2017: The Silence of the Frogs

 

AWARDEES: Joyce Longcore, Elaine Lamirande, Don Nichols, Allan Pessier

SCIENCE: The Silence of the Frogs

FEDERAL FUNDING AGENCIES: National Science Foundation and The Smithsonian Institution

 

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Joyce Longcore, Elaine Lamirande, Don Nichols, and Allan Pessier all share at least one thing in common: a love of “creepy, crawly things.”

They all grew up in rural towns and suburbs where their childhoods were spent splashing around in creeks, catching frogs and snakes. Like millions of other American children, they were inspired to be scientists by their inborn curiosity with nature. Frogs are one of the most accessible gateways to science for rural children, but beginning in the late 1980s scientists began documenting a troubling trend they ultimately labeled “enigmatic amphibian declines.”

Like “dark matter” in astronomy, this label was more a statement of lack of understanding than actual classification. Scientists weren’t sure what was causing massive declines in amphibian populations capable of driving entire species to extinction; several had already been lost. But thanks in large part to Joyce’s persistent study of an obscure branch of fungi known as chytridiomycetes (aka chytrids), this team of researchers helped unmask a primary culprit behind these declines – Batrachochytrium dendrobatidis, or Bd. Today, as researchers and conservationists around the world are racing to rescue species from extinction, we have a much clearer picture of the interconnectedness of our world and how a small event can have a global impact, and we are better prepared to deal with a rising tide of fungal diseases thanks in large part to this team of scientists.

  Joyce Longcore

  Joyce Longcore

The life of Longcore

Joyce Longcore has not had a “standard” academic career, if there is such a thing. After finishing her bachelor’s degree in biology at the University of Michigan in 1960, she remained there as a research technician with a National Science Foundation (NSF) funded mycologist (a biologist who studies fungi) and stumbled onto her life’s passion: chytrids, then a relatively obscure branch of the tree of life.

After obtaining her master’s in botany from Indiana University in 1963, Joyce’s budding academic career came to a pause: she married and had two sons to raise. That could have been where Joyce’s story in science ended, but just as Joyce’s older son was heading off to college, she got the first of two fateful pleas.

In 1984, University of Maine PhD student Joan Brooks came calling. With funding from NSF, Brooks was studying the organisms at work in a domestic septic system, and she needed a mycologist. One of Joan’s colleagues at Maine had been at Michigan with Joyce more than a decade prior, but knew Joan could do no better than Joyce Longcore.

One look through a microscope again was all Joyce needed to remind her how much she loved mycology. Her short stint working with Brooks, whose work would go on to improve rural septic systems, was one of the most important periods in Joyce’s career. Not only did the NSF-funded work bring her back into science, it also provided the lab equipment she would use for more than a decade to discover several entirely new species of chytrid fungi. Over the course of her ensuing Ph.D. studies at Maine, Joyce solidified her place as one of a handful of chytrid experts in the world.

  Don Nichols

  Don Nichols

Meanwhile, at the zoo…

In the fall of 1996, another enigmatic decline in frogs was happening, this one at the Smithsonian National Zoo: Blue poison dart frogs were dying at an alarming rate from a mysterious skin disease. As the Zoo’s associate veterinary pathologist (someone who studies disease and death in animals), Don Nichols was on the case, and he was having a serious case of déjà vu.

In 1991, Don had received a box full of dead toads in the mail (as one does) with the same mysterious skin disease. While his day job then was conducting post mortem exams on mice and rats at the National Institutes of Health, Don was moonlighting as a veterinary pathology consultant – helping friends, neighbors, colleagues, and researchers around the world figure out what was wrong with their animals. He was never able to figure out what kind of organism had killed his colleague’s toads in the early 90s, but it wasn’t for lack of trying.

Don is another researcher with a unique career path; he came to veterinary pathology by way of a degree in math. As a child he loved two things: being with animals and solving puzzles. A perfect combination for a veterinary pathologist, or, as he puts it, veterinary work for math majors.

The toads were a puzzle that Don tried everything to solve. He took samples and electron micrographs – pictures of an organism’s microscopic features taken with a powerful electron microscope – of the diseased skin and sent samples to experts in all manner of organisms to no avail. With the toad colony fully wiped out, there was nowhere to turn—that is until that fall, when Don Nichols landed his dream job: veterinary pathologist at the Smithsonian National Zoo.

At the Zoo, Don scoured the pathology files for a similar skin disease, and he found cases of it in three frogs from the Zoo’s collection. Don figured that since the disease had occurred before in the Zoo’s animals, it might occur again, so he and his pathology residents kept close watch on any amphibians that died. But for five years they found no new cases.

Rather than wait any longer for an event he couldn’t predict, in 1996, Don decided to present his mystery to other zoo veterinarians at their annual conference. As he prepared his talk, he stumbled across a textbook on microscopic organisms called Protista. In it, he found a category that seemed to match his organisms: “zoosporic fungi.” But still, his particular culprit wasn’t there. It did, however, finally arrive at the Zoo as a colony of blue poison dart frogs succumbed to Don’s mystery skin disease.

  Allan Pessier

  Allan Pessier

As the dead dart frogs came streaming into the pathology lab, Allan Pessier was a newly graduated veterinarian just beginning his residency in veterinary pathology at the Smithsonian National Zoo.

With more advanced tools at the Zoo and direct access to recently deceased frogs, which provided better samples for identifying the relevant organisms, Allan joined Don on his five-year quest to identify the culprit behind this recurring skin disease in captive frogs. They compared electron micrographs of these freshly infected frogs to Don’s textbook and they agreed that the organism looked most like the “zoosporic fungi” from the phylum Chytridiomycota, a group more commonly referred to as “chytrids.” Chytrids are unique microorganisms that have baffled zoologists for decades. Once thought to be an unusual group of fungi, they were later re-classified as protists, and finally returned to the kingdom of fungi.

The zoo pathologists did not have the first clue about this obscure branch of fungi, but Allan used their text-only web browser and managed to find one of the few people in the world who could help.

  Elaine Lamirande

  Elaine Lamirande

Joyce gets the mail she didn’t realize she was waiting for

When Joyce saw the Zoo team’s electron micrographs, she confirmed their suspicions. Yes, they had a chytrid, but this one was unlike anything she had ever seen.

The chytrids Joyce was accustomed to seeing grew on dead or decaying material or as parasites on other fungi, algae, microscopic animals or plants. None were reported to grow as parasites of vertebrate animals. Yet, here was a chytrid doing just that: growing as a parasite on living frogs.

Joyce was fascinated and requested samples of fresh frog tissue so she could study the living organism. Then, as she did with other chytrids she studied, she attempted to grow the new chytrid in pure culture – a colony of organisms with just one isolated species. This is not a straightforward task for chytrids in general, let alone one that grows on vertebrate animals like none ever seen before.

Every growth medium Joyce tried failed. At the end of her rope, she put the new chytrid samples in a flask of liquid medium and promptly forgot about it; she fully expected another dud.

A few days later, on Joyce’s birthday, out of the corner of her eye she saw something iridescent on a nearby lab bench. As she looked more closely, she realized her thrown together liquid medium had worked! And in the process, she had invented procedures and a recipe that others could use.  

As she studied this new chytrid, she realized she was looking not just at a new species, but an entirely new genus. She had her mycological discovery, and the Zoo pathologists, along with Zoo researcher Elaine Lamirande, had what they needed to pursue Koch’s postulates – a series of experimental steps to prove that the isolated organism was the cause of death of its amphibian hosts.

None of them had any idea where this new scientific discovery would lead them.

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The world comes knocking

On September 16th, 1997, the global race to identify the culprit behind “enigmatic amphibian declines” arrived at the Zoo’s pathology lab on the pages of The New York Times.

One of the local reptile keepers came into the pathology lab and showed Don, Allan, and Elaine an article entitled, “New Culprit in Deaths of Frogs.” The article described how teams of researchers, led by Karen Lips in Central America and Rick Speare in Australia, were finding sites of enigmatic amphibian declines a world apart from one another where frogs and toads were being “attacked by a protozoan.” Looking at the pictures in the article, the Zoo pathologists knew something no one else did: that was no protozoan.

They also realized at that moment that what they were hunting down was far more than a problem of captive animals. They might have stumbled onto the key culprit behind these worldwide “enigmatic” amphibian declines.

A month later, Allan, Don, and Joyce joined the Central American and Australian teams for a meeting in Urbana, Illinois. They shared their unique insights on the chytrid culprit they identified, and shared crucial expertise that would help their colleagues make huge strides in understanding and ultimately predicting where and when declines would pop up around the world.   

Over the course of the following several years, Don and Elaine proved Koch’s postulates and characterized this new species, which they named “something everyone else hates”: Batrachochytrium dendrobatidis, or Bd for short. The duo also developed a treatment that can be used to cure infected frogs and toads in captivity.

Their scientific colleagues from around the world would go on to definitively tie Bd to massive die-offs of wild amphibians around the globe. Each time they’ve collected samples in the wild, they have found this same single species: Bd.

The sound of silence

The severity of Bd’s impact on amphibian species was never clearer for Allan Pessier than in 2006 as he traipsed through the forests of Panama. While attending an amphibian conservation meeting in a location not yet affected by Bd, Allan and others hiked around in the forest one night; the chorus of frog calls filled his ears and animals were constantly underfoot.

When he went back to the same forest just six months later, Bd had arrived and the trails were silent and clear.

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Don, Allan, Elaine, and Joyce’s curiosity-driven work has had deep global impact. The organism they characterized, Bd, causes what has been called “the worst infectious disease ever recorded among vertebrates in terms of the number of species affected, and its propensity to drive them to extinction.” The pathogen has already killed off dozens of species and threatens hundreds more.

Thanks in large part to their insights, organizations around the world have set up “amphibian arks” to preserve rescued populations of frogs and toads until we can find a way to protect them from Bd. Researchers at the Smithsonian Tropical Research Institute in Panama are just now beginning experiments to understand how to reintroduce species like the iconic Panamanian Golden Frog into the wild.

For the golden frog, for our planet, and for the next generation of children inspired by catching frogs in the creek, federal investments by the National Science Foundation and the Smithsonian Institution have been a literal lifesaver. Joyce Longcore, Elaine Lamirande, Don Nichols, and Allan Pessier did not set out to unlock the centerpiece of a global catastrophe in the amphibian world; they wanted only to know what was around the next bend, what new things they could learn by looking. And in that quest, there’s so much left to uncover.