Spineless Jellies Have A Mind of Their own

水母沒有脊椎 不表示沒有大腦

By Natalie Angier

BALTIMORE – Among multicellular creatures, jellyfish seem like the ultimate other. Where is the head, the matched sets of organs, the bilateral symmetry?
水母有如多細胞生物中的終極另類。牠的頭、成對的器官、對稱的身體系統在哪裡？

Yet jellyfish, a diverse group of thousands of species of invertebrates found worldwide, are among the first animals, dating back 600 million to 700 million years or longer. That’s roughly twice as old as the earliest bony fish and insects.
水母這種無脊椎動物遍布全球各地水域，品類數以千計，存活至今已有六億到七億年，甚至更久，是最古老的生物之一。若論出現年代距今之久遠，大約是最早期硬骨魚類及昆蟲的兩倍。

“Jellyfish are the most ancient multiorgan animal on earth,” said David J. Albert, a jellyfish expert at the Roscoe Bay Marine Biological Laboratory in Vancouver, British Columbia.
加拿大卑詩省溫哥華市羅斯科灣海洋生物實驗室的水母專家艾伯特說：「水母是地球上最古老的多器官生物。」

Jellyfish have long been ignored by science, dismissed as mindless protoplasm. Now researchers are finding they have far more complexity. In the May 10 issue of the Current Biology, Anders Garm who studies jellyfish at the University of Copenhagen, and his colleagues describe the astonishing visual system of the box jellyfish, with an interactive matrix of 24 eyes of four distinct types – two very similar to our own eyes – allowing the jellies to navigate through water.
長久以來，科學家始終認為水母只不過是一團沒有思考能力的原生質，對牠們未予重視。研究人員如今發現，水母的構造其實遠較原本以為的複雜。丹麥首都哥本哈根市哥本哈根大學的水母研究員賈恩姆和他的研究夥伴們，在5月10日號《當代生物學》期刊上發表研究報告指出，箱形水母具有驚人的視覺系統：共有24個可以互動的眼睛，而且分為四種，其中二種與人類的眼睛非常類似。這使牠們得以在水中行進。

And in the Journal of Experimental Biology, Richard A. Satterlie, a marine biologist at the University of North Carolina Wilmington, disputed the conventional wisdom that jellyfish lack a central nervous system. Studies reveal evidence of “neuronal condensation,” places where the neurons coalesce to form structures that act as integrating centers – taking in sensory information and translating it into the appropriate response.
沙特里是威爾明頓市北卡羅來納大學的海洋生物學家，他在《實驗生物學》期刊上發表另一項研究報告，駁斥水母不具中樞神經系統的傳統看法。最新研究發現，有證據顯示水母有「神經元集中」的生理特質，牠的神經元結合之後，形成功能有如整合中樞的結構體，可接收知覺訊息，再根據這些訊息做出適當的反應動作。

“Jellyfish do a lot more than people think,” said Dr. Satterlie, adding that the claim they have no centralized nervous system, is “flat-out wrong.”
沙特里說：「水母的本領遠比一般人想像的要大。」他接著又說，所謂水母缺少中樞神經系統的說法「壓根兒就錯了」。

Dr. Albert insists that a jellyfish has a brain. In studying moon jellyfish in Roscoe Bay, he discovered that they are not passive floaters. When the tide flows out, they ride the wave until they hit a gravel bar, and then dive down to reach still waters. They remain there until the tide starts flowing back in, when they rise and get swept back into the bay. He also learned that the jellies have salinity meters to avoid the fresh water deposited by mountain snowmelt. And they like to form schools.
艾伯特認定水母具有大腦。他研究羅斯科灣的海月水母時發現，牠們並不是只會隨波逐流的被動式漂浮生物。海水退潮時，牠們會隨著浪潮退去，直到觸碰礫石沙洲，接著會往下沉到呈靜止狀態的水中，並一直留在原地。浪潮開始去而復返時，牠們會上升，並隨著浪潮回到灣內。艾伯特同時發現，水母具有可用於測量鹽性的計量器，使牠們得以避開山脈雪融形成的淡水。此外，牠們還喜歡成群結隊。

“If a moon jelly gets touched by a predatory jellyfish, it turns and swims up,” Dr. Albert said.
艾伯特說：「如果一隻海月水母被另一隻掠食性的水母觸碰到，牠會立刻轉身並往上游動。」

“These are not simple reflexes. They’re organized behaviors,” he said.
他說：「這不是單純的反射動作，而是有組織的行為。」

“That’s what a brain does,” he added. “It controls behaviors.”
他補充道：「這正是大腦發揮功能的結果。大腦控制行為。」

At the National Aquarium here, the jellyfish exhibit includes specimens that look like beating hearts, others that resemble spotted toadstools, and still others like parasols with ruffled streamers.
馬里蘭州巴爾的摩市國立水族館展示的水母種類形形色色，有的看似正在跳動的心臟，有些像是斑點傘菌（毒蘑菇），更有一些看來像是附有皺褶飄帶的陽傘。

They’re mesmerizing to visitor – a good thing, because the infrastructure needed to keep them can cost millions of dollars. “Keeping jellyfish,” said Vicky Poole, the exhibit manager, is “a little like maintaining phlegm.”
這些水母讓參觀者深深著迷。這是好事，因為用於保存牠們所需的基礎設施可能耗資數百萬美元。展示區經理維琪‧普爾說：「留住水母有點像是留住黏液。」

In the wild, jellies are found in open oceans, along coasts and in lagoons, and a few can handle fresh water. With their modest oxygen requirements, jellies can grow in post-algal “dead zones” and other polluted waters where most marine life can’t – not surprising for a group that has weathered five past mass extinctions.
在野外，水母可見於開放的海域、沿海水域與潟湖中。有一些水母可以適應淡水。由於對氧氣的需求不高，水母可以在多數海洋生物無法存活的後海藻「死亡區域」（含氧量不足以維繫水生生物生存的水域）及受汙染水域生長。對曾經挺過五次物種大滅絕的水母而言，這倒也不足為奇。

Jellies range in size from the fingernail-size Australian Irukandji to the lion’s mane jelly, with a bell 2.5 to 3 meters wide and tentacles trailing 30 or more meters.
水母體型大小不一，小者如澳洲伊魯坎吉水母，約只有指甲般大，大者如獅鬃水母，鐘狀體的寬度可達2.5公尺到3公尺，拖曳的觸鬚可長達30公尺，甚至更長。

A hallmark of jellies, their radial symmetry, allows them to swim or drift in straight lines.
呈輻射狀對稱是水母的特徵之一，這使牠們得以直線游動或漂浮。

All jellies are carnivorous, and they use their tentacles as drift nets. Should a fish brush against them, stinging cells release tiny harpoons packed with neurotoxins. In the most venomous jellyfish, the toxins work quickly.
水母全都是肉食性的，而且以觸鬚充當流刺網。如果一條魚不慎與牠擦身而過，水母的刺細胞會立刻釋出含有神經毒素的小叉。如果是毒性最強的水母，毒素會立刻發揮作用。

“If a jellyfish were to swallow a prawn that wasn’t completely dead,” said Dr. Garm, “the prawn would puncture its stomach.” Some of the poisons, like that of the sea wasp, an Australian box jelly, can kill humans in seconds. But because the harpoons are so shallow, swimmers can protect themselves by covering their exposed skin with pantyhose.
賈恩姆說：「如果一隻水母準備吞噬一隻尚未完全死亡的對蝦，對蝦會刺穿它的胃。」有些水母的毒素，如澳洲箱型水母之一的殺手水母（又稱海黃蜂），可在短短幾秒鐘內致人於死。不過由於小叉並不深，游泳者只要以褲襪蓋住皮膚就可以確保平安無事。

In their new report, Dr. Garm’s team studied box jellyfish’s complex battery of eyes. Not only do they have a cornea, lens and retina, but they are suspended on stalks anchored by heavy crystals.
賈恩姆團隊在其最新發表的研究報告中，說明了箱形水母的複雜眼睛組合。牠們不但有眼角膜、晶體及視網膜，而且懸吊在以厚重水晶體固定的細長支撐物上。

“The crystal works as a weight,” Dr. Garm said. “No matter how the jellyfish reorients itself, the stalk bends and the eyes face up.”
賈恩姆表示：「水晶體的功能有如錘。無論水母如何調整自己的方向，支撐物都會彎曲，讓眼睛始終向上。」

The researchers determined that the jellyfish, which feed in murky mangrove swamps, look upward for navigational guidance. Every night, they are swept away from the trees and sink to the bottom. Every morning they must return or risk starvation.
研究人員認為，在混濁紅樹林沼澤區覓食的箱形水母靠著往上看以確定行進方向。每天入夜時，牠們會隨著潮水離開紅樹林，然後沉入水底，次日早上必須回到原地，否則就會挨餓。

As they rise, their upturned eyes scan the sky, until they spy the mangrove canopy, and they start swimming home.
在上升時，水母向上翻轉的眼睛會掃描天空，直到看見紅樹林的樹冠為止。這時候，牠們會開始游回原地。

原文參照
http://www.nytimes.com/2011/06/04/business/global/04murano.html

Slideshow: The Complexity of Jellyfish
http://www.nytimes.com/slideshow/2011/06/07/science/0607-jellyfish.html

2011-06-21/聯合報/G5版/UNITEDDAILYNEWS 陳世欽譯  原文參見紐時週報十版上