Worldwide amphibians are the most threatened class in the animal kingdom. In recent years Batrachochytrium dendrobatidis, a fungal pathogen, has caused havoc among many species of frogs, toads and salamanders, decreasing populations and wiping out others.

Now research by Oregon State University, published in PNAS, says a positive feedback acts between the widespread fungus infections and the amphibian biodiversity decline it promotes.

It turned out that in a laboratory with many different amphibian species the fungus was much less successful infecting the different potential hosts, compared to a setting where all individuals belonged to a single species. For a frog the severity of the fungus infection is an important factor. It can survive the pathogen up to a certain dose – suffering cardiac arrest when the fungus is free to spread out.

The authors do not explain the exact mechanism. Most we know of amphibians we learned from closely monitoring that host in The Muppet Show, still we think we may have something clever to say about just why this amphibian biodiversity may be so important for the individual species.

Different amphibian immune systems can line up

Any infectious pathogen is in a constant battle with its host’s immune system, both of whom constantly try to be one step ahead of each other, designing specific antibodies and shielding proteins as they go. It’s microevolution – and neither the fungus nor the frog is genetically identical at any subsequent time in that process.

If the fungus manages to adapt to that one frog’s changing immune response – it has a good chance of being able to keep up the high infection rates. If however there are other frogs species around, with very different immune programmes, chances are it is going to be much more difficult for the fungus, waging simultaneous battles at too many fronts – resulting in one fungus population that is neither very good at infecting the one amphibian, as the other.

Take home message: take good care of your local amphibian populations – and especially try to prevent any extinctions of the most endangered ones – in order to keep the others healthy too.

Just how important ecosystem health can be in preventing plagues we may learn from the Permian-Triassic boundary. If disturbance reaches a tipping point, with fungi infections any ecological damage is possible.

© Rolf Schuttenhelm | www.bitsofscience.org