Tree frog with strange claw discovered in remote Andean dwarf forest

January 4, 2019, 8:20 a.m.
tree frog, Hyloscirtus hillisi
Photo: Gustavo Pazmiño/BIOWEB Ecuador

In a remote area of the tropical Andes, scientists have discovered an "extraordinary" new species of tree frog, they report in the journal Zoo Keys, offering yet another example of the incredible biodiversity that still inhabits this unique wilderness.

The tropical Andes in general is a global treasure, hosting one of the planet's richest hotspots of biological diversity. The region is home to about one-sixth of all known plant species, for example, as well as a wider variety of amphibian, bird and mammal life than any other biodiversity hotspot, according to the Critical Ecosystem Partnership Fund.

Within this region lies the Cordillera del Cóndor, a mountain range that's especially rich with biodiversity and remains "largely unexplored," the researchers write. That's where they discovered the previously unknown frog species, during a recent two-week expedition to a remote tabletop mountain. Thanks to its dark-brown skin dotted with bright orange flecks, the amphibian didn't exactly jump out from the tropical forest at first glance, as team member and field biologist Alex Achig explains in a statement:

"To reach the tabletop, we walked two days along a steep terrain. Then, between sweat and exhaustion, we arrived to the tabletop where we found a dwarf forest. The rivers had blackwater and the frogs were sitting along them, on branches of brown shrubs similar in color to the frogs' own. The frogs were difficult to find, because they blended with their background."

claw-like prepollex of Hyloscirtus hillisi tree frog, Ecuador
And camouflage isn't the only trick these frogs have up their sleeves. They also possess an enlarged claw-like structure, known as a prepollex, at the base of the thumb (see inset photo at left). Its function remains unclear, the study's authors write, although it could serve as a defensive adaptation against predators or as a weapon for fights between rival males.

Led by biologist Santiago Ron from Pontificia Universidad Católica del Ecuador, the team examined several adult and juvenile frogs of both sexes. By studying their DNA and comparing them with similar frogs, they realized they'd found a previously unknown species in the genus Hyloscirtus, which features 37 relatively large tree-frog species that reproduce along streams from Costa Rica to the Andes of Bolivia, Colombia, Ecuador, Peru and Venezuela.

Adults of the newly identified species have a "snout-to-vent length" of 6 to 7 centimeters (about 2.5 inches), and measure roughly 16 centimeters (about 6 inches) from head to toe, the researchers report. The species is named Hyloscirtus hillisi, in honor of U.S. evolutionary biologist David Hillis, an expert in Andean amphibians who discovered three closely related species in the 1980s.

Unfortunately, despite being unknown to science until now, these newfound frogs may already face a serious risk of extinction, the researchers note. They seem to have a small geographic range, with specimens only found at two nearby sites, which has helped them evade detection but also makes the entire species highly vulnerable to disturbance. That may not matter as long as their small habitat remains safe, but as the researchers point out, it's located near a large-scale mining operation run by a Chinese company, and the nonprofit Amazon Conservation Association has already documented habitat destruction in the region.

On the bright side, however, at least these frogs were discovered while there's still time to save them. In light of their small distribution, plus looming threats from mining and habitat loss, the researchers suggest listing the frogs as a Critically Endangered species, according to guidelines from the International Union for Conservation of Nature.

For a glimpse of these rare frogs in their element, see the video below from BIOWEB Ecuador:

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