Wednesday, January 16, 2008

Down to the Last Croak

The following caught my eye because of one line: "its breeding biology was unearthed when a wildlife enthusiast watched enthralled as a female in an aquarium spewed fully developed baby frogs from her mouth." It's not the fact that the froglets developed in a stomach (amazing as that may be) but the fact that this process was discovered by a 'wildlife enthusiast' NOT a scientist (who in fact did not believe it until they tested it themselves). Another great example of Citizen Science in Action. Read for yourself...

RHEOBATRACHUS silus was one of the world's truly remarkable animals. The so-called platypus frog was one of a kind. The only species of land vertebrate animal - amphibian, reptile, mammal or bird - to rear its young inside its stomach. That makes the small black frogs as special as kangaroos or koalas. They were found nowhere but in the rainforests of two mountain ranges in southern Queensland. Zoologist and environmental consultant Glen Ingram was studying them in 1977 in the Conondale Range, in the Sunshine Coast hinterland. "There were plenty of frogs in the streams at that time," Ingram recalls now. A year later, he could find just two. In 1979, there were none, and none have been found since, anywhere, despite exhaustive searches. "Like the Tasmanian tiger, it is one of the great wildlife tragedies that this astonishing animal is extinct," Ingram says. Also known as the gastric-brooding frog, Rheobatrachus was first discovered in 1972. A year later, its breeding biology was unearthed when a wildlife enthusiast watched enthralled as a female in an aquarium spewed fully developed baby frogs from her mouth. This was so bizarre - gastric juices would normally destroy young animals in a stomach - that scientists initially refused to believe it. Between discovery and extinction, the frog was known to humankind for less than a decade - an infinitesimal fraction of its time on Earth. By the early '90s, another seven Queensland frog species were also extinct. At the same time, frogs were disappearing from other continents. Observers declared that the phenomenon of the vanishing frogs was the "canary in the coalmine": the harbinger of insidious and potentially catastrophic global climate changes. The worldwide demise of amphibians continues, with a third of the 5700 frog and salamander species now considered at risk of extinction. Scientists have long established that frogs are being killed by chytrid fungal disease. Fungal spores attach to the amphibian's skin, thickening it and reducing the animal's capacity to drink and respire. The fungus also damages the nervous system. What puzzles the experts is that the chytrid fungus is not necessarily hazardous to frogs; it is established in many areas where amphibian populations have not declined. Conversely, the fungus has the potential to wipe out entire frog populations within several weeks. Scientists believe something is both facilitating the spread of the fungus and making it selectively fatal to frogs. A widely accepted theory is that the trigger is some kind of climate change. Increased ultraviolet radiation due to a shrinking ozone layer, or more cloud cover resulting from rising greenhouse gas emissions, are cited as potential factors that change the fungus from something benign to a killer. Now, however, researchers are increasingly convinced that agricultural chemicals are implicated in the frogs' demise, both by killing them directly and by making them more vulnerable to chytrid fungus and other diseases. Climate change may not be the critical factor it was thought to be, although opinion is divided on this score. Says Ingram: "One of the last platypus frogs I saw was sitting on a rock, covered in white slime. I never could work it out and I have a problem with the theory that the culprit is simply a fungus being spread by temperature changes. It makes sense to me that pesticides or other chemicals are implicated." No research in Australia has been done to determine a link between chemicals and disappearing frogs, but mounting evidence of one is reflected in a series of recent studies in California, where similar chemicals are used and where frog populations have similarly crashed. Guidelines for resource managers issued by the Western Ecological Research Centre in California say organophosphorus pesticides are highly toxic to amphibians and have been implicated in the decline of several species in the state. These chemicals include chlorpyrifos, malathion and diazinon, all of which have been used extensively as pesticides in Australia. A new study published in the journal Environmental Pollution concludes that concentrations of the three chemicals had been harmful to frogs in the California Central Valley. Chlorpyrifos is a commonly used insecticide in Australia. Malathion has been applied extensively to treat stored wheat and barley in Australia. Diazinon has been used widely in Australian sheep dips. A study in the Sierra Nevada in the US showed that pesticides are carried considerable distances by wind from agricultural areas, where they are sprayed, to otherwise pristine frog habitat in the mountains. These chemicals are associated with serious impacts on the development of tadpoles including depressed growth rates, increased vulnerability to predators, and greater mortality. Measurable concentrations of chlorpyrifos, malathion and diazinon were found in wilderness areas such as the Sequoia National Park. A recent study by University of California scientists showed that a combination of chemicals used on corn fields retarded growth in frogs and increased their susceptibility to meningitis. Another study by the university showed that the herbicide atrazine disrupted the sexual development of frogs, turning males into hermaphrodites; in effect, male frogs were being chemically castrated. Atrazine, which has been banned by the European Union, is also used widely in Australia. A study published in the journal Conservation Biology by three senior Californian scientists found that upwind agricultural land use, with the potential for windborne pesticides, was linked to declines in all four frog species which they studied. A 2004 review by the Australian Pesticides and Veterinary Medicines Authority noted claims about the impact of atrazine on frogs but said there were "inconsistencies between studies". An updated review of the herbicide will be released soon. APVMA chemical review chief Les Davies says he is unaware of the American studies suggesting adverse impacts on frogs from organophosphorus pesticides. However, approved uses for chlorpyrifos in Australia had been modified in response to concerns that the chemical damaged the brains of human fetuses. Davies says potentially toxic byproducts of malathion had been stabilised, while diazinon was being phased out as a sheep dip. Several overseas studies show that the sexual development and behaviour of frogs can be affected adversely by pesticides at much lower levels than those required to kill animals outright. Populations could be disappearing because of relatively subtle changes such as damage to the vocal cords of males, preventing them from calling and therefore attracting mates. The demise of frogs in Australia has parallels with changes in agricultural chemical regimes. Organochlorines such as DDT and dieldrin, which were connected to an extensive range of environmental and health problems, were largely phased out between the late '70s and late '80s, the period when most of Queensland's frog extinctions took place. The place of the organochlorines was taken by supposedly less toxic organophosphorus and other chemicals. Research by Griffith University scientists Jean-Marc Hero and Kerry Kriger has done much to unravel the mystery surrounding the chytrid fungus in Australia. An unpublished study shows that while the fungus is widespread, frogs from temperate regions have much more severe infections than frogs in the tropics. The severity of infections is greater at sites with high rainfall and cool temperatures. Another Griffith University study found that 38 per cent of 798 frogs sampled in southeast Queensland were infected with the fungus. Contrary to a generally accepted view, the study found that frogs at high altitudes - where all of Queensland's extinct species once lived - were no more likely to be infected than lowland frogs. Frogs that lay relatively small numbers of eggs are more vulnerable than more fecund species. Hero agrees that the big unanswered question is what makes the fungus selectively lethal. "The disease is everywhere, at all altitudes from Cairns to Victoria and across to the southwest of Western Australia. Yet it is present in populations which have not declined at all." The first Australian frog extinctions, in southeast Queensland in the late '70s, coincided with extinctions in Brazil and Costa Rica. Hero says there were no significant climate changes in southeast Queensland at the time, or in the wet tropics of north Queensland when several frog species became extinct there in the '80s. Hero suspects that chemicals are implicated. He recalls once being in the Eungella Range inland from Mackay, where two frog species became extinct, when he was showered with ashes from distant burning sugarcane fields. "We were 900m up and a long way away but we were covered in ash. There's every potential for chemical spray drift. There just hasn't been a debate in the scientific literature about the various theories for what's going on." James Cook University researcher Ross Alford and colleagues conducted tests for chemical residues in the wet tropics of north Queensland after rainforest frogs began declining. Alford says now that the testing was inadequate, and the sampling would not have necessarily picked up potentially lethal levels of chemicals. He believes chemicals could change micro-organisms on the skin of frogs in ways which allow the chytrid fungus to flourish. Alford says evidence in some places overseas suggests a climate change link to frog disappearances: for instance, in the cloud forests of Costa Rica. "I don't think it's one or the other, climate change or chemicals. I think there's good evidence for both. What we can be sure of is that amphibian populations are being stressed before they are hit with these outbreaks of fungus." There is a bright spot, albeit a dim one, on the horizon for the beleaguered amphibians. The Griffith University researchers have found that adult frogs infected with chytrid fungus are capable of shedding it. The fungus does not appear to thrive in warmer weather. Ironically, climate change may have a beneficial Greg Roberts of the Australian on January 5th, 2008.,25197,23007420-30417,00.html
From an emailed 'Frogwatch' digest. Join Frogwatch at

No comments: