Little is known about the longevity of T. granulosa, but marked specimens have been recaptured after 17-18 years.
Range lifespan
Status: wild: 18 (high) years.
Because of the extreme toxicity of rough-skinned newts, they have only one known predator, common garter snakes (Thamnophis sirtalis), which seem to be immune to tetrodotoxin. It has been proposed that these two species are competing against each other in an evolutionary arms race, in which a predator species and a prey species co-evolve, each developing greater defenses against the other. In this case, as the newts evolve greater toxicity, garter snakes evolve greater resistance to the toxicity.
Known Predators:
Anti-predator Adaptations: aposematic
The eggs of T. granulosa are each separately encased in a gelatinous substance, around 3 to 4 millimeters in diameter. The ova are generally light-brown on top and cream colored on the bottom.
Larvae are aquatic, with a faint dorsal stripe on either side of the body that fades as they mature. Larvae have a dark stripe that extends from the eye to the nostril as well as two rows of spots. One row is near the limb insertions and the other is near the fin. The fin is speckled with dark spots. Larvae measure around 18 mm in total length.
Adults range from about 12.7 to 21.6 cm in total length. They have rough, grainy skin that is dark-colored dorsally and orange to yellow-orange ventrally. Their textured skin has earned them the common name "rough-skinned newts." Their eyes are relatively small and do not extend beyond the edges of the head. The irises are yellow, and the lower eyelids are orange. The vomerine teeth are arranged in a V-shaped pattern. Costal grooves are absent. Males are larger than females, with longer vents. During the breeding season, males and females become temporarily aquatic. Males develop smooth, spongy skin that is lighter-colored than usual. Their vents are strongly pronounced and swollen. The tail crests become more pronounced, as do the nuptial pads on the tips of their toes. The appearance of the females does not change, though their vent becomes cone-shaped.
Some adults living at high elevations retain their gills and are totally aquatic, though they do not exhibit genuine paedomorphosis. Aquatic females can sometimes be confused with breeding males, because they have lighter, smoother skin, tail crests, and larger vents than do terrestrial females. However, these features are less pronounced than in breeding males.
Range length: 12.7 to 21.6 cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; poisonous
Sexual Dimorphism: male larger; sexes shaped differently
Taricha granulosa inhabits both aquatic and terrestrial environments. Though they generally spend more of their time on land, they must return to the water to breed. Many become temporarily aquatic during the summer months due to dry weather. It is possible for a newt to spend its entire life in an aquatic habitat. In the water, T. granulosa prefers areas of little or no current, such as ponds, lakes, and slow-moving streams, and sometimes small ephemeral wet areas such as ditches. Aggregations of adults have been discovered as deep as 12 meters underwater. On land, newts can usually be found under pieces of rotting wood on forested hills or mountains. They occasionally occur in open areas such as fields.
Range elevation: 0 to 2743 m.
Range depth: 0 to 12 m.
Habitat Regions: temperate ; terrestrial ; freshwater
Terrestrial Biomes: forest ; mountains
Aquatic Biomes: lakes and ponds; rivers and streams; temporary pools
Wetlands: marsh
Other Habitat Features: suburban ; agricultural ; riparian
Taricha granulosa is found along the Pacific coast of North America, with a range extending from Santa Cruz County, California, south of San Francisco Bay, into southeastern Alaska north to Juneau. Within this range, it is found at elevations from sea-level to 2743 m, or 9000 ft, and is found on many islands off the coast, including Vancouver Island. In northern California rough-skinned newts are found as far east as Shasta County, extending into northern Butte County. Isolated populations of T. granulosa occur in Latah County, Idaho and Saunders County, Montana. The Idaho population, at least, is probably introduced.
Biogeographic Regions: nearctic (Introduced , Native )
Larvae eat small aquatic invertebrates. Aquatic adults have been known to eat a variety of organisms, from snails and insects to other amphibians.
Adult terrestrial T. granulosa appear to be opportunistic carnivores, with insects making up a large portion of their diet.
Animal Foods: amphibians; insects; terrestrial non-insect arthropods; mollusks; zooplankton
Primary Diet: carnivore (Insectivore , Eats non-insect arthropods, Molluscivore )
Since T. granulosa is mainly an insect eater, it is important in keeping insect populations in check, possibly including some nuisance insect species, such as mosquitoes (Culicidae). Taricha granulosa is also an important food source for common garter snakes, which are in turn eaten by other animals.
Taricha granulosa is of particular interest to biologists because of its evolutionary arms race relationship with common garter snakes. This species is also exploited for the pet trade.
Positive Impacts: pet trade ; research and education
There are no known adverse effects of T. granulosa on humans, unless ingested. These newts contain enough toxin to kill several humans.
Negative Impacts: injures humans (poisonous )
Taricha granulosa exhibits an aquatic larval stage. Eggs hatch 3 to 4 weeks after being laid, and these newts spend 4 to 5 months as aquatic larvae before metamorphosing into juvenile adults. In some high elevation areas, newts overwinter as larvae and emerge in the spring or summer. They spend a couple of years as juvenile adults before returning to the water to breed. At high elevations, some adults retain their gills and spend their entire life cycle in the water. Adults reach sexual maturity at 4 to 5 years of age.
Development - Life Cycle: metamorphosis
Rough-skinned newts are not listed as threatened or endangered, but like many amphibian species may face such a distinction if their habitat is extensively threatened by human development.
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: least concern
It is unclear how T. granulosa individuals communicate with one another, but there is evidence that rough-skinned newts navigate using celestial cues, olfaction, and darkened areas caused by vegetation at the edges of water bodies.
Communication Channels: visual ; chemical
Perception Channels: visual ; ultraviolet; chemical
Breeding takes place underwater, and is initiated by the male. He climbs on top of the female, clasps her with his legs, and proceeds to rub the snout of the female with his chin while stroking her legs with his hind legs. This behavior is known as amplexus, and can last anywhere from several hours to two days. The male then releases the female, crawls in front of her, and deposits a spermatophore, which is a gelatinous mass with a small capsule of sperm at the top. The female picks up the sperm capsule with her cloaca (vent). In some instances other males will attempt to separate an amplexed pair.
Mating System: polygynandrous (promiscuous)
Reproduction in T. granulosa is totally aquatic, usually occurring in still or slow-moving waters near vegetation. The breeding season is highly variable depending on elevation. At lower elevations, most reproductive activity occurs in the spring, from January to May. At high elevations, most breeding occurs during late summer and early fall. Females lay their eggs soon after mating. The eggs are laid one at a time and are attached by the female to vegetable matter or detritus. They take 3 to 4 weeks to hatch.
Breeding interval: Rough-skinned newts breed annually or biennially, depending on their location.
Breeding season: At high elevations most breeding occurs during late summer, while at lower elevations most breeding occurs during the spring months.
Range time to hatching: 3 to 4 weeks.
Range age at sexual or reproductive maturity (female): 4 to 5 years.
Range age at sexual or reproductive maturity (male): 4 to 5 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous
There is no parental care exhibited by this species. The female takes care to attach her eggs to vegetation so they will not float away and provides nutrients for development.
Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female)
The rough-skinned newt or roughskin 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.[2][3] The skin is granular, but males are smooth-skinned during breeding season. They measure 6 to 9 cm (2.4 to 3.5 in) in snout-to-vent length, and 11 to 18 cm (4.3 to 7.1 in) overall.[3] 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.[2] Males can be distinguished from females during breeding season by large swollen vent lobes[3] and cornified toe pads.[2]
Habitats of rough-skinned newts are found throughout the Pacific Northwest. 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.[4]
A number of subspecies have been defined based on local variants, but only two subspecies have wider recognition:[2][5]
It is now believed that the Taricha granulosa mazamae subspecies is no longer valid, as specimens that look similar to T.g.m have been found in areas of Alaska as well.
Many newts produce toxins from skin glands as a defense against predation, but the toxins of the genus Taricha are particularly potent. An acrid smell radiates from the newt, which acts as a warning for animals to stay away.[6] 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. In 1979, a 29-year-old man from Oregon died after ingesting a rough-skinned newt.[7]
The newt produces a neurotoxin called tetrodotoxin (TTX), which in this species was formerly called "tarichatoxin". It is the same toxin found in pufferfish and a number of other marine animals.[8] This toxin targets voltage gated sodium channels via binding to distinct but allosterically coupled sites. Because TTX is much larger than a sodium ion, it acts like a cork in a bottle and prevents the flow of sodium. The reverse binding to sodium channels in nerve cells blocks electrical signals necessary for conducting nerve impulses. This inhibition of firing action potentials has the effect of inducing paralysis and death by asphyxiation.
Throughout much of the newt's range, the common garter snake (Thamnophis sirtalis) has been observed to exhibit resistance to the tetrodotoxin produced in the newt's 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. Successful predation of the rough-skinned newt by the common garter snake is made possible by the ability of individuals in a common garter snake population to gauge whether the newt's level of toxin is too high to feed on. T. sirtalis assays toxin levels of the rough-skinned newt and decides whether or not the levels are manageable by partially swallowing the newt, and either swallowing or releasing the newt.[9] 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.[10] 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 the amount of newt 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 because the two species compete in developing adaptations and counter adaptations against each other. This has resulted in the newts producing levels of toxin far in excess of what is needed to kill any other conceivable predator. Some newts secrete enough toxins to kill several adult humans. It appears that in some areas, the common garter snake has surpassed the newt in the evolutionary arms race by developing such a strong resistance to the toxin that the newt is unable to compete with its production of the toxin.[6] There has been phylogenetic evidence that indicates elevated resistance to TTX has originated independently and only in certain species of garter snakes. The resistance has evolved in at least two unrelated species in the genus Thamnophis and at least twice within T. sirtalis.[11]
The toxin, when injected into animals, may not kill resistant animals; however, they are normally slowed down by its toxic effects. In snakes, individuals who showed some resistance tended to move slower after TTX injection, while those with less resistance become paralyzed.[12]
Newts are not immune to their own toxin; they only have a heightened resistance. The toxin in newts consists of a tradeoff. Each time they release the toxin, they inject themselves with a few milligrams. The TTX becomes concentrated in certain parts of the tissue after passing through cell membranes. As a result of tissue exposure to the toxin, newts have evolved a protection mechanism via a single amino acid substitution to the voltage-gated sodium channel normally affected by TTX. Puffer fishes show a similar amino acid sequence that allows them to survive from their own toxin exposure.[8]
Predation on newts by T. sirtalis also shows evidence that tetrodotoxin may serve as protection of eggs by the mother. While TTX is mainly located in the glands of the skin, the rough-skinned newt, as well as some other amphibians also possesses TTX in the ovaries and eggs. The higher the skin toxin levels were in the female, the higher the toxin level found in the egg. This is evidence that high toxin levels of the skin may, in fact, be under indirect selection. Since egg toxin levels would ultimately increase the survivability from predators, such as the garter snake, of the offspring, egg toxin levels may be under direct selection by mates, which is detectable via skin toxin levels.[13]
The rough skinned newt uses a form of chemical based avoidance behavior to avoid being eaten by predators, mainly the common garter snake. The snakes, after swallowing, digesting, and metabolizing a rough-skinned newt, release a chemical signature. This stimulus can be detected by a nearby newt and trigger an avoidant response, which allows them to minimize predation risks. In this way, newts are able to differentiate whether a snake is resistant or sensitive to the toxin in order to avoid being preyed upon. However, newts do not avoid the corpses of a recently digested newt that has been left to decompose. This behavior is unlike salamanders that have been documented in avoiding other damaged salamanders.[14]
Parasites include the trematode Halipegus occidualis, the adult form of which may infest the newt's esophagus and the anterior of its stomach.[15]
Taricha granulosa egg in moss observed near Pe Ell, Washington on May 22, 2017 The rough-skinned newt or roughskin newt (Taricha granulosa) is a North American newt known for the strong toxin exuded from its skin.
