The deadly amphibian disease chytridiomycosis has caused the extinction of Darwin's frogs, according to scientists from the Zoological Society of Londonand Universidad Andrés Bello in Chile.
Conservation scientists found evidence of amphibian chytridiomycosis causing mortality in the the northern Rhinoderma rufum endemic to Chile, and linked this with both the population decline of the southern Rhinoderma darwinii from Chile and Argentina, including from undisturbed ecosystems.
Darwin's frogs were named after Charles Darwin who first discovered R. darwinii in 1834 in south Chile during his famous voyage around the globe. The species have a distinct appearance, having evolved to look like a leaf, with a pointy nose.
Skin histological section of a wild southern Darwin’s frog (Rhinoderma darwinii) with cutaneous chytridiomycosis. Note multiple empty zoosporangia (arrows) within the superficial keratinised layer of the epidermis. Several zoosporangia with an internal septum can be seen (arrowheads), morphologically typical of Batrachochytrium dendrobatidis. Stained with Periodic Acid-Shiff (PAS). Bar = 20 µm.
Hundreds of specimens of Darwin's frogs and other amphibians from similar habitats collected between 1835 and 1989 were tested in order to find DNA pieces of Batrachochytrium dendrobatidis (Bd), a fungus that causes the disease chytridiomycosis. In addition, 26 populations of Darwin's frogs were surveyed in Chile and Argentina between 2008 and 2012 for the presence of Bd.
Amphibians provide an important ecosystem service by maintaining balance in the environment. Without them insect plagues and their subsequent effect on agriculture and public health would be more frequent. ZSL scientists are working to further understand the reasons behind the extinction of Darwin's frogs, and ensure the long-term survival of the species.
Senior author Professor Andrew Cunningham from ZSL's Institute of Zoology says, "Only a few examples of the "extinction by infection" phenomenon exist. Although not entirely conclusive, the possibility of chytridiomycosis being associated with the extinction of the northern Darwin's frog gains further support with this study".