No Time for Bats to Rest Easy
by Natalie Angier
Jan. 12, 2015
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.
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.
“Well, that’s a lucky break,” said Thomas Lilley, a tall and crisply composed postdoctoral fellow from Finland. “Multiple rounds of bat drama.”
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.
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.
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.
“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.
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.
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.
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.
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.
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.
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.”
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.
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.
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.
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.
“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.
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.
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.
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.
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.
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.
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.”
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.
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.
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.
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.
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.
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.”
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.
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.
“And that,” Dr. Field said, “could be what’s dooming the bats.”
A version of this article appears in print on January 13, 2015, on page D1 of the New York edition with the headline: No Time for Bats to Rest Easy.