Name: 【TED-Ed】為什麼有毒的動物都不會毒死自己？ (Why don't poisonous animals poison themselves? - Rebecca D. Tarvin)
Uploaded: 2018-07-25T21:01:40.000Z
Duration: 5 min 10 s

when Charles Darwin was still  a student at Cambridge,

當查爾斯．達爾文還是劍橋的學生時

the budding naturalist tore some old bark off a tree

這位初嶄露頭角的博物學者從一棵樹上剝下了一些老樹皮

然後在底下發現了兩隻罕見的甲蟲

He'd just taken one beetle in each hand when he spotted a third beetle.

當他兩手各拿了一隻甲蟲時，他發現了第三隻

Stashing one of the insects  in his mouth for safekeeping,

他把其中一隻昆蟲塞到嘴裡以防牠逃走

when a sudden spray of hot,  bitter fluid scalded his tongue.

一陣突如其來的炙熱苦澀液體燙傷了他的舌頭

Darwin's assailant  was the bombardier beetle.

that use toxic chemicals  to defend themselves –

這些群體會利用有毒化學物質來防衛自己 --

in this case, by spewing poisonous liquid  from glands in its abdomen.

在這個例子中，就是藉由噴射腹部分泌腺的有毒液體

But why doesn't this caustic substance, ejected at 100 degrees Celsius,

但為什麼這種腐蝕性的物質，更不用說它噴射時溫度達攝氏一百度

In fact, how do any toxic animals  survive their own secretions?

事實上，任何有毒動物是如何活過他們自己的分泌物？

The answer is that they use one  of two basic strategies:

答案是牠們在兩個基本的策略之間擇一使用：

Bombardier beetles use the first approach.

They store ingredients for their poison  in two separate chambers.

牠們將毒藥的成分儲存在兩個獨立的腔室

When they're threatened, the valve  between the chambers opens

當牠們受到威脅，兩個腔室之間的閘門就會打開

and the substances combine  in a violent chemical reaction

物質混合成一種激烈的化學反應

that sends a corrosive spray  shooting out of the glands,

passing through a hardened chamber that protects the beetle's internal tissues.

途中經過硬化的、能夠保護甲蟲體內組織的腔室

Similarly, jellyfish package  their venom safely

同樣地，水母將牠們的毒液安全地包裹在

in harpoon-like structures  called nematocysts.

And venomous snakes store their flesh-eating, blood-clotting compounds

而有毒的蛇則是將牠們腐肉、凝血的混合物

in specialized compartments that only have one exit:

儲存在只有一個出口的特殊小隔間內：

through the fangs  and into their prey or predator.

只能經由獠牙進入牠們的獵物或是狩獵者

Snakes also employ the second strategy: built-in biochemical resistance.

蛇同樣採用了第二套策略：內建的生物化學抵抗力

Rattlesnakes and other types of vipers manufacture special proteins

響尾蛇和其他種類的毒蛇會製造一種特殊的蛋白質

that bind and inactivate venom  components in the blood.

能夠在血液中使毒液成分凝結、失效

Meanwhile, poison dart frogs have also evolved resistance to their own toxins,

同時，毒鏢蛙也演化出對牠們自己毒素的抗體

These tiny animals defend themselves  using hundreds of bitter-tasting compounds

這些小小的動物運用稱為生物鹼的

that they accumulate from consuming  small arthropods like mites and ants.

這些是從吃小小的節肢動物比如蟎蟲和螞蟻攝取而來

One of their most potent alkaloids  is the chemical epibatidine,

牠們其中最有效的一種生物鹼是化學巴蒂啶

which binds to the same receptors  in the brain as nicotine

與尼古丁作用於腦部中相同的受器

An amount barely heavier than  a grain of sugar would kill you.

只比些微糖粒多一點點的分量就能置你於死地

So what prevents poison frogs  from poisoning themselves?

所以是什麼預防了毒蛙毒死自己？

Think of the molecular target  of a neurotoxic alkaloid as a lock,

試著把神經中毒生物鹼的分子目標視為一個鎖

it sets off a cascade of chemical  and electrical signals

But if you change the shape of the lock, the key can't fit.

但如果你改變了鎖頭的形狀，鑰匙就會對不上

For poison dart frogs and many other animals with neurotoxic defenses,

對於毒箭蛙和許多其他有神經中毒防衛機制的動物

a few genetic changes alter the structure of the alkaloid-binding site

些微的基因改變會更改綁定生物鹼的區域構造

just enough to keep the neurotoxin  from exerting its adverse effects.

正好防止了神經毒素造成反效果

aren't the only ones that can develop  this resistance:

並不是唯一可以發展出抵抗力的一方：

The garter snake, which dines  on neurotoxic salamanders,

攝取帶有神經毒素的火蜥蜴為生的束帶蛇

has evolved resistance  to salamander toxins

透過一些與火蜥蜴本身相同的基因改變

through some of the same genetic changes  as the salamanders themselves.

已經演化出對火蜥蜴毒素的抵抗力

That means that only the most toxic  salamanders can avoid being eaten—

那就代表，只有最毒的火蜥蜴才不會被吃掉 --

and only the most resistant snakes will survive the meal.

而且只有抵抗力最強的蛇能活過這餐

The result is that the genes providing  the highest resistance and toxicity

結果是提供最高抵抗力和毒素的基因

will be passed on in greatest quantities  to the next generations.

As toxicity ramps up, resistance does too,

in an evolutionary arms race  that plays out over millions of years.

在這場演化軍備競賽中上演了百萬年

This pattern appears over and over again.

Grasshopper mice resist painful  venom from scorpion prey

沙居食蝗鼠藉由改變牠們神經系統中的基因

through genetic changes  in their nervous systems.

抵抗來自蝎子獵物帶來疼痛的毒液

Horned lizards readily  consume harvester ants,

resisting their envenomed sting  with specialized blood plasma.

抵抗牠們含有特殊血漿的有毒針刺

prevent their activation  with compounds in their mucus,

藉由牠們黏液中的混合物防止毒素激活

and repurpose them for their own defenses.

然後把它們重新利用為自己的防衛利器

can tolerate the caustic spray  that Darwin found so distasteful.

能夠忍受那種達爾文覺得非常討厭的腐蝕性噴霧

Most of the beetles  are spit up hours later,

多數甲蟲會在幾小時後被吐出來

But how do the toads  survive the experience?

但是蟾蜍又是如何活過這個經歷的？