Chytrid mushroom
| Chytrid mushroom | ||||||||||||
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Batrachochytrium dendrobatidis (arrows) in Atelopus varius |
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| Batrachochytrium dendrobatidis | ||||||||||||
| Longcore , Pessier & DK Nichols |
The chytrid fungus ( Batrachochytrium dendrobatidis ) is a potty fungus ( Chytridiomycota) that attacks amphibians and causes them a disease called chytridiomycosis . An infection with the fungus can be fatal in some species. There has been a real chytrid fungus epidemic since the 1980s , with the numbers of numerous amphibian species, mainly in Central and South America and Australia , decimated or even almost extinct. The phenomenon is under the heading of a global decrease in amphibians (engl. Globally amphibian decline ) discussed. The exact cause of this epidemic is still unclear, but it is believed that other factors are also involved in the sudden extinction of many species, such as environmental pollution , global warming , the destruction of the ozone layer or the use of pesticides .
description
The chytrid mushroom belongs to the group around the genus Rhizophydium , but a more precise assignment within the order Chytridiales is still pending.
Infections with chytrid fungi are by no means just a phenomenon of the last few years, but have been known for a long time. The oldest known infection was detected in Africa in the 1920s . Exactly how the fungus leads to the death of the infected animals is not yet fully understood, but it is assumed that the fungus either releases toxins that the amphibian absorbs through the skin , or that the fungus affects the water and electrolyte balance of the animals concerned so that they ultimately die. The barrier function of the skin against other pathogens is also likely to be affected by the fungal attack.
It is known that chytrid fungi only attack the upper skin layer of amphibians and only those areas in which the protein keratin , which is also found in feathers, hair and claws, is to be found. In frogs, only very few areas of the skin are permeated with keratin. Since frogs breathe through their skin to a large extent , the surface of the skin must remain very thin and moist. Therefore, in adult frogs, only the feet and the areas where the legs rub against the trunk are streaked with keratin, in tadpoles only the area around the mouth. Chytrid fungi can also be found there in many animals, but the infection is only dangerous when it has metamorphosed into an adult animal, as larger areas of skin are then affected.
Spread and endangerment of populations
The chytrid fungus originally comes from Africa and lives on the skin of African clawed frogs , which are immune to the effects of these fungi. The clawed frogs used for pregnancy tests ( frog test ), which are therefore also known as pharmacist frogs, were spread worldwide by humans and the fungus was introduced with them. Since amphibians in other areas have no immunity to the fungus, a global chytridiomycosis epidemic was triggered.
The danger is that the infected animals will spread the fungus further because they carry the fungus around with them. The spores of chytrid fungi can survive in water for up to 24 hours, so that the fungus spreads quickly, especially in flowing waters. As far as is known, the fungus also affects perfectly healthy animals and not just sick or weakened individuals, so that it can multiply quickly within an amphibian population. Furthermore, it would be possible that other cold-blooded animals, who do not mind the infection itself, could also spread the fungus. Unintentional spreading by humans - either directly through the transmission of the spores or indirectly through the accidental transport of infected animals - represents a danger for many amphibian populations, so it is advised to avoid closer contact with amphibians in nature if one does not Material such as B. has gloves with you to avoid further accelerating the spread of the chytrid fungi.
It is also known that there is a temperature effect in chytrid infections. At comparatively low temperatures (17 ° C) the death rate in infested populations is up to 100%, while at 27 ° C only 50% of the animals die. Therefore, amphibian populations in particular are threatened by the fungus, which are at a certain altitude (from 400 meters above sea level), since the temperatures here are naturally lower.
A study published in the journal Nature in January 2006 considers it to be proven that climate change over the tropical mountains of Latin America leads to increased cloud formation. This in turn results in cooler days and warmer nights, which is beneficial for the chytrid fungus, which thrives best at temperatures between 17 and 25 ° C.
Chytrid fungus infections also make populations overall less resistant to other threats such as predators or diseases, so that a chytrid fungus infection can be the trigger that populations, which could otherwise assert themselves in their environment, are no longer able to cope with it. There are dramatic collapses in population size or stocks and species even disappear completely.
As stated in a Science article published in March 2019, the chytrid fungus is responsible for population declines in more than 500 amphibian species and the extinction of 90 species. That is the largest species extinction caused by a single pathogen so far. The main cause of the worldwide decline in amphibian populations, however, is still considered to be habitat destruction by economic humans - this affects 90% of all species classified as endangered. The other risk factors, including fungal diseases, are added cumulatively and presumably reinforce each other interactively.
The genetically closely related Batrachochytrium salamandrivorans ("Bsal", also "salamander eater"), which was probably introduced with terrarium animals from Asia , led to a decrease in the fire salamander population of up to 96% in the Netherlands . It was also detected in Belgium , from private ownership for the first time in October 2015 in Germany.
See also
literature
- W. Ahne, S. Essbauer: Global amphibian dying: Are viral (iridoviruses) and fungal infections (chytridimycoses) involved? In: elaphe. 8 (2), 2000, pp. 82-86.
- Philip Bethge: An ark for the frogs. In: Der Spiegel . 47, Hamburg 2007, p. 176ff. ISSN 0038-7452
- J. Felger, J. Enssle, D. Mendez, R. Speare: Chytridiomycosis in El Salvador. In: Salamandra. 43 (2), 2007, pp. 122-127.
- FJ Mutschmann, C. Seybold: Guidelines for the hygienic handling of amphibians in the context of field herpetological work. In: elaphe. 10 (4), 2002, pp. 70-72.
- Torsten Ohst, Jörg Plötner, Frank Mutschmann , Yvonne Gräser: Chytridiomycosis - an infectious disease as the cause of the global amphibian death? In: Journal of Field Herpetology. Volume 13, No. 2, Laurenti-Verlag, Bielefeld October 2006, pp. 149-163. ISSN 0946-7998
- RA Farrer, LA Weinert et al. a .: Multiple emergences of genetically diverse amphibian-infecting chytrids include a globalized hypervirulent recombinant lineage. In: Proceedings of the National Academy of Sciences. 108, 2011, pp. 18732-18736, doi: 10.1073 / pnas.1111915108 .
Web links
- Quarks & Co - The Great Frog Death ( Memento from November 9, 2008 in the Internet Archive )
- amphibiaweb.org: Amphibian Declines (with overview map; probably state of knowledge from ~ 2003)
- Concern nature , February 2015, anl.bayern.de: “Salamander eater fungus” threatens European salamanders and newts
- bama.ua.edu: Information about the genus Rhizophydium (Engl.)
- nationalparks.nsw.gov.au: Information about the chytrid mushroom (Engl.)
Individual evidence
- ↑ JA Pounds, MR Bustamante et al .: Widespread amphibian extinctions from epidemic disease driven by global warming. In: Nature. Volume 439, number 7073, January 2006, ISSN 1476-4687 , pp. 161-167, doi : 10.1038 / nature04246 . PMID 16407945 .
- ↑ Ben C. Scheele, Frank Pasmans, Lee F. Skerratt, Lee Berger, An Martel, Wouter Beukema, Aldemar A. Acevedo: Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity. Science 29 Mar 2019: Vol. 363, Issue 6434, pp. 1459–1463 DOI: 10.1126 / science.aav0379
- ^ Matthew Warren: Skin-eating fungus is mighty species slayer. nature.com, March 28, 2019, doi : 10.1038 / d41586-019-01002-2
- ↑ nabu.de , News , October 2015: A skin fungus threatens the native fire salamanders (April 21, 2017)