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Common Indian Toad. Duttaphrynus melanostictus. Front view.
Photograph by L. Shyamal
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The unique wildlife of Madagascar is facing an invasion of
toxic toads that could devastate the island’s native species. Snakes feeding on
the toads are especially at risk of poisoning, as are a host of other animals
unique to the island — such as lemurs and endemic birds — and the species could
cause harm to humans as well.
In a letter to Nature published today, 11
researchers warn that Asian common toads (Duttaphrynus
melanostictus) were observed near Toamasina, the African country’s largest
seaport, in March. It is suspected that the amphibians arrived from Asia in
shipping containers, and are now taking advantage of what the writers describe
as “ideal resources and climate” to establish themselves.
“Time is short, so we are issuing an urgent call to the
conservation community and governments to prevent an ecological disaster,” say
Jonathan Kolby, a wildlife-health researcher at James Cook University in
Townsville, Australia, and his colleagues.
The discovery of the invasive amphibians recalls the
Australian plague of cane toads (Rhinella
marina). These animals, relatives of the Asian common toad, were
deliberately introduced to Australia in 1935; they proceeded to devastate
native animal populations and have spread across much of the country, defying
attempts to eradicate them.
Kolby and his colleagues warn that something similar could
now happen in Madagascar.
The toads are already reported to have been deadly to
snakes, including the ground boa (Acrantophis spp.),
which is found nowhere else, Kolby tells Nature. Drawing parallels with
the cane-toad situation, he warns that more than 50 species of endemic snake
could be threatened, because they are likely to eat the toxic toads. Iconic
Madagascan species such as the cat-like fossa (Cryptoprocta ferox), lemurs and endemic birds are also in jeopardy.
And the toads could spread diseases to other amphibians and even contaminate
drinking water and transmit parasites to humans.
The species is not yet widespread in Madagascar, but it has
been found a mere 25 kilometers away from the important Betampona nature
reserve, and a short distance further from other internationally important
biodiversity hotspots. It is unclear how fast it can travel, but cane toads
have been clocked expanding their range at 50 kilometers per year.
The potential tragedy is not restricted to Madagascar.
“There is now a high dispersal risk of these toads spreading from Madagascar to
other Indian Ocean islands such as the Mascarene Islands, Comoros and
Seychelles,” says Kolby.
Toads are already being collected and removed, he says, and
the Madagasikara Voakajy, a non-governmental organization in Antananarivo
devoted to biodiversity, is tracking the spread of the amphibians. The toads
should be hunted, their spawn should be destroyed and ponds should be drained
to stop their breeding, says Kolby. “We are still within the early stages of
population growth,” he says. An eradication program should be developed
swiftly, “while populations are still relatively small and manageable”.
Mark Hoddle, director of the Center for Invasive Species
Research at the University of California, Riverside, notes that to be
considered invasive, a non-native species must have established a reproductive
population that spreads and causes environmental and economic damage. On this
basis it may be too early to declare the Asian toad in Madagascar a problem
species, he says, but there are “very good reasons to be concerned”.
Citation
Kolby, J. E. 2014. Ecology: Stop Madagascar's toad invasion now Nature 509. doi:10.1038/509563a