When you walk through Dr. Matt Gray's lab, try not to bump into anything. It's dark in there.
The lights are out for the comfort of hellbenders lurking in their wall of glass tanks. If you are careless, you might upset the salamanders' fragile aquariums or trip over the blue plastic kiddie pool full of tadpoles. (About 500 of them, Gray thinks.)
The University of Tennessee professor dodges the pool without pausing, the way you dodge the well-known corner of your dresser on the way to bed in the dark. Gray heaves open the door of a giant refrigerator and checks the temperature settings. In a pressed shirt and tie, with his curly gray hair and long sideburns neatly clipped, he looks the professor today. But he's equally comfortable, on other work days, wearing his lamb chops immense and grizzled, accessorized with a uniform of jeans and hiking boots.
Gray is both a mild-mannered, measured scientist and a man who hunts a serial killer in the dark. The ranavirus he studies, both in the lab and under rocks in Smoky Mountain streams, has caused a rapid decline of amphibians in the United States and in regions with mild temperatures worldwide.
The wood frog tadpoles from the kiddie pool will be entering the refrigerator to help answer a question that could help save their species: At what temperature does the virus kill? And at what temperature will the killer be killed?
Gray pulls out a flashlight and peers beneath a small arched piece of plastic in one of the aquariums. He breaks into a pink-cheeked, boyish grin as he greets a rare Eastern hellbender. Right now, it's just a dark brown salamander no bigger than Gray's pinky. But when it grows up, it could be as long as two feet, the largest amphibian species in North America.
That is, if it grows up after being infected with the virus.
It's a race against the clock, since scientists estimate that at least one-third of the world's frogs and toads, and 47 percent of salamanders and newts, are close to extinction, Gray says. As a result, researching frogs involves more adrenaline than you might think.
"One thing about amphibians is that there's so little known," he says. And yet, "Amphibians are ancient, existing on Earth over 300 million years longer than humans—they even withstood the age of dinosaurs. … In our field, so many folks are attracted to the mega-fauna, the deer, bear, elk and ducks, and that's where the money lies—in species humans care about for sport or viewing. Now I sort of get bored with that a little bit."
In his Midwestern accent, Gray confesses this is not an interest he would have predicted when he was growing up shooting leopard frogs with his BB gun in Flushing, Mich., a suburb of Flint.
Raised in the land of 10,000 lakes, Gray loved being outside near the water. But when he went squelching through the mud it wasn't to hunt for tadpoles but for ducks, usually with a gun in his hand. A lover of hunting and fishing, Gray came to amphibians through wetlands.
"Amphibians are a good indicator of human effects on wetlands," he explains. Unlike ducks, they can't fly off.
He became intrigued with them, partly because he felt he could make a bigger difference studying creatures that are less understood and more threatened. More than 120 amphibian species are believed to have gone extinct in recent years.
"It's being on the cutting edge of science, knowing what you publish will be a real stepping stone," Gray says.
And it is. Gray is one of the world's leading researchers on ranavirus, which can infect frogs, toads, salamanders, fish, and turtles. But amphibians, which begin life with gills and grow lungs as they mature, are more likely to sicken and die from it.
Research and coverage of amphibian die-offs has focused mostly on a fungus, called chytrid, that has caused extinctions among tropical frogs. However, Gray was one of the first American biologists to realize that the lesser-known ranavirus is a bigger threat to amphibians outside the tropics. And he has led efforts to coordinate biologists from around the globe to fight its spread and effects.
Many species, from predators to decomposers, depend on amphibians for survival. Salamanders, for example, make up more biological matter in the Smoky Mountains than all the resident birds and mammals combined, including bears, Gray says.
And amphibians have important secrets to share.
"The skin of amphibians has miraculous properties, such as inhibiting the growth of HIV," Gray says. "And some species can turn off their digestive system, which could lead to scientific discoveries to treat gastrointestinal diseases in humans."
Singing Their Secrets
More of these secrets must be learned before humans can save amphibians. Gray and his students are listening.
This April, UT senior Martin Wood was driving in the dark through the back roads of Blount County listening for frogs as part of the Tennessee Amphibian Monitoring Program. Its work tracking frog and toad populations sets an important baseline for understanding why some species remain successful while others suffer.
Through the UT chapter of the Wildlife Society, Wood has been assigned to monitor frogs and toads on a route driven four times a year.
Wood shakes his head and laughs at himself as he takes a third wrong turn in his orange Honda Element. He throws it in reverse for a three-point turn on a narrow road while moths wheel in the headlights.
Already, a buoyant moon floats high and nearly full. It's a good night for romance, frog-style. Frogs have several different types of calls, but most of the time they are hanging out at the (literal) watering hole, hollering something like, "Hey babe, what's your sign?"
Generally, their pick-up lines are a long way from a "ribbit." The American toad has a long, sonorous trill, like a cricket on steroids. Spring peepers sound like very, very hungry baby chicks. Southern leopard frogs seem to be chuckling, and Southeastern chorus frogs ziiip like someone running a finger over the tines of a comb.
Wood and his fellow volunteer Ross Ketson step out near a gated neighborhood in Saddle Ridge. After waiting a few moments to let the frogs get comfortable with company, they listen for five minutes.
Wood lifts his hands to his ears and slowly rotates like a satellite dish. It helps him tune out the burbling stream nearby to hear distant toads and peepers. He judges the density of the sound and records the weather conditions (slight breeze, a few clouds) and amount of competing noise nearby (dog barking) before heading to the next of his 10 stops.
"I get a lot of funny looks," Wood says. "A lot of people think we're broken down, but some are suspicious." There is little traffic on these roads, and fewer strangers.
"It helps to have this accent," twangs Wood, who grew up on farm in Karns. His gigantic, bushy mountain-man beard might also play a part.
They listen at a cabin; at Blount County Forestry fire control headquarters; at a back entrance to Blackberry Farm. These places all have one thing in common: the bubbling sound of water and (usually) a few frogs.
At a few stops, there are no songs to be heard.
But at a pond on Miller Cove Road in Walland, the listeners hear the zipper-like snore of pickerel frogs for the first time. Wood and Ketson debate whether there was a Cope's gray tree frog chiming in. By this hour the moon is so bright it leaves an imprint on your retina.
At the next stop, the toads are chorusing.
From a Virus to a Family
These tunes have composed the course of Gray's life.
As a doctoral student, Gray was studying the effects of Texas cattle farming on frogs in farm ponds, expecting to simply learn more about human impacts, when a collaborator told him she was finding a lot of ranavirus in the frog tissue samples.
That collaborator, Debra Miller, ended up becoming his wife.
"Ranavirus brought us together," Gray jokes.
But it's true. The two, who met as grad students at Mississippi State University, kept trying to break up so they could head off in their own professional directions. But after a string of jobs in different states, they gave up and got married.
UT hired Gray, and he again tried to focus on the effects of farming on frogs, but again found ranavirus. Gray and Miller's early work became one of the first studies in the U.S. to put ranavirus in the context of the way people use land.
After UT eventually offered Miller a professorship too, the couple was finally able to live in the same place and work together. Gray designs the experiments, and Miller tests specimens for diseases and their symptoms.
"The part I love the most is to see the cellular changes taking place under the microscope," Miller says.
Their son Ethan, who is almost 2, took his first salamander sampling trip with his parents in April. He recognizes when the frogs are calling at from the fishless pond behind his house, where bullfrog tadpoles mass by the hundreds.
"I look at him and I wonder," Gray says. "When folks react to ‘slimy frogs,' I wonder if it's learned behavior. Because he wants to touch any animal he sees. He loves everything that's alive."
Gray grew up outdoors himself. He and his older brother took off two weeks from school every year to hunt deer with family and friends in the Upper Peninsula of Michigan, erecting army tents and a wood-burning stove to keep out the sub-freezing temperatures and the foot of falling snow.
Gray thought his dream job would be improving duck habitat for the state game agency 40 minutes from home. Then one of his professors at Michigan State University encouraged him to try grad school, and he got hooked on research. After a few years building and managing wetlands in Puerto Rico, where his mentor was a conservation biologist, Gray started to see the value of studying wetlands as a larger system.
Now Gray brings that appreciation of what he calls "the bigger picture" to his students and his son, at work and at home. On the 17 wooded acres between Knoxville and Alcoa where his family lives, Miller has focused game cameras on the food plots for deer and turkey. Gray and Ethan have made a ritual of checking the cameras each week.
"He sees me get out his little wagon and my laptop, and he knows we're going to go look at the pictures, and he gets pumped," Gray says.
Gray still marvels at the conjunction of his personal and professional good fortune. "Debra is a hell of a lot smarter than me. She's more talented than me. She has more degrees than me. There are easily less than 10 people in the U.S. with her wildlife pathology skills. … It's so convenient for me to have a pathologist that can make these beautiful slides of animals I care about."
Gray went on to found and direct the Global Ranavirus Consortium, which held its second international symposium in Knoxville last year. The group, which decides research priorities and teams scientists to pursue them, will publish a book on ranavirus later this year.
"Matt is the driving force behind setting up that organization," says Tom Waltzek, co-director of the Aquatic Animal Health Program at the University of Florida and a member of the consortium's board. "He has been a leader in organizing people across the U.S. and internationally."
Waltzek says that's partly because Gray has a quality often elusive among scientists: charisma.
"Scientists like to fight with each other, but he's good at bringing people together," Waltzek says. "By uniting, we're actually going to be able to solve some of the pressing issues with ranavirus."
Among those issues, Waltzek says, are the ways different strains travel among continents, the best tests to track those movements, and vaccines or other strategies that could prevent the spread.
Ground Zero, With Blue Gloves
The front line of Gray's research has been here in the Appalachian Mountains. Over the past seven years, his studies have found the virus even in isolated and protected waterways and among rare salamanders. In that time, Gray says he has seen the virus's presence in the creeks of Great Smoky Mountains National Park fluctuate between zero and 80 percent.
One morning this April, with temperatures hovering in the 40s, about 25 UT students pick their way through the cold waters of the park's Ash Hopper Branch with small, green fish nets like the ones sold at the pet store. Their hands, in bright blue plastic gloves to avoid spreading salamander diseases, seem to flutter above the creek among gray, unadorned trees.
They carefully turn over—or sometimes heave over—rocks in the burbling water across from the Sugarlands Visitor Center, looking for salamanders. Some remember doing the same thing, much less methodically, as children. Others are just getting their feet wet.
Nathan Wilhite whoops in triumph as he catches a big black-bellied salamander that repeatedly leaps from his net into the leaf litter, trying to squirm away. Eventually he manages to drop it into a plastic baggie so the salamander can complete a series of tests supervised by Gray and several other professors.
First, its species is confirmed; then it is measured and swabbed with a Q-tip for chytrid fungus. The fungus infects many frogs in the U.S. without sickening them, Gray says. And unlike ranavirus, the fungus can kill only adults.
For ranavirus testing, the tip of the salamander's tail is clipped off before it is returned to the stream. (They can regrow their tails, a feature they evolved to help them escape predators without harm.)
A student calls Gray over to examine a Blue Ridge two-lined salamander, orange with black lines and dots. It is missing a limb and its mouth is reddened. Were these symptoms of ranavirus or the fungus?
Sampling in the same creeks every year sheds light on these questions, but doesn't necessarily answer them.
At Gorley's Pond in Cades Cove, thousands of frogs die from ranavirus every year or two, Gray says, while two other ponds in Cade's Cove have had no outbreaks.
Recently, 100 dead wood frogs were found in the national park's Gum Swamp. Last year, a creek across from the park's Tremont Institute, where Gray says "probably thousands of kids every year" conduct stream sampling, had one of the highest levels of ranavirus infection Gray has seen outside a drought.
Ranavirus isn't new. It's been documented for 50 years, and the first major die-offs from it occurred in Arizona and England 30 years ago, Gray says.
Gray says the virus may have become more deadly in recent years for a variety of reasons, but most of them boil down to this: human population growth and travel. Amphibians can become stressed as development brings more pesticide and fertilizer runoff and reduces plant cover around waterways. Human demand for electricity causes climate change and acid rain. And people move the virus as they travel or transport living things.
People move around fish and turtles that carry the virus, Gray says. Hatchery fish, for example, may be spreading it to more vulnerable frogs and salamanders with the unwitting help of government stocking programs.
At UT, Gray and his team are trying to understand how the community of species in a habitat may affect the likelihood of a ranavirus outbreak. They are also studying how businesses that raise frogs—especially those that breed bullfrogs for the food and pet trade—may be helping the virus develop into a more deadly form.
Remarkably, when results from April's testing come in, for the first time ever they show none of the salamanders tested were infected, Gray says. This may be because of the unusually cold spring, since the virus doesn't replicate below 53 degrees. The team will return in June for another sampling to see if there is any change.
Etude With Attitude
The frog listeners are studying habitat, too. In the ecological community of East Tennessee—even down the long dirt roads—humans are close neighbors.
In a night-silvered valley, the students make their final stop to hear American toads performing a full nocturne. So many combine their voices that the trill sounds like both an alarm and a poignant "pleeease," a ghostly chorus of longing.
John Gibson, who lives next door to the toads and their stream, comes outside to learn from Wood about the species keeping him awake. It's after 11 p.m., but Gibson wants to talk about the creek.
"I remember when I was real young, we'd catch all kinds of tadpoles in the stream, and I put some in a bowl and raised them to frogs," he says. "Then we'd release 'em back in the creek. Then there were two decades when they're were hardly any tadpoles. Now they're back, but not nearly as many."
For Gibson, the frogs are part of what makes this particular countryside home.
For an ecosystem, they are a barometer of health, a key source of protein, an important mosquito control device, and a source of insights for the treatment of human disease.
Beyond all this, their song is a herald of the world to come. Because amphibians can absorb many pollutants directly through their skin, they are one of nature's early warning systems.
"Their declines can signal environmental chaos, and lead to negative effects on other wildlife and humans," Gray says. "Mother Nature is croaking to us through the frogs."