Will a Deadly Fungus Destroy N.H.'s Frog Population? The Answer is Complicated

Jun 21, 2017

A frog gets swabbed for BD
Credit Courtesy SNHU

A New Hampshire undergraduate has confirmed the presence of a fungus in the state that, over the past thirty years, has caused either extinction or massive decline in more than 200 species of frogs around the world.

That was enough to get Outside/In host Sam Evans-Brown interested.

This story begins in Tasmania and Australia, where in the 1970's and 1980's frog populations mysteriously began to crash. Then through the 90's into the 2000's, the die-offs swept through Central America, causing more than 50% of the frog species in some areas to go extinct.

Dede Olson, a researcher with the US Forest Service, says the cause was a mystery.

"So they were called enigmatic losses because we hadn’t figured that out yet."

Eventually scientists linked the enigmatic losses to a fungus.

"Chytrid fungus. It’s official name is  Batrachochytrium dendrobatidis."

That’s Mariah Mitchell, who just graduated from Southern New Hampshire University. The fungus is called BD for short.

"And it is a warm-loving fungus."

Since it was first discovered, BD has been implicated in massive die-offs of amphibians in the Caribbean, South America, in Spain and in Portugal, in a few Species in Africa, so it’s no surprise that researchers would want to know if this thing were here in New Hampshire.

Katherine York is a professor at SNHU and Mariah Mitchell’s advisor. She taught Mitchell how to catch frogs so that she could swab their skin and how to extract the DNA to search for the genetic markers of BD.

"No it didn’t hurt the frogs and they just hop right off and they were fine," she says.

Tests for the fungus are performed in a lab at SNHU

This DNA analysis used to be limited to a few big research labs, but as the equipment needed has become more commonplace in Universities, this has become the kind of study that an ambitious undergrad – like Mariah Mitchell – can do with an advisor, like Katherine York.

"I remember the day we did it, we’d be running all these different samples like, no no no… and then we had two that show up with this fluorescent band that match the positive and we were like *gasp* there it is!"

In an apple orchard smack in the middle of the state, they had found BD. By now, you’re probably thinking: this is a fungus that has killed millions of frogs in other parts of the world, and now they’ve found it here… our frogs are doomed!

But this story is actually a lot more complicated than that.

Because following the global frog pandemic of BD in the 90's and 2000's, researchers have been going back, to try to figure out where it came from.

Right away they found that BD was already present in the United States. And not only that, they tested some long dead frogs.

Joyce Longcore, a chytrid researcher at the University of Maine, says that means the fungus has been in parts of North America for more a century.

"They can go back to museum specimens and test, and I think they have gotten back into 1800's."

There are competing hypotheses as to where the fungus actually came from. A Japanese researcher thought it might have come from Asia… a South African researcher thought it might have been shipped around the globe on the skin of African Clawed frogs, which are widely used by researchers.

Frog-catching is the first-step in the hunt for BD
Credit Courtesy SNHU

But, Longcore says, our bullfrogs are actually resistant to BD. So, we might even have had the fungus all along and it might have spread to Central America from here!

So… why haven’t our frogs all died? Mariah Mitchell points out it gets a little too cold here for BD to be really happy.

"It really exploded in the tropical areas because it is such a warm loving fungus. It likes it between 17 and 25 degrees Celsius." 

That's between 62 and 77 Farenheit. So maybe warmer temperatures would turn this fungus deadly in New England… maybe more precipitation would make it worse?

Dede Olson from the Forest Service says we’ve just got to keep watching it, to see what happens.

"So we’re still in the era of figuring out, ‘is it a problem.’ What we don’t know are these tipping points these triggers that may cause the BD to go from something that’s benign to something triggering a decline."

Which means it’s a good thing that this testing can now get done by undergrads, at places like Southern New Hampshire University.