The Kihansi spray toad officially became extinct in the wild in 2004. The small toads, which are native to the Udzungwa Mountains in Tanzania, disappeared abruptly within a few years. Researchers have now identified the cause of their extinction.
A fungus – Batrachochytrium dendrobatidis (Bd) — has been raging around the world for decades. It is one of the deadliest diseases of wildlife in the world, responsible for the extinction of 90 species of amphibians and the near-extinction of another 500 species. Most of the victims are tropical frogs. One strain of the fungus is causing the most damage.
Vance Vredenburg, co-author of a Study 2023 Speaking about its emergence in Africa, he said this wild animal pandemic makes the Black Death of the Middle Ages seem “like a drop in the ocean” by comparison.
Bd fungal spores spread in water bodies, which is why they have such a big impact on amphibians. The spores float in the water and attach to unsuspecting animals through direct contact. Once they touch an animal’s skin, the pathogen invades the body of its host, leading to a horrific list of symptoms: skin flaking, ulcers, blocked joints, and eventually cardiac arrest.
Overlooked tension
New evidence suggests that another strain, previously considered relatively harmless, drove Kihansi spray toads to extinction. BdCAPE is endemic to Africa, but the main strain is so widespread in Europe and even Africa that the risk from the less common strain was overlooked for decades.
“It seems we have underestimated the aggressiveness of this particular lineage,” said Matthew Fisher, co-author of the new studytold Science.org. “Given that it’s all over Africa, this is a real problem.”
The Kihansi spray toad is bright yellow and only a few centimetres long. It lived in only one habitat: the wetlands next to the Kihansi River Falls, an area of just 0.01 square kilometres. The population seemed healthy, but in 2004 it disappeared for good.
The frogs’ decline began with the construction of a dam on the river. The wetlands began to dry out and the little toads could no longer survive. A sprinkler system was installed to save them. Although it worked for a while, the toads eventually died out. Everyone believed it was another result of the deadly Bd fungus combined with the stress of the new dam.
Waiting for science to catch up
It turns out that it was actually the spread of BdCAPE. Epidemiologist Che Weldon collected a number of dead frogs in 2004 and stored them in his lab for twenty years, waiting for technology to catch up and make it possible to study the dead frogs.
Twenty years later, a team sequenced the DNA of the fungus that infected the long-dead toads. The strain was definitely BdCAPE. The analysis also showed that the toads had started dying off just before the strain reached their small area.
Over the years, much research has been done on this biodiversity hotspot in Tanzania. Other studies from 2004 showed that many other amphibians were also infected with BdCAPE, although their symptoms were much milder than those of the Kihansi spraytoad.
Interested in the potential danger of this overlooked strain, the team conducted an experiment to show that BdCAPE is much more dangerous than anyone suspected. They infected amphibians with both strains to see exactly how BdCAPE compared to the more common global strain. In many amphibians, BdCAPE was much more aggressive.
“BdCAPE is not the good kid we thought it was, at least not in Africa,” Weldon said.
The mail Overlooked fungi are driving toads to extinction first appeared on Explorers Web.
