Rough-skinned yellow-bellied newt
| Rough-skinned yellow-bellied newt | ||||||||||||
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Taricha granulosa |
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| Taricha granulosa | ||||||||||||
| ( Skilton , 1849) |
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The rough-skinned yellow-bellied newt ( Taricha granulosa ), also West American rough-skinned newt (based on the English name Rough-skinned newt ), belongs to the family of real salamanders . A special feature of this newt is a protective mechanism against natural enemies through the formation of a strong poison , the tetrodotoxin (TTX).
features
The rough-skinned yellow-bellied newt becomes 12 to 22 centimeters long. The warty skin is light brown to black on the top and yellow to orange on the belly. In the mating season, the males have a widened tail edge, darkly horny toe tips and a more arched cloaca .
Occurrence
The rough-skinned yellow-bellied newt is found on the North American Pacific coast from southern Alaska to California . It lives in pools, lakes and slowly flowing streams at up to 2,700 meters above sea level.
Reproduction
The mating season lasts from December to July. In the water, the male clasps the female from above with his legs. The sperm is deposited on the bottom of a gelatinous cone and taken up by the female through the cloaca. The spawn is attached to the leaves of aquatic plants.
Toxicity and evolution
Protection through the formation of tetrodotoxin (TTX) is widespread in the animal kingdom. For example, you can find this protection mechanism u. a. in puffer fish and blue-ringed octopus . Due to the production of this poison, the genus Taricha is one of the most poisonous tailed amphibians . TTX is also known as Tarichatoxin; the genre gave it its name. The rough-skinned yellow-bellied newt is probably the most poisonous species of the genus. TTX is a neurotoxin that is produced in the glands of the skin and is a defense against predators. The common garter snake ( Thamnophis sirtalis ) is the only potential enemy that has developed resistance to this poison through evolutionary adaptation . After the newt has eaten, the snake has to go into a resting state for a few hours so that its immune system can work efficiently. The newt, in turn, shows a greatly increased production of the poison in regions where this snake occurs. One can speak of an evolutionary race ( coevolution ). Since the production rate of newt poison and the resistance of the snakes vary in different populations and regions, depending on the population density, one speaks in the Anglo-Saxon specialist literature of the "geographic mosaic theory of evolution".
In 1979, a 29-year-old man died in Oregon after swallowing a 20 cm long rough-skinned yellow-bellied newt as a test of courage. It is the only known death of a person from the newt to date.
The poison formation
How exactly tetrodotoxin is formed in the skin of the newt is still unclear. The production of the poison has been demonstrated in some bacteria (e.g. in species of Vibrion and Pseudomonas ). It is therefore assumed that such bacteria live as endosymbionts in the skin of the newt and produce this poison. However, this hypothesis was questioned: In a search for known tetrodotoxin-secreting bacteria within the tissue of the rough-skinned yellow-bellied newt, the 16S rRNA analysis was used, whereby no rRNA of these bacteria was found in the skin tissue, liver or in the egg tissue. Small traces of the rRNA from TTX-producing bacteria have been found inside the intestine, but the small amount of RNA, i.e. the number of these bacteria, does not appear to be sufficient to explain the amount of poison produced. The transport of the TTX to the skin tissue should also be detectable, which is not the case. Another study also speaks against the ingestion of the toxin-producing bacteria through food. The newt was kept in captivity for a year and during this time there was no decrease in the poisonous content, but rather an increase. If the poisonous organisms were ingested through the food, the poison content or the formation would have had to decrease, since at this time no natural food was available for the newt.
These results suggest that the newt has its own genes for the production of the poison and does not need any help from bacteria. This would mean that the ability to produce TTX developed independently of one another in the course of evolution in bacteria and newt species. Another publication questions the formation of TTX in the puffer fish by Vibrio . A final solution to these problems would be to analyze the genes responsible for poison production. The possibility of the independent formation of TTX with or without bacteria acting as endosymbionts is therefore still under discussion.
swell
- ↑ Sean B. Carroll: The Darwin DNA - How the Latest Research Confirms the Theory of Evolution , ISBN 978-3-10-010231-7 , p. 175.
- ↑ Elizabeth M. Lehman, Edmund D. Brodie and Edmund D. Brodie: No evidence for an endosymbiotic bacterial origin of tetrodotoxin in the newt Taricha granulosa In: Toxicon 44 (2004) 243-249, PMID 15302530 .
- ↑ Kendo Matsumura: Reexamination of Tetrodotoxin Production by Bacteria In: Applied and Environmental Microbiology , September 1995, pp. 3468-3470 AEM Online .
- ↑ Kim, DS, Kim, CH: No ability to produce tetrodotoxin in bacteria - authors reply. In: Applied and Environmental Microbiology , May 2001, pp. 2393-2394 AEM Online .
literature
- Edmund D. Brodie, Chris R. Feldman, Charles T. Hanifin, Jeffrey E. Motychak, Daniel G. Mulcahy, Becky L. Williams & Edmund D. Brodie: Parallel Arms Races between Garter Snakes and Newts Involving Tetrodotoxin as the Phenotypic Interface of Coevolution. - Journal of Chemical Ecology 31 (2), pp. 343-355 (2002), ISSN 0098-0331 , PMID 15856788 .
- Edmund D. Brodie Jr., BJ Ridenhour, ED Brodie III: The evolutionary response of predators to dangerous prey: hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts. - Evolution 56 (10), pp. 2067-2082 (2002) BioOne Online Journals .
Web links
- Amphibian Information Resource: Taricha
- Spiegel Online: The poison of hunters and the hunted
- Taricha granulosa in the Red List of Threatened Species of the IUCN 2006. Posted by: Hammerson, 2004. Retrieved on 12 May, 2006.