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Chytrid fungus was proved present on Platypelis pollicaris
from Ranomafana. Photo Credit: Miguel Vences / TU
Braunschweig
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The
chytrid fungus, which is fatal to amphibians, has been detected in Madagascar
for the first time. This means that the chytridiomycosis pandemic, which has
been largely responsible for the decimation of the salamander, frog and toad
populations in the USA, Central America and Australia, has now reached a
biodiversity hotspot. The island in the Indian Ocean is home to around 290
species of amphibians that are not found anywhere else in the world. Another
200 frog species that have not yet been classified are also thought to live on
the island. Researchers from the Helmholtz Centre for Environmental Research
(UFZ) and TU Braunschweig, together with international colleagues, are
therefore proposing an emergency plan. This includes monitoring the spread of
the pathogenic fungus, building amphibian breeding stations and developing
probiotic treatments, say the scientists, writing in Scientific Reports, the
acclaimed open-access journal from the publishers of Nature.
The
entire amphibian class is currently afflicted by a global pandemic that is
accelerating extinction at an alarming rate. Although habitat loss caused by
human activity still constitutes the main threat to amphibian populations,
habitat protection no longer provides any guarantee of amphibian survival.
Infectious diseases are now threatening even seemingly secluded habitats. The
most devastating of the known amphibian diseases is chytridiomycosis, which is
caused by a deadly chytrid fungus (Batrachochytrium
dendrobatidis, or Bd). The fungus attacks the skin, which is particularly
important in amphibians because they breathe through it. A large number of
species have already been lost in this way -- particularly in tropical Central
America, where two-thirds of the colorful harlequin frog species have already
been decimated across their entire area of distribution. Bd has now been
identified in over 500 amphibian species, 200 of which have seen a significant
decline in numbers. The pathogen is therefore classified worldwide as one of
the greatest threats to biodiversity.
Until
now, however, a few islands like Madagascar were thought not to have been
affected. The last series of tests from 2005 to 2010 found no trace of the
pathogenic fungus there. However, an analysis of the latest series of tests
shows that the chytrid fungus also poses a threat to amphibians in Madagascar.
"This is sad news for amphibian-lovers around the world," says Dr
Dirk Schmeller of the UFZ, who was involved in analyzing the samples.
"Firstly, it means that an island that is home to a particularly high
number of amphibian species is now at risk. Several hundred species live only
on this island. And, secondly, if the pathogen has managed to reach such a
secluded island, it can and will occur everywhere."
For
the study that has just been published, the research team analyzed samples from
over 4000 amphibians from 50 locations in Madagascar taken since 2005. Samples
from four species of Madagascan frog (Mantidactylus
sp.) taken in 2010, and from one Mascarene frog (Ptychadena mascareniensis) taken in 2011 from the remote Makay
massif tested positive for the fungus. In samples from 2013 and 2014 the
pathogen was found in five different regions. Prof. Miguel Vences from TU
Braunschweig says, "The chytrid fungus was found in all four families of
the indigenous Madagascan frogs, which means it has the potential to infect
diverse species. This is a shock!" The study also shows that the disease
affects amphibians at medium to high altitudes, which ties in with observations
from other parts of the world, where the effects of the amphibian epidemic have
been felt primarily in the mountains.
The
fact that the fungus has been identified in a very remote part of the island
has puzzled the researchers. There is some hope that it may prove to be a
previously undiscovered, native strain of the pathogen, which may have existed
in the region for some time and have gone undetected because of a lack of
samples. In this case, Madagascar's amphibians may have developed resistance to
it. However, further research is needed to confirm this hypothesis before the
all-clear can be given. It is also possible that the fungus was brought to the
island in crustaceans or the Asian common toad (Duttaphrynus melanostictus), carried in by migratory birds or
humans. "Luckily, there have not yet been any dramatic declines in
amphibian populations in Madagascar," Dirk Schmeller reports.
"However, the pathogen appears to be more widespread in some places than
others. Madagascar may have several strains of the pathogen, maybe even the
global, hypervirulent strain. This shows how important it is to be able to
isolate the pathogen and analyze it genetically, which is something we haven't
yet succeeded in doing." At the same time, the researchers recommend
continuing with the monitoring program across the entire country to observe the
spread of the disease. The scientists also suggest setting up extra breeding
stations for key species, in addition to the two centers already being built,
to act as arks, so that enough amphibians could be bred to recolonize the
habitats in a crisis. "We are also hopeful that we may be able to suppress
the growth of the Bd pathogen with the help of skin bacteria," says Miguel
Vences. "It might then be possible to use these bacteria as a kind of
probiotic skin ointment in the future." A high diversity of microbial
communities in the water could also reduce the potential for infection,
according to earlier investigations conducted by UFZ researchers and published
in Current
Biology.
The
outbreak of amphibian chytridiomycosis in Madagascar puts an additional seven
per cent of the world's amphibian species at risk, according to figures from
the Amphibian Survival Alliance (ASA). "The decline in Madagascan
amphibians is not just a concern for herpetologists and frog researchers,"
says Dr Franco Andreone from the International Union for Conservation of Nature
(IUCN), who is one of the study authors. "It would be a great loss for the
entire world." In the coming months, the scientists therefore plan to work
with the government to draw up an emergency plan to prevent this scenario.
Citation
Bletz MC, Rosa GM, Andreone F, Courtois EA,
Schmeller DS, Rabibisoa NHC, Rabemananjara FCE, Raharivololoniaina L, Vences M,
Weldon C, Edmonds D, Raxworthy CJ, Harris RN, Fisher MC, Crottini A. Widespread
presence of the pathogenic fungus Batrachochytrium
dendrobatidis in wild amphibian communities in Madagascar. Scientific
Reports, 2015; 5: 8633 DOI:10.1038/srep08633