Give Me Shelter from Extinction

The Colorado boreal toad is receiving experimental treatment to fight off widespread infection.

Biodiversity is an area of increasing concern to anyone who reads spooky headlines like “Birds are vanishing from North America.” Everything from birds and bugs to whales and crabs are in dwindling supply the world over. Three graduate students in a lab at CU Boulder are working to protect one such species from annihilation.  

The Colorado boreal toad, known to scientists as Anaxyrus boreas, was listed as endangered by the state in 1993 after years of increasing death rates. The population decline is attributed to a fungus called Bd, Batrachochytrium dendrobatidis, which embeds itself in the toad’s skin cells and then bursts out, destroying the cell and spreading its pores to further the processes of infection. 

“In terms of its effect on biodiversity, it’s probably the worst pathogen in the world,” said Tim Korpita, a graduate student in the McKenzie lab at CU Boulder, which is working with Colorado Parks and Wildlife on efforts to research possible ways to fight the pathogen.

The three graduate students share a tiny lab space, which is filled with three full-size refrigerators and a rickety old radiator hidden under boxes of equipment. One of the students, Alex Alexiev, places a few petri dishes on the small table that takes up the majority of the room. Each dish looks like it contains the makings of a lava lamp, with tiny violet bubbles growing throughout. What we are looking at is the growth of a bacteria that could be used to stop Bd from taking up residence on the endangered toad.  

Anyone who has seen or held a toad might suspect there’s a lot to learn about its warty outer layer. Toads rely on their skin for critical functions like gas exchange (breathing), predator defense (discharging poison), immune functions and osmoregulation (salt regulation), which means any bacteria that compromises the skin has deadly implications. And while Bd was only discovered 20 years ago, it has rapidly swept across the world’s population of amphibians thanks to immune carriers like humans and waterfowl who transport the fungus from one watershed to another.

The McKenzie lab is helping toads fight back against the bacteria that is killing them in vast numbers using a natural remedy: their own microbiome.

As it turns out, that purple lava on the petri dish we were looking at, Janthinobacterium lividum, grows naturally on the boreal toad, and researchers in the lab have discovered that enough of it applied to the skin during metamorphosis - when the tadpole is transforming into a toad - can actually inhibit Bd from taking over. 

The pathogen, which some are calling the source of an amphibian apocalypse, has already killed off hundreds of species of frog and salamander. Sometimes comedy is the best remedy for such grim numbers. 

“[In the future] it’ll just be starlings and cockroaches...and Keith Richards,” said Valerie McKenzie, evolutionary biology professor and founder of the lab, who has been studying Bd on amphibians since her graduate days in California. 

Ecologists like those in McKenzie’s lab are working to stop the impending doom of extinction, though even if successful, their efforts are still a drop in the bucket. Humans are cutting off migration corridors and destroying entire ecosystems with development, while climate change is altering what remains, making it hard for fragile species to survive the new conditions. 

Of course, us clever humans always try to technologize our way out of tricky situations. We can now use robots instead of hands in the operating theatre, and vaccinate our way around disease like we’re in complete control of whatever nature throws at us. But we still can’t stop ourselves from traveling the world, transporting deadly pathogens from lake to lake. McKenzie thinks we’re in over our heads when it comes to solving extinction. 

“We can’t engineer ourselves out of biodiversity loss,” she said. 

While humans are keen to solve anything we deem problematic, McKenzie pushes back on the idea of de-extinction - bringing back bygone species to restore the ecosystem - considering it radical and potentially useless. Even if we could bring it back, would the wooly mammoth be able to thrive in the current condition of its past habitat? The world is barely recognizable to our grandparents, let alone to an animal that roamed the continent in the Pleistocene era, thousands of years ago. 

But the work in McKenzie’s lab is not about solving all of the world’s existential problems using radical technological solutions. Keeping the toad safe from a pathogen that can be transported by vacationing humans is hardly extreme intervention. 

Extinction is not expected in the near-term for the boreal toad, thanks to the McKenzie lab and involvement of groups like the Denver Zoo, which launched a boreal toad breeding program and released 620 individuals in a remote area of Utah this summer. Lucky break for a species without much economic interest, which McKenzie said is unusual. 

But she doesn’t seem to care what the toad is worth on the market--it’s about keeping alive as many species as possible to protect the complex and interconnected global ecosystem of today. Because we know a lot, but it’s what we don’t know that gets us into trouble.