By Gigi Marino
Flashback four years to a dusky spring sunset on the Isle of Que. This lush strip of farmland and homeland surrounded by Penns Creek and the Susquehanna River, 15 miles south of Bucknell, is where Associate Professor of Biology DeeAnn Reeder often takes student researchers to study bats. There, roosting in the rafters of a massive barn, live nearly 2,000 little brown bats, the most abundant species not only in Pennsylvania but also in all of North America.
Reeder and her students are in the field studying the effect of stress on pregnant bats. Their first task: set up harp traps — aluminum frames strung with a netting of nylon line that impedes the bats’ flight, stunning them just enough that they drop into a shallow trough of plastic sheeting hung beneath the frames. In any bat-gathering situation, the harp traps are set before the sun goes down and bats leave the roost. On this particular trip, once the traps are prepared, Reeder pokes around the ground floor of the barn, shining a flashlight among the beams, illuminating some of the little browns hanging upside down, tucked away in available notches. She notices a bat lying on the ground and approaches it. Noting that it isn’t moving, she dons a pair of rubber gloves, confirms the bat is dead and bags it to take back to her lab. “Bats are dying, and people don’t know why,” she says, “but all of the affected bats have a powdery, white fungus around their noses. I don’t see any evidence on this bat, which is good. It may have just not gotten enough to eat.”
As evening approaches, bats start swooping out of the barn to begin their nightly feeding. They are impressive insectivores, consuming 1,000 bugs an hour. The music of their chittering and chirping is accompanied by a regular beat — the soft thwop of little browns hitting the plastic. The flight of the bats departing the barn en masse is glorious. The sky is raining bats. The air thrums alive with them. That night, the students catch, measure, assess, band and release hundreds of bats. No one thinks about that one little bat found dead earlier.
Four years later, that fungus has a name, white-nose syndrome (WNS), and it has killed 7 million bats.
“This is like bringing small pox to the New World,” says Reeder. “It is surely an unprecedented wildlife disaster for North America.”
Jeremy Coleman, a biologist with the U.S. Fish and Wildlife Service and national coordinator for WNS, says that bats are a “keystone species.” His term is telling. The state symbol for Pennsylvania is the keystone. Removing a keystone from the top of an arch leads the entire structure to fall apart. Keystone species are that vital to an ecosystem.
“Eliminating a keystone species has a great effect on the environment around them,” says Coleman. “The classic predator is the shark; its removal impacts the environment. Bats, in some ways, are like sharks in that they are a primary predator for flying insects.”
The role of bats in the human ecosystem cannot be underestimated — or replicated, as bats are the only flying nocturnal mammals, with 1 million bats consuming 692 tons of insects a summer. The loss of 7 million bats allows nearly 5 thousand tons of insects to live this year alone. Because both bats and insects are not well studied, researchers are cautious about forecasting exactly what the ripple effect will be. This much is known: Bats consume mosquitoes, which transmit deadly diseases, such as West Nile virus in humans and heartworm in dogs. The widespread death of bats multiplies the dangers posed by mosquitoes and other winged insects capable of doing harm.
The destruction of crops will be staggering without more chemicals to kill the insects that bats would normally eat. In 2011, the journal Science reported that bats save the U.S. agricultural industry more than $3 billion a year in pesticides. These costs will most likely be passed on to the consumer. Organic farmers in the Northeast Organic Farmers Association have already reported seeing an increase in insect infestation that correlates with the spread of WNS.
Ann Froschauer, the national WNS communications leader, says that the cascade effect is now appearing in the gray bat, a federally endangered, Southeast species that lives in caves year-round. “We just documented the disease in gray bats and are seeing an impact on cave ecosystems,” she says. “The gray bats bring nutrients into the cave in the form of guano. Many other endemic cave species depend on the bats for their nutrient input. If we start seeing mortality in gray bats as we have in other species, these cave systems will be deeply impacted.”
“We haven’t seen anything dire yet,” says Coleman. “We can anticipate that there will be some impact, potentially big increases in pests like the gypsy moth caterpillar outbreaks of the ’80s,” Coleman says. “There’s a winter moth found in New England that’s an invasive species. Its numbers are increasing. One hypothetical could be that these winter moths continue to increase and aren’t controllable in any way. We could also potentially be seeing major effects in forest health.”
Mylea Bayless, director of conservation programs for Bat Conservation International, agrees with Coleman. “We can speculate about the consequences of losing bats, but unfortunately we might not know the full cost until it is too late,” Bayless says. “We are in the middle of an accidental ecological experiment, and our best hope is to try to understand the problem and minimize the damage. We are not just talking about one species of bat, but an entire group of bats that eat insects and hibernate underground. Over half of our U.S. bat species are in this group and are likely at risk.”
In 1979, mathematician Edward Lorenz famously predicted — based on years of rigorous mathematical models — that the flapping of a distant butterfly’s wings could result in a hurricane weeks later. Although the butterfly effect may at first seems like an intellectual exercise, as a metaphor for proven interdependent systems in nature, it describes the risks that death to one species can pose. The death of bats may be nothing more than nature’s cruel winnowing, or it may have already set into motion drastic consequent risks.
In May of this year, Reeder returns to the Isle of Que with two students. “I haven’t been to this site for quite a while,” she says. “I’m hoping there are still some little browns left.”
Reeder is anxious to explore the barn’s ground floor. The air is thick and fetid, the rough beams covered with mud wasp nests. Reeder is a dynamo, talking and moving quickly. She scours the rafters looking for bats, shining a light into every nook and cranny. After several minutes, she says, “I found one. I’m so excited!” One of the students brings over a ladder, and the group peers expectantly at the lone little brown bat. As Reeder moves closer, she notices it hasn’t chirped or stirred. Her enthusiasm wanes. “I’d so hoped we would find a survivor,” she says. She removes the mummified bat from its perch. Mud wasps alone own this part of the barn.
Reeder and her students spend the rest of the evening in the upper sections of the barn, populated by big brown bats, a species that has been affected, but not decimated, by the devastating WNS. First observed in 2006 by a caver in upstate New York, WNS has spread faster than anyone could have imagined. By the end of the 2010–11 hibernating season, WNS was confirmed in 20 Eastern states and four Canadian provinces. Nearly a quarter of the 47 bats species in the United States have been affected. Reeder, a mammologist who specializes in species taxonomy and biodiversity worldwide and an ecophysiologist who studies the hibernation patterns of mammals, has turned most of her attention to understanding and, perhaps, one day curing WNS.
Reeder came to Bucknell in 2005, bringing with her an interest in the ecophysiology of bats, which she introduced to her students. “We were asking questions about hibernation physiology and immune systems and what bats might be doing when they hibernate,” she says.
To answer these questions, Reeder’s lab at Bucknell not only developed tools to study the immune systems of bats but also set up a flight cage and environmental chambers for hibernating bats in the basement of the Biology Building. Reeder shared research interests with Greg Turner, a biologist with the Pennsylvania Game Commission, who was independently studying bat hibernation.
Reeder and Turner joined forces as soon as reports surfaced about a puzzling, bat-killing disease. They both were part of the group of academic researchers, conservationists and federal and state agency biologists that organized an emergency meeting to discuss WNS, its origin, disease vector and ramifications in June 2008 in Albany, N.Y., near the site of the original detection. (A WNS symposium has been held at a different site every year since then.) “Mass die-offs happen in wildlife,” Reeder says. “We quickly became aware that this wasn’t an isolated incident, but an emergent disease.”
As a result of the Albany meeting, Reeder and Turner were awarded $50,000 from the Northeast Association of Fish and Wildlife Agencies Regional Conservation Needs grant program to study hibernation. “We knew that bats were dying in hibernation, and it appeared the WNS animals were starving, which suggests that their energy balance during hibernation was disrupted,” says Reeder. “We had field sites in Michigan, Pennsylvania, New York, West Virginia and Vermont. Eventually we added histology to our studies so we could quantify the level of infection.”
As a part of this study, Reeder and Turner focused their attention on little brown bats living in the Shindle Iron Mine in Mifflin County, Pa. They attached specialized radiofrequency transmitters that tracked bat body temperatures, allowing for the study of hibernation patterns. The data receivers required a battery change every week. Shortly before Christmas in 2008, Reeder returned to change the battery and detected the telltale white fungus on the bats. She called Turner; they sent three bats to the U.S. Geological Survey’s National Wildlife Health Center in Madison, Wis. The diagnosis was confirmed: WNS had hit Pennsylvania.
“I was in disbelief that the state had gotten infected so fast,” Turner says. “It was unreal, especially since this was a protected and remote site. The Game Commission had been watching this site for years. Within two to three months, we saw all 2,300 bats die. They flew out in the winter and never returned.”
Likewise, Reeder was consumed with “an overwhelming feeling of nausea. But there also was an adrenaline rush because I knew we had a lot of work ahead of us, and we had to get started immediately.”
Reeder was in the right place at the right time to lead the study of the dying bats in a lab equipped with just the right tools. “We were poised to start the work,” she says. “I had a facility at Bucknell that was unmatched anywhere else to my knowledge.”
Says Turner, “DeeAnn is a central point in the major research going on. She is connected to all of the work being done with WNS.”
Early on, researchers working with the dying populations knew that the white powder found on the bats’ noses was a fungus. At Bucknell, Reeder sought the expertise of her colleague, Associate Professor of Biology Ken Field, an immunologist. “It’s rare for a fungus to cause a disease, even rarer for a fungus to kill. We thought something else was suppressing the immune systems of the bats, and the fungus was only a symptom. An analogy is that in people with AIDS, thrush can be very serious. People with healthy immune systems don’t succumb to thrush,” Field says. “Initially, we thought there was going to be some other cause of WNS, and the fungus was going to be an opportunistic infection. It turns out we were wrong. DeeAnn collaborated with a group that showed that the fungus was actually the cause of the disease.”
Unraveling the mysteries of WNS has given Reeder and other researchers the opportunity to collaborate in ways they had never imagined. Because of WNS, Reeder works with mycologists, veterinary pathologists and cave microbiologists. “These are people I wouldn’t have interacted with before,” she says. “It adds a richness to our understanding of the data. We can each contribute with our own very specific expertise.”
It was this collaboration that proved that the fungus Geomyces destructans was the pathogen responsible for killing the bats. The work was done at the National Wildlife Health Center. “This was the appropriate place to do the infectious trials to try to prove the fungus was the causative agent. The National Wildlife Health Center had a bio-secure lab where they study wildlife diseases. They know how to do these kinds of experiments. But they didn’t know much about bats,” Reeder says. “They needed me, and I needed them in order to understand what was killing the bats.”
The results, published in the journal Nature in October 2011, were a breakthrough for those studying WNS.
“There’s something about having fungal infection in your skin. So what? I’ve had ringworm. People get jock itch or athlete’s foot. They don’t cause death. Typically, those that die are immune-suppressed, like AIDS patients,” Reeder says. “One piece of the puzzle is that we know that bats are dying during hibernation. We’ve pieced together that their physiology is altered, but we don’t know what’s really causing them to die. The good news is that we’re increasing our knowledge all the time.”
Healthy bats hibernate normally. Reeder points out that while many people think that animals in hibernation are sleeping, they aren’t. Bats and other hibernating creatures go into a state of torpor by slowing their metabolic rates and reducing body temperatures. The body of a hibernating bat is the same temperature as a refrigerator. Under normal hibernating conditions, bats are less prone to infection because bacterial and viral pathogens are not especially virulent at low temperatures, but Geomyces destructans is an insidious organism that thrives in the cold. “Most fungi don’t cause disease,” says Field, “because most mammals aren’t cold.”
Reeder and Turner have just published a paper in PLoS One showing that unhealthy bats leave the hibernating state too early and too often. Their work is based on three years of studies in multiple states from the data produced by loggers attached to 504 bats.
“We have demonstrated that one of the primary mechanisms of why bats die is because their hibernation patterns are significantly altered,” Reeder says. Healthy bats come out of hibernation every 12 to 15 days. WNS-affected bats are coming out of their torpor, at least twice as frequently as healthy animals. “It’s just not sustainable from an energetic perspective,” says Reeder. “It takes so much energy to be in a cold environment, crank your body temperature up and stay up for a little bit then drop it down again. Something about this fungal infection is causing them to come out of hibernation.”
In Pennsylvania, we’re looking at a 99 percent decline in all of our hibernating bats,” Turner says, “and there’s just no way to sugarcoat that.”
Despite the grim outlook for affected species, one slender ray of hope is that not all species are affected, and not all affected species carry a death sentence. Back at the Isle of Que, the barn shelters a maternal colony of big brown bats that is increasing its numbers. “We do have some mortality associated with WNS here, but the numbers are much lower than in heavily impacted species. These guys are doing pretty well,” Reeder says. “Another species, the Virginia big-eared bat, a critically endangered species, appears not to get WNS at all. We’re trying to understand what it is these particular species are doing that allows them to survive, which will allow us to predict, as WNS moves across the country, which species will succumb and which won’t.”
In April of this year, Reeder and Field received a $481,000 grant to continue their studies of WNS in bats, specifically looking at who survives WNS and why. (The U.S. Fish and Wildlife Service contributed $289,000; Bucknell funded the rest.) For Field, who has been studying mouse immunology, this is new territory. He explains that while assays are readily available for mice, he and his students must develop their own for bats. “Unfortunately, bats are not flying mice,” he says. (This is a common misconception. In fact, the German word for bat, fledermaus, means “flying mouse.”) Surprisingly, bats are more closely related to whales and sheep than mice. In the process of developing reagents — chemicals or antibodies — for the assays that will be used to test bat blood, Field’s students are testing sheep, goat, donkey and cow antibodies. The Field lab will work with the bat genome, which was sequenced in 2010 at the Broad Institute in Cambridge, Mass., providing a genetic map for studying the disease. “We’re predicting that the infected bats will respond by changing the expression of their immune genes,” says Field. “For example, when you get a cold and have a fever, the fever is being caused by a protein called a cytokine. We expect that same cytokine may be expressed by bats.”
Bats are slow breeders, only birthing one pup a year. Even in the best of circumstances, Reeder explains, healthy bats have a 50 percent survival rate during their first winter. After this year’s WNS symposium held in Madison, Wis., she came away feeling that people are making progress, particularly in the basic science of understanding the disease. Yet, she says, “The problem is incredibly pressing. The number of bats dead is very high.” Her main focus is on the survivors. If the disease can be treated and mitigated, bat populations can rebound, though Reeder fears it will take decades or even centuries. The impact of a cure could be dramatic for all the other elements of nature that bats influence — insects, crops, disease, food supplies.
For Reeder, the work is paramount: “I’ve come to realize that this is the probably the most important work I will do in my life.”
Photos: top, Bill Cardoni; middle, Greg Turner
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