C. Michael Hogan PhD
November 4, 2008
This lunged newt is one of the most abundant amphibians in the northwestern USA. Its life-cycle responds to the winter wet season of the far western continent, with adults making their way from quiescent hiding to the filling streams and ponds for mating. The Rough-skinned Newt discourages predators with tetrodotoxin, one of the most highly toxic chemicals in nature. Lifespan of an individual may be ten to thirteen years.
SUBSPECIES AND DISTRIBUTION
T. granulosa occurs from Admiralty Island in Alaska southward to the Santa Cruz Mountains in California at elevations below 2800 meters. Inland the species is found along the east slopes of the Washington Cascades southerly to the western slopes of the Sierra Mountains as far south as Magalia in Butte County. Disjunctive populations are found near Thompson Falls, Montana and Moscow, Idaho. There are two subspecies of Rough-skinned Newt: T. g. granulosa has the most widespread range, with certain populations in Oregon and California manifesting dark dorsal blotches. T. g. mazamae occurs only in the Crater Lake basin of Oregon and Gravina Island, Alaska. The latter subspecies is termed Crater Lake newt, and it is morphologically characterized by darker coloration encroaching on the underside, and sometimes presenting dark dorsal patches.
Adults attain a length of 10 to 20 cm, with snout to vent dimension of six to nine cm. This lunged species is of stocky stature and clad with somewhat dry and granular skin. It ventrum is typically brown or reddish brown, with a starkly contrasting orange to yellow underneath; costal grooves are lacking. Certain populations manifest dark patches on the ventrum or venter. Toe tips have a horny black coating. (Behler) The palatine bone has a V-shaped tooth pattern. Lower eyelids have a dark appearance. In the breeding season the skin of males becomes smoother, the cloaca swollen and rough nuptial excrescences develop on the feet undersides, the latter effect assisting in gripping on females during amplexus. The males also have a flattened tail that enables swimming power and. Lower eyelids are dark, but the irises are yellow. The pond type larvae present a brown coloration with a row of lighter blotches on the flanks.
Adults are carnivorous, consuming of a gamut of aquatic and terrestrial invertebrates as well as amphibian eggs and larvae. (Chandler) Invertebrate prey include insecta, crustaceans (especially amphipods, copepods, and ostracods), arachnids, mollusks (e.g.freshwater bivalves), annelids (oligochaetes and leeches), and freshwater sponges. Adults are nocturnal feeders that chiefly consume soft-bodied prey, which lack swiftness. Some feeding occurs during the day, allowing observers to document adults slowly stalking prey, then swiftly capturing it by suction feeding.. The olfactory sense is utilized used for finding concentrations of hatchling tadpoles and certain other prey. Vertebrates consumed include eggs of conspecifics, including the Taricha tortosa, Rana aurora, Pseudacris regilla, and Bufo boreas, and also conspecific larvae and tadpoles of Rana boylii. Younger larvae prey on protozoans, scraped from vegetation and rocks. Gradually larval feeding moves to larval insects (chironomids and corixids) and minute crustaceans (ostracods, copepods, and daphnids). The final larval stage sometimes consumes smaller larvae of its own species.
BREEDING AND LIFE CYCLE
Aestivation occurs by adults hiding in cool crevices or subterranean burrows over the warm season. As early as October males begin to migrate toward breeding waters, triggered by the first rains of the season; correspondingly, females migrate in groups to these slow moving streams and shallow pond edges. (Pimentel) Directional sense is governed by olfactory senses and humidity, as well as downslope sense and some evidence of sun-compass use. Higher latitudes generally yield later breeding times, although some high latitude, high elevation habitats may actually generate late summer migration, in the case of permanent lake settings.
Mating may occur as early as October in milder, low elevation habitats, but is carried out in winter and spring for areas taking longer for ponds to thaw or sufficient surface waters to accumulate. Mating is generally aquatic with the male in a superior position. Amplexus occurs aquatically, after which the male dismounts and deposits a spermataphore. Oviposition typically occurs in the same quiet waters used for breeding approximately 14 days after mating. Females typically lay eggs singly on submerged vegetation about five to ten cm below the water surace. Eggs are about two mm in diameter during the morula stage and three mm at a later stage, with the animal pole showing light tan and vegetal pole being cream-color; moreover, each egg has three envelopes in addition to the vitelline envelope. Embryonic development requires 20 to 26 days.
The pond type larvae manifest sizable tail fins and bushy gills. Hatchlings have balancers, a pair of ventrolateral appendages projecting from the side of the head and developing prior to the forelimbs. Hatchling length varies between seven and 12 mm. Some larvae transform by early fall of the calendar year of their hatching, but others overwinter aquatically, transforming the subsequent summer. (Marks)
Following metamorphosis, juveniles become terrestrial and migrate distances of hundreds of meters, searching out subsurface resting places. Juveniles lead a chiefly fossorial existence, embedding under deep moist substrate, although they are active on the ground surface during rainy interval. After initial aestivation, these juveniles reach sexual maturity between age two and four, at which time they will return to waters for their first breeding.
Some adults retain gills or gill vestiges (a phenomenon of neoteny) and remain in permanent surface waters year-round. Vestiges of gills have been observed on certain populations including Latah County, Idaho and Kittitas County, Washington. Paedomorphism has been observed at some high elevation lakes in the Cascade Mountains. Some of these perennibranchiate populations have an unusually high proportion (87 to 100 percent) of individuals retaining gills or gill stubs, with most individuals possessing three gill pairs. Gill rami were evident, but fimbriae typically were absent. When such neotonous animals were observed in the laboratory at 20 degrees C, they resorbed gill tissue, even without exposure to exogenous thyroxin, suggesting that the natural cold water is associated with gill retention. In general, perennibranchiate occurrence is associated with winter temperatures below freezing and deep surface waters.
HABITAT AND ECOLOGY
Toward the end of the wet season adults migrate from surface waters to upland habitat in oak woodlands, coniferous forests and sometimes grassland. (Nussbaum) A typical example of this habitat is an oak woodland of the California Outer North Coast Range. Their burrows must keep the animal below its critical thermal maximum of 35 degrees C. Most burrow within one kilometer of their aquatic breeding waters, which may be slightly basic to relatively acidic. In the drier parts of the range in California, adults spend most of the year terrestrially, especially when intermittent streams or vernal pools are the aquatic base. At the opposite extreme, on Vancouver Island, adult males are aquatic throughout most of the year, contrasted with females, who exit surface waters at the start of the rainy season, migrate to land for the winter and return to breeding waters in the spring. Another lifestyle is found at Marion Lake, where both sexes make landfall in autumn, spending the entire winter terrestrially. Torpor sets in below a temperature of five decrees C, but winter movement out of ponds is important to avoid freezing
This non-territorial species actually can be found in aggregations in many instances. While typical organism densities are in the range of 2500 newts per hectare, some agglomerations have amazing densities; for example a cluster of both sexes numbering 5000 was seen on a side channel of Clear Lake. T. granulosa is sympatric with T. torosa and and T. rivularis over parts of its range, with Sonoma and Mendocino Counties comprising the overlap of the three. The paedomorphic form of Ambystoma gracile is syntopic with T. granulosa at Crater Lake. T. granulosa may also associate with Ambystoma macrodactylum, in locations such as Benton County, Oregon. A common associate in coastal California Black Oak dominated woodlands is the California Giant Salamander. Other common forest tree associates are California Buckeye and understory species Toyon and Whitebark raspberry.
The only common predator of the Rough-skinned newt is Thamnophis sirtalis, since it can tolerate tetrodotoxin, one of the most highly toxic non-protein toxins known. This chemical is found in the skin, muscles and ovaries of T. granulosa. Occasionally, other species such as Rana catesbeiana are known to have consumed T. granulosa, but in virtually all cases die from the toxicity. On land, adults manifest a posture called the unken reflex when approached by a predator, a stiffened U-shaped posture displaying bright orange ventrum. During this display, eyes close, limbs extend, the head raises up, the back lowers, and the tail raises up and forward over the body. A release of tetrodotoxin skin secretions occurs as part of the unken reflix.
Protozoans, nematodes, trematodes, acanthocephalans, and leeches are known parasites of T. granulosa. Protozoan flagellates Trypanosoma ambystomae and T. granulosae have been found in the blood of Rough-skinned Newts in Linn County, Oregon and Sonoma County, California respectively. Hexamita ovatus, Karotomorpha swezyi, and Tritrichomonas augusta were observed in T. granulosa in Northern California coastal counties.
The trematode Megalodiscus microphagus attack the Rough-skinned newt in much of the northwest USA, with aquatic snails Menetus cooperi and Gyraulus spp. being intermediate hosts; cercariae emerge from the snails and encyst on the adult T. granulosa skin, which is shed and ingested by the newt, producing Metacercariae in the newt digestive tract. Infection rates of these trematodes is quite high in T.granulosa, often affecting most of the adults. The trematode, Cephalouterina dicamptodonti, was isolated in adult Rough-skinned newts in British Columbia, and Megalodiscus americanus was found in the digestive tract of aquatic adults in Oregon; moreover, Brachycoelium salamandrae has been seen in the gut. Ribeiroia ondatrae has also been isolated in T. granulosa, with an intermediate of the genus Planorbella hosting rediae and cercariae stages. While Ribeiroia produces morphological abnormalities in some amphibians, its role in T. granulosa genetic defects is unclear.
The nematode species Megalobatrachonema moraveci was isolated in the gut of adult T.granulosa on Vancouver Island; the nematode species Cosmocercoides dukae and Hedruris siredonis along with species in the genus Neoechinorhynchus have also been found in Rough-skinned newts. Leeches of the family Glossiphonidae have been found widely in the oral cavities of T. granulosa; these occurrences are seasonal, but widespread in the spring to mid-summer.
Rough-skinned Newts are threatened by habitat fragmentation, especially when drainages are disturbed or cut off from upland migration paths. Clearcutting of forests is also a threat, not only due to decrease in habitat, but also increase of UV-B radiation which is implicated with adverse effects on T. granulosa, via the release of excessive corticosterone in this newt. Conversion of oak woodland and mixed conifer forests also pose a threat, in that monocultures such as Douglas fir are less supportive of robust T. granulosa populations as reported by Cole, Gomez and my own observations.
Application of urea is widespead over much of the range of T. granulosa for the purpose of enhancing timber production. Rough-skinned newts are less affected by urea than, for example, Plethodon vehiculum, Rhyacotriton variegatus, Bufo boreas and Rana cascadae, all of whom suffer appreciable mortality increases upon dermal exposure.
* John L. Behler (1996) Field Guide to North American Reptiles and Amphibians, National Audubon Society, Alfred A. Knopf, New York
* Sharyn B. Marks and Darrin Doyle (2005) Taricha granulosa in "Amphibian Declines: The Conservation Status of United States Species", Michael Lannoo ed., University of California Press
* A.C. Chandler (1918) The western newt or water-dog, a natural enemy of mosquitos, Oregon Agricultural College Experimental Station Bulletin 152, Corvallis, Oregon
* R.A. Pimentel (1960) Inter and intra-habitat movement of the Rough-skinned newt, American Midland Naturalist 63:470-496
* R.A. Nussbaum, E.D. Brodie Jr. and R.M. Storm (1983) Amphibians and reptiles of the Pacific Northwest, University Press of Idaho, Moscow, Idaho
* E.C. Cole, W.C. McComb, M. Newton, C.L.Chambers and J.P. Leeming (1997) Response of amphibians to glycophosate application in the Oregon Coast Range, Journal of Wildlife Management, 61:656-654
* G.M. Gomez (1993) Small mammal and herpetofaunal abundance in riparian and upslope areas of five forest conditions, Masters Thesis, Oregon State University, Corvallis, Oregon