蝙蝠之劫 生命力聚散与死神的召唤

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.

宾夕法尼亚州刘易斯堡——10只冬眠的小棕蝙蝠倒挂在巴克内尔大学专为它们定制的低温舱室里面，仿佛几块陈土豆皮，只是几乎比土豆皮更缺乏生气。冬眠的蝙蝠会和周遭的冬日环境融为一体，体温降低至略微高于冰点，心率只有每分钟一到两次，呼吸几乎感觉不到。

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，其中一只雄性蝙蝠一跃而起，跳到地板上的一只碟子前面。它不紧不慢地饮着水，半晌，才用它那折叠膜翼上的脚爪爬上舱室侧壁的铁丝网。它沿着倾斜的路线向上爬，仿佛深思熟虑的样子，那姿态有点像蜘蛛。第二只蝙蝠翩然而下，去喝水；然后是第三只。

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

“真是太走运了，蝙蝠世界好戏连台，”托马斯·利理(Thomas Lilley)说道。这位清炯沉静的高个子学者来自芬兰，在这里做博士后。

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.

利理博士是巴克内尔大学的蝙蝠大管家，他负责让野生蝙蝠适应笼舍的生活。这份工作很艰巨，又很紧迫。他和同事们下了巨大的工夫，研究一种叫做白鼻综合症的疾病。这是一种真菌引起的致命疾病，10年前在奥尔巴尼首次发现以来，北美地区至少600万蝙蝠死于这种病，一些种的蝙蝠几乎因而绝迹。

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.

这种真菌是在冬眠期感染蝙蝠的，因此，科学家正在研究正常蝙蝠冬眠的复杂生理现象。其中被称为间歇性苏醒的行为成了揭开谜底的关键，生物学副教授肯尼斯·菲尔德(Kenneth Field)说。

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两周，会醒过来几个小时。学者还不清楚这种体温升降周期的原因，但他们已经可以量化这种苏醒对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.

“整个秋天，蝙蝠唯一的工作就是不停进食，储存脂肪，直到它们吃得好像黄油球长了翅膀似的，这些能量90%都被用在冬眠中的间歇性苏醒时了，”美国权威蝙蝠生态专家、生物学教授德安·里德(DeAnn Reeder)说。

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.

新的研究显示，早在蝙蝠面部和翼上出现病态的白色绒毛之前，白鼻综合症已经开始扰乱它们的休眠觉醒周期。等到免疫系统开始出现迥异于正常蝙蝠的行为方式，对真菌孢子做出强烈反应，就已经病入膏肓了。

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.

之所以说这时的免疫系统异于正常蝙蝠，是因为科学家已经知道，蝙蝠的免疫系统对多数病原体有着惊人的耐受力。蝙蝠的这种特性会给人类构成威胁，但也为人类攻克衰老型疾病，包括癌症，提供了启示。

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.

不断有证据表明，蝙蝠可以成为世界上众多致命病毒的贮主，包括埃博拉、马尔堡及引发相关出血热的病原体，还有烈性呼吸道疾病如SARS和中东呼吸道综合症的背后元凶。麻疹和腮腺炎也可由蝙蝠传播。

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，蝙蝠对自身携带的这些病毒基本都可以免疫，很少得病。任何人类、猴子、马、猪和其他哺乳类宿主感染后都会很快病倒。

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.

科学家还发现，作为体型微小的动物，蝙蝠的寿命极长。亚欧大陆上的布氏鼠耳蝠，体重平均只有六克，一只老鼠也有20克。但老鼠活到一年已属长寿，而布氏鼠耳蝠却能活到40多岁。发表在《自然通讯》上的一篇文章称如此大的寿命与体重差异是所有哺乳动物中“最极端的”。

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.”

蝙蝠可能还不会得癌症。“现阶段，还只有零星的证据，”新加坡杜克-国大医学研究生院和澳大利亚吉朗的澳大利亚动物卫生实验室的蝙蝠病毒学家王林发（音译，Lin-Fa Wang）说。“但我和这么多蝙蝠病毒学家交谈过，我只听说过一两例蝙蝠得肿瘤的案例。”

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.

科学家正在研究蝙蝠DNA和蝙蝠生理机能的细节，希望找到是什么让这种会飞的哺乳动物显得如此与众不同。初步的发现显示，蝙蝠对体内的病毒显得若无其事，寿命又超长，这似乎都与它们适应飞翔生活有关。

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.

蝙蝠专家认为，更深入了解蝙蝠的生理机能，不但有助于避免下一次埃博拉或其他跨物种疫情的大爆发，而且也会给免疫系统和炎症类疾病如糖尿病和心脏病的研究提供一个新的角度。

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.

科学家呼吁不要在一些地区盲目扑杀蝙蝠，以为那样做可以降低病毒传播的风险；而且他们也敦促公众，不要被传统的蝙蝠恐惧心理影响，因为历史上蝙蝠往往和巫术、吸血鬼、恶魔和蛛网联系在一起。

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.

他们说，蝙蝠在自然环境中发挥着重要的作用。猎食昆虫的蝙蝠是夜行昆虫包括蚊子的头号天敌：里德估计，每有100万只蝙蝠死于白鼻综合症，一个夏季就会有692吨昆虫不能被消灭。摄食果实和吸食花蜜的蝙蝠是重要的传播花粉、散播种子的物种。

“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.

王林发说：“澳大利亚一个政客说要轰炸蝙蝠。如果你这么做，你会破坏生态系统，结果传染性疾病会更多，而不是更少。”过量施用灭菌剂的危险很可能会即时显现：近期的研究显示，蝙蝠在承受生存压力和种群缩小的情况下最容易传播病毒。

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.

况且，无论你到哪儿，蝙蝠无处不在。在哺乳动物纲翼手目下面，有大约1200个蝙蝠的种，它们是仅次于啮齿目的第二大哺乳动物类群。“所有的哺乳动物，五分之一是蝙蝠，”里德说。

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.

除了南极洲之外的各大陆上都有蝙蝠分布，它们的体型从仅有1英寸长的基氏猪鼻蝠（和小臭鼬并称世界最小的哺乳动物）到巨大的鬃毛利齿狐蝠，翼展接近6英尺，有一张表情丰富的脸，蒙大拿大学传染病生态学家和蝙蝠专家雷娜·普罗莱特(Raina Plowright)说样子就像小狗。

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.

科学家传统上把蝙蝠分为两个亚目：食果实的大型蝙蝠和食昆虫的小蝙蝠，认为这两个群体如此不同，一定是彼此独立进化出飞翔能力的。

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，不久前发表于《科学》杂志的一个基因组分析显示，飞行的能力早在蝙蝠大家族形成之初就已经具备了，那还是9000万年前的事，之后又过了1000万年，大蝙蝠才和小蝙蝠分道扬镳，那以后，小型蝙蝠才独立进化出了回声定位的功能，用来猎食昆虫。

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.

新研究还发现了两大类群之间更多相似点。比如，科学家发现了一个基因的“意外集群”，这些基因和修复受损DNA的需要有关。科学家认为，这些修复基因可能是根据飞行生活的高强度需求而产生的。

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.”

蝙蝠飞行时，心跳达到惊人的每分钟1000次，代谢水平达到安静状态的15倍。相比之下，啮齿类动物奔跑中的代谢水平只是安静状态下的七倍，威斯康星州麦迪逊美国地质测绘局国家野生动物卫生中心的大卫·布莱赫特(David Blehert)说。而且那只是啮齿类“短跑时的能量消耗，蝙蝠却能以15倍的代谢速率飞行好几小时”，他说。

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.

如此高能耗的振翅运动，其结果是产生大量代谢副产品，被称为自由基。如果不是有超强的修复基因，自由基就会破坏蝙蝠的DNA。而且，对抗DNA受损的机能碰巧还是一个伟大的健康策略，可以解释蝙蝠超长的寿命和抗癌特性。

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.

蝙蝠的分子特征也揭示着它们的独特性。作为机体第一道防线的免疫因子被极大地加强，多数哺乳动物体内在感染后积极反抗的免疫分子，在蝙蝠体内却被弱化。

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.

结果就是，“病毒侵入后，蝙蝠可以高效应对”，王林发说。“但它们不会反应过激。”科学家发现，这种过激反应经常比病毒感染本身更危险。

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.

科学家认为，蝙蝠免疫系统的变化源于这种对修复受损DNA的高强度需求，后来也成为它们日常生存中的有价值的功能。

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.

蝙蝠往往是数十万只结成群体生活。它们长距离飞行，接触到多种多样的病原体。如果每次染上一种微生物，它们都反应过激，蝙蝠会受不了。事实上它们也很少反应过激。

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.”

这就让白鼻综合症的致命性越发令人不解。“这种动物不怕我们已知的最可怕的病毒，一种普通的土壤里的真菌却能要了它的命，”布莱赫特说。

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.

他和同事发现，在感染的最初阶段，冬眠的蝙蝠消耗的能量达到健康蝙蝠的两倍。里德和同事们也发现，染上白鼻病的蝙蝠从冬眠中苏醒的次数是健康蝙蝠的两倍。

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.

正常蝙蝠醒来后大部分时间安静不动，但“染病的蝙蝠不是这样，”她说。“它们不停地梳理毛发，因此它们消耗能量也更多。”最后的打击可能来自免疫系统对真菌的反应，初步研究发现，这种反应通常很强烈。

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

“那可能就是导致蝙蝠死亡的原因，”菲尔德说。