Evolution is an arms race, with animals and plants trying to stay a step ahead of their parasites and pathogens.
Although diseases often spread without killing many of their hosts (think the common cold for humans), sometimes, a new ingredient can massively change the balance. This is exactly what happened to bats in North America, who are now fighting not just an infection, but for the survival of their entire species.
Flitting about on summer nights, bats eat more insects than any other creature. They used to be a common sight in forests and fields alike. In the last decade, the situation rapidly changed. Now, many bat species are listed as threatened or endangered, including the little brown bat (Myotis lucifugus), which used to be the most common bat in North America. Over 5.5 million have died of a rapidly spreading disease.
Scientists have been frantically began piecing together the picture. One of those scientists is Dr. Craig Willis, an associate professor in the biology department at the University of Winnipeg, his lab studies behavioural and hibernation physiology. They focus a great deal on bats, and what has been since named ‘white-nose syndrome’.
‘The disease was first discovered by New York state biologists doing their annual hibernaculum surveys,’ says Dr. Willis, referring to the caves where hundreds or thousands of bats gather to spend the winter huddled underground. ‘In 2006, the first year of white nose syndrome, they found thousands of dead and dying bats carpeting the floors of the caves.’
Shortly after, scientists across eastern and central North America began to notice hibernating bats clad with a white, fuzzy coating. It spread over their muzzles, ears, and even onto their wings, eating into their flesh.
At first, this infection (caused by a fungus aptly named Geomyces destructans) was simply a puzzle for academics. What was it, and where had it come from? As they were uncovering the first clues, the disease shifted from a research question to an epidemic. It devastated millions of bats, destroying 80-100% of the eastern populations of several bat specie. Entire hibernacula were killed in a single winter.
Photo source: Greg Turner / rcngrants.org
The fungus grows in cold weather, and over the bats as they cool their bodies down to save resources while hibernating (down to as low as 1°C). However, it isn’t the fungus that kills them. Bats are efficient creatures: they build up just enough fat reserves in the summer to keep them comfortable hibernating through the cold winter.
Once infected, they wake up more frequently, trying to warm up and clear the infection. Raising their body temperature more often than normal causes them to burn up their precious food and water reserves earlier than anticipated. Those that don’t die up in the caves are forced to leave their caves before spring in search of food and water. With insects not yet emerged and water still frozen, they ultimately die of dehydration or starvation.
Dr. Willis explains its origin. ‘We know the fungal pathogen is common on bats in the old world, throughout Europe, and it’s now clear that it’s an invasive species to North America. Some experimental work from our lab helped support this invasive species hypothesis.’
European bats evolved with the fungus, and are adapted to it. They don’t experience outbreaks of white nose syndrome—at least not yet. Wildlife agencies in Europe are preparing for what might happen if the strain mutates beyond what their bats are already resistant to. It’s thought that like so many other diseases spread from Europe to North America, it was transported by humans… and could just as easily be brought back.
In North America, the disease spreads by about 250-300 kilometres each year. Although other invasive pathogens have affected animals before—like amphibians—nothing has ever been seen on this scale for mammals. According to Dr. Willis, white-nose syndrome has caused the fastest declines of wild mammals ever observed. There’s nothing that compares.
The situation is certainly terrible, but not just for bats. Bats can eat up to 600 mosquitoes in a single hour, and contribute a huge amount of ecosystem services. First to feel the loss of bats will be the farmers, who are losing the free insect suppression services the bats deliver, estimated to be worth $5-40 billion each year.
There might be some hope, but it comes from an unlikely place—using one infectious organism to destroy another. U.S. researchers have been experimenting with the use of bacteria to destroy the fungus. One bacteria strain (Rhodoccocus rhodocrous), known to reduce fungus on bananas, inhibits the growth of the fungus causing white-nose and can cure mild infections entirely.
It was first tested in 2011 by Chris Cornelison, an applied microbiologist at Georgia State University in Atlanta. It’s since gone into field trials by U.S. wildlife agencies. Other strains found naturally on bat species that are resistant to the disease are undergoing testing, led by graduate student Joseph Hoyt at UC Santa Cruz. He and his team hope that they could eventually develop a bacterial spray to apply to hibernating bats.
Dr. Willis isn’t so convinced about the feasibility of these treatments. ‘We’re still a long way from being able to cure bats in the wild.’ He says. ‘What I call the “spray stuff on bats” kind of treatments may also have significant limitations in western North America because we have no idea where most of our bats are hibernating. If you can’t find them, you can’t treat them.’
Is there a future for the little brown bat, and other bat species in North America?
Evolution could provide the answer. Although often, every bat in a colony dies of the disease, sometimes there are a few lucky survivors. Some bats can clear the disease once they emerge from hibernation and raise their body heat level. If this trait is heritable, these bats might be able to pass on their resistance, and the population can adapt. In lieu of that, the best that can be done is educate people to stay away from caves with hibernating bats.
Otherwise, we will almost certainly see the loss of many bat species from at least parts of North America, or perhaps rendered extinct altogether.
In the evolutionary arms race, fungus might win this round.
NOTE TO READERS:
The fungus is primarily transferred bat-to-bat, and cannot infect humans. If you see a dead bat, report it to your local wildlife agency. Citizen science is critical for helping track and support bat populations. To learn more or get involved, visit www.batwatch.ca.