A
mphibians are the most
endangered group of vertebrates
on the planet. The IUCN
(International Union for the
Conservation of Nature)
estimates that about 33% of the
7,000 or so recognised species
are threatened with extinction.
Over the past three decades
amphibians have been disap-
pearing at an alarming rate. Over
200 species have become
extinct, and about 43% of all
amphibians are considered to be
declining – and this is likely to be
an underestimate given how little
is known about many of these
unassuming animals and their
population dynamics. Indeed,
new species of amphibians
continue to be discovered every
year, many of which are vulner-
able because they are restricted
to small geographic ranges.
Moreover, for at least a quarter of
the species currently recognised,
there is insufficient available data
to even form an assessment of
their conservation status. The
imperilled state of amphibians is
not confined to poor regions
overseas: in Australia almost one
quarter of species are acknowl-
edged to be of conservation
concern.
The threats faced by amphibians
are numerous: habitat loss and
degradation (largely stemming
from land clearing to make way
for livestock); climate change
(driven by massive use of fossil
fuels, with the livestock industry
also being a key contributor);
collection for consumption and
the pet trade; pollution including
pesticides; and disease. All
except the latter are attributable
to the detrimental effects human-
kind’s exploitive actions have
upon the environment; hence, in
theory, they can be readily
corrected and prevented.
Disease is a lot more difficult to
address, yet disease, often acting
in addition to or in synergy with
other factors, is one of the major
reasons amphibians across the
globe are in jeopardy.
Chytridiomycosis is an emerging
infectious disease caused by the
aquatic fungal pathogen,
Batrachochytrium dendrobatidis
(or Bd), a chytrid fungus. Bd
infects the superficial, keratin-
containing layers of amphibian
skin, and the mouthparts of
tadpoles. This inhibits osmoregu-
lation, ionoregulation and
cutaneous respiration. Symptoms
include lethargy, sitting in an
abnormal position and in the sun,
excessive skin sloughing, and
eventually death.
‘ Bd
and in protected areas.
Against the global amphibian
extinction crisis and ongoing
catastrophic declines of amphibi-
ans in the face of Bd, there is
nevertheless some hope. One
amazing Australian species has
been confirmed to have begun
the road to recovery: Fleay’s
Barred Frog (Mixophyes fleayi).
The effects of Bd have been
particularly prevalent amongst
native stream-breeding frogs like
is responsible for the
greatest
loss of biodiversity
disease in
due to
recorded history
history.’
Bd is responsible for the greatest
loss of biodiversity due to disease
in recorded history, and more
than 350 amphibian species are
known to have been infected.
Australia’s anuran fauna have
been hard hit, with rapid declines
beginning in the late 1970s in
southern Queensland, near
Brisbane. In fact, it was
Australian scientists who, in
1996, first posited that disease
was the culprit behind the devas-
tation of frog populations. The
pathogen responsible was
confirmed in 1998, and Bd was
described in 1999. Since then,
exhaustive efforts have been
made to elucidate the genetics
and biology of the fungus and the
disease it causes, and to devise
strategies to prevent its
potentially cataclysmic impact.
Despite some progress, much
remains unknown, and there is
no universal cure for chytridiomy-
cosis or means of eradicating the
pathogen that causes it. Many
proven strategies for species
preservation - like habitat protec-
tion - are insufficient to stem
declines caused by this disease,
which has wiped out populations
in the most pristine of habitats
M. fleayi, with over ten species
from the subtropical and tropical
rainforests of eastern Australia
suffering serious declines since
1979. In this same region Bd has
also caused the extinction of four
species: the Southern Gastric-
brooding Frog (Rheobatrachus
silus - last seen 1981); the
Northern Gastric-brooding Frog
(R. vitellinus – 1985); the Sharp-
snouted Day Frog (Taudactylus
acutirostris - 1997); and the
Southern Day Frog (T. diurnus -
1979). In southeastern
Queensland and adjacent New
South Wales, near where
declines from Bd were first
detected in the 1970s, popula-
tions of M. fleayi, along with the
closely-related Giant Barred Frog
(Mixophyes iteratus), and the
Cascade Tree Frog (Litoria
pearsoniana), underwent precipi-
tous collapses over just a few
short years. With declines of over
90%, it seemed these species
were also heading inexorably
towards extinction.
Mixophyes fleayi has a narrow
distribution along the Great
Dividing Range and coast from
the Conondale Range in south-
east Queensland to the vicinity of