出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/10/14 00:58:53」(JST)
| Rough-skinned newt | |
|---|---|
| Conservation status | |
|
Least Concern (IUCN 3.1) |
|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Amphibia |
| Order: | Caudata |
| Family: | Salamandridae |
| Genus: | Taricha |
| Species: | T. granulosa |
| Binomial name | |
| Taricha granulosa |
|
The rough-skinned newt (Taricha granulosa) is a North American newt known for the strong toxin exuded from its skin.
A stocky newt with rounded snout, it ranges from light brown to olive or brownish-black on top, with the underside, including the head, legs, and tail, a contrasting orange to yellow.[1][2] The skin is granular, but males are smooth-skinned during breeding season. They measure 6 to 9 cm in snout-to-vent length, and 11 to 18 cm overall.[2] They are similar to the California newt (Taricha torosa) but differ in having smaller eyes, yellow irises, V-shaped tooth patterns, and uniformly dark eyelids.[1] Males can be distinguished from females during breeding season by large swollen vent lobes[2] and cornified toe pads.[1]
Habitats of rough-skinned newts are found throughout the West Coast of the United States and British Columbia. Their range extends south to Santa Cruz, California, and north to Alaska. They are uncommon east of the Cascade Mountains, though occasionally are found (and considered exotic, and possibly artificially introduced) as far as Montana. One isolated population lives in several ponds just north of Moscow, Idaho, and was most likely introduced.[3]
A number of subspecies have been defined based on local variants, but only two subspecies have wider recognition:[4][5]
Many newts produce toxins from skin glands as a defense against predation, but the toxins of the genus Taricha are particularly potent. Toxicity is generally experienced only if the newt is ingested, although some individuals have been reported to experience skin irritation after dermal contact, particularly if the eyes are touched after handling the animal without washing hands. On a dare, a 29-year-old man in Oregon swallowed a 20-cm rough-skinned newt and died.[6]
The newt's toxin is a neurotoxin called tetrodotoxin, which in this species was formerly called "tarichatoxin". It is the same toxin found in pufferfish and a number of other marine animals. This toxin binds reversibly to sodium channels in nerve cells and interferes with the normal flow of sodium ions in and out of the cell. This has the effect of inducing paralysis and death.
Throughout much of the newt’s range, the common garter snake (Thamnophis sirtalis) has been observed to exhibit resistance to the tetrodotoxin produced in its skin. While in principle the toxin binds to a tube-shaped protein that acts as a sodium channel in the snake's nerve cells, researchers have identified a genetic disposition in several snake populations where the protein is configured in such a way as to hamper or prevent binding of the toxin. In each of these populations, the snakes exhibit resistance to the toxin and successfully prey upon the newts. Toxin-resistant garter snakes are the only known animals today that can eat a rough-skinned newt and survive.
In evolutionary theory, the relationship between the rough-skinned newt and the common garter snake is considered an example of co-evolution.[7] The mutations in the snake’s genes that conferred resistance to the toxin have resulted in a selective pressure that favors newts which produce more potent levels of toxin. Increases in newt toxicity then apply a selective pressure favoring snakes with mutations conferring even greater resistance. This cycle of a predator and prey evolving to one another is sometimes termed an evolutionary arms race and has resulted in the newts producing levels of toxin far in excess of what is needed to kill any other conceivable predator.
Parasites include the trematode Helipegus occidualis, the adult form of which may infest the newt's esophagus and the anterior of its stomach.[8]
Data related to Taricha granulosa at Wikispecies Media related to Taricha granulosa at Wikimedia Commons
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| リンク元 | 「サメハダイモリ」 |
| 関連記事 | 「Taricha」「granulosa」 |