Many newts produce toxins to avoid predation, but the toxins of the genus Taricha are particularly potent. Toxicity is generally experienced only if the newt is ingested, although there are reports that some individuals experience skin irritation after dermal contact.
The rough-skinned newt possesses tetrodotoxin, which in this species was formerly called "tarichatoxin". 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.
Toxin resistance and predation
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 T. granulosa 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. 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.
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 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 were most likely introduced.
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- Natureserve Explorer
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- Geffeney, Shana L., et al. “Evolutionary diversification of TTX-resistant sodium channels in a predatorÂ-prey interaction”. Nature 434 (2005): 759–763.
- "Taricha granulosa granulosa – Rough-Skinned Newt". California Herps. http://www.californiaherps.com/salamanders/pages/t.granulosa.html. Retrieved 2006-12-10.
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