A stocky, large-bodied salamander. Dorsal coloration varies from light brown to blackish brown. The venter is light yellow to orangish red. Upper and lower eyelids are dark. The iris is yellow and the eyes are relatively small. This species has a dry, warty skin, except in mating season when adult males develop a smooth, even slimy, skin. The skin of both males and females is lighter colored during the mating season. Adults are 5.6-8.7 cm snout to vent length (12.5-22 cm total length). Some populations have adults which retain gills (Stebbins 1985; Petranka 1998). Hatchlings are 8-12 mm total length (Stebbins 1951; Riemer 1958). Larvae are pond type with busy gills ande a tail fin which extends foward to the shoulder area. Young larvae have a weak dorsal stripe which becomes diffuse a few weeks after hatching. The color pattern of older larvae is a mottled or reticulate pattern of pigmentation, usually with two rows of light spots on the sides of the body. A dark stripe extends from the nostril to the eye. Populations of T. granulosa in and around Crater Lake, Oregon, are sometimes treated as a distinct subspecies (T. g. mazamae) based on the presence of dark blotching on the venter (Nussbaum and Brodie 1981; Stebbins 1985; Petranka 1998).
Taricha granulosa may be distinguished from T. torosa by the V-shaped pattern of the palatine teeth (compared to Y-shaped), dark lower eyelid, and less protruberant eyes. These species also differ in their defensive posture (see below) (Stebbins 1985).
This species was featured as News of the Week on 28 September 2020:
Dangerously poisonous newts (Taricha granulosa), which sequester the toxin tetrodotoxin (TTX), and predatory garter snakes (Thamnophis sirtalis), which can evolve TTX resistance, are engaged in a classic coevolutionary arms race. While generally roughly matched, in western Oregon and Washington other factors are important. While local adaptation dominates, a study (Hague et al. 2020) of geographic variation found that toxin levels are clearly predicted by the phylogeographic population genetic structure of newts and by factors in local environments. Still, predators have higher levels of resistance than the toxins of co-existing newts, suggesting intense selection. What at first seems to be intense arm race coevolution is shown to be a landscape level pattern-- a geographic mosaic of coevolution based on a mixture of often intense natural selection as well as demographic and environmental effects. This study enriches our understanding of this fascinating phenomenon, which is taking place over a large expanse of time and space (Written by David B. Wake).
This species was featured in the News of the Week, 11 May 2020:
Many salamandrids possess tetrodotoxin (TTX), the same neurotoxin found in pufferfish. Although TTX in marine animals derives from symbiotic bacteria or diet, the source in amphibians has been controversial. Populations of rough-skinned newts (Taricha granulosa) possess different amounts of TTX due to the evolution of TTX resistance in populations of predatory garter snakes. Vaelli et al. (2020) examined the skin microbiome in high- and low-TTX populations of newts and found that bacterial diversity was lower in the highly toxic population, suggesting their skin microbiota is tightly regulated. Several strains of bacteria, particularly Pseudomonas, cultured from the skin of toxic newts were shown to produce TTX in the lab, and Pseudomonas were significantly more abundant in toxic than non-toxic newts. The ability of rough-skinned newts to resist TTX appears to derive from mutations in the target of the toxin, voltage-gated sodium channels (NaVs); all six NaV genes possess mutations in the TTX-binding region of the channel, and electrophysiological experiments with the most widely expressed channel (NaV1.6) verify the mutations confer resistance to almost infinite concentrations of TTX. They show an important role that symbiotic microbes play in the physiology and evolution of their multicellular hosts. (Heather Eisthen and Patric Vaelli)
This species was featured in the News of the Week, 4 April 2016:
The Rough-skinned Newt, Taricha granulosa, is engaged in an evolutionary arms race with its only known significant predator, the Common Garter Snake, Thamnophis sirtalis. In regions where snakes are absent (such as some islands near Vancouver Island, Canada), newt toxicity is low to absent, whereas in sites where toxicity-resistant snakes are common (various sites in California and Oregon), newt toxicity is high to very high. The authors of a new paper (Hague et al. 2016) studied newts in southeast Alaska, where snakes are absent, and as expected, toxicity levels were low at most sites examined. However, puzzling variation was found. In one lake on Wrangell Island, no toxicity was found, but newts from another lake on the same island displayed surprisingly high levels, rivaling those in some areas where snake predators have high toxin resistance. Various explanations are offered, but reciprocal selection does not fully explain the toxicity variation in newts (David B. Wake).
See another account at californiaherps.com.
This species ranges from southwestern Alaska, along the coast of North America through British Columbia, Canada, Washington, Oregon, and California to the San Francisco Bay area. Terrestrial habitat is forests in hilly or mountainous areas, occasionally grasslands or pastures. Aquatic habitat includes seasonally ephemeral ponds, as well as lakes and sluggish areas of streams. Rarely found in fast-flowing water (Riemer 1958; Stebbins 1985; Petranka 1998).
Populations in Idaho are considered introduced by the Idaho State Department of Fish and Game (https://idfg.idaho.gov/species/taxa/15503).
Rough-skinned newts migrate annually to and from their aquatic breeding sites. Migration occurs primarily in rainy weather when the temperature is >5º. Breeding season varies with latitude, and has been recorded over most months of the year with a peak from March to early May. Courtship includes a period of amplexus of the female by the male. During amplexus, the male rubs his head over the females. Fertilization is internal by means of a spermatophore, deposited by the male on the substrate and picked up by the female in her cloaca. Oviposition takes place shortly after mating. Eggs are layed singly, attached to submerged vegetation, rootlets, or detritus. (Nussbaum and Brodie 1981; Petranka 1998). Development time and length of the larval period vary geographically. Larvae eat small aquatic invertebrates. Prey of adults includes aquatic and terrestrial invertebrates, and also amphibian larvae and eggs (Petranka 1998).
While T. granulosa is the most toxic newt in North America, all species of Taricha possess the potent neurotoxin known as tetrodotoxin. This serves the newt as an antipredator defense, and is also harmful to humans (Brodie et al. 1974; Petranka 1998). Despite their toxicity, newts are subject to predation by racoons and garter snakes (Thamnophis.) Thamnophis sirtalis is a specialist predator on newts and has evolved resistance to the tetrodotoxin (Brodie and Brodie 1990; Petranka 1998; Motychak et al. 1999). When harassed, Taricha assume the “unken reflex” where the head is raised, the tail is turned up and held straight over the body, the limbs are extended, and the eyes are closed (Riemer 1958; Brodie 1977). This action exposes the bright aposomatic coloration found on the newt's belly. The exact pattern of this reflex is a species-specific character, distinguishable from sympatric T. torosa, which holds the tail straight, while T. granulosa curls the tip (Stebbins 1985; Petranka 1998).
Regional differences exist in the preferred habitat of T. granulosa. Populations in the Cascades and Coast Range of Washington are most dense in mature and old-growth forests (Aubry and Hall 1991; Corn and Bury 1991), while popuations in the Oregon Cascades are relatively dense in younger stands. These differences should be considered for species management. Logging has a negative impact on the terrestrial habitat and migration corridors of this species and this should be investigated in detail (Petranka 1998).
The most toxic newt, Taricha granulosa has been responsible for severe illness and even death of people who have eaten it (e. g., Petranka 1998). Care should be taken when handling these animals. Wash hands after holding newts and do not touch eyes or mouth area.
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)
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
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
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
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 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
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.
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 )
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 )
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
Other Habitat Features: suburban ; agricultural ; riparian
Little is known about the longevity of T. granulosa, but marked specimens have been recaptured after 17-18 years.
Status: wild: 18 (high) years.
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
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.
Anti-predator Adaptations: aposematic
The Crater Lake newt or Mazama newt, Taricha granulosa mazamae, is a subspecies of the rough-skinned newt. Its type locality is Crater Lake, Oregon. Similar newts have been found in Alaska, but their identity is unclear.
The Crater Lake newt or Mazama newt, Taricha granulosa mazamae, is a subspecies of the rough-skinned newt. Its type locality is Crater Lake, Oregon. Similar newts have been found in Alaska, but their identity is unclear.
The Crater Lake newt population is under threat due to predation from crayfish and rainbow trout that have been introduced into the lake.
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. 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. 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. Males can be distinguished from females during breeding season by large swollen vent lobes and cornified toe pads.
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.
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. 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 person died after ingesting a newt.
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. 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. 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. 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. 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.
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.
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.
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.
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.