Thursday, January 23, 2014

A micro-predator limits the spread of amphibian chytrid disease

Amphibians worldwide are succumbing to a fungal infection driven by a parasitic chytrid fungus,  Batrachochytrium dendrobatidis , which infects amphibian skin,  interfering with their ability to regulate salts and causing cardiac arrest. This fungal disease is thought to be a major factor in
Possibly a frog's best friend
devastating declines in amphibian numbers in Australia, New Zealand, and Central America-- and it's still going.

B. dendrobatidis fungus appears to have originally been endemic to southern Africa.  A plausible hypothesis is that international trade of the south Africa toed frog, i.e.  Xenopus Laevis,  which started in the 1930s, may be behind its worldwide spread. It's a little uncomfortable to think that a laboratory organism studied by developmental biologists may have promoted such a devastating spread.

There may be some hope for control of this disease through fungus-eating protists native to the frog's home ponds. Even in heavily infected areas, amphibians in some ponds appear to remain relatively unscathed while populations in nearby ponds are decimated. A recent study of frog populations in the Pyrenees suggest that one key difference in the disease course is the numbers of rotifers, pond denizens which eat a lot of fungus. Importantly, the rotifers seem to preferentially eat the infectious stage, or zoospores, of the chytrid. Thus the fungus has trouble spreading from host to host, possibly keeping the whole amphibian population safer. If this observation is correct, then at least laboratory ponds could be stocked with rotifers or other fungus-eating protists to control chytrid.

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