A fungus that causes the disease chytridriomycosis, which has plagued frogs and toads around the world, now holds the title of being the world’s worst invader killer, displacing cats – which threaten 430 species – and rodents – which threaten to 420 species-. It is the Batrachochytrium dendrobatidis fungus.
The first global count caused by a chytridriomycosis infection shows that it is responsible for the population decline in at least 500 species of amphibians, including 90 that are now extinct. And it appears that this is a conservative estimate, scientists say.
Pandemic
Affected amphibians, mostly frogs and toads, represent 6.5% of known amphibian species, making the pandemic “the largest documented loss of biodiversity attributable to a pathogen,” the experts say in the journal. Science collecting work.
Batrachochytrium dendrobatidis, a widespread pathogen found in the wildlife trade, is the main culprit. This invasive fungus, first identified in 1998 , has caused the massive death of frogs and toads. Although the presence of this fungus peaked in the 1980s in Central and South America and Australia, it remains a constant threat.
The fungus infects the keratinized skin that amphibians develop when they mature and pass from water to land. The resulting chytridiomycosis destroys an amphibian’s ability to regulate the proper flow of electrolytes and fluids through its skin, usually leading to heart failure within a few weeks.
Ben Scheele, an ecologist at the Australian National University in Canberra, coordinated 40 other researchers with knowledge of regional amphibians. The team analyzed published literature and unpublished data, including interviews with experienced researchers in 24 countries known to have chytridriomycosis infections. In an epidemiological analysis, the researchers integrated the data to determine the severity, timing, and geographic distribution of amphibian declines due to chytridiomycosis.
The data is very alarming
Of the 500 species affected, about 40% continue to decline. And 124 species, or 25%, have been reduced to less than 10% of their previous numbers. The most affected have been the larger, slow-growing species that do not reach reproductive maturity as quickly, the species that live in more humid areas (which the fungus prefers) or at higher altitudes (where the animals are more isolated and have fewer habitat options).
Amphibians extinct because of the fungus
Among those extinct in nature or presumably extinct, are: the golden toad or the Panamanian golden frog. A second related fungus, B. salamandrivorans or Bsal, mainly affects salamanders and was responsible for the decline of one species.
The team found that only 12% of species show some limited signs of recovery. Those amphibians may be developing immunity, or perhaps other threats, such as habitat loss or pollution, may have decreased, the researchers say.
The results, while not surprising, are “sad,” Scheele says, and the reality may be even worse. The fungus probably affected many of the as yet unnamed amphibian species in the Neotropics, and for other species in decline, there was insufficient evidence linking their decreasing numbers to chytridiomycosis.
The invasive fungus responsible remains “a very serious threat ,” Scheele says, especially to unexposed amphibian populations, such as those in Papua New Guinea. And, with the global spread of pathogens, new strains of the fungus may continue to evolve, exceeding the adaptive capacities of the species. Once released into the environment, the only way to contain it is through better biosecurity measures and better wildlife monitoring, says the expert.
Reference: BC Scheele et al. Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity. Science. Vol. 363, March 29, 2019, p. 1459.
