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The amphibian apocalypse - fungus causes mass extinctions
For the first time in the time that humans are on the planet, an entire class of vertebrates is threatened with extinction. The amphibian death continues to advance.
That would have ecological consequences that we cannot even estimate. The uninhibited proliferation of insects that transmit dangerous diseases is only one of them, and the loss of an essential source of food for countless bird species is another. The apocalyptic riders for the amphibians are habitat loss, environmental toxins such as pesticides and climate change. Added to this is an old adversary who is more deadly than ever.
Every third frog is threatened
Every third frog, salamander and every third toad worldwide are on the Red Lists of Endangered Species. The stocks of the amphibians are exposed to thousands of damages anyway - their habitats disappear, the environmental impact particularly affects them. They are very sensitive to climate change because, unlike warm-blooded animals, they are directly dependent on a specific temperature and humidity.
165 species have already died out
The greatest danger, however, comes from the chytrid fungus Batrachochytrium dendrobatidis. He has been diagnosed since 1999, originally comes from Africa and has caused the greatest extinction of modernism in the shortest possible time: since 1980, 165 species of frogs, toads, newts and salamanders have died out, 435 have migrated to a higher category of endangerment.
In Ecuador, for example, the country with the greatest biodiversity of amphibians, 156 of more than 700 species of frog are threatened with extinction today - 16 of them have already been killed. So far, South and North America and Australia have been particularly affected.
The most threatened by the fungus are highly specialized species such as the Kihansi spray toad, which live in a special biotope in a small area and have always recorded only a few individuals. But the mushroom also eradicates former common species without further notice. The pathogen in the water infects the upper skin layer of the animals, which then die within a few weeks.
Hundreds of species are unlikely to survive in their natural habitat and require short-term breeding stations in human care that are free of the fungus so as not to share the fate of the dinosaurs and to develop outdoor populations again in the long term.
The spray toad
The Kihansi spray toad was eliminated by the mushroom in the wild in 2009. It lived in the Kihansi waterfalls in Tanzania. It was, however, very common in this special place, with an estimated 17,000 adult animals.
A dam, which reduced the amount of water to a tenth, led to a massive drop in the population. Then the mushroom came and with it the end for the toad. Today the spray toad lives only in a few zoos.
The last rabb tree frog from Panama died in human care in the United States in 2016. The fungus had previously wiped out the species in the wild in a few years.
The global nature conservation organization IUCN demands that all amphibian species that are endangered in nature be systematically bred in human care. For this purpose, zoos and aquariums should also work together with qualified private owners.
In fact, with today's technical possibilities, most amphibian species can easily be bred in human care, and in a much smaller area than, for example, endangered large mammals.
In addition, most amphibians produce a lot of spawning, since in nature most tadpoles and juveniles fall prey to predators. Assuming a coordinated network of breeders, captive populations can grow quickly as a multiple of the hatchlings survive.
The amphibian ark
The World Association of Zoos and Aquariums has therefore been developing a program, the amphibian ark, since 2005.
The key points are as follows:
Every zoo and aquarium should participate in the amphibian protection program as far as possible. This can include the following measures:
- Information for visitors about the dangers that amphibians are exposed to today through appropriately designed exhibitions and information boards in the zoo or in the aquarium.
- Addressing amphibian protection as part of the zoo lessons.
- Information to the general public via press releases, the Internet, etc.
- Creation of the personal and spatial conditions to keep amphibians in large numbers and to breed them within the framework of long-term programs.
- Ecological upgrading of the zoo area in order to create habitats for domestic amphibians.
- Management of protected areas or participation in actions to protect the local amphibian fauna.
- Support zoos, aquariums and nature conservation authorities in developing countries with a high biodiversity of amphibians through knowledge transfer and the provision of housing facilities and other material.
- Participation in research and protection projects in developing countries.
Spotted Tree Frog back in the wild
In the meantime, some extremely endangered species have not only been bred in human care, but are being released again in fungus-free areas. In 2001, the spotted tree frog died out in the wild in the central highlands of Victoria, Australia.
Dr. David Hunter from the NSW Office of Environment and Heritage led the team that caught the last tree frogs in Kosciuszko National in 2001 to build a protected population.
16 years later, he reintroduced the offspring to a remote area of the national park that will most likely remain free of fungus. Hunter explains that the frogs are a key in the food chain because they offer a resource for reptiles, birds and mammals.
The new home of the frogs is warmer and drier than their usual habitat and therefore unsuitable for the mushroom, because it doesn't like temperatures above 28 degrees. So far, more than half of the frogs released have survived and the animals have reproduced.
The fire salamander
Batrachochytrium dendrobatidis (Bd) has a relative: Batrachochytrium salamandrivorans (Bsal). This has struck with fire salamanders in the Netherlands in recent years. Of these, only 4% have probably survived the infestation since 2010.
The related species needs colder temperatures and dies at 25 degrees Celsius. Unfortunately, fire salamanders prefer cool forest areas, and their tadpoles also grow in cool flowing waters. The salamanders die because the fungus changes the top layer of skin, and ulcers form as a result.
The private keeping of amphibians is prohibited in the Netherlands. What initially speaks for a particular awareness of nature conservation is now proving to be counterproductive, since the Dutch cannot access private stocks to preserve the salamanders.
Nine out of ten animals die
The experience with the killer mushroom teaches above all: Even a small amount of the highly infectious mushroom could destroy the entire population of fire salamanders in Western Europe. Around 90% of the animals in an infected population die within six months.
With both variants of the fungus, the classic means of controlling animal diseases fail: neither vaccination nor repopulation is possible, and the fungus cannot be removed from the biotopes either.
The midwife toad
The midwife toad of Western Europe also suffers from the fungus. People may have spread the mushrooms with their shoes, because the infected animals were increasingly found near hiking trails. More than a quarter of midwife toads are found on the Iberian Peninsula.
How did the mushroom spread?
The mushroom probably spread in America and Australia with African talons. These have been used for pregnancy tests since the 1930s, as urine sprayed into the skin of pregnant women causes the females to develop eggs.
Furthermore, the worldwide trade in terrarium animals may have spread the mushroom. It has also become the leading cause of death for frogs and toads in private ownership. The European first evidence was in 2000 for poison dart frogs that were freshly imported from Costa Rica.
Was the fungus fatal before?
The fungus has been around for millions of years, however, and it is still unclear whether it was responsible for past amphibian deaths. The population of lungless salamanders in Guatemala declined massively in the 1980s, although their habitats remained undisturbed.
Researchers found that this decline coincided with the spread of the chytride fungus. He appeared in Mexico in the early 1970s, shortly afterwards in southern Guatemala and in 1987 in Costa Rica - and there were local drops in amphibian populations everywhere.
The hypothesis is that the fungus has always been present in the environment. The cold-loving pathogen was able to spread with climate change. However, it remains unclear how the water-borne fungus attacked amphibians in the rainforest, which do not target large areas of water and even lay their eggs in the small accumulations of rainwater that form in the leaf funnels of bromeliads.
Why are mushrooms dangerous for amphibians?
Fungus on the skin is uncomfortable for people, it threatens life in amphibians. Because frogs, toads and salamanders absorb liquid like minerals through the skin and excrete waste materials. Lungless salamanders even breathe through the skin.
If the chytrid fungus attacks the animals, keratin clogs the pores and the amphibians suffocate.
However, Batrachochytrium salamandrivorans does not seem to kill amphibians with a stable immune system either. However, if other pathogens, a change in climate and stress are added, the disease breaks out. This can be inferred from bullfrogs in captivity, who were in good health and who could not harm the fungus.
Strengthen the immune system
Researchers from James Madison University made a discovery that gives hope. Salamanders and many frogs naturally have a defense against the chytrid fungus in the form of bacteria on their skin and skin proteins.
The scientists suspect that an increase in these beneficial bacteria could reduce the contagion and start the immune system. One idea is to make amphibians in human care more resistant to the pathogen in order to release these starched animals in the wild again. If the animals were less susceptible, this could slow down the spread of the pathogen. (Dr. Utz Anhalt)
Author and source information
This text corresponds to the specifications of the medical literature, medical guidelines and current studies and has been checked by medical doctors.
Dipl. Social Science Nina Reese
- Mutschmann, Frank: Diseases of the Amphibians, Enke, 2009
- Wilson, Edward O .: Half the Earth: A Planet Fights for its Life, C.H.Beck, 2016
- The Bund Naturschutz: www.bund-naturschutz.de (accessed: May 28, 2017), practical tips: How to protect amphibians and help frogs, toads, etc.! TE & CO!
- Glandt, Dieter: Amphibians and Reptiles: Herpetology for Beginners, Springer, 2016
- Glandt, Dieter: Practical Guide to Amphibian and Reptile Protection: Fast - Precise - Helpful, Springer, 2018