Fungal Pandemic wipes out Frogs
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Fungal Pandemic wipes out Frogs |
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Across the world frogs are disappearing at an alarming rate. Climate change, pollution and a silent killer, a fungal disease of unknown origin, are the main suspects in the mass extinctions.* Chytridiomycosis
is caused by the fungus Batrachochytrium dendrobatidis.
It is spreading world-wide and is today found in 93 species in six continents.
Australia has the most species infected of any country. 48 species or
22% of its 218 native frog species are infected in the wild. The only
good news in this being that the fungus does not spare the cane toads
either. While some species seem less susceptible, the disease proves fatal for others. There is no known treatment for animals in the wild once they have contracted the fungus. Successful treatments which include exposure to high temperatures and/or fungicidal baths, have been used in captivity but this is not a viable solution for wild animals. These treatments stress the animals and may reduce their fitness in the longer term. Frogs with chytridiomycosis can die, be ill or can appear clinically normal. The top layer of skin is thickened, rough and often sloughs off with small skin tags developing on the toes. These skin changes however are often not visible with the naked eye.
Animals suffering from the disease also change their behaviour. They become reluctant to flee and seek shelter, lose their righting reflex and keep their hind legs away from the body While scientists still don’t know exactly how the disease kills the animals, we know that amphibians drink and breathe through their skins, and the fungus affects exactly this outer layer of the frogs’ skin. Although frog eggs cannot be infected, tadpoles can carry the fungus on their mouthparts, which invades the frogs’ skin once they metamorphose. The disease, being highly virulent, is easily and rapidly spread from frog to frog or from one contaminated water pool to another. Scientists at James Cook University in Queensland have tracked the fungus back to the earliest Australian record in December 1978 and believe that it escaped from captivity in Brisbane and spread from there, colonising frogs and water bodies, as an advancing front. How quickly the fungus spreads seems to be closely linked to environmental factors in the invaded ecosystems. In coastal Queensland the front is estimated to advance about 100 km / year, about four times faster than in Central America. In Australia frog populations began to decline in the late 1970s. By the 1980s, the southern day frog, Taudactylus diurnus, become the first species to disappear, soon to be followed by the southern gastric brooding frog, Rheobatrachus silus. The epidemic of declines continues to spread, taking its toll on many frog populations and threatening the existence of entire species including the endangered Corroboree Frog. The table below gives an overview of what is currently known about the infection status of Australian frogs by species and state. Not all species however have been tested yet and research is continuing.
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Scientists believe the fungus may have originally
developed in South Africa. Credit
for information and pictures in this article: |
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