LINCOLN, Massachusetts – Sara Lewis is fluent in firefly. On this night she walks through a farm field in eastern Massachusetts, watching the first fireflies of the evening rise into the air and begin to blink on and off. Dr. Lewis, an evolutionary ecologist at Tufts University, points out six species in this meadow, each with its own pattern of flashes.
莎拉‧劉易斯對螢火蟲真是如數家珍。這天晚上，她步行穿越麻州東部一塊農地，觀察當晚飛到空中，開始發光閃啊閃的第一批螢火蟲。劉易斯博士是鄰近塔夫茨大學的演化生態學家，她指出，這塊草地一共有六種螢火蟲，每種都有自己的閃光模式。

Along one edge of the meadow are Photinus greeni, with double pulses separated by three seconds of darkness. And near a forest are Pyractomena angulata, which make Dr. Lewis’s favorite flash pattern. “It’s like a flickering orange rain,” she said.
在草地邊上的，是一種叫Photinus greeni的螢火蟲，每波發兩次光，中間間隔三秒。在靠近森林那頭的，叫Pyractomena angulata，劉易斯最愛牠閃光的模式。「就像下著橙光閃閃的雨，」她說道。

The fireflies flashing in the air are all males. Down in the grass, Dr. Lewis points out, females look for flash patterns of males of their own species, and sometimes they respond. Dr. Lewis takes out a penlight and clicks it twice, in perfect Photinus greeni. A female Photinus greeni flashes back.
在空中發光閃爍的，都是公螢。劉易斯指出，母螢待在下方草叢，依照閃光模式搜尋和自己同種的公螢，三不五時回應一下。劉易斯拿出閃光筆，連按兩次，和Photinus greeni的閃光頻率簡直一模一樣。有一隻Photinus greeni母螢以閃光應答。

“Most people don’t realize there’s this call and response going on,” Dr. Lewis said. “But it’s very, very easy to talk to fireflies.”
「大多數的人都不知道，那裡正進行著這樣的呼叫與應答，」劉易斯說。「其實，和螢火蟲對話，非常、非常、非常容易。」

For Dr. Lewis, this meadow is the stage for an invertebrate melodrama, of courtship duets and competitions for affection, of cruel deception and gruesome death. For the past 16 years, Dr. Lewis has been coming to this field to decipher the evolutionary forces at play in this production.
對劉易斯而言，這塊草地恰似無脊椎動物表演通俗劇的舞台，上演打情罵俏、爭風吃醋、狠心欺騙、不得好死等戲碼。過去16年間，劉易斯頻頻造訪，目的就在解開這齣大戲當中運作的進化力密碼。

She searched for mating fireflies in the evening, marked their locations with surveyor’s flags and then revisited them through the night. They were still mating at dawn.
夜裡，她搜尋交尾中的愛侶，在那個地點插上標示旗；夜更深時，再去拜訪牠們。天已破曉，牠們仍在交尾。

“It was cool to watch the sun rise and see the couples breaking up and the females crawling down the grass to lay their eggs,” Dr. Lewis said.
「看到太陽升起時，這對愛侶才分開，母螢沿草莖爬下，產卵，實在很酷，」劉易斯說。

The more Dr. Lewis watched firefly courtship, the clearer it became that the females were carefully choosing mates. They start dialogues with up to 10 males and can keep several conversations going at once. But a female mates with only one male.
劉易斯觀察愈多的螢火蟲求歡戲碼，心裡就愈明白，母螢選擇交尾對象非常慎重。母螢可和多達10隻公螢展開對話，而且可以同時和數隻公螢交談。但到最後，只有一隻能成功達陣。

Dr. Lewis wondered if the female fireflies were picking their mates based on variations in the flashes of the males. She took female fireflies to her lab, where she has computer-controlled light systems that can mimic firefly flashes.
令劉易斯好奇的是，母螢是否根據公螢閃光的變化擇偶？她捉了幾隻母螢到實驗室，那裡的電腦閃光控制設備，可以模擬螢火蟲發光閃爍。

The female fireflies turned out to be quite picky. In many cases, a male flash got no response at all. In some species, females preferred faster pulse rates. In others, the females preferred males that made long-lasting pulses.
結果發現，母螢真的很挑剔。在許多實驗案例中，公螢怎麼閃光，母螢就是不回應。有些品種的螢火蟲，母螢喜歡較快的閃光頻率；在其他的品種中，母螢則喜歡發光時間較長的公螢。

In many invertebrate species, the males provide females with food to help nourish their eggs. Dr. Lewis and her colleagues discovered that fireflies also made these so-called nuptial gifts – packages of protein they inject with their sperm.
在其他無脊椎動物中，公的會提供母的食物協助孵卵。劉易斯和研究同仁發現，螢火蟲也有這種所謂的「聘禮」現象－公螢藉著射精，把大量的蛋白質送給母螢。

Receiving nuptial gifts, Dr. Lewis and her colleagues have shown, can make a huge difference in the reproductive success of a female firefly. “It just about doubles the number of eggs a female can lay in her lifetime,” she said.
劉易斯和研究同仁指出，母螢有沒有接受聘禮，對繁殖是否成功，真的差很大。「母螢畢生產卵的數量，約莫可因而多一倍，」她說。

In at least some species, females may use flashes to pick out males with the biggest gifts. “In some cases they could be honest signals, and in some cases they could be deceptive signals,” Dr. Lewis said.
至少，某些螢火蟲的母螢會利用閃光，挑選禮送得最大的公螢。「在某些案例中，母螢的訊號是真心；但在部分案例，母螢訊號純屬假意，」劉易斯說。

Deception may, in fact, evolve very easily among fireflies. It turns out that a male firefly does not need to burn many extra calories to make flashes. “It takes some energy, but it’s tiny. It’s less costly for a male than flying around,” Dr. Lewis said.
事實上，螢火蟲要彼此欺騙，易如反掌。實驗發現，公螢發光閃爍，根本不需額外燃燒許多卡路里。「那的確會消耗一些能源，但微不足道。對公螢而言，不會比到處瞎飛費勁，」劉易斯說。

If making light is so cheap for males, it seems odd that they have not all evolved to be more attractive to females. “What is it that keeps their flashes from getting longer and longer or faster and faster?” Dr. Lewis asked.
如果公螢發光這麼容易，那牠們不能全部朝更吸引母螢的方向演化，似乎就有蹊蹺。劉易斯問：「公螢的閃光不能愈來愈長或愈來愈快的原因何在？」

One answer to her question may come from an animal called photuris, a firefly that eats other fireflies. The scientists found that Photuris was more likely to attack when flash rates were faster. In other words, conspicuous flashes – the ones females prefer – also make males more likely to be killed. “At least where Photuris predators are around,” Dr. Lewis said, “there’s going to be a strong selection for less conspicuous flashes.”
答案之一，可能要從一種叫Photuris，會獵食其他螢類的螢火蟲身上去探索。科學家發現，閃光愈快的螢火蟲，愈可能遭Photuris攻擊。換言之，閃光愈醒目的公螢，雖較能討母螢歡心，卻也愈容易惹來殺身之禍。「至少，只要附近有Photuris，公螢選擇招搖閃爍的意願就低很多。」

關鍵字句

螢火蟲firefly 又稱lightning buglighting bug， 昆蟲專家統計，全球已知的螢火蟲約2000多種，大多生長在氣候溫和（temperate）的熱帶（tropical environment），地處亞熱帶（subtropics） 的台灣， 已確定約有44 種。根據德籍昆蟲專家H. Sauter，台灣研究螢火蟲始自1910 年；日據時代，日人也積極投入研究，當時約調查出32種。

科學家對螢光蟲的發光，興趣很大，因為目前效能比白熾光燈泡（Incandescent light bulb）及省電燈泡（compact fluorescent light bulb, CFL）更高的發光二極體（Light Emitting Diode），光能轉換效能（efficiency of energy converting into light）只略高於20%，而且生產成本仍壓不下來，而螢火蟲生物發光（Bioluminescence）效能則高達90%。若能以其為師，則是人類一大福音。

維基百科指出，螢火蟲的生物發光，屬於化學作用（chemical-produced）的「冷光」（cold light），不含紫外線（ultraviolet） 或紅外線（infrared rays），不會產生高溫，有黃、綠、淡紅（pale red）等色，缺點是光度弱，只在昏暗的（crepuscular）環境中才比較顯著。

作者稱讚莎拉‧ 劉易斯博士對螢火蟲很有研究（fluent in firefly）。根據韋氏字典，fluent 除作「流動」capable of flowing、「流利」speak fluent English、「能言善道」a fluent speaker 解外，亦作專精某業showing mastery of a subject 解，如fluent in mathematics。

原文參照
http://www.nytimes.com/2009/06/30/science/30firefly.html 

2009-07-28/聯合報/G9版/UNITED DAILY NEWS 蔡繼光 原文請見7月22日紐時周報十版右