2018-08-17 09:47     供稿單位: 新航道    

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  The first clear evidence of a sense of magnetism in insects

  《昆蟲能感知磁力的個確鑿證據》 摘自The Economist June 23rd 2018


  Bogong moths are not as glamorous as monarch butterflies. Their name means “brown” in Dhudhuroa, a now-extinct language once spoken in eastern Australia, where they live. And that is what they are—in contradistinction to a monarch’s glorious orange and black. But drab though they may be, bogongs surely match monarchs in migratory tenacity.


  布岡夜蛾 (澳大利亞的一種夜蛾)不如帝王蝴蝶那么魅力四射。它們的名字在Dhudhuroa語言中是棕色的意思—Dhudhuroa語曾在澳大利亞東部使用的一種語言,現已消亡,Bogone飛蛾也在那里生活。就是這種褐色的飛蛾,與帝王蝶鮮艷的橙黑相間的顏色顯著不同。不過盡管它們看起來單調乏味,這些飛蛾在遷徙當中表現出來的堅韌卻可以與帝王蝴蝶相媲美。



  Monarchs, famously, fly across much of North America, starting or ending their journeys in one of a few groves of trees in central Mexico. An adult monarch, though, migrates only once. During their lifetimes, Bogong moths that survive to do so will make a pair of 1,000km journeys. One is from their winter birthing grounds in sun-scorched Queensland and New South Wales to a small number of cool caves in the mountains of Victoria where they will spend the summer months resting. The other is back again.





  How they find their way to and from these caves is a mystery. But it is less mysterious in light of work by David Dreyer and Eric Warrant at the University of Lund, in Sweden, published this week in Current Biology. Dr. Dreyer and Dr. Warrant suggest that bogongs use a combination of magnetic compasses and topography.


  關于它們是如何找到飛往這些洞穴的仍然是個謎。但是從瑞典隆德大學David Dreyer和Eric Warrant發表在本周《當代生物學》期刊上的文章來看,就不那么神秘了。Dreyer和Warrant博士認為布岡夜蛾是結合使用了磁針羅盤以及地形兩個方法。



  Several types of animals, including birds, turtles and fish, are known to sense and navigate by Earth’s magnetic field, but evidence for such powers in migratory insects has been tenuous. A lone experiment has suggested monarchs may be able to detect magnetism—but, if so, that is probably just a back-up mechanism. Abundant other evidence suggests monarchs navigate mainly by the sun. For a night-flying moth, though, that is not an option.




  To explore any magnetic sense bogongs might possess Dr. Dreyer and Dr. Warrant used light traps to capture hundreds of the moths during their migrations over the course of two seasons. They and their colleagues then glued stalks to the moths’ backs and, using those stalks, tethered the insects inside a flight simulator in which they were free to “fly” in any direction they wished—though, of course, they could not actually move. The simulator was surrounded by a pair of magnetic coils that cancelled out Earth’s field and replaced it with one of similar strength that could be turned through 120°. Because experiments like these, conducted on birds such as pigeons, have revealed that those animals do use Earth’s magnetic field for navigation, the researchers hoped their set up would to do the same with the moths.


  為了探究布岡夜蛾可能擁有的磁感應,Dreyer和Warrant博士在兩個季節遷徙時利用光捕捉器抓捕了數百只飛蛾。然后他們及其同事們將追蹤裝置用膠水粘到飛蛾的后背上,同時利用這些追蹤器把這些昆蟲拴到一個模擬飛行器中,在那里面它們可以自由地朝任何方向飛--- 當然它們實際上無法移動。這個模擬器周圍有一對電磁線圈可以抵消地球磁力并用類似強度但可以120度轉向的磁力取代。因為類似這樣的實驗曾在鴿子這樣的鳥類身上做過,表明了這些動物確實使用地球磁場導航,研究人員希望他們的設置能夠在飛蛾方面的出同樣的結果。



  It did not. Unlike birds, the moths either failed to react to the movement of the field or reacted in an unpredictable manner. Unwilling to give up their hypothesis, though, Dr. Dreyer and Dr. Warrant wondered if they had simplified their apparatus too much. Many nocturnal insects have exquisite night vision, so the two researchers thought that perhaps the absence of visual cues within their flight simulator, which had been intentional, might actually have confounded their experiment.


  但是并沒有。跟鳥類不同,飛蛾要么無法對磁場運動作出反應,要么反應的方式沒法預測。不過,Dreyer和Warrant博士并不想放棄他們的假設,他們相要知道是否是設備太過簡化的原因。很多夜間活躍的昆蟲都有極其敏銳的夜視能力,因此這兩位研究人員認為也許是飛行模擬器當中缺少了視覺信號--- 是刻意為之的–可能是實驗失敗的原因。



  To test this, they lined the simulator’s interior with white felt and introduced a triangular black “mountain” above a black horizon as a landmark. During the experiment they started by keeping their magnetic field in alignment with Earth’s and then, after five minutes, began moving it. The moths continued to travel in the same direction with respect to the field for about three minutes after the field began moving but then, presumably as they realised that their visual cue and their magnetic cue were now in conflict with one another, they became disoriented.





  This finding suggests that the moths do indeed depend on a magnetic sense to navigate during their long journey, but that they cannot, as it were, fly on instruments alone. They have rather to have sight of visual markers as well. The test of this will be in the next series of experiments Dr. Dreyer and Dr. Warrant are planning, which will move the “mountain” and the magnetic field simultaneously. That, they hope will fool the insects into thinking they are flying home.