its brain coordinates this complex information between the eyes and the wings and turns hunting into a simple reflex. To study this, Jaimie's been spending a lot of time socializing with dragonflies. What do you need to do your experiments?
蜻蜓是如何成為動物中 最成功的捕食者之一呢? 第一,是牠的眼睛構造。 蜻蜓擁有接近 360° 的視角。 第二,翅膀結構。 通過對翅膀的獨立控制, 蜻蜓可以在任何方向精確移動。 但蜻蜓成功的真正秘訣 是其大腦可以整合來自眼睛 和翅膀的複雜信號 並將捕獵行為轉變為簡單反射。 為了研究當中的原理, 傑米花了很多時間 和蜻蜓相處。 你做實驗需要些什麼?
Jaimie Spahr: First of all, you need dragonflies.
傑米·斯帕爾:首先,你需要蜻蜓。
Oliver: I have a mesh cage to catch the dragonflies.
奧利弗: 我用捕蟲網去捉牠們。
JS: The more I worked with them, the more terrified I got of them. They're actually very scary, especially under a microscope. They have really sharp mandibles, are generally pretty aggressive, which I guess also helps them to be really good predators.
傑米:越研究牠們,就越害怕牠們。 牠們實際上非常嚇人, 特別是在顯微鏡下。 牠們的下頜骨非常鋒利, 而且很有攻擊性, 我相信這幫助牠們成為捕食好手。
GG: In order to learn what's going on inside the dragonfly's brain when it sees a prey, we're going to eavesdrop in on a conversation between the eyes and the wings, and to do that, we need to anesthetize the dragonfly on ice and make sure we protect its wings so that we can release it afterwards. Now, the dragonfly's brain is made up of specialized cells called neurons and these neurons are what allow the dragonfly to see and move so quickly. The individual neurons form circuits by connecting to each other via long, tiny threads called axons and the neurons communicate over these axons using electricity. In the dragonfly, we're going to place little metal wires, or electrodes, along the axon tracks, and this is what's really cool. In the dragonfly, there's only 16 neurons; that's eight per eye that tell the wings exactly where the target is. We've placed the electrodes so that we can record from these neurons that connect the eyes to the wings. Whenever a message is being passed from the eye to the wing, our electrode intercepts that conversation in the form of an electrical current, and it amplifies it. Now, we can both hear it and see it in the form of a spike, which we also call an action potential.
GG:為了進一步研究 當蜻蜓看到獵物時的大腦活動, 我們決定偷聽蜻蜓 眼睛和翅膀間的對話, 為此,我們需要用冰塊麻醉蜻蜓, 並確保翅膀完好無損, 以便我們之後放走牠。 蜻蜓大腦中有很多 特殊的細胞,即是神經元 而就是這些神經元讓蜻蜓 能夠快速見到物件和移動。 獨立的神經元通過細長的軸突 連接彼此, 進而組成神經迴路, 在軸突上用電信號進行交流。 在蜻蜓體內,我們將沿著軸突 放置一些小的金屬線和電極, 這整個過程很酷。 在蜻蜓體內只有 16 個神經元: 每隻眼睛有 8 個, 用來告訴翅膀目標的具體方位。 放置電極後,我們就可以記錄 眼睛和翅膀之間的神經元電信號。 每當有訊息從眼睛傳遞到翅膀, 我們的電極都會將這次對話 以電流的形式記錄下來, 並放大電流。 我們能看到並聽到電流脈衝, 我們稱之為動作電位。
Now let's listen in. Right now, we have the dragonfly flipped upside down, so he's looking down towards the ground. We're going to take a prey, or what we sometimes call a target. In this case, the target's going to be a fake fly. We're going to move it into the dragonfly's sights.
現在一起來聽聽。 我們馬上把蜻蜓倒置, 牠現在眼朝地面。 我們現在放置一個獵物,或者說目標, 這裡我們使用一隻假蒼蠅作為目標。 我們將在蜻蜓的視野範圍內移動牠。
(Buzzing)
(電流聲)
Oh! Oh, look at that. Look at that, but it's only in one direction. Oh, yes! You don't see any spikes when I go forward, but they're all when I come back.
哦! 哦,你看這裡。 快看這裡,但只在 朝特定方向時發生電位變化。 哦,好! 當我向前移動時,不會出現任何脈衝, 但回來的時候脈衝會出現。
In our experiments, we were able to see that the neurons of the dragonfly fired when we moved the target in one direction but not the other.
在實驗中, 我們見到當目標僅朝一個方向移動時, 蜻蜓的神經元會被啟動, 但在向另一個方向移動時卻沒有。
Now, why is that? Remember when I said that the dragonfly had near 360-degree vision. Well, there's a section of the eye called the fovea and this is the part that has the sharpest visual acuity, and you can think of it as its crosshairs. Remember when I told you the dragonfly had individual precise control of its wings? When a dragonfly sees its prey, it trains its crosshairs on it and along its axons it sends messages only to the neurons that control the parts of the wings that are needed to keep that dragonfly on target. So if the prey is on the left of the dragonfly, only the neurons that are tugging the wings to the left are fired. And if the prey moves to the right of the dragonfly, those same neurons are not needed, so they're going to remain quiet. And the dragonfly speeds toward the prey at a fixed angle that's communicated by this crosshairs to the wings, and then boom, dinner.
這是為什麼呢? 記得我之前提及到 蜻蜓擁有 360° 的可視範圍。 同時,蜻蜓眼睛上有一個 稱為中央凹的區域 而這也是蜻蜓視力最敏銳的部分, 你可以把它看作瞄準線。 還記得我給你說過蜻蜓能獨立 控制每個翅膀嗎 ? 當蜻蜓發現獵物時 會試圖將瞄準線對準獵物, 會沿著軸突發送訊號給 控制翅膀的神經元 來對準目標。 所以,如果獵物在蜻蜓的左側, 那麼只有控制左側翅膀的 神經元會被啟動。 如果獵物飛向蜻蜓的右側, 那就不需要這些神經元了, 它們就會在靜止狀態。 當神經元確定好翅膀的角度後, 蜻蜓會依照瞄準線朝獵物飛去。 一擊直中,晚餐到手。
Now, all this happens in a split second, and it's effortless for the dragonfly. It's almost like a reflex. And this whole incredibly efficient process is called fixation.
現在,這些都是一瞬間發生的事, 這對蜻蜓來說不費吹灰之力, 就像本能反應。 而這個驚人高效的捕獵過程 被稱為固定(fixation)。
But there's one more story to this process. We saw how the neurons respond to movements, but how does the dragonfly know that something really is prey? This is where size matters.
但是還有一件需要考慮的事情。 我們看到神經元如何回應運動, 但是蜻蜓如何判斷誰是獵物呢? 這就需要考慮獵物的體型了。
Let's show the dragonfly a series of dots. Oh, yeah!
讓我們來給蜻蜓展示一系列圓點。 哦,對了!
JS: Yeah, it prefers that one.
傑米:對,牠對那個比較有反應。
GG: Out of all the sizes, we found that the dragonfly responded to smaller targets over larger ones. In other words, the dragonfly was programmed to go after smaller flies versus something much larger, like a bird. And as soon as it recognizes something as prey, that poor little fly only has seconds to live. Today we got to see how the dragonfly's brain works to make it a very efficient killer. And let's be thankful that we didn't live 300 million years ago when dragonflies were the size of cats.
GG: 在所有的體型中, 我們發現蜻蜓更傾向於 選擇體型小的目標。 換句話說,蜻蜓被設定為 捕捉體型比自己小的飛蟲, 而不是更大的目標,比如鳥類。 而只要牠識別出了獵物, 那隻可憐的小飛蟲 只有幾秒鐘的逃生時間。 今天我們看到了蜻蜓的腦如何工作 使得蜻蜓成為一個高效的獵手。 而且我們要慶幸 自己不是生活在 3 億年前, 那時的蜻蜓跟貓一樣大。