Resilient wood frogs keep researcher hopping

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One of the Churchill region’s most resilient animals is a lesser-known critter, one that has the ability to freeze like a hockey puck to weather the North’s frigid winters and has a habitat range that dips south all the way to North Carolina.

It’s Canada’s most widely distributed amphibian: the wood frog.

Jon Davenport, assistant professor of biology at Appalachian State University in North Carolina, makes annual trips to Churchill (at least when he isn’t blocked from field work by a global pandemic) to monitor the wood frog population and understand how it is being affected by climate change.

“It’s amazing to me that they’re even up there. Why go through all the trouble to be up there when it’s so extreme? And that’s what we’re trying to understand. And as the environment becomes even more extreme, how resilient are they?” Davenport says.

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Overall, the northern Manitoba population remains stable, but there are stressors, such as drying ponds where frogs lay eggs.

In tracking adult and juvenile frog movements over the past four years, unsurprisingly, the animals avoid hot, dry areas, Davenport says. What is surprising is the amount of time the frogs spend on the tundra landscape when they are more adapted to living in the woods.

“We’re trying to understand how are they so stable, given that the environment is changing? There’s a couple things we think are going on. Because maybe the ponds are drying earlier, and the frogs aren’t necessarily getting there any earlier, but they can speed up their growth to respond to that,” he says.

“And even as those ponds are drying, and they come out, the adults and some of the smaller ones do spend a lot of time out in the open tundra…. We think it’s because the shrubs — which (previously) weren’t on the tundra as much — they’ve encroached onto the tundra. So the frogs can hop out of the pond, even if they have to a little earlier… and there’s a shrub that provides them with some relief from the UV radiation.

“So, that shrub encroachment, that changing of the environment, could actually benefit the adults in some ways, but the ponds drying could negatively affect the juveniles and the larvae.”

This led Davenport to venture into the frog real-estate market. He started building what he calls “frog condos” — cages the research team erects around a frog as it selects its winter hibernation spot.

“They basically turn into a little frozen hockey puck. We call it super-cooling. They prevent ice crystals from forming in organs and they change over their sugars in a manner that prevents them from getting any damage to organs and basically allows them to shut down most functions and just be a little frozen Popsicle for, roughly up there in Churchill, it’s about 8 1/2 months of the year,” he says.

“At that spot, they dig a little bit into the soil and they just freeze.”

He’s itching to know: why that spot?

Based on limited data so far, Davenport believes the longer time spent in hibernation expands the frog’s lifespan. Where he lives, in North Carolina, the lifespan of frogs is two to three years; in Churchill, they know the frogs can live until they’re at least four, with some evidence suggesting there are eight-year-old frogs hopping around.

“It kind of makes sense, if you think about it. If they’re frozen for eight months of the year, they’re really only actively hopping around doing stuff for four months, so their equivalent of eight years is really only 2 1/2 years for a normal frog,” he says.

Monitoring of the frog population, despite its continued stability, is important, Davenport says, because of its position at the bottom of the food web.

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After 10 years of research, going in with an expectation he would see declines in this frog population, Davenport is now reasonably confident in the animal’s incredible ability to adapt to whatever Mother Nature throws at it.

“They are being pushed, but these are the populations that are on the edge of their range and have already been pushed for however many thousands of years. So maybe for them, they are actually more resilient and we shouldn’t expect as crazy of a change for them, as we should expect if those changes occur at lower (latitudes).”

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