蝙蝠之劫 生命力聚散與死神的召喚

LEWISBURG, PA. — The 10 hibernating little brown bats hang from a corner of their tailor-made refrigeration chamber at Bucknell University like a clump of old potato skins, only less animated. In torpor, bats become one with their wintry surroundings, their body temperatures falling to just above freezing, their heart rates slowing to one or two beats a minute, their breathing virtually undetectable.

賓夕法尼亞州劉易斯堡——10只冬眠的小棕蝙蝠倒掛在巴克內爾大學專爲它們定製的低溫艙室裏面，彷彿幾塊陳土豆皮，只是幾乎比土豆皮更缺乏生氣。冬眠的蝙蝠會和周遭的冬日環境融爲一體，體溫降低至略微高於冰點，心率只有每分鐘一到兩次，呼吸幾乎感覺不到。

But suddenly, a male yanks himself free of the bunch and hops down to a dish on the floor. After taking a long, slow drink of water, the bat uses the claws on his folded wings to hoist himself along the wire mesh of the chamber, his motions angular, deliberative and spidery. A second bat rappels down for a drink, and then a third.

突然，其中一隻雄性蝙蝠一躍而起，跳到地板上的一隻碟子前面。它不緊不慢地飲着水，半晌，才用它那摺疊膜翼上的腳爪爬上艙室側壁的鐵絲網。它沿着傾斜的路線向上爬，彷彿深思熟慮的樣子，那姿態有點像蜘蛛。第二隻蝙蝠翩然而下，去喝水；然後是第三隻。

“Well, that’s a lucky break,” said Thomas Lilley, a tall and crisply composed postdoctoral fellow from Finland. “Multiple rounds of bat drama.”

“真是太走運了，蝙蝠世界好戲連臺，”托馬斯·利理(Thomas Lilley)說道。這位清炯沉靜的高個子學者來自芬蘭，在這裏做博士後。

As Bucknell’s de facto bat concierge, Dr. Lilley helps wild bats acclimate to life in captivity, a difficult task with an urgent spur. He and his colleagues are Laboring mightily to understand white-nose syndrome, a devastating fungal disease that has killed at least six million North American bats since it first appeared in Albany a decade ago and that threatens to annihilate some bat species entirely.

利理博士是巴克內爾大學的蝙蝠大管家，他負責讓野生蝙蝠適應籠舍的生活。這份工作很艱鉅，又很緊迫。他和同事們下了巨大的工夫，研究一種叫做白鼻綜合症的疾病。這是一種真菌引起的致命疾病，10年前在奧爾巴尼首次發現以來，北美地區至少600萬蝙蝠死於這種病，一些種的蝙蝠幾乎因而絕跡。

Because the fungus attacks bats as they hibernate in caves, the researchers are exploring the complex biology of normal bat hibernation, and so-called arousal bouts turn out to be a big part of the puzzle, said Kenneth Field, an associate professor of biology.

這種真菌是在冬眠期感染蝙蝠的，因此，科學家正在研究正常蝙蝠冬眠的複雜生理現象。其中被稱爲間歇性甦醒的行爲成了揭開謎底的關鍵，生物學副教授肯尼斯·菲爾德(Kenneth Field)說。

Hibernating bats will warm themselves out of torpor every week or two throughout the winter, for several hours at a stretch. Though researchers don’t yet understand the reasons for the thermal interludes, they have quantified just how important such thaws must be to bat survival.

冬眠中的蝙蝠每隔一到兩週，會醒過來幾個小時。學者還不清楚這種體溫升降週期的原因，但他們已經可以量化這種甦醒對蝙蝠生存的重要性了。

“All the work that bats do during the fall, feeding nonstop and putting on fat until they’re like butterballs on wings, and 90 percent is spent to sustain the winter warm-ups,” said DeAnn Reeder, a professor of biology and one of the nation’s leading bat ecologists.

“整個秋天，蝙蝠唯一的工作就是不停進食，儲存脂肪，直到它們吃得好像黃油球長了翅膀似的，這些能量90%都被用在冬眠中的間歇性甦醒時了，”美國權威蝙蝠生態專家、生物學教授德安·裏德(DeAnn Reeder)說。

New research suggests that white-nose syndrome begins disrupting the arousal-torpor cycle long before any telltale white fuzz appears on the bat’s face and wings, and that the disorder really spins out of control when the bat’s immune system behaves in a distinctly unbatlike manner, mounting a zealous response against the fungal spores.

新的研究顯示，早在蝙蝠面部和翼上出現病態的白色絨毛之前，白鼻綜合症已經開始擾亂它們的休眠覺醒週期。等到免疫系統開始出現迥異於正常蝙蝠的行爲方式，對真菌孢子做出強烈反應，就已經病入膏肓了。

Unbatlike because, as scientists are discovering, the bat immune system is astonishingly tolerant of most pathogens — a trait that could pose risks to people, but that also offers clues to preventing human diseases of aging, including cancer.

之所以說這時的免疫系統異於正常蝙蝠，是因爲科學家已經知道，蝙蝠的免疫系統對多數病原體有着驚人的耐受力。蝙蝠的這種特性會給人類構成威脅，但也爲人類攻克衰老型疾病，包括癌症，提供了啓示。

Evidence is mounting that bats can serve as reservoirs of many of the world’s deadliest viruses, including the pathogens behind Ebola, Marburg and related hemorrhagic fevers; acute respiratory syndromes like SARS and MERS; and even familiar villains like measles and mumps.

不斷有證據表明，蝙蝠可以成爲世界上衆多致命病毒的貯主，包括埃博拉、馬爾堡及引發相關出血熱的病原體，還有烈性呼吸道疾病如SARS和中東呼吸道綜合症的背後元兇。麻疹和腮腺炎也可由蝙蝠傳播。

Yet bats appear largely immune to the many viruses they carry and rarely show signs of the diseases that will rapidly overwhelm any human, monkey, horse, pig or other mammalian host the microbes manage to infiltrate.

但是，蝙蝠對自身攜帶的這些病毒基本都可以免疫，很少得病。任何人類、猴子、馬、豬和其他哺乳類宿主感染後都會很快病倒。

Scientists have also learned that bats live a seriously long time for creatures of their small size. The insectivorous Brandt’s bat of Eurasia, for example, weighs an average of just six grams, compared with 20 grams for a mouse. But while a mouse is lucky to live for a year, the Brandt’s bat can survive well into its 40s — a disparity between life span and body mass that a report in Nature Communications called “the most extreme” of all mammals.

科學家還發現，作爲體型微小的動物，蝙蝠的壽命極長。亞歐大陸上的布氏鼠耳蝠，體重平均只有六克，一隻老鼠也有20克。但老鼠活到一年已屬長壽，而布氏鼠耳蝠卻能活到40多歲。發表在《自然通訊》上的一篇文章稱如此大的壽命與體重差異是所有哺乳動物中“最極端的”。

Bats may be girded against cancer, too. “At this stage, the evidence is anecdotal,” said Lin-Fa Wang, a bat virologist at the Duke-NUS Graduate School in Singapore and the Australian Animal Health Laboratory in Geelong. “But of all the bat biologists I’ve spoken with, I’ve only heard of one or two cases of bat tumors.”

蝙蝠可能還不會得癌症。“現階段，還只有零星的證據，”新加坡杜克-國大醫學研究生院和澳大利亞吉朗的澳大利亞動物衛生實驗室的蝙蝠病毒學家王林發（音譯，Lin-Fa Wang）說。“但我和這麼多蝙蝠病毒學家交談過，我只聽說過一兩例蝙蝠得腫瘤的案例。”

Researchers are scrutinizing bat DNA and the details of the bat vocation for clues to what sets the flying mammals apart from other members of the lactating clade. Preliminary findings indicate that bats’ apparent indifference to the viral throngs they harbor, together with their Methuselah-grade longevity, probably arose from the adaptations needed to grant them the power of flight.

科學家正在研究蝙蝠DNA和蝙蝠生理機能的細節，希望找到是什麼讓這種會飛的哺乳動物顯得如此與衆不同。初步的發現顯示，蝙蝠對體內的病毒顯得若無其事，壽命又超長，這似乎都與它們適應飛翔生活有關。

Bat experts argue that a keener understanding of bat biology could not only help prevent the next outbreak of Ebola or other cross-species “zoonotic” infection, but also offer a fresh take on immune and inflammatory disorders like diabetes or heart disease.

蝙蝠專家認爲，更深入瞭解蝙蝠的生理機能，不但有助於避免下一次埃博拉或其他跨物種疫情的大爆發，而且也會給免疫系統和炎症類疾病如糖尿病和心臟病的研究提供一個新的角度。

Scientists warn against misguided calls in some areas for the culling of bats as a way to combat the risk of viral transmission, and they urge the public not to succumb to old-fashioned bat phobia that long linked bats to witches, vampires, demons and cobwebs.

科學家呼籲不要在一些地區盲目撲殺蝙蝠，以爲那樣做可以降低病毒傳播的風險；而且他們也敦促公衆，不要被傳統的蝙蝠恐懼心理影響，因爲歷史上蝙蝠往往和巫術、吸血鬼、惡魔和蛛網聯繫在一起。

Bats play essential roles in the environment, researchers said. Insectivorous bats are the top predators of night-flying insects, including mosquitoes: Dr. Reeder estimated that for every million bats killed by white-nose syndrome, 692 tons of insects go undevoured each summer. Fruit- and nectar-eating bats are major pollinators and seed dispersers.

他們說，蝙蝠在自然環境中發揮着重要的作用。獵食昆蟲的蝙蝠是夜行昆蟲包括蚊子的頭號天敵：裏德估計，每有100萬隻蝙蝠死於白鼻綜合症，一個夏季就會有692噸昆蟲不能被消滅。攝食果實和吸食花蜜的蝙蝠是重要的傳播花粉、散播種子的物種。

“A politician in Australia said, ‘Bomb the bats,’ ” Dr. Wang said. “But if you do that, you’ll destroy the ecosystem and then you’ll get more infectious disease, not less.” The risks from wanton batricide could well be immediate: Recent research suggests that bats are likeliest to shed viral particles when they are under stress and their numbers are shrinking.

王林發說：“澳大利亞一個政客說要轟炸蝙蝠。如果你這麼做，你會破壞生態系統，結果傳染性疾病會更多，而不是更少。”過量施用滅菌劑的危險很可能會即時顯現：近期的研究顯示，蝙蝠在承受生存壓力和種羣縮小的情況下最容易傳播病毒。

Besides, wherever you go, there they are. With some 1,200 species under the Chiroptera trademark, bats are the second-most populous mammalian order, after rodents. “One in every five mammals is a bat,” Dr. Reeder said.

況且，無論你到哪兒，蝙蝠無處不在。在哺乳動物綱翼手目下面，有大約1200個蝙蝠的種，它們是僅次於齧齒目的第二大哺乳動物類羣。“所有的哺乳動物，五分之一是蝙蝠，”裏德說。

They’re found on every continent but Antarctica and range in size from the Kitti’s hog-nosed bat — which at an inch long vies with the Etruscan shrew for the title of world’s smallest mammal — to the giant golden-crowned flying fox, with a wingspan approaching six feet and a soulful face that Raina Plowright, an infectious disease ecologist and bat expert at Montana State University, likened to that of a puppy dog.

除了南極洲之外的各大陸上都有蝙蝠分佈，它們的體型從僅有1英寸長的基氏豬鼻蝠（和小臭鼬並稱世界最小的哺乳動物）到巨大的鬃毛利齒狐蝠，翼展接近6英尺，有一張表情豐富的臉，蒙大拿大學傳染病生態學家和蝙蝠專家雷娜·普羅萊特(Raina Plowright)說樣子就像小狗。

Scientists traditionally have divided bats into two big suborders: the fruit-eating megabats and insect-eating microbats, deeming the groups so distinct they might have evolved flight independently.

科學家傳統上把蝙蝠分爲兩個亞目：食果實的大型蝙蝠和食昆蟲的小蝙蝠，認爲這兩個羣體如此不同，一定是彼此獨立進化出飛翔能力的。

Yet a recent genomic analysis in the journal Science reveals that the ability to fly dates to the earliest days of the bat lineage, some 90 million years ago, and that megas did not split from micros for another 10 million years, after which the micros alone evolved the capacity for echolocation, to help them hunt their insect prey.

但是，不久前發表於《科學》雜誌的一個基因組分析顯示，飛行的能力早在蝙蝠大家族形成之初就已經具備了，那還是9000萬年前的事，之後又過了1000萬年，大蝙蝠才和小蝙蝠分道揚鑣，那以後，小型蝙蝠才獨立進化出了回聲定位的功能，用來獵食昆蟲。

The new study also described other important traits that bats of both suborders share. For one thing, researchers found an “unexpected concentration” of genes involved in repairing damaged DNA. Those fix-it factors, the scientists proposed, are the bat’s solution to the blistering demands of flight.

新研究還發現了兩大類羣之間更多相似點。比如，科學家發現了一個基因的“意外集羣”，這些基因和修復受損DNA的需要有關。科學家認爲，這些修復基因可能是根據飛行生活的高強度需求而產生的。

When a bat flies, its heart beats an impressive 1,000 times a minute, and its metabolism ramps up 15-fold over resting rate. By contrast, said David Blehert of the United States Geological Survey’s National Wildlife Health Center in Madison, Wis., the metabolism of a running rodent is seven times normal, “and that’s only for a short burst, whereas a bat can fly at 15-fold metabolic rate for hours.”

蝙蝠飛行時，心跳達到驚人的每分鐘1000次，代謝水平達到安靜狀態的15倍。相比之下，齧齒類動物奔跑中的代謝水平只是安靜狀態下的七倍，威斯康星州麥迪遜美國地質測繪局國家野生動物衛生中心的大衛·布萊赫特(David Blehert)說。而且那只是齧齒類“短跑時的能量消耗，蝙蝠卻能以15倍的代謝速率飛行好幾小時”，他說。

All that fiery flapping ends up generating a huge number of metabolic byproducts called free radicals, which could mutilate the bat’s DNA were it not for its extra-strength molecular repair crew. And countering DNA damage happens to be a great strategy for overall health, which could explain bats’ exceptional longevity and apparent resistance to cancer.

如此高能耗的振翅運動，其結果是產生大量代謝副產品，被稱爲自由基。如果不是有超強的修復基因，自由基就會破壞蝙蝠的DNA。而且，對抗DNA受損的機能碰巧還是一個偉大的健康策略，可以解釋蝙蝠超長的壽命和抗癌特性。

Other clues to bat exceptionalism can be found in its molecular profile. Immune factors that serve as the body’s first responders have been ramped up, while immune molecules that in most mammals turn aggressive at later stages of an infection are damped down in bats.

蝙蝠的分子特徵也揭示着它們的獨特性。作爲機體第一道防線的免疫因子被極大地加強，多數哺乳動物體內在感染後積極反抗的免疫分子，在蝙蝠體內卻被弱化。

As a result, Dr. Wang said, “when a virus comes in, bats are very efficient at handling it, but they don’t overreact.” And the overreaction of the body’s immune system, scientists have found, often proves far more dangerous than the viral infection itself.

結果就是，“病毒侵入後，蝙蝠可以高效應對”，王林發說。“但它們不會反應過激。”科學家發現，這種過激反應經常比病毒感染本身更危險。

Researchers suggest that changes to the bat’s immune system originated as part of the heightened demand for DNA repair, and later proved valuable for its general life strategy.

科學家認爲，蝙蝠免疫系統的變化源於這種對修復受損DNA的高強度需求，後來也成爲它們日常生存中的有價值的功能。

Bats often live in colonies of hundreds of thousands. They travel long distances and are exposed to a staggering array of pathogens. They cannot afford to be flustered by every freeloading microbe, and for the most part, they do not.

蝙蝠往往是數十萬只結成羣體生活。它們長距離飛行，接觸到多種多樣的病原體。如果每次染上一種微生物，它們都反應過激，蝙蝠會受不了。事實上它們也很少反應過激。

That makes the lethality of white-nose syndrome that much more confounding. “Here we have an animal that can survive some of the scariest viruses we know,” Dr. Blehert said, “and it’s undone by a common soil fungus.”

這就讓白鼻綜合症的致命性越發令人不解。“這種動物不怕我們已知的最可怕的病毒，一種普通的土壤裏的真菌卻能要了它的命，”布萊赫特說。

He and his colleagues have found that, starting at the earliest stages of infection, afflicted hibernating bats begin burning twice as much energy as unaffected bats. Dr. Reeder and her colleagues have shown that bats with white-nose come out of hibernation twice as often as healthy bats.

他和同事發現，在感染的最初階段，冬眠的蝙蝠消耗的能量達到健康蝙蝠的兩倍。裏德和同事們也發現，染上白鼻病的蝙蝠從冬眠中甦醒的次數是健康蝙蝠的兩倍。

And while normal bats spend much of their arousal time resting, “sick bats don’t,” she said. “Instead, they’re grooming constantly, so their arousals are even more costly.” The ultimate blow may come from the bats’ immune response to the fungus, which preliminary evidence suggests is unusually strong.

正常蝙蝠醒來後大部分時間安靜不動，但“染病的蝙蝠不是這樣，”她說。“它們不停地梳理毛髮，因此它們消耗能量也更多。”最後的打擊可能來自免疫系統對真菌的反應，初步研究發現，這種反應通常很強烈。

“And that,” Dr. Field said, “could be what’s dooming the bats.”

“那可能就是導致蝙蝠死亡的原因，”菲爾德說。