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以假乱真的动物伪装术

更新时间:2015-10-3 8:32:51 来源:纽约时报中文网 作者:佚名

Evolving a Defense, Mimics Save Themselves
以假乱真的动物伪装术

The Canadian tiger swallowtail caterpillar is a plump green creature that spends all its time munching leaves. It ought to be an easy meal for a bird, yet many birds pass it by.

加拿大虎斑燕尾蝶(Papilio Canadensis)的幼虫是一种肉肉的绿色生物。在它的整个生命周期里,就是不停的咀嚼植物的树叶。对鸟儿来说,它应该是最容易捕获的目标。可是偏偏大多数鸟儿都对它视而不见。

The caterpillar is protected by a remarkable defense, researchers have found: It tricks birds into thinking it’s a snake.

研究人员发现,这种幼虫有一种神奇的自我保护机制,它能骗过鸟儿,让鸟儿误以为自己遇到了一条蛇。

The caterpillar grows a pair of concentric yellow and black rings that look like a giant pair of eyes. When the caterpillar senses a bird nearby, it quickly inflates the front part of its body, making it resemble a snake’s head.

在这种幼虫的身上长有一对黄黑相间的同心圆斑点,看起来就像一对巨大的眼睛。当幼虫感觉到附近有鸟儿飞来时,它还会膨大自己的身体前部,让它看起来更像一条蛇的头部。

Astonishing as this deception may be, the tiger swallowtail is hardly unique. Many species have evolved ways to fool their would-be predators. Some insects look like twigs, even mimicking the way that twigs sway in the breeze.

像这种让人瞠目结舌的伪装术,加拿大虎斑燕尾蝶不是独此一家。自然界很多生物都进化出了不同的伪装术来迷惑潜在的天敌。有些昆虫长的像树枝,甚至会模仿树枝在微风中摇动的样子。

Harmless snakes scare off predators by mimicking the look of venomous ones. Some species of hoverflies have the yellow and black stripes of stinging wasps. They even pretend to sting their enemies, despite having no stinger at all.

有些无毒的蛇会模拟有毒蛇的外观来吓跑天敌。有些食蚜蝇身上长有像蜇人的黄蜂一样黄黑相间的条纹。它们甚至能做出蜇人的动作,尽管它们并没有蜇刺。

But mimicry has revealed a puzzle at its heart: Time and again, scientists find examples of overkill. Animals don’t seem to get an extra benefit from making their disguises more elaborate.

可是这种伪装术本身也有很多不解之迷。科学家们常常会发现有些伪装术伪装的过了头。这些过分的伪装并没有给它们带来额外的保护作用。

The Canadian tiger swallowtail is an excellent example. Over the past few years, Thomas N. Sherratt, a behavioral ecologist at Carleton University in Ontario, and his graduate student Thomas J. Hossie have studied the caterpillar’s strategy by creating “pastry caterpillars” of flour, water, shortening and green food coloring.

加拿大虎斑燕尾蝶就是一个极好的例子。在过去的几年里,在安大略省,卡尔顿(Carleton)大学工作的动物行为生态学家,Thomas N Sherratt 和他的博士研究生Thomas J. Hossie对虎斑燕尾蝶的幼虫伪装术进行了详细的研究。他们用面粉,水,起酥油,加上绿色的食品染料捏成“面泥幼虫”。

They are apparently tasty. When the scientists placed pastry caterpillars on tree branches, many of them quickly disappeared. “Birds are really motivated to eat them,” said Dr. Sherratt.

这种“面泥幼虫”显然味道喷香。当科学家们把这些“面泥幼虫”放在树枝上,大多数“面泥幼虫”很快就消失了。Sherrat博士说:“鸟儿们特别喜欢吃这些“幼虫”。

Dr. Hossie, who is now a post-doctoral researcher at Trent University in Ontario, created a batch of pastry caterpillars with eye spots and snake-like heads. A substantial number of these more elaborate models remained on the branches, presumably because they scared away many birds.

Hossie博士现在是Trent大学的博士后。他做了一批这样的“面泥幼虫”。这些“幼虫”既有像眼睛一样的斑点,又有蛇头状的身体。有相当一部分这些双重伪装的“幼虫”留在了树枝上,很有可能这些伪装吓跑了许多鸟儿。

Surprisingly, though, pastry caterpillars don’t require a complicated disguise to deter birds. The scientists also created faux caterpillars with eyespots but no snakelike head. The birds avoided these simpler mimics about as often as they did the more elaborate ones.

令人惊讶的是,这些“面泥幼虫”并不需要很复杂的伪装来驱赶鸟儿。科学家们制作了另一批人造“面泥幼虫”,它们仅仅只有眼斑而没有蛇头状的身体。鸟儿对这些具有简单伪装的“幼虫”也是避之不及。其效果和对有复杂伪装的“幼虫“一样。

If real caterpillars don’t gain extra protection from extra deception, the scientists wondered, then how could their disguise have evolved?

科学家们对此观察结果有些困惑:如果这些真的幼虫并没有从复杂的伪装中得到额外的保护,那么这些复杂的伪装是如何进化来的?

The researchers suspected that they had missed something in their experiments in the woods. For one thing, they had not actually watched birds as they ate or avoided the pastry caterpillars. They had simply counted up the pastries that remained on branches.

科学家们怀疑在他们的树林实验中可能缺失了某些东西。比如,他们并没有直接观察到鸟儿们是如何吃这些“面泥幼虫”或者如何避免吃这些“面泥幼虫”。他们只是对那些残留在树枝上的“面泥幼虫”进行了计数。

To get a closer look at the birds, the Canadian scientists teamed up with Dr. Skelhorn, who studies mimicry in his Newcastle laboratory.

为了对鸟儿的行为做近距离的观察,加拿大的科学家们和Skehorn博士进行了合作。Skehorn博士是在Newcastle的实验室对“伪装术”进行研究的。

The scientists baked more batches of pastry caterpillars, but this time they didn’t put them on tree branches. Instead, they presented the models to day-old chicks.

科学家们又烘焙出了更多的“面泥幼虫”。这次科学家们没有把这些“幼虫”放在树林里,而是将它们放在了刚刚孵化出只有一天的小鸡面前。

They picked such young animals in order to judge whether the birds are born with a fear of snakes and snakelike objects. “These chicks haven’t seen anything like a snake before,” said Dr. Sherratt.

科学家们之所以选用这些刚刚出生的小鸡,是想看看这些小鸡是否对蛇和蛇状物有与生俱来的恐惧。Sherratt博士说:“这些小鸡从来就没看见过像蛇一样的东西”。

When the chicks were presented with simple green cylinders, they happily pecked at them. But if the scientists added eyespots, the chicks became far more wary. Consistent with earlier research, the scientists found that adding a snakelike head didn’t make the chicks any more fearful.

当把一些简单的绿色条状的面泥放在小鸡面前时,小鸡们挺喜欢吃这些条状面泥的。可是当科学家们在这些绿色条状物的面泥上再画上像眼睛一样的斑点,小鸡们就开始对这些条状面泥提高了警惕。如果将这些有眼斑的条状物再加上蛇样的头部,这并不会增加小鸡的恐惧感,这个结果与先前的观察一致。

But the experiment didn’t end there. Over the next two days, the scientists presented the chicks with pastry caterpillars five more times. By the end, the chicks had learned that cylinders with eye spots were in fact tasty snacks.

可是实验并没有在这里结束。在接下来的两天里,科学家们又把只带眼斑的条状物连续给小鸡喂了五次。最终小鸡们认可了这些带眼斑的条状物实际上是美味可口的小点心。

That was not the case when the chicks were presented with pastry caterpillars with both eye spots and snakelike heads. Even at the end of the study, the chicks were still fairly wary of the more realistic mimics.

可对那些既有眼斑又有蛇状头部的面泥条状物情况则是另一个样子。直到实验结束,小鸡们始终对这些更逼真的模拟物疑心重重。

The researchers published their results on Aug. 14 in the journal Behavioral Ecology.

研究人员把他们的这些研究结果发表在八月十四号的杂志“行为生态学”上了。

Dr. Skelhorn and his colleagues suspect that birds have evolved a healthy fear of snakes, present from the moment they hatch from their eggs. They don’t need to see a snake in full detail before deciding to flee. Just a few distinctive features — like snake eyes — may be enough. The caterpillars exploit that quick response to deter the birds.

Skelhorn博士和他的同事认为鸟儿们已经进化出了一种对蛇的天生的恐惧,这种恐惧感在鸟儿刚刚从蛋里孵化出来的时候就有了。它们并不需要看到蛇的全貌才决定是否逃跑。只需要几个典型的特征,比如像蛇的眼睛,就能让它们做出逃跑的决定。昆虫的幼虫就是利用鸟儿的这些快速反应来逃避鸟儿的捕食。

But birds, like other animals, can learn to tell objects apart. This ability may have driven caterpillars to evolve more elaborate disguises, which are harder for birds to learn to distinguish from snakes.

像其它动物一样,鸟儿们也能够学着区分出不同的伪装信号。因此,昆虫的幼虫进化出更为复杂的伪装术来,使得鸟儿们学习辩别出真蛇与伪装的“蛇”的能力变得更加困难。

“It takes more information for the birds to be convinced they’re not a snake,” said Dr. Skelhorn. The caterpillars “can fool predators for longer and survive.”

Skelhorn博士说:“鸟儿们需要更多的信息来确认这些伪装的幼虫不是真正的蛇”。这样,幼虫们“就能延长欺骗捕食者的时间而得以幸存”。

Olof Leimar, an evolutionary biologist at Stockholm University who was not involved in the study, said that it demonstrated how deceptive animals can exploit the wiring of their predators’ brains. “Without understanding the psychology, you can’t understand the phenomenon,” he said.

斯德哥尔摩大学的进化生物学家Olof Leimar指出以上的研究证明了这些伪装的动物知道如何利用捕食者大脑中预先编码好的思维方式。Olof Leimar 说:“如果不懂心理学,你就无法理解所观察到的现象”。(Olof Leimer本人并没有参与该课题的研究。)

Dr. Sherratt hopes that their experiment will inspire other researchers to run similar studies on other mimics. He suspects that other “over-evolved” deceivers may actually be exploiting how their enemies learn.

Sherratt博士希望他们的研究能激发起其他研究者的兴趣来对其它伪装术做相类似的研究。他猜测其它一些“过分进化”的伪装者实际上是巧妙的利用它们的天敌们学习辨别真伪的过程。

“Of course, you need to do it a few more times to see if it’s real,” he said.

他指出:“当然,你需要反复做几次实验来证明你的结果是否真实可靠”。

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