Museum Frogs Solve a 50-Year Mystery of Brazil's Vanishing Amphibians

The team tested samples from more than 370 preserved amphibians representing 17 species, hunting for chytrid DNA and tracking how often it appeared over time. The result was unambiguous: zero infections before 1979, more than 50 percent positivity in the 1980s samples.

In short, the fungus arrived right as the frogs vanished.

Why did the hardest-hit species test clean?

Here the data took a strange turn. Species that declined most severely showed no detectable infection in the preserved specimens. Species that stayed stable often carried the fungus. That looks like a contradiction, but the researchers think it reflects how differently species respond to the disease.

"The species that didn't decline may have naturally tolerated the fungus, allowing them to become infected without suffering mass mortality," Boyette said. "By contrast, the species that declined most dramatically may have been so susceptible that infected frogs died before Heyer could collect them."

Susceptible frogs died too fast to be preserved. Tolerant frogs lived long enough to end up in a jar. The takeaway is simple: absence of infection in a museum drawer doesn't mean absence of disease.

Why do decades-old specimens matter?

For Michael Campana, a genomicist at NZCBI who contributed to the research, the study proves the scientific value of natural history museums. Specimens preserved decades ago contain biological evidence that collectors at the time had no way to recognize.

"Museum collectors could not have anticipated how important their collections would be to our modern conservation challenges, but without them, we would never be able to detect pathogens that went unnoticed for decades and reconstruct disease outbreaks that would otherwise remain a mystery," Campana said.

That matters for the future, too. Another fungal pathogen, B. salamandrivorans, is currently threatening salamanders in Europe and could endanger North American species. Reconstructing how past outbreaks spread may help scientists spot the next one earlier.

Have Brazil's frogs recovered?

Surprisingly, yes — mostly. Working with researchers from the University of São Paulo, the team made six visits to Boracéia between 2022 and 2024. They found 12 of the 17 species from Heyer's historical collection. The other five went undetected, and their status — possibly local extinction — remains uncertain.

Chytrid is still there, infecting local frogs. But the infection pattern suggests species once hit hardest may have built up tolerance over successive generations. That helps explain why populations rebounded despite ongoing exposure.

The distinction matters: carrying a pathogen isn't the same as dying from it.

What are the study's limits?

The researchers are careful here. The findings apply to Boracéia specifically. They cannot automatically explain amphibian disappearances elsewhere in the Atlantic Forest.

The work continues. The team is now examining DNA from museum specimens to identify the genetic mechanisms that shaped how different species responded to chytrid, and separate projects are using ancient environmental DNA — genetic traces organisms leave in their surroundings — to fill gaps in the historical record.

The bottom line: a 47-year-old wildlife cold case now has a prime suspect, and the frogs themselves appear to be fighting back.