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鲸鱼是如何变得如此巨大的?

更新时间:2017-5-30 8:02:39 来源:纽约时报中文网 作者:佚名

How Whales Became the Biggest Animals on the Planet
鲸鱼是如何变得如此巨大的?

Whales are big. Really big. Enormously big. Tremendously big.

鲸鱼很大。非常大。无比庞大。大得出奇。

Fin whales can be 140,000 pounds. Bowhead whales tip the scales at 200,000 pounds. And the big mama of them all, the blue whale, can reach a whopping 380,000 pounds — making it the largest animal to have ever lived.

长须鲸重14万磅。弓头鲸则可重达20万磅。其中的老大则是蓝鲸,重量可达38万磅之巨,这也使蓝鲸成为了有史以来最为大型的动物。

But for as long as whales have awed us with their great size, people have wondered how they became so colossal.

鲸鱼以其庞大的身型令我们惊叹,人们也在一直好奇:它们是如何变得如此巨大的?

In a study published Tuesday in the journal Proceedings of the Royal Society B, a team of researchers investigated gigantism in baleen whales, the filter-feeding leviathans that include blue whales, bowhead whales and fin whales. The marine mammals became jumbo-size relatively recently, they found, only within the past 4.5 million years. The cause? A climatic change that allowed the behemoths to binge-eat.

周二,在一项发表在《英国皇家学报》B辑(Proceedings of the Royal Society B)的研究中,一组研究人员对须鲸科的“巨人症”进行了研究,这一滤食性庞然大物包括蓝鲸、弓头鲸及长须鲸。研究人员发现,这种海洋哺乳动物是在较为近期,仅在过去450万年间才变成巨无霸的。原因?一场导致这种巨型生物大量进食的气候变化。

Whales have an interesting evolutionary history. They began as land-dwelling, hoofed mammals some 50 million years ago. Over several millions of years they developed fins and became marine creatures. Between about 20 million and 30 million years ago, some of these ancient whales developed the ability to filter-feed, which meant they could swallow swarms of tiny prey in a single gargantuan gulp. But even with this feeding ability, whales remained only moderately large for millions of years.

鲸鱼的进化历史颇为有趣。起初,在约5000万年前,它们是栖息在陆地上的蹄目哺乳动物。经过数千万年的演化,它们进化出了鳍,成为了海洋生物。约2000至3000万年前,这些古鲸鱼中的一部分进化出了滤食的能力,这也就意味着它们能一大口吞下大量猎物。但尽管有了这种进食的能力,在数千万年间,鲸鱼仍然只保持着相对较大的体型。

“But then all of a sudden — ‘boom’ — we see them get very big, like blue whales,” said Nick Pyenson, the curator of fossil marine mammals at the Smithsonian Institution’s National Museum of Natural History and an author of the paper. “It’s like going from whales the size of minivans to longer than two school buses.”

“但突然间——‘轰’地一下——它们变得非常巨大,比如蓝鲸”,史密森尼学会国立自然历史博物馆(Smithsonian Institution’s National Museum of Natural History)策展人、该论文的作者尼克·佩尔森(Nick Pyenson)说。“鲸鱼的体型变化就像从小货车变得比两个校车还大。”

Dr. Pyenson and his colleagues measured more than 140 museum specimens of fossilized whales, and then plugged that data into a statistical model. It showed that several distinct lineages of baleen whales became giants around the same time, independently of one another. Starting around 4.5 million years ago, giant blue whales were popping up in oceans across the world alongside giant bowhead whales and giant fin whales.

佩尔森及同事测量了超过140个鲸鱼化石样本,然后将数据输入统计模型。结果显示,有几个特殊谱系的须鲸是在大约同一时间、分别变得巨大无比的。约从450万年前开始,巨型蓝鲸开始出现在全世界的海洋中,同一时间出现的还有巨型弓头鲸及巨型长须鲸。

The researchers suspected that an environmental change happened during that time that essentially caused the baleen whales to bulk up. After some investigation, they found that this time period coincided with the early beginnings of when ice sheets increasingly covered the Northern Hemisphere.

研究人员怀疑,该时期或许曾发生过一场环境变化,从根本上导致了这些须鲸身型变大。经过一番研究,他们发现在这个时期与北半球开始被冰川越来越多覆盖的时间相一致。

Runoff from the glaciers would have washed nutrients like iron into coastal waters and intense seasonal upwelling cycles would have caused cold water from deep below to rise, bringing organic material toward the surface. Together these ecological effects brought large amounts of nutrients into the water at specific times and places, which had a cascading effect on the ocean’s food web.

冰川径流可能将诸如铁这样的营养物质冲入沿海水域,季节性的上升流周期也使得深海里的冷水上涌,将有机物质带至海面。在特定的时间和地点,这些生态效应将大量营养物质带入水中,对海洋中的食物链造成了层叠效应。

Throngs of zooplankton and krill would gather to feast on the nutrients. They would form dense patches that could stretch many miles long and wide and be more than 65 feet thick. The oceans became the whales’ giant all-you-can-eat buffets.

大量的浮游生物和磷虾会聚集在一起,尽情享用这些营养物质,结成长、宽可达数英里,厚度逾65英尺的紧密的一大片。海洋也就成了鲸鱼们大型的“随你吃”自助餐。

“Even though they had the anatomical machinery to filter-feed for a long, long time,” said Jeremy Goldbogen, a comparative physiologist from Stanford University and author of the paper, “it wasn’t until the ocean provided these patchy resources that it made bulk filter-feeding so efficient.”

“尽管它们有着能够长期滤食的生理结构,”斯坦福比较生理学家、论文作者杰里米·戈登伯根(Jeremy Goldbogen)说,“直到海洋提供了这些大片资源,才使得大量滤食如此有效。”

The baleen whales could now gulp down much larger amounts of prey, which allowed them to get bigger. But that was only part of the equation.

如今的须鲸科可吞下数量大得多的食物,它们也因此变得更为庞大。但这只是其中的一部分原因。

“Plentiful food everywhere isn’t going to get you giant whales,” said Graham Slater, an evolutionary biologist at the University of Chicago and the study’s lead author. “They have to be separated by big distances.”

“到处都是充足的食物是无法让让鲸鱼变成巨型的,”芝加哥大学进化生物学家格雷厄姆· 斯莱特(Graham Slater)、论文的主要作者说。“必须被遥远的距离分隔开才行。”

Because the ecological cycles that fuel the explosions of krill and zooplankton occur seasonally, Dr. Slater said the whales must migrate thousands of miles from food patch to food patch. Bigger whale ancestors that had bigger fuel tanks had a better chance of surviving the long seasonal migrations to feed, while smaller baleen whales became extinct.

斯莱特说,由于导致磷虾和浮游生物大量爆发式出现的生态效应是季节性出现的,鲸鱼也就必须在各个食物块之间移动数千公里。在长期的为了食物的季节性迁移中,有着更多食物储存空间的体型较大的鲸鱼祖先更容易生存下来,而较为小型的须鲸则走向了灭绝。

If the food patches were not far apart, Dr. Slater said, the whales would have grown to a certain body size that was comfortable for that environment, but they would not be the giants we see today.

斯莱特说,如果食物块之间相隔不远,鲸鱼就会长到一定的大小,进而适应该环境,但就不会成为我们如今看到的的庞然大物了。

“A blue whale is able to move so much further using so much less energy than a small-bodied whale,” Dr. Slater said. “It became really advantageous if you’re going to move long distances if you’re big.”

“与小型鲸鱼相比,一条蓝鲸能以少得多的精力游得更远,”斯莱特说,“如果你体型很大,要去很远的地方时就非常占优势。”

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