Rough-skinned Newt, Roughskin Newt, Northern Rough Skin Newt, Crater Lake Newt
© 2004 Henk Wallays (1 of 132)
Taricha granulosa (Skilton, 1849)
Sharyn B. Marks1
1. Historical versus Current Distribution. Rough-skinned newts (Taricha granulosa) have the widest distribution among the three species of Taricha, ranging from the Coast Range mountains in Santa Cruz County, California, to Admiralty Island, Alaska (Myers, 1942b; Riemer, 1958; Nussbaum and Brodie, 1981; Stebbins, 1985; Petranka, 1998). They extend inland to the east slope of the Cascades in Washington and along the west slope of the Sierra Nevada in northern California. Isolated and extremely small populations exist near Moscow, Idaho, and Thompson Falls, Montana, and may be the result of introductions (Nussbaum et al., 1983; Monello and Wright, 1997). Rough-skinned newts occur from sea level to about 2,800 m in elevation. No recent studies have investigated the distribution of this species, thus, the limits of the current distribution are uncertain.
2. Historical versus Current Abundance. Rough-skinned newts are one of the most common salamanders in the Pacific Northwest (Nussbaum et al., 1983; Bury et al., 1991; Corn and Bury, 1991; Gilbert and Allwine, 1991). Gomez and Anthony (1996) compared relative abundance of herpetofauna in five forest types in western Oregon and found rough-skinned newts to be the most abundant salamander, representing 86% of salamander captures. Terrestrial adults were encountered more frequently in riparian than upslope habitats and were most abundant associated with deciduous forests. Numerous studies have examined the relationship between forest stand age and amphibian abundance, but results have been equivocal for rough-skinned newts. In the Oregon Coast Range and southern Washington Cascade Range, newts were more abundant in old-growth stands than in mature and young stands, but differences among forest age classes were not statistically significant (Aubry and Hall, 1991; Bury et al., 1991; Corn and Bury, 1991). By contrast, in the Oregon Cascade Range, newts were most abundant in young stands (Gilbert and Allwine, 1991). However, proximity to aquatic breeding sites is probably a more important factor influencing the relative abundance of this species, and probably is a confounding factor in studies examining the effects of forest age on newt abundance (Bury et al., 1991). Estimates of population size, density, and salamander biomass have been made for aquatic rough-skinned newts at Marion Lake, a small (approximately 10-ha) lake in British Columbia. Efford and Mathias (1969) estimated adult population size at 3,965 individuals, average adult density at 300/ha, and maximum adult densities to be as high as 2,700/ha near the edge of the lake. Neish (1971) estimated adult population size at 2,450 individuals and total biomass of aquatic adult newts at approximately 18 kg. Differences in population estimates are due to different methods of newt capture and data analysis and differences in the years during which the studies were conducted. Several reports of the abundance of rough-skinned newts are striking. Farner and Kezer (1953) noted an aggregation of 259 individuals (large larvae, recently metamorphosed animals, and adults), the majority of which were found under a single flat rock 0.9 m2 (approximately 9 ft2) in Crater Lake, Klamath County, Oregon. Coates (1970) observed a large aggregation (an oval cluster measuring 2 x 9.2 m) of approximately 5,000 post-reproductive males and females in a channel of water meandering through the lakebed of Clear Lake (Wasco County, Oregon). Both the Crater Lake and Clear Lake aggregations were observed in autumn.
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Timing of breeding migrations varies with latitude and elevation. Late fall migrations are characteristic of mild-winter areas (Pimentel, 1960), spring migrations characterize low altitude sites at higher latitudes (Neish, 1971; Oliver and McCurdy, 1974), and summer migrations may be seen at high elevation sites (Nussbaum et al., 1983). There may also be variation in timing associated with the permanence and depth of bodies of water used for breeding. Pimentel (1952) observed slightly later breeding migrations to temporary ponds relative to nearby permanent ponds, because the former take some time to achieve optimal depth for breeding following the onset of fall rains. Males migrate individually and generally arrive at breeding sites about 1 mo before females, which often migrate in groups (Pimentel, 1960). In general, both sexes participate in breeding migrations. However, at a site on Vancouver Island, British Columbia, only females migrate since males remain in the water throughout the year except for brief terrestrial excursions (Oliver and McCurdy, 1974). Experiments by Pimentel (1960) suggest that olfaction is important for locating breeding sites and that humidity perception and downhill slopes to ponds may be of secondary importance in this regard. Laboratory and field experiments by Landreth and Ferguson (1967a,b) demonstrate that adults locate breeding sites using a sun-compass mechanism to orient themselves in the proper direction. Also see "Seasonal Migrations" below.
ii. Breeding habitat. Mating occurs in quiet water habitats including ponds, lakes, reservoirs, drainage ditches, and slowly flowing sections of streams (Gordon, 1939; Bishop, 1947; Stebbins, 1985). The timing of breeding varies substantially over the range of rough-skinned newts. At low elevation sites in northern California, mating may occur from late December to June, with peak activity in March and April (Twitty, 1935; Stebbins, 1951). Breeding occurs in winter in western Oregon (Gordon, 1939). At moderate to high elevation lakes in northern California and Oregon, mating occurs during summer and autumn (Chandler, 1918; Farner and Kezer, 1953; Garber and Garber, 1978; Marangio, 1978).
i. Egg deposition sites. Oviposition usually occurs within a couple of weeks after mating (Storm, 1948) in the same habitats chosen for breeding. An extended oviposition season is typical (Bishop, 1947), with females at a single locality spawning or with eggs in their oviducts from late December to June in northern California (Twitty, 1942). Egg-laying usually occurs in late winter to spring in western Oregon (Chandler, 1918; Gordon, 1939), and occurs during June and July at low elevations in British Columbia (Efford and Mathias, 1969). Spawning probably occurs in autumn in most montane populations in northern California and Oregon (Chandler, 1918; Garber and Garber, 1978; Marangio, 1978). Rough-skinned newts show a stronger preference for spawning in quiet water habitats than any other species in this genus (Twitty, 1942). Females usually deposit eggs singly onto stems and leaves of submerged plants, usually within a few inches of the water’s surface (Chandler, 1918; Twitty, 1935). At approximately 1.8 mm in diameter (measured during the morula stage; Twitty, 1935), eggs are smaller than those of other members of the genus (Twitty, 1942). Bishop (1947) reports egg diameters of 1.85–2.0 mm without envelopes or an average of 3.3 mm with envelopes. Eggs appear light tan on the top (animal hemisphere) and cream on the bottom (vegetal hemisphere; Riemer, 1958) and have three envelopes in addition to the vitelline envelope. Oviposition is cyclic, occurring for a few days, followed by a period of non-laying, with this process being repeated at intervals (Oliver and McCurdy, 1974).
ii. Clutch size. No information is available on the total number of eggs laid by an individual female during the breeding season. Embryonic development is complete between 20 and 26 d (Nussbaum et al., 1983), but length of time to complete embryonic development undoubtedly varies considerably with water temperature.
i. Length of larval stage. Larvae are regarded as pond type, having bushy gills and a large tail fin (Stebbins, 1951). Balancers, a pair of ventrolateral appendages projecting from the side of the head and arising before the forelimbs develop, are always present in hatchlings (Riemer, 1958). The average size of hatchlings is variable, ranging from 7.6–12 mm TL at different localities (Twitty, 1935; Bishop, 1947; Stebbins, 1951; Riemer, 1958). There is also variation in the length of the larval period. At the same locality, larvae may transform in late summer or early fall of the year in which they were hatched (4–5 mo after hatching) or they may overwinter in the water and transform the following summer at larger size (more than a year after hatching; Bishop, 1947). Chandler (1918) and Gordon (1939) report that populations in Oregon may take two summers to complete metamorphosis. Chandler based his conclusion on his observations of two size classes of larvae at a locality in Corvallis, Oregon, suggesting that this may be due to the late breeding time at this locality. However, breeding there occurs from February–mid July, which is not particularly late relative to other low elevation populations. Two scenarios seem conceivable to explain these observations. One possibility is that there may be variation within the population, with some larvae metamorphosing after one summer (i.e., offspring of early breeding females) and others taking two summers (i.e., offspring of late-breeding females). A second possibility is that the two size classes are a direct result of the long breeding season, with the larger larvae a product of early breeding and the smaller ones a product of late breeding. Even the offspring of late breeding females may have time to metamorphose before the end of fall. At high elevations at Crater Lake, limited data suggest that two seasons of growth are necessary before metamorphosis (Farner and Kezer, 1953).
ii. Larval requirements. In the field, rough-skinned newt larvae were found to be most abundant at water temperatures ranging from 22–26 ˚C. When exposed to thermal gradients in the lab, larvae chose temperatures ranging from 17–28 ˚C (Licht and Brown, 1967).
b. Cover. Larvae hide under stones or in vegetation during the day (Pimentel, 1952; Licht and Brown, 1967).
iii. Larval polymorphisms. None reported.
iv. Features of metamorphosis. Timing of metamorphosis varies over the extensive range of this species. Furthermore, even within the same population, larvae apparently either metamorphose in their first summer (around August) or their second summer (see "Length of larval stage" above). It is difficult to compare the size at metamorphosis in different populations because authors variously report snout-vent lengths, snout-pelvis lengths, or total lengths. Larvae at Marion Lake (300 m elevation), British Columbia, metamorphose at 23 mm snout-pelvis length (Efford and Mathias, 1969) or 25–27 mm SVL (Neish, 1970). Twitty (1935) collected larvae ≤ 75 mm in TL from low elevation streams in the coast range of northwestern California . Larvae of some populations at high altitudes do not metamorphose until their second summer (June–July) at 70–75 mm TL (Bishop, 1947). Larvae at Crater Lake (1,860 m elevation) attained total lengths as great as 95 mm prior to metamorphosis (Farner and Kezer, 1953). Chandler (1918) reports that 3–4 wk are required to complete metamorphosis based on his observations of larvae in Corvallis, Oregon.
v. Post-metamorphic migrations. After metamorphosis, juveniles exit the water and move onto land, often migrating considerable distances (Chandler, 1918; Twitty, 1955; Efford and Mathias, 1969). Pimentel (1952) suggests that juveniles quickly seek subterranean retreats following emergence and remain there. The length of time they remain on land before returning to the water is in dispute. Chandler (1918) states that juveniles return to the water the following spring. By contrast, observations by Storm (1948), Pimentel (1952) and Efford and Mathias (1969) indicate that juveniles do not return to water the year after metamorphosis and remain terrestrial until mature. According to Twitty (1955), all species of Taricha remain on land until they reach sexual maturity in 3–4 yr.
vi. Neoteny. Adults in some populations retain gills or gill vestiges and remain in permanent bodies of water year-round. Bishop (1947) and Farner and Kezer (1953) described adults retaining varying amounts of external gill tissue at Crater Lake in Oregon; in all cases, these gills had less gill tissue than on an ordinary newt larva. Riemer (1958) reported adults with gill vestiges in San Mateo County, California, and in Latah County, Idaho. Nussbaum and Brodie (1971) described adults bearing gill remnants from Latah County, Idaho, and Kittitas County, Washington. Marangio (1978) found populations of paedomorphic rough-skinned newts at seven high elevation lakes and ponds in the Cascade Mountains of southern Oregon. Unlike other reports in which the percentage of perennibranchiate individuals was relatively low, in several of these populations the proportion of individuals retaining gills or gill stubs ranged from 87–100%. Gills were in various stages of development, with most individuals possessing three pairs. Some individuals possessed remnants of larval gill arches and gill rakers. Gill rami were present, but fimbriae generally were lacking or few in number, presumably limiting the usefulness of these vestigial gills for respiration. When these animals were held in the laboratory in aged tap water at 20 ˚C, they resorbed their gill tissue, with or without exposure to exogenous thyroxin, suggesting that the cold water temperatures experienced in nature are important for gill retention. In general, perennibranchiate individuals seem to be associated with winter temperatures below freezing and bodies of water that are deep enough that they do not dry up during the summer (Nussbaum and Brodie, 1971; Marangio, 1978); the San Mateo County specimens are a notable exception to this generalization.
D. Juvenile Habitat. Juveniles are thought to lead a predominantly fossorial existence, and Pimentel (1952) notes that they are found under deeply embedded material in moist situations. However, juveniles are active on the ground surface during wet periods, based on observations that juveniles and adults were captured in terrestrial traps in roughly equal numbers (Twitty et al., 1967b).
E. Adult Habitat. In most populations, adults migrate seasonally between terrestrial and aquatic habitats. Terrestrial adults are found in a variety of habitats such as coniferous forests, redwood forests, oak-woodland, farmlands, and grassland. Terrestrial animals spend much of their time underground in burrows, and also may be found beneath cover objects such as logs, bark, or boards (Bishop, 1947; Stebbins, 1951; Nussbaum et al., 1983). Most adults can be found in underground retreats within 400 km (1/4 m) of ponds used for breeding (Pimentel, 1960). Adults may be found crawling in the open during fall rains (Stebbins, 1951; Pimentel, 1960). Rough-skinned newts are the most aquatic of the three species of Taricha (Twitty, 1942). Aquatic habitats include lakes, ponds, roadside ditches, and slow-moving portions of streams (Stebbins, 1951; Nussbaum et al., 1983), but bodies of water lacking surrounding vegetation are avoided (Pimentel, 1960). Rough-skinned newts may be found in bogs of relatively low pH (Pimentel, 1960). The amount of time spent in aquatic versus terrestrial habitats varies with permanence of the aquatic habitat, elevation, locality, and sex. The length of time spent in aquatic habitats generally differs between the sexes, with males spending more time in the water than females (Pimentel, 1960). Furthermore, in northwestern California and western Oregon, adults breeding in permanent lakes and ponds spend more time in aquatic habitats than those occupying temporary bodies of water. At permanent ponds, males spend about 10 mo in the water, whereas females spend about 8 mo. In temporary ponds, males were present for approximately 7 mo, while females were present for only 6 mo (Pimentel, 1960). Studies of lakes in different regions of British Columbia revealed substantial differences between localities with regard to migratory behavior. In southern Vancouver Island, adult males remain mostly aquatic throughout the year, whereas females leave the pond with the onset of fall rains, overwinter on land, and migrate in spring to breeding ponds (Oliver and McCurdy, 1974). This pattern contrasts with the findings of Efford and Mathias (1969) at Marion Lake, a permanent pond on the southwestern British Columbia mainland, in which males and females all leave the water in the fall to overwinter on land. At a few localities in California, Oregon, Washington, and Idaho, permanently aquatic, perennibranchiate individuals of both sexes have been reported, mostly at high elevation sites (see "Neoteny" above). In California, adults using streams usually remain aquatic all year unless forced to leave when water flow rises during winter floods (Packer, 1961; Twitty, 1942).
F. Home Range Size. It is difficult to apply the concept of home range to this species, because adults in most populations spend part of their life in the water and part on land. To my knowledge, no investigations of home range size have been performed on terrestrial phase newts. Under certain conditions (during and after the breeding season) aquatic newts form large aggregations, which may serve as a “home range” for the animals inhabiting them, in the sense that displaced individuals rapidly return to the site from which they were captured, traveling ≤ 550 m to do so (Efford and Mathias, 1969; Neish, 1970). However, this philopatry is of a temporary nature, because these concentration centers tend to shift over time. Mark-recapture studies of these aquatic newts indicate that movements of individuals from one area to another is typical; most recaptured individuals showed at least one location shift, and at least one animal was caught in 7 (of a total of 12) areas in the lake over a 21-wk period (Neish, 1970).
G. Territories. Territoriality has not been reported for this species.
H. Aestivation/Avoiding Dessication. Terrestrial newts spend the summer beneath surface cover objects, in rock crevices, inside decaying logs, and in other animals’ burrows (Stebbins, 1985), during which time they are thought to achieve a physiological state of quiescence (Pimentel, 1960). Subterranean retreats offer lower environmental temperatures and higher humidity relative to surface environments. This coupled with a reduced metabolic rate (associated with quiescence) allows for a decreased rate of evaporative water loss through the salamander’s skin and lungs. The critical thermal maximum (CTM) for rough-skinned newts is about 36 ˚C (based on laboratory specimens acclimated at 20 ˚C; Hutchison, 1961). At the CTM, locomotion becomes disorganized and animals lose their ability to escape from life-threatening situations; from an ecological and evolutionary perspective, the CTM is the lethal temperature.
I. Seasonal Migrations. Based on studies of several low elevation permanent and temporary ponds in western Oregon and northwestern California, Pimentel (1960) made the following generalizations regarding seasonal migrations in rough-skinned newts. In most populations, individuals breed every other year and there is no evidence that non-reproductive animals migrate to water; these individuals remain on land for approximately 18 mo between breeding periods. Reproductive adults exhibit four basic types of movements: (1) sporadic movements following emergence from subterranean retreat sites; (2) migration to aquatic breeding sites; (3) wandering movements between aquatic and surrounding terrestrial habitats; and (4) post-reproductive migration to subterranean retreats.
i. Sporadic movements. Rainfall is the primary stimulus that initiates emergence from subterranean retreats. After surfacing, adults exhibit sporadic and apparently non-directional movements that are estimated to last from 6–8 wk and may be associated with foraging. Juveniles and non-reproductive adults may be involved in this period of sporadic activity. For reproductive individuals, sporadic movements are followed by a directional migration to breeding sites.
ii. Migration to breeding sites. Rainfall is the triggering mechanism initiating movement towards ponds. However, temperatures must not be too low, or movement will not occur. Newts will not migrate toward water until they have achieved a certain degree of sexual development in preparation for mating. The final approach of animals to ponds is not random but occurs along definite “highways” or preferred entrance routes. These paths may extend for as long as 400 km (0.25 mi), but length varies with locality; distances of ≤ 183 m (200 yd) are probably more typical.
iii. Wandering movements. Once in the water, some individuals exhibit “wandering,” which involves exit from and return to the breeding habitat. The reasons for this behavior are unknown. These movements are usually limited to short distances from the ponds, and the duration of time spent on land is generally brief (only lasting several days), but one male remained out of the pond for as long as 51 d. Wandering movements tend to occur in greater frequency during periods of warm rainfall. A similar percentage of males and females engage in wandering movements, but males tend to wander more frequently and for a greater duration of time than females.
iv. Post-reproductive migration. Post-breeding migrations from breeding sites to terrestrial retreats are associated with high water temperature and lowering water level. Both factors are important for animals in temporary ponds, but only the former is relevant for animals in permanent bodies of water. These final exits from the pond occur later in spring and are shorter in duration than the breeding migration to the ponds. Vision and movement toward dark horizons are thought to be important mechanisms for locating underground retreats (Pimentel, 1960).
J. Torpor (Hibernation). The activity of rough-skinned newts is affected by cold temperatures in aquatic and terrestrial habitats. Movement does not occur at air or water temperatures below 5 ˚C (Pimentel, 1960). Nussbaum and Brodie (1971) reported finding torpid newts at the bottom of an Idaho pond in early spring when water temperatures ranged from - 1 ˚C to + 1 ˚C, suggesting that adults probably overwinter in the pond in a torpid state. By contrast, in the Cascade Range, most adults leave the water after spawning and move to underground retreats to hibernate during winter (Chandler, 1918). At low elevations in Oregon, the behavior is a bit different. Adults emerge from the water in October–November and wander about on land, then curl up in cavities under stumps, logs, or stones in November–December to spend the cold part of the winter, sometimes forming aggregations of > 12 animals. They emerge from their underground retreats on warm days to forage. Chandler (1918) speculates that in the northern portion of their range, rough-skinned newts leave the water to escape being frozen into small pools in their aquatic habitats.
K. Interspecific Associations/Exclusions. Over parts of their range in northwestern California, rough-skinned newts are sympatric with California newts (T. torosa) and/or red-bellied newts (T. rivularis), with all three species co-occurring in Sonoma and Mendocino counties. Their interactions are complex, may be correlated with habitat and topography, and vary even over a fairly small geographic area. Twitty (1942) made frequent observations over many years at several different sites in the vicinity of Ukiah, Mendocino County. In this area, the Russian River flows through a narrow valley and receives tributaries from mountains to the east and west. Rough-skinned newts and red-bellied newts were found coexisting in and around mountain brooks flowing from the western side of the valley at certain times of year. Both species entered the water for breeding around the same time, but rough-skinned newts mated and laid their eggs in slower stream sections. Interestingly, California newts were not observed in these streams, even though they contained microhabitats similar to those chosen for spawning by this species in other parts of its range. By contrast, at a nearby site on the eastern side of the valley, rough-skinned newts and California newts were found together in two adjacent artificial reservoirs supplied by a small tributary of the Russian River. Only one adult male red-bellied newt was seen here, even though portions of the stream seemed suitable for this species. At a small spring-fed pool north of Ukiah, only rough-skinned newts were found, even though California newts use these same types of habitats in other parts of its range. This pattern of exclusion of California newts by rough-skinned newts has also been reported at ponds in other parts of their range.
Where their distributions overlap, rough-skinned newts and paedomorphic northwestern salamanders (Ambystoma gracile) are frequently syntopic in ponds and lakes. Their interactions have been studied in the Cascade Mountains in Oregon and at Marion Lake, British Columbia. These species are similar in their habitat use and diets (Efford and Mathias, 1969; Neish, 1971; Efford and Tsumura, 1973; Taylor, 1984), so there is potential for competition between them. In the Oregon Cascades, abundance of rough-skinned newts was not related to abundance of northwestern salamanders; however, in lakes with high densities of northwestern salamanders, rough-skinned newts were significantly smaller in length and weight relative to individuals from lakes with low densities of northwestern salamanders. If competition between these two species is occurring, there is neither evidence of resource partitioning nor numerical release when competition is reduced, counter to the predictions of competition theory (Taylor, 1984). In Marion Lake, habitat use by northwestern salamanders and rough-skinned newts was similar, but the distributions were different in that the former species had a widely dispersed, stable distribution, while the latter had a temporally unstable and highly contagious distribution, with individuals frequently forming large aggregations (Neish, 1971). Trout frequently co-occur in lakes with rough-skinned newts and northwestern salamanders, but the abundance of rough-skinned newts is not related to the presence of trout, perhaps not surprisingly since trout do not ordinarily prey on rough-skinned newts (but see "Feeding Behavior" below; Taylor, 1984). Rough-skinned newts also may associate with long-toed salamanders (Ambystoma macrodactylum); these two species were found together under rocks and driftwood along the shore of Crater Lake in the Oregon Cascades (Farner and Kezer, 1953) and they have been reported to co-occur in a pond in Benton County, Oregon (Pimentel, 1960). It is likely that they coexist in other parts of their range where they overlap. Stomach content analysis of shoreline Crater Lake specimens reveals that these 2 species have different feeding habits, at least during terrestrial existence (Farner, 1947).
L. Age/Size at Reproductive Maturity. Rough-skinned newts are thought to be reproductively mature at 4–5 yr (Chandler, 1918; Efford and Mathias, 1969). Size at reproductive maturity varies considerably between populations, with adult SVLs ranging from 5.6–8.7 cm (Stebbins, 1985). Males tend to be larger than females (Neish, 1970; Nussbaum et al., 1983; Taylor, 1984). Body size may be linked to mating success; males in amplexus or attempting to gain amplexus were found to be significantly larger than males not engaged in sexual activity (Janzen and Brodie, 1989). During the breeding season, males undergo substantial morphological change, while little change is observed in females. Breeding males develop smooth, turgid, lighter-colored skin; swollen cloacal lips; prominent tail crest; and nuptial excrescences on the underside of hands and feet (Oliver and McCurdy, 1974). In breeding females, the skin is smoother and lighter-colored relative to the terrestrial phase, the cloacal lips appear as a small conical elevation, and the tail crest is not as pronounced as it is in males (Riemer, 1958). The frequency of reproduction varies among populations. Adults breeding at Oak Creek pond and Peavy Arboretum pond near Corvallis, Oregon, reproduce on alternate years (Pimentel, 1960). However, at Marion Lake in British Columbia, adults are thought to reproduce annually (Efford and Mathias, 1969).
M. Longevity. The average longevity is estimated to be 12 yr, based on the size of animals and growth rates calculated from mark-recapture studies at Marion Lake, British Columbia (Efford and Mathias, 1969).
N. Feeding Behavior. Adults feed mostly on soft-bodied, slow-moving prey, though they also may feed on sedentary animals (Chandler, 1918). Direct observation and examination of stomach contents indicates that most feeding takes place at night (Chandler, 1918; Efford and Mathias, 1969; Neish, 1970), but at least in some localities, feeding takes place throughout the day (Kelly, 1951). Adults will approach a prey item slowly and deliberately, and then quickly snap at it (Chandler, 1918). Suction feeding is used for capture of most prey, though large prey may be grasped with the jaws (Neish, 1970). Visual, tactile, and olfactory cues are important for locating and capturing prey (Chandler, 1918; Neish, 1970). Based on observations made during feeding experiments, Chandler (1918) concluded that conspicuous movement of the prey is important in eliciting feeding behavior, but that individuals may also learn to identify the forms of particular prey items and search specifically for those prey. Olfactory cues are used for locating high concentrations of prey (Neish, 1970), such as hatchling tadpoles. The adult diet consists of a wide range of aquatic and terrestrial invertebrates as well as amphibian eggs and larvae. Invertebrate prey include crustaceans (especially amphipods, copepods, and ostracods), insects, arachnids (spiders and mites), mollusks (gastropods, small freshwater bivalves), annelids (oligochaetes and leeches), and freshwater sponges (Chandler, 1918; Farner, 1947; Evenden, 1948; Packer, 1961; White, 1977; Taylor, 1984). Vertebrate prey consists of amphibian eggs and larvae (Chandler, 1918; Evenden, 1948; Pimentel, 1952; Neish, 1971; Nussbaum et al., 1983; Blaustein et al., 1995; Rathbun, 1998), including eggs of conspecifics, long-toed salamanders, northwestern salamanders, northern red-legged frogs (Rana aurora), Pacific treefrogs (Pseudacris regilla), and western toads (Bufo boreas), conspecific larvae, and tadpoles of northern red-legged frogs and foothill yellow-legged frogs (Rana boylii). Small fishes may be eaten on the rare occasions when they can be caught; upon being collected, a rough-skinned newt regurgitated a 7.5-cm- (3-in-) long rainbow trout (Pimentel, 1952). Algae and plant matter are found in stomachs (Evenden, 1948; Kelly, 1951), but apparently these are not digested and probably are consumed incidentally with animal prey (Kelly, 1951). Although rough-skinned newts have been considered generalist carnivores, feeding on any soft-bodied prey they encounter and which will fit in their mouths (Pimentel, 1952; White, 1977), there is some evidence for variation between adults regarding food preferences. Chandler (1918) found variation in stomach contents between individuals collected at the same time from the same stream pool; for example, at a couple of localities, most individuals fed on small, shelled mollusks, whereas a few individuals fed almost exclusively on insects. However, in the absence of information on sample sizes or statistical analysis, it is difficult to evaluate the significance of these findings. There are no data concerning the diet of juveniles, but presumably it is similar to that of larvae (see "Food" under "Larval requirements" above) and adults.
O. Predators. As a consequence of being highly toxic, these rough-skinned newt adults have few predators. Their only regular predators are common garter snakes (Thamnophis sirtalis) and rough-skinned newts themselves. Common garter snakes frequently prey on larval and adult newts (Storm, 1948; Farner and Kezer, 1953; Brodie, 1968b; Gregory, 1978; Nussbaum et al., 1983) and are resistant to the effects of tetrodotoxin (see "Anti-Predator Mechanisms" below). There is a single report of a juvenile Oregon gray garter snake (Thamnophis ordinoides hydrophila) having eaten a small newt larva (Fitch, 1936). Most snakes do not prey on rough-skinned newts. Nine of ten species of snakes refused to consume newts in laboratory trials (Brodie, 1968b). Rough-skinned newts regularly eat conspecific eggs and larvae (Chandler, 1918; Evenden, 1948; Pimentel, 1952; Nussbaum et al., 1983). There are scattered reports of newts being eaten by fishes, American bullfrogs (Rana catesbeiana), and birds, but in most of these cases the individuals that had consumed the newts were found dead, presumably due to the effects of tetrodotoxin. Newts have been found in the stomach of black bass (probably Micropterus salmoides), rainbow trout (Oncorhynchus mykiss), and catfish (Siluriformes; Chandler, 1918; Vincent, 1947; Brodie, 1968b). The catfish was found dead with the tail of an adult newt protruding from its mouth (Brodie, 1968b). Apparently, at least in some localities, trout regularly consume newts without lethal consequences. There are several reports of rainbow trout caught with rough-skinned newts in their stomachs (Vincent, 1947; Pimentel, 1952; Twitty, 1966) suggesting that at least some rainbow trout are resistant to ingestion of tetrodotoxin. By contrast, in Marion Lake in British Columbia, newts were never found in the stomachs of rainbow trout, in spite of detailed investigations of the diets of these fishes (Efford and Mathias, 1969). Newts have been used as bait by black bass fisherman (Twitty, 1966), but whether these fish regularly feed on newts under natural conditions and their degree of resistance to tetrodotoxin is unknown. An American bullfrog was found dead with an adult newt in its stomach, but bullfrogs are non-native in Oregon, and because these frogs had only recently been introduced into the pond at the time the predation event occurred, this species probably had no previous experience with rough-skinned newts (Brodie, 1968b). Adult newts have been found in the stomachs of dead ducks (Storm, 1948; Nussbaum et al., 1983) and dead pied-billed grebes (McAllister et al., 1997); chickens (Gallus domesticus) have been reported dead after consuming newts (Storm, 1948). Humans have occasionally been known to consume newts (under the influence of alcohol and peer pressure) and are highly susceptible to the effects of tetrodotoxin, sometimes with lethal results (Brodie et al., 1974b; Bradley and Klika, 1981).
P. Anti-Predator Mechanisms. Rough-skinned newts possess a variety of anti-predator mechanisms that include body posture, aposematic ventral coloration, and chemical defense. Adults are dark-colored dorsally and bright orange ventrally. The brown or black dorsum is cryptic in many terrestrial and aquatic situations. When threatened by a predator, adults display a characteristic body posture called the unken reflex, a rigid U-shaped posture that reveals the bright orange ventral coloration (see Petranka, 1998). During the unken reflex, eyes are closed, limbs extend laterally, the head is raised vertically, the back is depressed, and the tail is raised forward over the body (Stebbins, 1951; Riemer, 1958; Johnson and Brodie, 1975; Brodie, 1977). A release of toxic skin secretions accompanies the defensive posture. The brightly colored venter is a warning to predators that the newt is toxic and unpalatable. The unken reflex is an aposematic cue that elicits avoidance by birds; it has been demonstrated experimentally that the posture plus ventral coloration is a stronger aposematic cue than ventral coloration alone (Johnson and Brodie, 1975).
If the predator is not deterred by the unken reflex, the newt must rely on chemical defense. Adults possess tetrodotoxin (sometimes referred to as tarichatoxin), a potent neurotoxin that is concentrated in the skin, ovaries, muscles, and blood of adults (Wakely et al., 1966, based on studies of California newts). Tetrodotoxin is one of the most toxic non-protein substances known, and it also occurs in pufferfishes and relatives (suborder Tetraodontoidae; Buchwald et al., 1964; Mosher et al., 1964). The skin from adult rough-skinned newts is several times more toxic than skin from other species of Taricha (Brodie et al., 1974b). Tetrodotoxin is also present in the eggs of all species of Taricha at levels of toxicity equal to that of the skin of adult California and red-bellied newts (Mosher et al., 1964; Brodie et al., 1974b). Nussbaum et al. (1983) state that tetrodotoxin is present in the skin of larvae, but this conflicts with studies on California newts that conclude that larvae possess little or no toxin (Twitty, 1937). Brodie (1968b) studied the effects of tetrodotoxin on a variety of potential predators and found that all test subjects force-fed adult newt tissue (amphibians, birds, and reptiles) or injected with skin extract (mammals) are susceptible to the toxin, exhibiting symptoms including muscular weakness, loss of righting reflex, convulsions, gasping, gaping, regurgitation, flaccid paralysis, decrease in blood pressure, and continuous heartbeat after cessation of respiration. White mice were killed in < 10 min by as little as 0.0002 ml of skin extract taken from the dorsum of rough-skinned newt adults; other mammals and birds are susceptible to similar relative amounts of toxin. Rough-skinned newts were susceptible to tetrodotoxin, but only at high doses. Most snakes were roughly 200 times more resistant than white mice, and garter snakes were 2,000 times more resistant. In contrast to snakes, southern alligator lizards (Elgaria multicarinata) were highly susceptible to tetrodotoxin.
Different species of garter snakes on Vancouver Island vary with respect to their susceptibility to tetrodotoxin. When force-fed whole newts, western terrestrial garter snakes (T. elegans) and northwestern garter snakes (T. ordinoides) showed apparent loss of motor function, though effects were non-lethal and recovery was complete within 3 d. By contrast, most common garter snakes were unaffected, though there was variability between individuals with regard to tetrodotoxin susceptibility (Macartney and Gregory, 1981). Brodie and Brodie (1990) also reported intrapopulational variation in tetrodotoxin resistance in a population of common garter snakes in Oregon that feeds on newts, and they showed that the degree of tetrodotoxin resistance has a genetic basis. There is also interpopulational variation in tetrodotoxin susceptibility. Common garter snakes from a population co-occurring with rough-skinned newts were much more resistant to tetrodotoxin than those from a population outside the range of the newt (Brodie and Brodie, 1990). There is considerable variation in the degree of toxicity of rough-skinned newts in different parts of their range. Skin extracts from Vancouver Island newts were at least 1,000 times less toxic than those of newts from the Willamette Valley of Oregon. The degree of tetrodotoxin resistance in populations of common garter snakes is roughly correlated with the degree of toxicity of co-occurring populations of rough-skinned newts. Common garter snakes are highly tetrodotoxin-resistant in the Willamette Valley, where newts are highly toxic; whereas on Vancouver Island, common garter snakes have relatively low tetrodotoxin resistance, only slightly higher than conspecifics occurring outside the range of rough-skinned newts (Brodie and Brodie, 1991).
Q. Diseases. None have been reported.
R. Parasites. Adults are parasitized by protozoans, trematodes, nematodes, acanthocephalans, and leeches. Most of the accounts simply report the presence of a particular parasite; only a few studies attempt to correlate the presence of these parasites with the biology of the host.
i. Protozoans (Kingdom Protista). Several flagellates (Phylum Sarcomastigophora, Subphylum Mastigophora) have been reported. Trypanosoma ambystomae and Trypanosoma granulosae have been found in the blood of rough-skinned newts from Linn County, Oregon, and Sonoma County, California, respectively (Lehmann, 1955, 1959). Hexamita ovatus, Karotomorpha swezi, and Tritrichomona augusta were found in the cloaca in specimens from Marin and Sonoma counties, California (Lehmann, 1960).
ii. Trematodes (Kingdom Animalia, Phylum Platyhelminthes, Class Trematoda). Infestations of the trematode Ophioxenos microphagus (= Megalodiscus microphagus) have been reported at a few localities in Oregon, Washington, and British Columbia (Macy, 1960; Efford and Tsumura, 1969; Moravec, 1984; Beverly-Burton, 1987). The aquatic snails Menetus cooperi and Gyraulus sp. serve as intermediate hosts (Macy, 1960), and cercariae emerge from the snails and encyst on the skin of the adult newts. Rough-skinned newts shed their skin in one piece and eat it, thereby ingesting the cysts. Metacercariae emerge in the digestive tract and are found from foregut to cloaca, with the highest concentration in the rectum. Infection occurs mainly in the spring, but continues throughout the aquatic phase of the adult newt’s life cycle. This fluke also is found in other species of aquatic amphibians that coexist with rough-skinned newts, but infection rates are much higher in rough-skinned newts, both in terms of the percentage of individuals infected (varying seasonally from 67–100%) and the number of parasites/infected individual (as many as 77 cysts in the gut of one female). However, almost no sexually mature flukes are found in the gut of rough-skinned newts, although large, egg-bearing adults are found in other amphibian species at the same localities, suggesting that rough-skinned newts somehow prevent growth and development of this parasite (Efford and Tsumura, 1969). Sexually mature specimens of another trematode, Cephalouterina dicamptodonti, were found in adult rough-skinned newts in British Columbia (Efford and Tsumura, 1969). Megalodiscus americanus was found in the rectum of aquatic adults from Benton County, Oregon, and Brachycoelium salamandrae was found in the intestines of a terrestrial adult from Marion County, Oregon (Lehmann, 1954).
Ribeiroia ondatrae was recently reported to be present in rough-skinned newts (Johnson et al., 2002). For infected animals, the number of metacercariae/individual ranged from 1–41, with a mean of 12.7. Metacercariae were located subcutaneously, at the base of fore- and hindlimbs, and among the gills or within the ventral head musculature. Aquatic snails in the genus Planorbella are first intermediate hosts for Ribeiroia, hosting rediae and cercariae stages. Although Ribeiroia infection has been shown to cause morphological abnormalities in some species of amphibians, its role in causing malformations in rough-skinned newts is somewhat ambiguous. Morphological abnormalities, such as missing limbs and digits, were found in fairly low frequencies (range 4.2–7.4%) both at sites with and without Ribeiroia; however, abnormalities significantly exceeded 5% only at sites where Ribeiroia was present (Johnson et al., 2002).
iii. Nematodes (Phylum Nematoda) and Acanthocephalans (Phylum Acanthocephala). The nematodes Megalobatrachonema moraveci were found in the intestine of adult rough-skinned newts from Vancouver Island; the authors do not indicate if the newts were aquatic or terrestrial when collected. Half of the 12 specimens collected were infected, and the mean intensity of infection was 5.8 worms/host (Richardson and Adamson, 1988). Examination of aquatic and terrestrial adult newts from Benton and Marion counties in Oregon revealed the nematodes Cosmocercoides dukae in the intestine and rectum and Hedruris siredonis in the stomach (Lehmann, 1954). In the course of stomach content analyses for the purpose of ascertaining diet, parasitic nematodes (Hedruris and Cosmocerca sp.) and acanthocephalans (Neoechinorhynchus sp.) were discovered in the stomach of adult rough-skinned newts (Chandler, 1918; Taylor, 1984).
iv. Leeches (Phylum Annelida, Class Hirudinea). Kelly (1951) found leeches (family Glossiphonidae) in the mouth cavity of rough-skinned newts. In most cases only a single leech was found/animal, but multiple parasites were found in several cases, with one newt infected with 44 leeches. Infection was seasonal, temporary, and widespread, occurring only between May–July; about 90% of the newts examined were infected with leeches during this period.
4. Conservation. Timber harvesting has the potential to directly impact rough-skinned newt populations, but most studies have been unable to draw strong conclusions regarding the effects of these practices on rough-skinned newts. To my knowledge, there have been no studies on the long-term effects of timber harvest practices on rough-skinned newts, but two studies have attempted to elucidate short-term effects (Cole et al., 1997; Grialou et al., 2000). Conversion of hardwood stands to more profitable Douglas-fir (Pseudotsuga menziesii) stands has been a common practice on federal and private lands in the Oregon Coast Range. For this conversion, hardwoods are typically clearcut, and then the site is burned before planting with Douglas-fir seedlings. During the first few years after planting, herbicides such as glyphosate may be applied to control competing vegetation. Cole et al. (1997) investigated the effects of clearcut logging, broadcast burning, and application of glyphosate on amphibian populations in red alder (Alnus rubra) sites in the Oregon Coast Range. In this study, three treatments were applied at each of three sites: (1) control (uncut); (2) clearcut and burned; and (3) clearcut, burned, and sprayed with glyphosate. Sites were sampled 1 yr before, and 1 and 2 yr after treatment, using pitfall traps. This study did not detect any short-term effects of logging, burning, or glyphosate application on rough-skinned newts; there were no significant differences in capture rates before and after treatments. However, there were relatively low capture rates and high variability in the capture rates between sites, resulting in low statistical power of these comparisons. As a result, there may have been effects that the study design and sampling techniques were unable to detect (Cole et al., 1997). Gomez (1993) demonstrated that newts tend to be less abundant in Douglas-fir stands (regardless of stand age) than in deciduous stands; based on these results Cole et al. (1997) suggest that conversion of red alder stands to Douglas-fir may result in long-term declines in newt populations. Grialou et al. (2000) investigated the short-term effects of clearcutting and thinning on terrestrial salamanders, including rough-skinned newts, in southwestern Washington. Using pitfall traps, they captured rough-skinned newts in both forested areas and clearcuts, but did not capture them in sufficient numbers to conduct statistical tests to determine the response of newts to clearcut harvesting or thinning (Grialou et al., 2000). Both these studies attempted to look at the response of multiple species of amphibians to timber harvest practices, and their sampling techniques and study design may not have been especially well-suited to detecting rough-skinned newts. The life history of this species complicates sampling, since there are restricted periods of time when the animals are terrestrial and above ground, and the number of active individuals is highly variable over time in response to rainfall and temperature patterns. Because pitfall traps sample migratory animals, sampling periods ideally would coincide with peak newt activity periods. Knowledge of local newt migratory pathways would be useful in establishing the placement of pitfall traps.
In the Pacific Northwest, nitrogen fertilizers (e.g., granular urea) are commonly used in commercial timber production to maintain or boost timber production. Urea is commonly applied by helicopters, and potentially could have negative effects on forest amphibians through dermal exposure. Two studies have demonstrated that rough-skinned newts are less sensitive to urea exposure than some other species of forest amphibians. Laboratory experiments demonstrated that adult rough-skinned newts will avoid exposure to urea, yet when newts were exposed to urea for 4 d, at concentrations comparable to recommended application rates for fertilization, no mortality occurred. By contrast, these same urea doses had acute effects on western red-backed salamanders (Plethodon vehiculum) and southern torrent salamanders (Rhyacotriton variegatus), resulting in substantial mortality (60% and 40%, respectively, at the higher of the two urea doses after only 12 hr of exposure; Marco et al., 2001). Hatch et al. (2001) examined the effects of urea exposure on the survival and feeding behavior of four species of newly metamorphosed terrestrial amphibians. Neither mortality nor reduced prey consumption was observed in juvenile rough-skinned newts as a result of a 5-d exposure to urea at an application rate consistent with reported field application rates. Similar results were obtained for long-toed salamanders, but juvenile Western toads (Bufo boreas) and Cascade frogs (Rana cascadae) exposed to urea suffered substantial mortality and consumed significantly fewer prey items than non-exposed individuals.
Several laboratory studies have investigated potential sublethal effects of UV-B radiation on rough-skinned newts. Belden (2002) demonstrated that the skin of rough-skinned newt larvae darkens in response to short-term exposure (i.e., 5 d) to UV-B; however, whether skin darkening provides protection from UV-B damage remains unclear. A related experiment showed that longer term exposure (i.e., 3 wk) to UV-B led to decreased growth rates in northwestern salamander and long-toed salamander larvae (Belden, 2002). Although Taricha larvae were not investigated in this regard, it is probable that UV-B has similar effects on rough-skinned newts. Blaustein et al. (2000) used rough-skinned newts as a model to examine potential effects of UV-B radiation on amphibian behavior. Adult newts were exposed to low-level doses of UV-B in the laboratory for 14 d, and then tested in the field, where treatment animals were compared to control (i.e., UV-B blocked) animals with regard to (1) orientation towards water and (2) locomotor activity levels. There was no significant difference in orientation between control and treatment animals; both showed significant orientation towards water. However, newts exposed to UV-B were significantly more active than control animals. This increased activity may be a stress response to UV-B exposure, related to an increase in circulating levels of the hormone corticosterone (Blaustein et al., 2000; Belden et al., 2001). Kats et al. (2000) investigated the effects of short-term (i.e., 18 d) exposure to UV-B radiation on the anti-predator behavior of rough-skinned newt larvae. Both UV-B exposed and control (UV-B blocked) larvae responded to chemical cues from conspecific adult predators by increasing the amount of time spent in shelter. UV-B exposed larvae showed a reduced response to conspecific predator cues relative to non-exposed larvae, but these differences were not statistically significant. These studies suggest that UV-B exposure may negatively affect rough-skinned newts, and there is concern that these impacts may be exacerbated by human or natural disturbances (e.g., forest clearcutting, fire) that decrease canopy cover, potentially exposing eggs, larvae, juveniles, and adults to increased doses of ambient UV-B radiation (Blaustein et al., 2000; Kats et al., 2000). Further studies on sublethal effects of UV-B on rough-skinned newts and other amphibians are warranted.
Life history patterns should be considered when developing management or conservation plans for rough-skinned newt populations. Effective management plans must take into account the habitat requirements of all stages of the life cycle, including upland overwintering and foraging sites and migratory pathways between upland sites and aquatic breeding sites, as well as aquatic sites for eggs, larvae, and breeding adults. Information about local migration patterns may be critical to reducing mortality from various anthropogenic disturbances, such as increased vehicular traffic. In addition, the homing behavior of newts (i.e., high degree of site fidelity for breeding) most likely reduces the dispersal of individuals to alternate breeding sites, limits recolonization of sites (Blaustein et al., 1995), and may increase the likelihood of extinction of local populations in the event of the loss or destruction of aquatic breeding sites.
Rough-skinned newts have been introduced into Idaho, where they are considered an Exotic species (www2.state.id.us).
1Sharyn B. Marks
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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