Let us sit upon the ground …

… and tell sad stories on the death of frogs.

The chytrid fungus outbreak among mountain yellow-legged frogs (Rana muscosa) in California. A: Frog showing the peculiar posture of infected animals; B: Mass deaths from the fungus.

The decimation of frogs continues worldwide.

The reason is chytriomycosis, a highly infectious disease caused by an aquatic fungal pathogen, Batrachochytrium dendrobatidis. It is thought that zoospores adhere to the frog’s skin where the fungus produces sporangia, in turn producing more zoospores, which reinfect the animal through its skin. The mechanics of this pathology is known almost exclusively from laboratory experiments and it is still unclear. A study published in PloS ONE yesterday by Jamie Voyles of Berkeley and others (open access article here) shows the results of field collections of blood of mountain yellow-legged frogs (Rana muscosa) during a chytrid outbreak in the Sierra Nevada Mountains of California. They found that pathogen load is associated with disruptions in fluid and electrolyte balance, resulting in severe dehydration. (This of course is an understandable consequence given that frogs absorb water and electrolytes through their skin.)

It is apparently easy to treat the disease in the laboratory with anti-fungals. In the wild, however, it is near impossible, as is shown by the fact that since the blood samples were collected, the Rana muscosa population has declined by 95%. The main unanswered question is how chytrid spreads. Meanwhile 200 species of amphibians have already been killed off.

The imminent extinction of a class of tetrapods that have lived since well before mammals and dinosaurs is a stunning prospect. The effect on fresh water ecosystems is likely to be substantial, and, as we’ve come to learn, widespread disruptions caused by us usually have a substantial blowback on us. And while frogs are highly derived (their skeletons are designed to absorb the shock of landings; many have suction cups on their digits), when you look at a frog, you can see our very design in them.

Green and black poison dart frog (Dendrobates auratus) from Costa Rica climbing the glass of a terrarium. (Photo by Drriss on Flickr.)

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