Rabb’s Fringe-limbed Treefrog

Toughie—another endling

A few treefrogs — among them a male named Toughie—arrived in 2005 from the montane cloud forest of central Panama at the Atlanta Botanical Garden, where they were cared for and where attempts were made to breed them. In vain: the tadpoles died every time before metamorphosing into frogs. Then, on September 26, 2016, Toughie died. He was probably the last of his species, a Rabb’s fringe-limbed treefrog. His conspecifics in the Botanical Garden’s Frog Pod had died years before him.

Toughie was a so-called endling. This is what the last known specimen of a biological species is called. Just as Martha was an endling when the passenger pigeons became extinct in 1914, or Benjamin was the last thylacine and died in 1936.

Rabb’s fringe-limbed treefrog was discovered in 2005. When biologists traveled to Panama again in 2008 to scientifically describe the new frog species, Rabb’s fringe-limbed treefrog already appeared to be extinct in the wild. The species was named after the American zoologist and conservationist George B. Rabb and his wife Mary S. Rabb (hence the plural form rabborum).

The frog species is known from only three or four sites in the El Valle region, in the immediate vicinity of the town of El Valle de Antón in central Panama. It was probably endemic only at elevations of 900 to 1,150 meters above sea level. Scientists estimate that the range of this frog (Anura) covered far less than 100 square kilometers.

Rabb’s fringe-limbed treefrog – fact sheet

scientific name	Ecnomiohyla rabborum
original distribution area	Panama
time of extinction	2016
causes of extinction	Habitat loss, forest clearing, chytridiomycosis (fungal disease)
IUCN status	critically endangered (possibly extinct)

Rabb’s fringe-limbed treefrog: A victim of the global amphibian crisis?

As early as 2005, scientists knew that a fungal disease fatal to amphibians called chytridiomycosis had recently begun circulating in the range of Rabb’s fringe-limbed treefrog, which had only just been discovered at the time. Since there was also a population collapse among the fringe-limbed treefrogs at that time, it is assumed that the fungal disease ultimately led to the extinction of the frog species. Despite intensive searches, by the end of 2007 only the calls of one male could still be heard.

Chytridiomycosis probably originated in Africa. The disease was first detected in clawed frogs, and through the trade in these frogs it spread around the world. Scientists estimate that around 500 amphibian species from 60 countries are affected.

It is disputed whether chytridiomycosis alone is the cause of the global phenomenon of amphibian decline that has been taking place since the early 1990s. Studies such as The Cause Of The Global Amphibian Declines (2010) by the American biologist Tyrone B. Hayes have shown that animals become infected with the fungus or die from the fungal disease above all when their immune systems have already been impaired by other influences. Hayes names four decisive factors that influence the success of pathogens: climatic changes, environmental pollutants, habitat changes and invasive species.

In addition to chytridiomycosis, the IUCN also names other suspected causes of extinction, such as the still ongoing deforestation of forests in the range of the frog species to make room for luxury hotels. Urban development also leads to the fragmentation and degradation of the forest, and more and more conifer plantations are replacing the habitat needed by the species. The conservation organization currently lists Rabb’s fringe-limbed treefrog as Critically Endangered (Possibly Extinct).

The frogs’ behavior makes searching for them difficult

As early as 2005 and 2006, researchers encountered Rabb’s fringe-limbed treefrog only extremely rarely in its range. They could hear only one or two male frogs each night. After the fungal disease had reached the region, the frog species became even rarer. Even the nighttime calls of the males fell silent. The last call heard in El Valle was in 2008. More extensive searches covering a larger area than the known range of Rabb’s fringe-limbed treefrog also produced no success.

Because Rabb’s fringe-limbed treefrogs stay in the canopy of the rainforest and are nocturnal, searching for the animals is particularly difficult. At the same time, this behavior gives reason to hope that the species may have survived up there in the treetops.

These frogs not only stay in the canopy, but also reproduce there in water-filled tree hollows. Female frogs lay the spawn in portions of 60 to 200 eggs on the water surface, attached to pieces of wood or to the bark of tree holes. The males guard the clutch and feed the tadpoles, while the females disappear shortly after laying the eggs.

Feeding the tadpoles is unique and has so far not been observed in any other frog species: The male sits in the water where the offspring are located while the tadpoles eat particles of his skin.

Because of the behavior of Rabb’s fringe-limbed treefrog, the IUCN notes that acoustic searches would be the most likely way to determine whether specimens of Rabb’s fringe-limbed treefrog still exist. The area where the frog species may live or may have lived has still not been placed under protection. This minimizes the chance that any frogs that may still exist can survive and reproduce.

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