On Mon, Oct 25, 2004 at 12:28:43AM +1000, Chris Sanderson wrote:
> I'm told one of the big concerns about the
> spreading of Cane Toads is a particular chytrid fungus that is
> believed to be responsible for many native frog extinctions and may be
> carried by the toads into new areas. Whether the fungus is really the
> cause of the problem is still an area of contention amongst experts
The chytrid fungus, Batrachochytrium dendrobatidis, looks the most likely
cause of a number of (upto 7) Australian frog extinctions. There are
other possibilities and plenty of unanswered questions but I haven't
heard of any expert who doesn't consider that the fungus was involved
in some declines. Much more info can be found at:
http://www.deh.gov.au/biodiversity/threatened/tap/amphibians/index.html
and more general info here:
http://www.deh.gov.au/biodiversity/threatened/information/frogs.html
The fungus can infect toads and they might be a vector/reservoir but
the fungus is present in areas where toads are absent (Victoria, WA
and SA) and the apparent epidemiology in Queensland doesn't suggest
that toads were a significant part of its spread. Mortality from the
fungus decreases at higher temperatures and arid conditions also maybe
unsuitable for the fungus so hopefully frogs in the Top End and Kimberley
will not succumb. But it certainly a concern that toads might convey
this or another pathogen into the NT or WA.
On Sun, Oct 24, 2004 at 10:18:03AM +1000, Tim Murphy wrote:
> Biological controls can never wipe out a species - it just reduces it's
> number and the number is already low around here.
The fungus mentioned above is an (unfortunate and accidental)
counter-example. In principle, the absence of other toads (Bufonids)
from Australia facilitates discovery/synthesis of biological controls for
toads which don't affect native species. But I've become very doubful
about the possibilitites for such biological control.
The spread and apparent impact of chytrid fungus raises the concern of
a pathogen released in Australia spreading across Wallace's line and
affecting native bufonids in Asia or in the case of a synthetic pathogen,
its accidental transferto the Cane Toad's home range in the Americas.
This isn't a concern if an Asian pathogen specific to bufonids is
transfered to Australia. Discovery of such a pathogen which has a major
impact on Cane Toad seems unlikely - but unfortunately this may the most
promising
avenue and we should be funding a search. Ignoring the question of unintended
impact, the discovery/synthesis of any pathogen which will have a major
impact on Cane Toad populations seems problematic. For example a pathogen
might produce high mortality but be useless because it doesn't spread.
There is also a poverty of knowledge about amphibian disease in Australia
and globally, and in particular the ecology of amphibian disease. Not to
mention little definitely known about the long-term impact of toads.
Andrew
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