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Deadly frog pathogen eliminates 90 species, is the most destructive disease we have seen

It started as a puzzle. Biologists all over the world reported that frogs just disappeared.

Costa Rica 1987: The golden toad is missing. Australia, 1979: the stomach brood frog, gone. In Ecuador, Arthur's Stubfußkröte was last seen in 1988.

Until 1990, cases of inexplicable frog decreases were mounting. These were not isolated incidents; It was a global pattern – one we now know to be due to chytridiomycosis, a fungal disease that infects and kills a variety of frogs, toads, and salamanders.

Our research results published today in Science show the worldwide number of affected amphibian species. At least 501 species have declined due to chytrids, and 90 of them have been confirmed or considered extinct.

When biologists first investigated the mysterious disappearance of the species, they could not explain it. In many cases, the species rapidly declined in a seemingly pristine habitat.

The decline of species usually has obvious causes, such as habitat loss or introduced species such as rats. This was different.

The first major breakthrough came in 1

998, when a team of Australian and international scientists, led by Lee Berger, discovered an amphibious chytrid fungus.

Their research showed that this unusual fungal pathogen was the cause of the frog's decline in the rainforests of Australia and Central America.

There were still many unknowns. Where does this pathogen come from? How does it kill frogs? And why were so many different species affected?

After years of painstaking research, biologists have filled many pieces of the puzzle. In 2009 researchers discovered how the chytrid fungus kills frogs. In 2018, the Korean peninsula was identified as the most likely source of the deadliest lineage of the chytrid fungus and the spread of amphibians by humans as a potential source of worldwide spread of the pathogens.

But when the puzzle was slowly but surely resolved, a key question remained: how many amphibian species were affected by chytrid fungi?

Earlier estimates suggested that around 200 species were affected. Unfortunately, our new study shows that the total is much larger: 501 species have declined and a total of 90 species have been confirmed or suspected to have been killed.

 The number of amphibians around the world infested with chyrophid fungi. Each bar represents one kind; Colors show the extent of the population decline. (Scheele et al., Science 2019) The release that chytrid fungus causes on amphibians around the world. Each bar represents one kind; Colors show the extent of the population decline. (Scheele et al., Science, 2019)

Devastating Murderer

These numbers place the chytrid fungus in the worst league of invasive species worldwide, threatening a similar number of species as rats and Cats

The most affected areas were Australia and Central and South America with many different frog species and ideal conditions for the growth of chytrid fungi.

Large species and those with small distributions and height differences were most likely to experience a sharp decline or extinction.

Together with 41 amphibious experts from around the world, we compiled information on the timing of species waste records, survey data and museum collections.

We found that the decline peaked worldwide in the 1980s, about 15 years before the disease was discovered. This climax coincides with the anecdotal reports of biologists, who recorded unusual decreases in amphibians with increasing frequency in the late 1980s.

Some species were encouraging that they recovered naturally. Twelve percent of the 501 species recovered in some places. For the vast majority of species, however, the population is still far below what they once were.

Most of the affected species have not recovered yet and many are continuing to decline. Fast and comprehensive action by governments and conservation organizations is needed if we want to keep these species out of the list of extinct species.

 The Southern Field Clover Frog: hopefully no disappearing symbol. (Corey Doughty) The frog of Southern Corroboree: hopefully no missing symbol. (Corey Doughty)

In Australia, the chytrid fungus has caused the decline of 43 frog species. Of these, seven are now extinct and six are threatened with extinction due to severe and progressive declines.

Preservation of these species depends on targeted management, such as the recovery program for iconic Corroboree frogs.

It is important that there are still some areas of the world that Chytrid has not yet reached, such as New Guinea. To stop the spread of chytrid fungus in these areas, global amphibious trade and biosafety measures are being drastically reduced.

The unprecedented lethality of a single disease that affects an entire class of animals highlights the need for governments and international organizations to take the threat of wildlife seriously.

Losing more amazing species like the Golden Toad and the Stomach Brood Frog is a tragedy we can avoid.  The Conversation

Benjamin Scheele, Research Associate in Ecology, Australian National University and Claire Foster, Research Associate in Ecology and Conservation, Australian National University.

This article is being re-released under the Creative Commons license of The Conversation. Read the original article.

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