Elizabeth Shadle: Climate change effects on frogs

The following story was written in May 2020 by Jacob Merkel in ENGL 4824: Science Writing as part of a collaboration between the English department and the Center for Communicating Science.

This photo shows a young Caucasian woman with light brown hair and a blue baseball cap, darker blue shirt, and black pants. She is seated, smiling, and leaning forward over her task of counting tadpoles. She has a dropper in one hand and a white plastic hexagonal container of water and tadpoles in the other. — Virginia Tech biological sciences graduate student Elizabeth Shadle counts tadpoles as part of her research. (Photo courtesy of Elizabeth Shadle)

Peep. Peep peep peep. PEEEEEPPPP!

“Everyone remembers catching tadpoles in their backyard,” says Elizabeth Shadle.

If you didn’t catch tadpoles, perhaps you remember chasing a frog, trying to catch it before it hops out of reach.

Not many people think about their childhood frog adventures ever again, but that is not true of Shadle and her team of undergraduates. A second-year master’s student in the biological sciences department at Virginia Tech, Shadle works in the Mims lab, a lab focusing on freshwater ecology. She is interested in climate change, specifically how climate change affects amphibians.

Her amphibian of choice? Frogs.

Shadle conducted a 13-week experiment that included two different species of frogs common in Virginia: wood frogs and spring peepers. The research began in January of 2019 and required hours of meticulous effort from Shadle, her team of undergraduate assistants, and her advisor, Dr. Meryl Mims.

“My hope for this research was to be able to actually have an experimental approach of seeing in the future what can we predict is going to happen to these frogs in your common backyard wetland,” Shadle said.

The challenge of controlling variables like temperature and drying led her to create artificial ponds, or mesocosms, that represented natural wetlands. Her mesocosm study entailed the use of forty-eight tanks, each approximately the size of a hot tub, that simulated the wetland ecosystems wood frogs and spring peepers most commonly inhabit.

This photo shows four rows of circular blue "kiddie pool" tanks stretching into the distance. There's grass in the foreground and background, with woods in the far background. — Shadle's artificial wetlands mesocosm tanks can be seen on the edge of the Virginia Tech campus. (Photo courtesy of Elizabeth Shadle)

“We wanted our tanks to be as similar as possible to the wetland,” Shadle said.

To accomplish this, she spared no effort.

“The first thing I added [to the tanks] was water, and I had to treat all the water because water that comes out of the tap has chlorine in it and different chemicals used to treat it,” she explained.

She also added to each tank two kilograms of leaves, gathered from various faculty member’s lawns by Shadle herself.

“I asked professors if I could rake the leaves in their yard, and I collected four truckloads worth of leaves,” she recalled. Since she wanted the tanks to be as similar as possible, she weighed the leaves and mixed the different collections to create a homogenous mixture that was added in equal parts to each tank.

This photo shows a golden brown frog looking directly at the camera. — Shadle's research focused on two species: the wood frog, shown here, and spring peepers. (Photo courtesy of Elizabeth Shadle)

The final ingredient of the tanks was a surprising one: rabbit chow. The rabbit chow is used in experiments to help stimulate the growth of algae, an integral part of the wetland ecosystem and a food source for frogs.

Shadle collected her frog eggs from a natural wetland in February and March of 2019 and reared them until they were free-swimming tadpoles. The tadpoles were then added to the tanks, and measurements were taken at consistent intervals to create a data set.

“We took a lot of data,” Shadle said with a laugh. The main measurements that the study focused on were time to metamorphosis of the tadpoles, weight of the tadpoles and frogs, and “snout-vent length” for the frogs. Weights were taken at Day 15 and Day 30, which required “a full day’s work, 14 hours of measuring very small tadpoles,” said Shadle.

“You have to put them in water to measure them, so you have to measure out the water first, quickly add the tadpole in, and then subtract the weight of the water from the weight of the water and tadpole combined,” she explained.

Additionally, Shadle kept detailed records on variables from the tanks themselves, including hourly water temperature; depth measurements to get a gauge of water volume over time; and pH, dissolved oxygen, and conductivity of the tank water weekly. Shadle also took measurements of pH, dissolved oxygen, and other parameters in natural wetlands to compare to data for the tanks.

Currently, Shadle is dissecting her vast data set in the hopes of publishing her research and informing future experiments.

This photo shows the faces and upper torsos of four young women, one African American and three Caucasian, dressed for cold weather and smiling at the camera. In the background are leafless trees. — Shadle (far right) and her team of undergraduate researchers, left to right: Alexis "AJ" Jackson, Kara Hall, and Mackenzi Hallmark. (Photo courtesy of Elizabeth Shadle)

“I took a lot of data on the water chemistry and the temperatures to really get at what is happening in these tanks,” she explained. “Are they as similar to the natural wetland as we think they are? I’m hoping to really be able to talk about that—how similar are experimental ponds [to natural wetlands]—and also understand what is happening to these two different species of frogs when raised in different temperature and drying conditions.”

The current COVID-19 pandemic that is gripping the world and forcing large swaths of the population into quarantine has made this section of her research more challenging. She can still do the writing and data analysis, but the virus has made it more difficult to discuss her results and future implications with her advisors. Online tools like Zoom have helped to bridge the gap of having no live, face-to-face interaction, but it is much more difficult.

Still, things could have been worse for Shadle.

“This virus has given me a new sense of appreciation that my experiment went smoothly last year,” she said, “and I feel for fellow graduate students whose fieldwork and experiments have been upended.”

The pandemic has not changed how she feels about the urgency and importance of her research.

“I definitely—when Coronavirus first started happening—was lacking some motivation to work on my research,” she said, “because I felt there’s a pandemic going on; what do frogs have to do with it? But then, after giving it a lot of thought and realizing the world is still changing, I remembered we are still experiencing more droughts. We are still going to have record high temperatures this summer. It’s still important to get out [our research] and we still need to know how our natural environment is going to be changing over time.”

For people like Shadle, it is vitally important that we still are able to hear the peeping of spring peeper frogs in our backyards and that future generations of children are still able to catch tadpoles for years to come.