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为什么有毒的动物没有毒死自己? – 译学馆
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为什么有毒的动物没有毒死自己?

Why don’t poisonous animals poison themselves? - Rebecca D. Tarvin

“所有物质都是毒药 因万物皆有毒只是剂量决定了其毒性”
—— 帕拉塞尔苏斯
.
那是晴朗的一天
One fine day,
查尔斯·达尔文当时是剑桥的学生
when Charles Darwin was still a student at Cambridge,
这个未来的博物学家从树上撕下了一些老树皮
the budding naturalist tore someold bark off a tree
在树皮下发现了两只稀有的甲虫
and found two rare beetles underneath.
他发现第三只甲虫时
He ’ d just taken one beetle
手中已各有一只
in each hand when he spotted a third beetle.
为妥善保管 他把一只甲虫放在嘴里
Stashing one of the insectsin his mouth for safekeeping,
伸手去够这种新的甲虫
he reached for the new specimen –
突然被一股苦涩 热雾状液体灼伤了他的舌头
when a sudden spray of hot,bitter fluid scalded his tongue.
袭击达尔文的正是这只放屁虫
Darwin’s assailantwas the bombardier beetle.
它是像青蛙 水母 火蜥蜴以及蛇一样
It’s one of thousands of animal species,
用有毒的化学物质保护自己的
like frogs, jellyfish, salamanders, and snakes,
数千种生物之一
that use toxic chemicals to defend themselves –
这次 放屁甲虫从腹腔腺体中喷出有毒的液体
in this case, by spewing poisonous liquid from glands in its abdomen.
但为什么这种腐蚀性物质在高达100℃ 时 喷射出来
But why doesn’t this caustic substance,ejected at 100 degrees Celsius,
没有使甲虫自己受伤呢?
hurt the beetle itself?
有毒的动物实际上是如何幸免于自身分泌物的呢?
In fact, how do any toxic animalssurvive their own secretions?
答案就是它们使用了两种基本对策的其中之一:
The answer is that they use oneof two basic strategies:
安全储存这些化合物
securely storing these compounds
或者进化出抗体
or evolving resistance to them.
放屁甲虫使用的是前者
Bombardier beetles use the first approach.
它们把毒性物质储藏在腹中两个隔开的腔内
They store ingredients for their poisonin two separate chambers.
当它们受到威胁时 两腔之间的阀门会打开
When they’re threatened, the valvebetween the chambers opens
这些物质结合 发生剧烈的化学反应
and the substances combinein a violent chemical reaction
从而腺体喷出腐蚀性喷雾
that sends a corrosive sprayshooting out of the glands,
并通过变硬的腔来保护自身内部组织
passing through a hardened chamber thatprotects the beetle’s internal tissues.
同样地 水母在类似鱼叉的刺丝囊结构中
Similarly, jellyfish package their venom safely
安全保管毒液
in harpoon-like structurescalled nematocysts.
毒蛇把食肉与凝血的混合物
And venomous snakes store theirflesh-eating, blood-clotting compounds
储存在只有一个出口的特殊隔室中
in specialized compartmentsthat only have one exit:
通过毒牙进入猎物或者捕食者
through the fangsand into their prey or predator.
蛇也用第二种对策:分泌化学抗体
Snakes also employ the second strategy:built-in biochemical resistance.
响尾蛇和其他类型的毒蛇体内有特殊的蛋白质
Rattlesnakes and other types of vipersmanufacture special proteins
它能合并血液中的毒性成分 且阻止其发生效力
that bind and inactivate venomcomponents in the blood.
同时毒镖蛙
Meanwhile, poison dart frogs have
也通过不同机制进化出
also evolved resistance to their own toxins,
能应对自身毒液的抗体
but through a different mechanism.
这些小生物通过消化
These tiny animals defend themselvesusing hundreds of
像蚂蚁蠕虫一类小型节肢动物
bitter-tasting compounds called alkaloids
积聚了数百种名为生物碱的苦味物质来保护自己
that they accumulate from consumingsmall arthropods like mites and ants.
其中最有效的生物碱之一是化学地棘硅素
One of their most potent alkaloidsis the chemical epibatidine,
它像尼古丁一样结合到大脑的受体上
which binds to the same receptorsin the brain as nicotine
而且至少是尼古丁十倍的强度
but is at least ten times stronger.
仅比一粒砂糖多一点的剂量就能杀死你
An amount barely heavier than a grain of sugar would kill you.
那是什么使毒镖蛙不会让自己中毒呢?
So what prevents poison frogsfrom poisoning themselves?
可以想像神经毒性生物碱的
Think of the molecular target
分子目标就像一把锁
of a neurotoxic alkaloid as a lock,
生物碱本身像钥匙
and the alkaloid itself as the key.
当有毒的钥匙插入锁内
When the toxic key slides into the lock,
它发送一系列化学与电学信号
it sets off a cascade of chemicaland electrical signals
这些信号会产生麻痹 意识不清的症状 直至死亡
that can cause paralysis, unconsciousness, and eventually death.
但是如果你改变锁的形状
But if you change the shape of the lock,
钥匙就不会发挥作用
the key can ’ t fit.
毒镖蛙与其他有毒害神经防御的动物
For poison dart frogs and many otheranimals with neurotoxic defenses,
会通过一些 刚好足够阻止神经毒素发挥其反作用的基因变化
a few genetic changes alterthe structure of the alkaloid-binding site
来改变生物碱结合位置的结构
just enough to keep the neurotoxinfrom exerting its adverse effects.
不是只有有毒的动物
Poisonous and venomous animals aren’t the only ones
可以产生抗体
that can develop this resistance:
它们的天敌与猎物也可产生这种抵抗力
their predators and prey can, too.
专食有毒的火蜥蜴的花纹蛇
The garter snake, which dineson neurotoxic salamanders,
通过做出一些与火蜥蜴的自身变化相同的基因改变
has evolved resistanceto salamander toxins
而产生抵抗火蜥蜴毒素的能力
through some of the same genetic changesas the salamanders themselves.
这就意味着
That means that only the most
只有毒性最强的火蜥蜴可以避免被吃
toxic salamanders can avoid being eaten—
也只有最耐毒性的蛇在吃过有毒的猎物后能幸存
and only the most resistant snakeswill survive the meal.
这会导致
The result is
最强的抗体和毒性的基因
that the genes providing the highest resistance and toxicity
会大量遗传给下一代
will be passed on in greatest quantitiesto the next generations.
在持续了数百万年的军备进化竞赛中
As toxicity ramps up, resistance does too,
毒性增加时 抗体也同时增强
in an evolutionary arms race that plays out over millions of years.
这种模式会反复出现
This pattern appears over and over again.
食蝗鼠通过自身神经系统的基因变化
Grasshopper mice resist painfulvenom from scorpion prey
来抵御蝎子的毒液
through genetic changesin their nervous systems.
角蜥用自己特有的血浆抵抗蚂蚁的毒刺
Horned lizards readilyconsume harvester ants,
可以轻而易举地吃掉它们
resisting their envenomed stingwith specialized blood plasma.
海蛞蝓吃水母的刺丝囊
And sea slugs eat jellyfish nematocysts,
避免他们唾液中的化合物被激活
prevent their activationwith compounds in their mucus,
并可将其用做自身防御
and repurpose them for their own defenses.
放屁甲虫也不例外:
The bombardier beetle is no exception:
蟾蜍吞下它们并可以忍受
the toads that swallow them can tolerate the
达尔文觉得非常恶心的腐蚀性喷雾
caustic spray that Darwin found so distasteful.
大部分甲虫几小时后就会被蟾蜍吐出
Most of the beetles are spit up hours later,
可以奇迹般存活
amazingly alive and well.
但蟾蜍是如何幸免于这个过程的呢?
But how do the toads survive the experience?
这依旧是个谜
That is still a mystery.

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视频概述

介绍有毒的动物避免自己被毒的原因

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视频来源

https://www.youtube.com/watch?v=-sEpBGF106k

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