ZooNooz Article - MARCH 2008

Just a hop away from extinction

If eight species of Australian bird or mammal disappeared
without a trace, it would be considered a national tragedy.
But that’s what’s happened to Australia’s frogs in the last
30 years, and still few people are aware of it. Story and
photographs Peter Harlow.

The most recent review of our frog fauna lists 27% of the 225 Australian species as threatened with extinction, and 33% as either endangered or critically endangered. One of the first to go was the Gastric-brooding Frog; just after its amazing breeding behaviour was discovered, it was extinct. This was the only frog in the world that ate its eggs to breed; the tadpoles developed inside its stomach, to be regurgitated weeks later as tiny, fully-formed frogs!

So what's happening? All the usual suspects have been investigated: loss of habitat, invasive species and climate change, but the evidence is increasingly suggesting that the main culprit is a microscopic fungus. The chytrid fungus was only properly identified as a deadly frog pathogen in 1998, but it had been killing our frogs since at least 1978. And not just in Australia, but in Europe, New Zealand, and North and Central America. Luckily for the world’s tropical frogs, chytrid fungus seems to thrive only in cool climates, or at cool, high altitudes in tropical areas. In Australia most of the species that are disappearing, or have already gone extinct, are stream-breeding frogs in alpine or upland areas.

The chytrid fungus destroys keratin, the tough fibrous protein in frog skin. Tadpoles have no keratin in their skin, so they are not affected by the fungus, however once they metamorphose into tiny frogs, susceptible species quickly die. Not all frog species are susceptible; many are seemingly immune and show no effects of living with the fungus, while other species have been entirely wiped out by it.

Only last year the puzzle of the origin of chytrid fungus was solved. The first human pregnancy test was developed in the 1930s, and involved injecting a female African Clawed Toad with a sample of a woman’s urine. A woman in early pregnancy produces large amounts of a hormone that will cause the toad to ovulate and lay its eggs within 12 hours. This was the most reliable pregnancy test available up until the late 1950s, and millions of African Clawed Toads were captured and exported. Many no doubt were carrying the invisible chytrid fungus, which is naturally occurring and seemingly harmless in these wild toads. From hospital laboratories, the water-borne and contagious fungus could easily escape down drains and into the local frog pond.

This year is an important one for our froggy friends. ARAZPA zoos from all over Australasia will meet at Taronga this March for their annual conference and to officially declare 2008 the “Year of the Frog”. This will raise public awareness and generate funds for future zoo-based frog conservation projects. Taronga has a long history of involvement in such programs, starting in 1994 when a small number of Green-andgolden Bell Frogs were rescued from a Sydney development site and brought into captivity. These large and beautiful frogs were once one of the most common species in the Sydney area, however in recent decades they have disappeared from over 90% of their former habitat, leaving only a small number of isolated populations today. The reasons for the demise involve a combination of factors including chytrid fungus, increasing urbanisation and introduced fish which eat the tadpoles. Taronga has had great success breeding this frog, with over 20,000 tadpoles and frogs released in experimental reintroductions over many years.

Current frog conservation programs at Taronga involve the critically endangered Corroboree and Booroolong Frogs. Corroboree Frogs
are restricted to the high alpine areas
of Kosciuszko National Park in NSW. Although only 2-3 cm long, they are one of Australia’s most recognisable frogs with bright yellow and black markings. Totally harmless to touch, the colours however warn that they are poisonous to eat, and predatory birds and snakes avoid them. They lay their eggs in thick sphagnum bogs above the summer water level, and when melting snow and spring rain flood the nest, the tadpoles can swim away.

Over the last three decades, the Corroboree Frog has undergone a dramatic and continuing decline. Current estimates are that less than 100 remain in the Kosciuszko high country, and that it will become extinct in the wild within the next few years. In 2006, Taronga became involved in the ex-situ conservation of this species by setting up a refrigerated container to house and breed an insurance population. Our facility currently holds over 250 frogs which will be used for breeding and reintroduction attempts in coming years.

The critically endangered Booroolong Frog is a stream-dwelling species that was once found on the western slopes of the entire NSW Great Dividing Range. In recent decades it has disappeared from most of its former habitat and the last remaining populations are found around the south-western slopes. This species has declined due to the combined effects of chytrid fungus, extended drought, creek siltation and invasive weeds. Taronga Zoo is now breeding Booroolong Frogs and the first experimental releases into the wild are scheduled for March this year – an important occurrence in this The Year of the Frog.

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