Fungus apocalypse: Tanzanian toads extinct as new parasite emerges

According to the latest research, a fungus species previously considered mildly harmful is wreaking havoc among African amphibians. Scientists claim that a scenario similar to the TV series "The Last of Us" is unfolding in Africa, and Tanzanian toads have gone extinct due to the parasite.

Batrachochytrium dendrobatidis (Bd), a microscopic parasitic fungus originating from Africa, causes chytridiomycosis – the deadliest disease identified in wild animals. First identified in 1999, this fungus has spread virtually worldwide, leading to the extinction of many amphibian species on six continents. According to experts, the chytridiomycosis pandemic has caused the death of at least 90 amphibian species, mainly tropical frogs, almost driving another 500 species to extinction.

However, Batrachochytrium dendrobatidis is not the only threat. An international team of researchers, publishing their findings in the journal Proceedings of the Royal Society B: Biological Sciences, points to another dangerous chytrid species – BdCAPE. Previously, biologists believed it was less threatening, but they were mistaken.

"It appears that we've underestimated the aggressiveness of this particular lineage," said Dr. Matthew Fisher, a mycologist and geneticist at Imperial College London, the study's lead author.

The Kihansi toad (Nectophrynoides asperginis), an endemic species from the vicinity of an approximately 800-metre waterfall in Tanzania, fell victim to BdCAPE. In 2000, the construction of a dam on the Kihansi River led to the drying up of the waterfall, changing the microclimate of the toad's habitat. Installing sprinklers was meant to save the yellow amphibians, but the appearance of BdCAPE in the Udzungwa Mountains in 2004 sealed their fate – the Kihansi toads were declared extinct in the wild.

While Tanzanian amphibians were dying, Professor Ché Weldon from North-West University in South Africa collected a few dead specimens and stored them in a laboratory. Twenty years later, Dr. Fisher's team, through DNA sequencing, discovered that BdCAPE, not Bd, was responsible for the toads' extinction. The Kihansi Gorge became the site where the severe population decline of these amphibians began.

Dr. Fisher and his team confirmed the aggressiveness of BdCAPE in laboratory studies where amphibians were infected with fungi of both species.

"We have many species of frogs where Bd is implicated in declines and extinctions, but very few cases where Bd can directly be assigned as the causal factor. This is the first case where BdCAPE is the cause of an extinction, which is important for helping us understand which strains are lethal under which conditions," said ecologist Anna Savage from the University of Central Florida.

Dr Jaime Bosch from the University of Oviedo noted the presence of BdCAPE in France, both Americas and Mallorca, where the pathogen has significantly reduced the population of the endemic Majorcan midwife toad (Alytes muleteers).

Efforts are ongoing to reintroduce the Kihansi toads to their natural environment. Before they went extinct, about 400 individuals were sent to American zoos, where they began reproducing. Young generations of these toads are being reintroduced in the Udzungwa Mountains, although scientists are still uncertain whether they will be able to rebuild their population.