Chytridiomycota
| Chytridiomycota | |
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| Division: | Chytridiomycota Doweld (2001)
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Chytridiomycota is a division of the kingdom Fungi. The name is derived from the Greek chytridion, meaning "little pot", describing the structure containing unreleased spores. In older classifications, chytrids (except the recently established order Spizellomycetales) were placed in the class Phycomycetes under the subdivision Myxomycophyta of the kingdom Fungi. Also, in an older and more restricted sense (not used here), the term "chytrids" referred just to those fungi in the order Chytridiales. The chytrids have also been included among the Protista, but are now regularly classed as fungi.
The chytrids are one of the early diverging lineages of the fungi and are mostly saprobic, degrading refractory materials such as chitin and keratin. The thalli are coenocytic and usually form no true mycelium (having rhizoids instead). Some species are unicellular. As with other fungi, the cell wall in chytrids is composed of chitin.
Many chytrids are aquatic (mostly found in fresh water). There are approximately 1,000 chytrid species, in 127 genera, distributed among 5 orders.
Reproduction
Both zoospores and gametes of the chytrids are mobile by their flagella, one whiplash per individual.
In Allomyces, the thallus (body) is attached by rhizoids, and has an erect trunk on which reproductive organs are formed at the end of branches. The life cycle has the ability to change from haploid and diploid generations. The haploid thallus forms male and female gametangia from which flagellated gametes are released and merge to form a Zygote. Gametes and female gametangia attract the opposite sex by producing pheromones. The germinated zygote produces a diploid thallus with two sorts of sporangia; thin-walled zoosporangia which release diploid zoospores resulting in a diploid thalli and thick-walled sporangia which after meiosis release haploid zoospores which form haploid thalli.[citation needed]. Chytridiomycosis is a serious threat to amphibian species as it is positively correlated with mass mortalities, declines of populations, and overall may lead to species extintions worldwide.Cite error: A <ref> tag is missing the closing </ref> (see the help page). Another example is that it's also responsible for the extinction of the golden toad in 1989. The process leading to frog mortality is thought to be the loss of essential ions through pores made in the epidermal cells by the chytrid during its replication. [1]
Chytrids may also infect plant species; in particular, maize-attacking and alfalfa-attacking species have been described.[2] Synchytrium endobioticum is an important potato pathogen.[3] Chytrid-like fungal sporangia are known to occur in the saccate pollen grains of the Pennsylvanian age. The presence of light refractile body in some zoospores have been know to imply a relationship with Chytridales. Along with the presence of light, the choice of substrate and sporangial features also lead to the suggestion that these zoospores are related to Chytridiales.[4].
Many observations have lead scientists to find a new genus of Chytrid called Nephrochtrium. Although Nephrochtrium is considered a new fungi due to its distinct method of development it is still found to be part of the Chytrid family as it has been discovered in Nitella and Chara. The discovery of this new genus of Chytrids has led scientists to be on the look out for newly developing forms of the fungi which may lead to more amphibian extinctions in the future.Cite error: A <ref> tag is missing the closing </ref> (see the help page). Holocarpic chytrid remains were found in cherts from Combres in central France that dates back to the late Visean. These remains were found along eucarpic remains and are ambiguous in nature though are thought to be chytrid remains. [5] Other chytrid-like fossils were found in cherts in Western Europe, especially France, dating between 300 and 350ma. Another such example is the chert from the upper Pennsylvanian in the Saint-Etienne Basin in France. [6] While none of the fossils found before the Permian system are specifically chytrids, their chytrid-like qualities give impressive insight into the evolutionary path of Fungi.[citation needed]
Spread of Chytrid Fungus Batrachochytrium dendrobatidis
It has been suggested that the amphibian killing chytrid fungus Batrachochytrium dendrobatidis was spread all over the world by the South African "Clawed Toad" Xenopus laevis. This fungus grows on the back of the Xenopus laevis[7] An article written in The British Medical Journal from 1939 outlines clearly how the "Clawed Toad" may be to blame. The article outline a comparison between rabbits, mice and the "Clawed Toad" (later classified as a frog) in use for pregnancy testing. Testing for pregnancy required exposure of the preferred animal to a woman's urine. If the urine contains human chorionic gonadotropin, or hCG which is the pregnancy hormone, the animal would display a specific reaction. In the case of mice the results may not be known for up to 5 days. The Friedman test was considered a "rapid" test using rabbits that would give results in 24 to 48 hours. The Hogben test using Xenopus laevis would yield test results in as little as 6 to 15 hours. "Impressed by the reports of Bellerby (1934) and of Shapiro and Zwarenstein (1934) concerning the usefulness of the "Clawed Toad" of South African (Xenopus laevis Daud.)as an experimental animal in biological tests for the diagnosis of pregnancy, I imported 1,500 well-grown females in 1937..."[8] "Crew encouraged New York gynaecologist Abner Weisman’s interest in importing Xenopus for pregnancy testing into the United States, and Weisman proved a tireless campaigner for the frog (Weisman and Coates, 1944). Other enthusiasts ensured that by the end of the War (World War II) there were Xenopus colonies in laboratories and clinics all over the world."[9]
It has been found that when comparing frogs from temperate and tropical regions, those that dwell in temperate regions have significantly more intense Chytrid attacks than their counter parts. It is now known that the prevalence rates of the Chytrid attacks are higher in areas with higher elevations, more rainfall, and cooler temperatures. Cite error: A <ref> tag is missing the closing </ref> (see the help page).
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External links
- Chytrid Fungi Online: by the University of Alabama
- Introduction to the Chytridiomycota: at the UC Museum of Paleontology
- Impact of chytrid fungus on frogs (Foundation for National Parks & Wildlife)
- 'Amphibian Ark' aims to save frogs from fungus
- The Aquarium Wiki Encyclopaedia on Chytrid Fungus and how it impacts amphibians kept as domestic pets.
- NIH
- Chytridiomycota at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- ^ (Voyles, J., L. Berger, S. Young, et al. 2007. Electrolyte depletion and osmotic imbalance in amphibians with chytridiomycosis. Dis Aquat Organ. 77: 113-118.)
- ^ a b Schaechter M. (2011). Eukaryotic Microbes. Academic Press. p. 116. ISBN 978-0-12-383877-3.
- ^ Cite error: The named reference
Hooker 1981was invoked but never defined (see the help page). - ^ (Chytrid-Like Fossils of Pennsylvanian Age.M. A. Millay, T. N. Taylor.Science, New Series, Vol. 200, No. 4346 (Jun. 9, 1978), pp. 1147-1149)
- ^ Krings, Micheal (2009). "Microfungi from the upper Visean (Mississippian) of central France: Chytridiomycota and chytrid-like remains of uncertain affinity". Review of Palaeobotany and Palynology. 156 (3–4): 319–328. doi:10.1016/j.revpalbo.2009.03.011.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Krings, Micheal (2009). "Chytrid-like microfungi in Biscalitheca cf. musata (Zygopteridales) from the Upper Pennsylvanian Grand-Croix cherts (Saint-Etienne Basin, France)". Review of Palaeobotany and Palynology. 157 (3–4): 309–316. doi:10.1016/j.revpalbo.2009.06.001.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Egber, D. (2006, January 12). The Amphibian Pregnancy Test: How Does a Frog Know You're Knocked Up? Retrieved from Slate.com
- ^ Crew, F. (1939). Biological Pregnancy Diagnosis Tests: A Comparison Of The Rabbit, The Mouse, And The "Clawed Toad" (Xenopus Laevis) As the Experimental Animal. British Medical Journal, 766-770.
- ^ HOPWOOD2, J. B. (200). The introduction of Xenopus laevis into developmental biology: of empire, pregnancy testing and ribosomal genes. Int. J. Dev. Biol, 43-50.