The toads are the size of my fingernail — dark blobs with spindly appendages and toes as fine as hairs. Some still have the vestiges of tails. They’re passing through their most vulnerable life stage, the brief period when they change from writhing tadpoles to tiny, fully formed toads, and they’re using an enormous amount of energy to do so — the kind you or I might expend running an ultramarathon. In this compromised state, amphibians are especially susceptible to disease, predation and starvation. Many die.
Biologist Valerie McKenzie is trying to use the toads’ own microbes to save their lives. Standing in the muck of a swampy pond at 10,000 feet elevation in Colorado’s San Isabel National Forest, McKenzie nudges a toad onto her blue-gloved finger. She holds it up against the sky, squinting at it for a moment before dabbing it with a cotton swab, handing the swab off to a research assistant, and gently dropping the toad into a plastic sandwich container with about a dozen others. Soon, she’ll pour a mixture of water and cultured Janthinobacterium lividum bacteria into the container, bathing the toads in a solution that she hopes will help them survive to adulthood — and that could have ramifications for conservation far beyond this pond in the Rockies.
J-liv, as the bacterium is better known, is found all over the world, from bird feathers to Antarctic lakes to amphibians’ mucous skin. For years, scientists largely ignored it, as they ignored millions of other microbes living in, on and around all living things — a collection of microscopic hitchhikers collectively known as an organism’s microbiome. Unless they made us sick, the majority of these microbes weren’t considered important. That’s changing. Scientists are learning that microbiomes shape humans’ and animals’ mental health, physical makeup and ability to fight disease. That last factor is where J-liv comes in.
Like many amphibians, the boreal toads McKenzie is trying to save already suffer from habitat loss, pesticide use and competition from non-native species. But in the past 15 years, scientists have learned they’ve also been wracked by a deadly fungus commonly known as chytrid. No one’s quite sure how it spreads, but chytrid has caused the collapse or extinction of some 200 amphibian species worldwide, from salamanders in Europe to tropical frogs in Madagascar. And the fungus shows no signs of slowing. “It’s terrifying that one pathogen can wreak such havoc across such a broad, diverse group of animals,” McKenzie said. “People in the amphibian world are freaking out.”
Because J-liv produces a metabolite that inhibits fungal growth, McKenzie and other researchers think it can help frogs and toads survive chytrid. Lab tests have already shown that amphibians with naturally occurring J-liv on their skin are far less susceptible to the fungus than those without it: In one experiment, biologist Vance Vredenburg from San Francisco State University exposed one group of frogs to chytrid and another to chytrid and J-liv. All the frogs in the first group died. All those in the second group lived.
But though Vredenburg tried to replicate the experiment in the field, California’s drought caused the pond where he was working to dry up. The entire population of frogs croaked.
That’s why McKenzie’s latest research is so promising. Last year, her team at the University of Colorado isolated a local strain of J-liv from boreal toads in the Collegiate Peaks, a crest of mountains in Central Colorado recently infected with chytrid. On Sept. 5, the researchers hiked three miles up a drainage there, hauling pipettes, swabs, Petri dishes and a clear plastic bottle filled with freshly cultured J-liv. Since J-liv forms a violet cloud when grown in the lab, McKenzie also carried all of Prince’s greatest hits on her phone. “We’re calling this Operation Purple Rain,” she told me gleefully, “because we’re going to rain down purple bacteria!”
Until recently, most wildlife microbiome research has focused on collecting baseline data: What kinds of microbes live on animals’ skin and in their guts, and what purpose do they serve? The next step — the one McKenzie is helping to pioneer — is to apply that information to actual conservation strategies.
But a number of basic questions must be answered before scientists can widely employ microbes for amphibian conservation. Why, for example, do frogs in some ponds have J-liv on their skin, while the same species just a few ponds over lacks it? Katherine Krynak, an assistant professor of biology at Ohio Northern University, studies how environmental factors affect the microbiomes of Blanchard’s cricket frogs in Ohio and Michigan, and last year she published a paper in the journal Biological Conservation that suggests a number of factors are at play, including water quality. Frogs living in residential or agricultural areas, for example, host strikingly different microbes than frogs in woods or meadows. (Another study found similar differences in black howler monkeys living in untouched jungle compared with those in forests fragmented by roads, logging and development.)
When an animal’s environment changes even more drastically — say, from a jungle to an enclosure in an urban zoo — the impact on its microbial community can be equally drastic. Some species of monkeys living in captivity, for instance, develop a microbiome that more closely resembles a human’s than that of their wild peers (!).
As wild as this is, it also makes sense. Humans’ microbiomes differ wildly based on what we eat, where we live and how we interact with our surroundings, so it’s not surprising that animals’ microbial communities are similarly influenced. But the differences between wild and captive animals may be crucial to endangered species’ survival. Gut microbes, for example, make it possible for animals to absorb certain nutrients from foods, so even if a captive animal is getting the same diet it would eat in the wild, it may not be absorbing the same nutrients. Such differences could impact disease and mortality rates.
Take gorillas. Heart trouble is a major cause of death among captive gorillas, and Krynak — who works with western lowland gorillas in conjunction with the Cleveland Metroparks Zoo when she’s not studying frogs — has found that captive gorillas with heart conditions host different gut microbes than those without heart conditions. She hopes that eventually, zookeepers will be able to manipulate captive gorillas’ gut bacteria by adjusting their diets, perhaps preventing heart disease and improving the success of captive breeding programs.
Still, she and other researchers stress that the field is in its infancy — McKenzie is taking some of the first steps toward manipulating wild animals’ microbiomes to prevent them from going extinct. “We’re at the cusp of being able to say, ‘This is a healthy microbiome, and if we change the environment in some way and change the microbiome, these are the consequences,’” Krynak said. “We may not be able to see the intricate details yet, but we can see the big picture.”
As the sun sank toward the edge of the mountains and “Purple Rain” played from a tinny portable speaker, McKenzie and her team rushed to swab the toads for samples and soak them in J-liv. The wild boreal toad population in this particular pond was wiped out by chytrid a couple of years ago, so these juvenile toads were raised and released by Colorado Parks and Wildlife, a state agency trying to rebuild the wild population. Although the effort has been successful elsewhere, the toads here were weak; dozens already floated belly-up in the pond.
Initially, McKenzie hoped to release the treated toads and monitor their survival rates, but the animals she found were so fragile that she wasn’t sure they could handle the injection that would tag them as “treated.” Instead, she modified the experiment: Both the treated and untreated toads would be kept in separate “toad hotels” — temporary terrariums in plastic bins — and she and her team would camp in the mountains for several days, watching the toads and periodically swabbing them for samples of their microbiomes.
After treating the juvenile toads in their bacterial bath, McKenzie looked at them worriedly. “Aww,” she said to one that looked like it might not survive the night, let alone its first year. “You’re just not well-equipped for life, are you, buddy?” The toad sat in the shallow water, not responding.
Even if that particular toad dies, though, McKenzie’s efforts might eventually help boreal toads as a whole — as well as other threatened species. The samples she took in the field are now being processed to answer questions about whether a J-liv boost lasts long enough to help juvenile toads make it through metamorphosis, and McKenzie hopes to repeat the experiment in another drainage this fall, where the juvenile toads might be stronger. “The more we learn about how much the microbiome contributes to the health and functioning of hosts,” she said, “the more we start to think about how it’s an under-recognized piece of some of these bigger biological puzzles.”