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Researchers associate fungus with the extinction of frogs in the Atlantic Forest

Unicamp study may have unraveled an enigma that has intrigued scientists since the 1970s

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The mysterious and, until now, unexplained disappearance of amphibian populations in Brazil between the 1970s and 1980s can be attributed to the chytrid fungus, implicated in an international wave of frog extinctions that has been causing alarm among scientists and conservationists since the end of the 1990s. XNUMX. The conclusion comes from research carried out by Tamilie Carvalho for her master's thesis, defended at the Institute of Biology (IB) at Unicamp, supervised by professor Luís Felipe Toledo. Carvalho, Toledo and researcher Guilherme Becker also wrote an article on the subject published in the journal Proceedings of the Royal Society B.

The disappearance of amphibians in the Atlantic Forest region was an old enigma for Brazilian science. “Some researchers who were working in the Atlantic Forest, in the 70s and 80s, made collections, from time to time, in the same locations. And they realized that there were some animals that were either declining in abundance or even disappearing,” said Toledo. “In the articles that dealt with these declines, the researchers suggested some possible causes: a strong frost a year before the animals disappeared; it was an increase in pollution – in the 80s there was a lot of concern about acid rain, pollution from cars, factories. At that time, we didn’t even know about this disease that we are studying now.”

Photo: Antonio Scarpinetti
Tamilie Carvalho, author of the dissertation, in the laboratory of the Institute of Biology: analyzes of more than 30 thousand tadpoles preserved in collections

“That was a decades-old question,” Becker added. “Any herpetology conference, every year was that question. The dramatic way in which the declines were described – the previous year there were so many of this species, there were so many animals, and the following year there was nothing left – left everyone speculating: what was the cause?”

To discover the fungus, Tamilie Carvalho traveled across Brazil, visiting museums with amphibian collections, and analyzed more than 30 tadpoles preserved in these collections. The tadpoles infected by the chytrid had whitish mouths, she explained, because the fungus consumes keratin, a structural protein – present, for example, in human nails and hair – and which forms the beak and horny denticles, the oral apparatus of the chytrid. tadpoles.

“The fungus, when it infects the tadpoles, stays in the region of the beak and denticles, which is the region that has keratin,” said the researcher. “And it consumes keratin. Then, both the horny beak and the denticles, which are usually black, turn white. Through this method, we were able to look at all the tadpoles and categorize them: positive or negative. There is a pattern of depigmentation by the fungus that we have studied well – and we use this pattern to categorize all the individuals analyzed.”

Photo: Antonio Scarpinetti
Professor Luís Felipe Toledo, study advisor: the next step in the research is to investigate the causes of the increase in infection

“When amphibian declines in the Atlantic Forest were noticed way back when, it was suggested that it could be pollution, deforestation, climate change, but these were all hypotheses that were never tested,” Toledo said. “We tested only the disease, which does not mean that other causes did not also contribute: there may have been a combination between the agents, but chytrid was certainly part of this story.”

“What draws special attention to chytrid is that all the places where there was a decline are areas of intact forests, protected areas, which somewhat undermines the hypothesis that the decline would have been caused by deforestation”, added Carvalho. “And that’s what led us to think it could be the disease.”

The researchers point out that the fungus was already present in the Atlantic Forest before the recorded declines, and well before the global chytrid epidemic was discovered in the late 1990s.

Photo: Antonio Scarpinetti
Tadpoles infected by the chytrid fungus: depigmentation of denticles and horny beak

“One thing that differentiates our work from others that deal with declines caused by the fungus is that, in most places, the arrival of chytrid is reported, followed by decline,” said Carvalho. “And in Brazil, no: the fungus was already present here, but suddenly something turned the key and the declines began. Our work sends this warning: that regardless of whether the fungus already exists in other places, other countries, this does not eliminate the chance of further declines.”

The question of what transformed the chytrid present in Brazil into a threat still awaits an answer: climate change – which would have allowed the fungus to conquer environments inhabited by more sensitive animals – or the emergence of a new strain are possibilities. 

“Along these lines that we are commenting on, the next question is: what caused the increase in infection? Understand this mechanism. This is a question we are exploring in Tamilie’s doctoral research,” said Toledo.

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