Experiment

Unexplored and Unexpected

Biologist Sandra Goutte scaled a remote mountain in Ethiopia to find a new species of frog. But her most surprising discovery was back home in the lab—where a tiny toadlet glowed blue.

By Lindsy Van Gelder

As a specialist in frog acoustics, Sandra Goutte knows that exploring the unknown for tiny creatures can yield big discoveries. That’s why she and her NYU Abu Dhabi colleagues set out on an expedition to the isolated and unexplored Bibita Mountain in southwestern Ethiopia—though it took multiple attempts over two years to actually reach it. “No biologist had ever been there before,” she says of the virgin forest with no roads. Steep and overgrown, the area is particularly inaccessible during the muddy rain season—from the spring through August—but that’s also the best time to catch frogs. And in the summer of 2018, Goutte found a new species in Bibita’s swamps.

From a remote village reached by four-wheel drive (the last vehicle its residents had seen was an ambulance called in for a difficult labor the year before), Goutte and fellow NYU Abu Dhabi postdoctoral associate Jacobo Reyes-Velasco began their trek up the mountain at night, when frogs are active. Through the darkness, they spotted the tracks of what appeared to be a leopard and her cub. Almost immediately, Goutte caught a frog that looked like no other she had seen before—and then it slipped through her hands. “I found a new species and I just missed it!” she yelled across the pond at Reyes-Velasco. Fortunately, another turned up a few minutes later.

Lab results confirmed that the frog—a tiny amber creature with long E.T.-like fingers—was indeed a species previously unknown to scientists. The researchers named it the Bibita Mountain dwarf puddle frog.

This wasn’t the first major discovery for Goutte, who has a master’s degree in ecology from the École Normale Supérieure in Paris and a PhD from the French Museum of Natural History. In 2016 she led an international team on an expedition to the Atlantic forest of Brazil, near São Paulo. Her goal was to learn more about the soft, buzzing mating call of a brightly colored, toxic frog called the pumpkin toadlet. Much to her surprise, she found that the creatures were partially deaf.

Goutte spent the next year and a half conducting lab experiments to ascertain whether visual cues, such as the toadlet male inflating a sac on his neck, took the place of the apparently useless mating call. During a brainstorming session, she and her colleagues remembered that some plants and flowers have patterns that are undetectable to humans, but can be seen by insects using their ultraviolet vision. Could something similar be going on with the frogs? They arranged to have the frogs photographed by a UV camera, which takes pictures using only light from the ultraviolet spectrum. (Such cameras are used to create visible images of things unseeable by the naked human eye, from artifacts at archaeological sites to certain medical conditions.)

But due to a misunderstanding, a camera that takes pictures under a UV lamp, rather than a UV camera, was provided—“which is a very different thing,” says Goutte. “It doesn’t give you the same result at all.” The researchers decided to check it out anyway. To their amazement, the backs and heads of the frogs glowed a bright fluorescent blue. “We had no idea this would happen,” she says, “honestly—no idea.”

Goutte has since discovered that the entire skeletons of the pumpkin toadlets are fluorescent, but the skin on their backs and heads is so thin and unpigmented that the skeletons there are visible under UV light. Is the fluorescence designed to warn certain predators of the frogs’ toxicity? No one yet knows. Meanwhile, Goutte believes that the mating call around which the original expedition began is simply vestigial. “I think they lost their hearing, but not yet the call,” she explains. Although similar, nonpoisonous species hide under vegetation, the toadlets make their calls out in the open on the forest floor and have no real biological motivation to cease.

Both of Goutte’s discoveries are now the subject of published papers, the pumpkin toadlets in Scientific Reports and the Bibita Mountain dwarf puddle frog in ZooKeys, written by Goutte, Reyes-Velasco, and Stéphane Boissinot, program head of the Biology Department at NYU Abu Dhabi. Although the Brazilian study is over, Goutte hopes to eventually get back to Bibita Mountain.

Boissinot, who has been studying Ethiopian frogs for a decade, believes that the Bibita area is so fecund and so unexplored that any future expeditions are likely to yield even more discoveries—not just of amphibians, but of insects and mammals. But, he cautions, “Let’s face it—things are going extinct at the rate we are discovering new ones, and the future of a lot of species is very bleak. If they found uranium or oil there [in the Bibita area], you know it would be gone.”