High up in the relatively pristine rain forest streams of the Blackall and Conondale Ranges in South East Queensland, Australia, there once lived a semi-aquatic
frog species with a reproductive strategy like no other. Its name was the southern gastric brooding frog (
Rheobatrachus silus), and it was only discovered in 1972.
During the spring season, the male frog’s call would lure potential mates to shallow sections along the streams. After a successful courtship, the female frog would lay eggs and then swallow these newly fertilized eggs. Rather than becoming a nutritious treat, the frog eggs would produce a hormone that prevented the release of digestive acids. Over the following weeks, the eggs would hatch, proceed through their tadpole stage and move toward metamorphosis within the safety of the mother frog’s stomach. After six to eight long weeks, small versions of the mother would emerge from her mouth, ready for life on the streams. This frog species became extinct in 1981.
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Endangered green and golden bell frog (Litoria aurea). |
Chytrid fungus has caused the waterfall mist frog (Litoria nannotis) to decline to critically low numbers. |
Endangered giant barred frog (Mixophyes iteratus). |
Another Loss
A little more than 460 miles to the north, in the protected forests of Eungella National Park, Australia, a second gastric-brooding frog species was discovered in 1984, giving scientists a new opportunity to study this bizarre reproductive behaviour. With such pristine habitat, one would have thought that the status of this frog species would be secure. Unfortunately, the northern gastric brooding frog (R. vitellinus) then became extinct the following year in 1985. With the disappearance of these two frog species, Australia not only lost a unique taxa with an unusual method of reproduction, but also any medicinal value for treating gastrointestinal ailments (including stomach ulcers) that these frog species could have provided.
The disappearance of these frog species marked a bleak time in the history of Australia’s amphibian fauna. From 1975 to 1995, six species of endemic frogs were sighted for the last time. For one of these species, the sharp-snouted day frog (Taudactylus acutirostris), a last-minute attempt was made to prevent its extinction by securing the last remaining wild tadpoles for captivity. A number of tadpoles were gathered and sent to two zoos and two universities. Unfortunately, this proved to be too little too late. The last of this frog species died in captivity in 1995 from the same disease that undoubtedly helped to cause their extinction in the wild: chytridiomycosis, caused by the deadly chytrid fungus (Batrachochytrium dendrobatidis).
An Insidious Killer
Chytrid fungus was not officially discovered until 1998 and formally described until 1999. By this time, it was already causing devastating effects to the amphibians of Australia and Central America. The first historical evidence of the pathogen in Australia can be traced back to a museum specimen of the dainty treefrog (Litoria gracilenta) collected in 1978. It is believed that it invaded South East Queensland, Australia, soon before then and travelled north and south at a rate of approximately 60 miles per year. This same pattern of movement correlated with a wave of frog declines and disappearances.
Although habitat loss, introduced predators and a number of other threats have affected the frogs of Australia, no threat has struck as rapidly and with as devastating an effect as chytrid fungus. Stream-dwelling frogs that have abounded in numbers one year have disappeared the next as the fungus slowly spread along Australia’s east coast. Currently, close to a quarter of the approximately 230 frog species in Australia are now listed as threatened with extinction.
Australian Zoos Respond
The unprecedented rate of amphibian declines in Australia has resulted in the need for an urgent response by the zoo community. Zoos are placed in a unique position of responsibility, as they possess the required husbandry skills to manage a frog conservation program, and they have the ability to expose the plight of these declining species to a broad audience. Historically, amphibians have not comprised a large part of zoological collections. The many roles that zoos can play in this crisis have only recently been realized.
As late as 2001 there were only a total of three threatened frog species in Australian zoos. Three years later in 2004, this number had only increased to include a fourth species. One of these species was the green and golden bell frog (Litoria aurea). This medium-sized, pond-dwelling frog was once extremely common throughout South East Australia, especially in the Sydney area. However, with increasing land clearing, the introduction of the eastern mosquitofish and the arrival of chytrid fungus, this frog species quickly slid into its current endangered status. Between 1996 and 2004, a breeding program at the Taronga Zoo in Sydney resulted in the release of 20,000 tadpoles and frogs of this species at five sites in the greater Sydney area. Another captive amphibian breeding program took place at the same time at Melbourne Zoo. There, Romer’s treefrog (Chirixalus romeri), an endemic to Hong Kong, were successfully bred and returned to their country of origin as part of a collaborative release program with Hong Kong University. Next Page>>
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