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Thanks to globalisation, an ancient stain of fungi has recently escaped its niche and is now suspected of killing off many of the world’s frogs. This is according to a new genetic analysis of chytrid fungus, published in the Proceedings of the National Academy of Sciences, which is the latest in a long line of research, dating back to the 80s, since the frogs started going extinct in Australia and South America.
According to Australian team member Dr Lee Berger, of James Cook University in Townsville, ‘It’s an older strain that has spread into new areas. The most likely reason for the spread is trade.’ As part of her PhD under Professor Rick Speare, Berger was the first to identify chytrid fungus in the bodies of many dead frogs back in 1998, and her subsequent 2011 genetic analysis indicated that the global pandemic strain of chytrid fungus had only evolved in the 1970s, through hybridisation of a number of different strains.
This timeline that fitted with the decline of frogs in the 1980s, but Berger and her colleagues’ new research complicates this picture, as it shows that the pandemic strain actually evolved thousands of years ago. An analysis of the genome of 49 samples of chytrid fungus from around the world gave the researchers a family tree of the fungus, which provided clues as to the origins of the pandemic strain.
Berger says, ‘This paper says that that global pandemic strain has been around a long time before the frog declines occurred.’ The ancestor for the pandemic strain arose at least 1000 years ago and maybe even as early 26,000 years ago, the researchers claim. Berger explains, ‘A new strain has not evolved. It’s just that globalisation has allowed the fungus to escape from its niche and spread.’
However, Professor Hamish McCallum, a chytrid expert from Griffith University says that, although he welcomes the new research, it raises more questions than it answers. ‘It is an interesting piece of work but it literally opens up a can of worms,’ he commented. ‘Even if one is looking at a particular strain that has been obtained from one source, its virulence varies substantially between frog species. The critical thing to understand in all of this is that virulence of a pathogen is not an intrinsic property of the pathogen itself. It’s a property of the interaction between the pathogen and its host in a particular environment.’