BBC News just ran this Q&A on Bd, the chytrid fungus that is a major villain in the demise of amphibians. One thing that surprised me is that there is another theory about how chytrid has spread worldwide. (I had thought it was simply fact what I recounted in an earlier post about the fungus spreading on the backs of African Clawed Frogs that were being exported from Africa as a pregnancy test.) Excerpt from the BBC Q&A:

Scientists are not sure where the fungus came from, and are currently investigating two possibilities. Jon Bielby, an amphibian expert from the Zoological Society of London, explains: “One hypothesis is that is was that was already all over the place – and it could be that something suddenly changed, like the weather, causing amphibians to become more vulnerable to the fungus or the fungus to become more pathogenic.”

This is called the “endemic pathogen hypothesis”. The other is described as the “naïve pathogen hypothesis”.

Dr Bielbly said: “This is the idea that it came from one area and then spread all around the world – and because it is being introduced to populations that have never seen the fungus before – naïve populations – it has a serious effect.

“The evidence at the moment seems to favour this slightly – the first records of the fungus go back to Southern Africa in the 1920s.”

Around this time, he said, an aquatic amphibian called the xenopus toad, that was native to the area, was being exported all over the world for use in pregnancy tests – certain hormones only found in pregnant females make the amphibian spawn.

This toad is able to carry – and spread – the fungus without suffering any ill effects.

Dr Bielby added: “This was a possible way that it spread from South Africa.”

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