Double whammy for the disappearing frogs

New species of red-eyed toad New frog and toad species are being discovered - others may be wiped out before being identified

There's a strange twist this week to the long-running story of the disappearing frogs.

As regular readers of these pages will know, frogs and their amphibian cousins, the salamanders and caecilians, are more threatened than any other group of animals, with more than a third of assessed species on the danger list.

With some species, it's easy to find a single culprit for the decline. With others, as I've noted before, it's a bit of this and a bit of that - the attack of the killer everything.

Usually, the various threats are symbiotic; pollution reduces resistance to disease, for example, while loss of habitat caused by expansion of the human footprint also brings invasive species.

Frog's eye (Image: AP) The study reveals something rarely seen before

This week's unusual twist comes in the shape of a paper in Proceedings of the National Academy of Sciences (PNAS), which suggests a very different relationship between two of the major amphibian threats: loss of habitat, and the fungal disease chytridiomycosis.

Gui Becker and Kelly Zamudio from Cornell University in the US analysed statistics on amphibian decline in Brazil, Costa Rica and Australia, and found that chytrid appears to do more damage in pristine forests than in lands that have been cleared or otherwise modified by human hands.

Why this should be the case isn't entirely clear.

One possible link is temperature; where forests have been cleared, daytime temperatures will be higher (at least in the regions studied), and the Batrachochytrium dendrobatidis (Bd) fungus doesn't like such hot conditions.

An alternative idea is that the greater diversity of amphibian species in virgin forest helps the fungus to spread.

Each species will breed, for example, or disperse, at a different point in the year; so the more species there are, the more frequent these events will be.

And these activities are likely to carry the fungus from one place to another.

The finding has been greeted with some caution, and Nature News carries a good discussion of arguments over what might lie behind it.

The Cornell team now plans to do some laboratory experiments to see whether species richness does encourage chytrid to spread.

Scarlet frog The scarlet frog of Venezuela may have been a victim of chytridiomycosis

In the meantime, if the finding is correct, what does it mean?

One interpretation is that there is now "no hiding place", in Gui Becker's words - with amphibians damned either by loss of their home, or by the visit of a lethal fungus that prefers to knock at unopened doors.

Comments by Karen Lips, one of the world authorities on chytrid, on the Nature post amplify the point.

"This is now a Bd world," she says.

With the fungus active on every continent except Antarctica, the point is well made.

What the new work doesn't do is point a way forward for conservation. Encouraging the destruction of habitat in order to hinder the spread of a disease would hardly be a rational strategy.

But it does confirm that just preserving tracts of intact forest and wetland isn't going to be enough to save all the extant species of amphibian.

Doing that is likely to need something that can tackle chytrid in the wild - which, as yet, does not exist.

Richard Black Article written by Richard Black Richard Black Former environment correspondent

Farewell and thanks for reading

This is my last entry for this page - I'm leaving the BBC to work, initially, on ocean conservation issues.

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  • rate this

    Comment number 47.

    Hi - I am new here, and I am here because a frog moved into the 'water feature' in my back yard - an old iron bath tub with water plants and solar fountain. I live in upstate NY. Can anyone help me with information about how to keep him safe this winter? The tub will freeze over. I can keep a hole in the ice for air, but I am worried that won't be enough. I think he is a green frog. Any ideas?

  • rate this

    Comment number 46.

    @ 10. blefuscu

    Water-borne and direct frog to frog contact are not the same thing - you can't catch cholera by hugging someone! I don't think keeping biologists 'out' will help increase our knowledge and therefore ability to take positive action.

  • rate this

    Comment number 45.

    "Nature tends toward balance."

    No it doesn't, this was disproved in the 1970s with the in depth study of grasslands in the US - the more detailed you look at nature, the more you notice that things are changing and never go back to the way the were. There is no balance or equilibirum, just perpetual change and adjustment.

  • rate this

    Comment number 44.

    Frogs make mistakes too

  • rate this

    Comment number 43.

    Plants and animals adjust over time or disappear. Would not jump to any conclusions based on a point in time study. Nature tends toward balance. Sometimes that is difficult, especially when human beings can create environments in days or weeks that would have taken hundreds of years in some natural process. Humans make many mistakes..i.e. History.


Comments 5 of 47



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