Zoos release eggs to help corroboree frogs leap out of extinction

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Flaviemys purvisi

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By Joe Hinchliffe
30 April 2018

Until recent decades, there were hundreds of thousands of southern corroboree frogs clambering around snow gum trees and wallowing in the frigid waters of the Australian Alps.

Now, less than 50 of the vividly-coloured, poisonous little frogs are left in the wild.

But those numbers are set to swell this week with the release of about 1000 captive-bred southern corroboree frog eggs into Kosciuszko National Park.
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Less than 50 corroboree frogs remain in the wild.
Photo: Rick Hammond


On Monday, Zoos Victoria herpetofauna expert Deon Gilbert delivered the eggs from Melbourne – where they were bred – to Australia's highest mountain, the only place in the world which they call home.

Mr Gilbert said the frogs went swiftly from "very common" to critically endangered after their population was decimated by the arrival of amphibian chytrid fungus to the high country, which probably occurred during the 1970s.

The fungus infects the amphibians with Chytridiomycosis disease to which the frogs are particularly susceptible. “It’s difficult to give precise numbers but we’re talking many hundreds of thousands, potentially more,” he guessed of the number of frogs before the arrival of the fungus.

"[But] we started seeing population declines in '80s and then they dropped out really quickly over the preceding decades to the point where there are now virtually no frogs left in wild."

During the 1990s herpetologists recognised the population crash and began collecting frog eggs for captive breeding programs at Taronga Zoo and Zoos Victoria.

Mr Gilbert said enough genetic diversity had been captured to ensure a viable population at the zoos, which had slowly been built-up to the point that the species will survive in captivity and was now producing thousands of eggs every year.
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The tadpoles will hatch soon.
Photo: Rick Hammond


In 2011, Zoos Victoria began releasing some of those eggs into the wild. They have done so once a year, every year since, just before the tadpoles hatch from their eggs in autumn.

As a result of the programs, Mr Gilbert said he now had high hopes the species would once again have a stable wild population.

“The southern corroboree frog program is right up there amongst conservation stories," he said. "Without it, the frogs would almost certainly be extinct.”

The zoos hope that by releasing frog eggs back into the wild the species will eventually build a genetic resistance to the fungus, but Mr Gilbert said that such a natural immune response would not emerge overnight.

"It takes many years, potentially decades to be able build up large, healthy populations."
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It is hoped that the southern corroboree frog will one day develop an immunity to the chytrid fungus.
Photo: Rick Hammond


The thousand or so little eggs released this week will hatch in disease-free "semi-wild" enclosures in the national park.
 
There is hope!

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Tim Roberts | Frogs jump fungal foe
MAY 6 2018
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Late last century a parasitic chytrid fungus began to decimate frog species around the world. Apparently spread by the global trade in amphibians, this primitive fungus was the cause of species after species of frogs across Australia disappearing from their known habitats. For the last two decades, the fear among herpetologists has been that they were witnessing extinction on a vast scale worldwide. These mass die-offs were reported universally across almost every continent and the chytrid fungus was purported to be “the worst infectious disease ever recorded among vertebrates in terms of the number of species impacted, and its propensity to drive them to extinction”. Laboratory studies have shown that there is a more complex phenomenon occurring involving other bacteria and skin proteins and the immune system of the particular frog, rather than a simple infection leading to death.

Nevertheless, nature appears to be showing light at the end of the tunnel with reports appearing in the scientific literature recently of field survey data that shows some species of frogs are coming back up to previous numbers. Nine amphibian species in the jungles of Panama seem to be evolving resistance with numbers almost back to previous levels. In Australia, where we have over 400 species affected, a group from Southern Cross University have just published data gathered over seven years, which show that the endangered Fleay’s barred frog is showing strong signs of recovery.

Evidence once again of the theory of Natural Selection put forward by Darwin and Wallace that individual members of a species are genetically unique and that some individuals will be better able to resist infection and thus go ahead to adulthood, reproduce and then put more of their genes into the next generation.

Professor Tim Roberts is the director of the Tom Farrell Institute for the Environment, University of Newcastle
 
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