Eastern Newt, Broken-Striped Newt, Central Newt, Peninsula Newt, Red Spotted Newt
© 2007 Twan Leenders (1 of 127)
Notophthalmus viridescens (Rafinesque, 1820)
Todd W. Hunsinger1
1. Historical versus Current Distribution. According to Hurlbert (1969) eastern newts (Notophthalmus viridescens) are second only to tiger salamanders (Ambystoma tigrinum) among U.S. salamanders in the extent of their distribution. Specifically, eastern newts are found throughout the eastern United States in historically forested areas from northern and central Minnesota, eastern and southern Wisconsin, eastern Iowa, northern and southern Illinois, extreme east-central and southeastern Kansas, and eastern Oklahoma and Texas to the Gulf of Mexico and the Atlantic Ocean. Four subspecies are recognized. Broken-striped newts (N. v. dorsalis) are distributed in southeastern North Carolina and northeastern South Carolina. Central newts (N. v. louisianensis) have a disjunct distribution. Southern populations are distributed along the Atlantic and Gulf Coastal Plains, except for most of peninsular Florida, and up the Mississippi River drainage into northern Missouri, southern Illinois, and southwestern Indiana. Northern populations are distributed from southeastern Iowa, north around southern and western Lake Superior and surrounding Lake Michigan. Peninsula newts (N. d. piaropicola) inhabit the southern 4/5 of peninsular Florida. Red-spotted newts (N. v. viridescens) have the largest distribution of the four subspecies and are found along the Appalachian spine from central Indiana and the eastern half of the Lower Peninsula in Michigan to the Atlantic Coast in northern North Carolina and north into and throughout New England.
The current distribution most likely resembles the historical distribution, with some losses of local demes. Newts have not been reported from Hamilton County, Ohio, in over 70 yr (Smith and Pfingsten, 1989; Davis et al., 1998). However, newts are good colonizers (Fauth and Resetarits, 1991; see also, Brandon and Bremer, 1966; Hurlbert, 1969), occupying suitable habitat modified by beaver (Castor canadensis) and created by farm ponds (Petranka, 1998). Newts also benefit from reforestation (Skelly et al., 1999) occurring throughout much of their range.
2. Historical versus Current Abundance. Little data exist for this far-ranging species. Abundance may vary within and between years (Harris et al., 1988). In southeastern Michigan, with expanding reforestation, eastern newt populations experienced a 25-fold increase in range and colonized five breeding ponds over a 20-yr period (Skelly et al., 1999). Cortwright (1998) reports that southern Indiana populations are widespread and common, and that populations in 36 wetlands showed no upward or downward trends. He also reports that local populations tend to fluctuate more than metapopulations, suggesting that populations connected by dispersive eft stages are more stable than isolated populations. Brown (E.E., 1992) reports eastern newts are rare in the Piedmont of North Carolina.
Because eft movements, feeding, and growth rates are climate dependent (Hurlbert, 1969; Healy, 1973, 1975b), and adults are less tolerant than juveniles to drought conditions (Healy, 1970; Healy, 1974; Morin, 1983a; Gillis and Breuer, 1984), the potential exists for populations to be impacted in the future by climate change, particularly in regions where drought conditions may persist.
3. Life History Features. Eastern newts have among the most variable life histories of North American amphibians. Most populations have aquatic egg, larval, and adult stages and a terrestrial eft stage. Environmental factors, as well as larval and adult densities, can influence the presence and timing of life history stages between and within populations (Healy, 1970; Morin et al., 1983; Harris, 1987a). Illinois populations have four morphological stages: larvae, terrestrial efts, fully transformed adults, and neotenic adults (Brandon and Bremer, 1966). It is not surprising that Noble (1926, 1929b) and P.H. Pope (1921, 1924, 1928b) engaged in heated exchanges over the ontogeny of efts.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Efts migrate from forested terrestrial sites into aquatic habitats and become reproductively mature. Breeding adults that have overwintered on land follow distinct migratory routes, entering the pond at the same point (Hurlbert, 1970b). They will home (Gill, 1979). Migrations are concentrated around rainy days and nights and often follow streams and wet sloughs (Stein, 1938; Hurlbert, 1969). The timing of migration varies, depending on location. Some researchers report a spring migration only, which peaks in late March in Virginia (Gill, 1978; Massey, 1990). Other populations have only fall migrations (Brimley, 1921b; Chadwick, 1944; Healy, 1974). Fall breeding migrations occur from July to early November, including July–August in Massachusetts (Healy, 1975a), September–October in south-central New York (Hurlbert, 1969), and late October in Massachusetts (Stein, 1938). Most fall migrants do not attain reproductive condition until the following spring (Bishop, 1941b). Some New York populations experience fall and spring migrations to the breeding sites (Bishop, 1941b; Hurlbert, 1969). Adult densities in breeding ponds peak in February–March in North Carolina (Harris et al., 1988). Eastern newts are reported to be highly philopatric (Gill, 1978; Massey, 1990) but at the same time demonstrate enough flexibility in breeding sites to support metapopulations (Hurlbert, 1969; Gill, 1978; Cortwright, 1998).
Males identify females through chemoreception (Dawley, 1984) and are attracted to larger females that have a greater fecundity (Verrell, 1982, 1985). Males select females using both olfactory and visual cues (Verrell, 1985).
Breeding success is episodic. Semlitsch et al. (1996) report that > 15,000 newts metamorphosed from a Carolina bay in two years, yet in nine other years no newts were collected. Factors such as newt density and predator density may influence reproductive success (see Morin, 1983a; Morin et al., 1983).
ii. Breeding habitat. The same as the adult habitats, which include pools, ponds, wetlands, and low-flow areas of streams in forests (see "Adult Habitat" below). Both permanent and semi-permanent bodies of water are used (see Hurlbert, 1969). Male courtship and amplexus of females occurs in shallow water (Pitkin and Tilley, 1982; T.W.H., unpublished observations). Most adults appear to breed annually, although females will skip years (Gill et al., 1983; Gill, 1985). Massey (1990) found that females are capable of sperm storage for upwards of 10 mo.
i. Egg deposition sites. Eggs are deposited singly; the female wraps each in a folded leaf of a submerged macrophyte, in a decaying leaf, or in other detritus (Bishop, 1941b; Goin, 1951; Morin et al., 1983). Mature, overwintering adults deposit eggs earlier in the breeding season than do efts returning to the water to breed for the first time (Hurlbert, 1970b). Females in southern populations begin egg deposition in early winter (Goin, 1951). Deposition in a Kansas population occurred in March–April (Ashton, 1977), while dates for northern populations include late April–May (Smallwood, 1928), sometimes late May (Hurlbert, 1970b), and even early July (Gage, 1891; Pope, 1924; Bishop, 1941b; Chadwick, 1944; Worthington, 1969; Ashton, 1977; Harris et al., 1988). Worthington (1969) speculated that extended egg deposition could minimize larval competition with other spring-breeding amphibians.
ii. Clutch size. Each female lays between 200–375 eggs, at a rate of several eggs/day (Bishop, 1941b). Thus, time to complete ovipositing can take many weeks (Bishop, 1941b; Chadwick, 1944; Morin, 1983a). It is unclear whether a female will lay all of her eggs in 1 yr (Bishop, 1941b). Individual eggs have a diameter of about 1.5 mm (Bishop, 1941b; Brandon and Bremer, 1966). Incubation lasts between 20–35 d (Gage, 1891; Bishop, 1941b).
i. Length of larval stage. The length of the larval stage and size at metamorphosis varies across their range, among water bodies (Hurlbert, 1970b), and among years (Harris et al., 1988). Greater competition between larvae at high densities also affects the timing and size at metamorphosis (Harris, 1987a).
Bishop (1941b) reported that in New York, larvae hatch at about 7.5 mm and metamorphose to the eft stage in 2–3 mo at an average of 36.7 mm TL. Hurlbert (1970b) reported a range of 28–47 mm TL in south-central New York. In a Massachusetts population, the larval period lasts from 2–5 mo, and larvae metamorphose at about 19–21 mm SVL (35–38 mm TL; Healy, 1973, 1974). In Maine, metamorphosis occurs in 3–5 mo at 29–32 mm TL (Pope, 1921). Larvae from Maine raised in the laboratory metamorphosed at 28–34 mm TL (Pope, 1928b). Western North Carolina larvae metamorphose at 34–43 mm TL (Chadwick, 1950), while larvae in the sandhills metamorphose at 24 mm SVL (Harris et al., 1988). Metamorphosis in Illinois occurs at 33–40 mm TL (Brandon and Bremer, 1966). Ashton (1977) found three distinct larval classes in a Kansas pond in late June, including individuals close to metamorphosis. Hurlbert (1970b) noted two size classes of larvae in ponds where females overwinter. Larval mortality rates may be high in some populations (Massey, 1990).
In some populations, the eft stage is abandoned and larvae transform directly into adults. In populations with neotenic adults, metamorphic size ranges from 46–75 mm (Noble, 1929b). Harris et al. (1988) found that some larvae overwinter in the ponds in western North Carolina.
ii. Larval requirements.
a. Food. Newts are carnivorous during all life history stages. Newly hatched larvae feed at night on small invertebrates such as zooplankton; larger larvae include larger invertebrates in their diet and are cannibalistic when confined in the laboratory (Pope, 1924; Walters, 1975; Morin, 1983a; Harris, 1987b; Harris et al., 1988). Cannibalism can occur between different size classes of larvae, but does not occur within size classes (Harris, 1987b). Eastern newts appear to feed on prey in roughly the same proportions to their abundance (Hamilton, 1940; Burton, 1977). Hamilton (1940) concluded that larvae use visual cues in prey selection. Notable prey include protozoans, cladocerans, ostracods, copepods, dipteran larvae, snails, fingernail clams, clams, and mites.
b. Cover. Larval newts are found in water < 0.5 m deep (Burton, 1977; see also Forester and Lykens, 1991). During the day, they seek cover under bottom debris (Chadwick, 1950; Ashton, 1977; Morin, 1983a). Larvae exhibit spatial segregation by size class (Harris et al., 1988). This may serve to limit competition or cannibalism with larger conspecifics.
iii. Larval polymorphisms. None reported.
iv. Features of metamorphosis. Newly metamorphosed eastern newts have been observed or collected as follows: July to early November in Massachusetts (Healy, 1974, 1975b) and New York (Bishop, 1941b; Hurlbert, 1970b); July–August in Massachusetts (Smith, 1920; Noble, 1929b); late June in Maryland (Worthington, 1969); mid August to November in Virginia (Gill, 1978); September in Illinois (Brophy, 1980), coastal North Carolina (Taylor et al., 1988), and western North Carolina (Chadwick, 1950).
Hurlbert (1970b) found that size at metamorphosis is correlated to water temperatures. Due to potential competitive pressures, larvae mature at a larger size in ponds where the adults have emigrated after breeding (Morin, 1983a; Harris, 1987a).
v. Post-metamorphic migrations. Larvae aggregate in one region of the pond just prior to metamorphosis (Hurlbert, 1970b; Ashton, 1977). In populations with efts, newly metamorphosed individuals will migrate away from ponds into upland forests. Migrations occur in waves, usually at night during or following rains (Chadwick, 1950; Hurlbert, 1970b; Healy, 1975b). Efts require about 1 yr to migrate to woodlands 800 m distant (Healy, 1974, 1975a).
vi. Neoteny. Pike (1886) was the first to call attention to neoteny in the newt. Sherwood (1895) noted a scarcity of efts in populations around New York City and Mount Vernon, New York. He suggested that the entire life cycle of newts is aquatic. Noble verified neoteny for populations on Long Island (Noble, 1926) and Cape Cod (Noble, 1929b). Bishop (1943) reported additional populations in Louisiana and Florida. It is now known that neotenic adults occur in populations of all four subspecies, having been reported from Florida, Illinois, Indiana, Louisiana, Massachusetts, New Jersey, New York, North Carolina, and Tennessee (Gage, 1891; Noble, 1926, 1929b; Schmidt and Necker, 1935; Bishop, 1943; Peterson, 1952; Schwartz and Duellman, 1952; Gentry, 1955; Brandon and Bremer, 1966; Healy, 1970; Harris, 1987a).
Neoteny in eastern newts is based on the presence or remnants of external gills, gill slits, and a gular cleft in sexually mature individuals. Newts do not retain as many larval characteristics as neotenic Ambystoma (Reilly, 1987).
Many of the populations with neotenic adults occur in sandy, coastal sites, where terrestrial conditions are suboptimal (Noble, 1926; Bishop, 1941b; Brandon and Bremer, 1966). The tendency for neotenic adults to occur in these sites has lead to the implication that the terrestrial eft is selected against (see Petranka, 1998). However, adults will lose their gills and transform if their breeding sites dry (Noble, 1929b; Healy, 1970). Healy (1970) found that the persistence of drought conditions changed a population from nearly all neotenic adults to one of all metamorphosed individuals within a few years. Although environmental factors may influence metamorphosis (Healy, 1970; Harris, 1987a), it has been demonstrated that the extent of neoteny in a population is negatively correlated to larval density (Healy, 1974; Harris, 1987a; Harris et al., 1988). Therefore, metamorphosis may result from resource partitioning between age classes. When compared with other salamander species, in eastern newts, populations with neotenic adults are nearly as genetically variable as populations where adults metamorphose (Petranka, 1998).
D. Juvenile Habitat. Terrestrial efts are usually found in wooded areas (Bishop, 1941b; Evans, 1947; Williams, 1947). Efts are diurnal and nocturnal, moving about on rainy or humid days and nights when the ground is moist (Healy, 1973). Movement peaks during May–June, and again in the autumn (Healy, 1975a). During dry periods, they seek cover in leaf litter or under logs and other objects (Bishop, 1941b; Williams, 1947; Healy, 1974, 1975a). Efts rarely move about when the temperature drops below 10 ˚C, but will be active above 12 ˚C (Healy, 1975a). Pough (1974) found that efts select for environmental temperatures of 26–28 ˚C.
Efts establish home ranges that increase annually (Healy, 1975a); they will home (Gill, 1979). Home ranges averaged 266.9 m2 in one season and 353 m2 over two seasons. Individuals have been recaptured within a few centimeters of previous captures in successive years. The average distance from breeding ponds is 800 m.
Efts forage in the forest floor leaf litter, especially during rains. Eft growth, which is temperature and moisture dependent, is concentrated during the summer (Healy, 1973). They feed on invertebrates and have a slight preference for larger prey (MacNamara, 1977). Prey include 58 families from 25 orders of invertebrates. Efts cluster around and under mushrooms in late August to September to feed on dipterans attracted to these fungi (Healy, 1975a).
The eft stage is estimated to last 2–3 yr in New York (Bishop, 1941b); 3–4 yr in Québec (Caetano and Leclair, 1996); 4 yr in the North Carolina mountains (Chadwick, 1944); 3–7 yr in Massachusetts (Healy, 1974); and 4–7 yr, with a mean of 4.4 yr, in a Maryland population (Forester and Likens, 1991). The Québec data suggest that males reach sexual maturity slightly sooner than females (Caetano and Leclair, 1996). Harris et al. (1988) found the eft stage may last only 1 yr. The eft stage may be similarly reduced in southern populations (see Huheey and Brandon, 1974). Chadwick (1944) found that the largest efts exceeded the mean length of aquatic adults in North Carolina.
Where the eft stage is abandoned and larvae transform directly into adults, the juvenile habitat characteristics are similar to larval and adult habitat characteristics. Aquatic larvae grow faster than terrestrial efts, taking a shorter time to metamorphose (Healy, 1973, 1974). Here, juvenile growth occurs throughout the year, with the greatest increment in the spring (Healy, 1973).
E. Adult Habitat. Aquatic adults inhabit pools, ponds, wetlands, sloughs, canals, and quiet areas of streams in upland and bottomland regions (Bishop, 1943; Schwartz and Duellman, 1952; Bellis, 1968; Gates and Thompson, 1982; Petranka, 1998). Adults are found primarily in open, sunny areas. Sites with submergent and emergent vegetation often harbor large populations (Schwartz and Duellman, 1952; George, 1977; Gates and Thompson, 1982). As with efts, adults show a thermal preference. George et al. (1977) found that newts stayed just below the thermocline in mid summer. During the winter, aquatic adults will sometimes congregate in ice-free areas of ponds where temperatures are at 5–6 ˚C (Morgan and Grierson, 1932; Pitkin and Tilley, 1982). Both sexes are equally represented.
Adults will leave drying ponds for protected upland sites to avoid desiccation and heat stress (Hurlbert, 1969; Gill, 1978). During this time, adults will mimic eft behavior, hiding under rotten logs and vegetation clumps (Gill, 1978). Adults that remain terrestrial for a long period will develop a more granular skin and reduced tail fin (Noble, 1926; Hurlbert, 1969; Gill, 1978; Massey, 1990).
F. Home Range Size. Petranka (1998) notes that the extent to which adults establish home ranges varies across populations. Bellis (1968) reports aquatic adults staying in the same portion of a pond for weeks (but see Harris, 1981). Reductions in water levels cause adults to move, but following pond-refilling, animals move back to their original sites. Males move more than females. Individuals can identify nearest neighbors (Wise et al., 1993).
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Adults will abandon aquatic sites during dry conditions when water levels drop and water temperatures rise. In North Carolina, newts will leave the ponds after breeding and remain terrestrial until November (Brimley, 1921b). They seek refuge in moist sites beneath logs, rocks, and other detritus (Hurlbert, 1969; Gill, 1978; Massey, 1990).
Efts seek cover in leaf litter and other objects during dry conditions (Bishop, 1941b; Williams, 1947; Healy, 1974, 1975a).
I. Seasonal Migrations. Variable. Efts will leave ponds to forage for 2–7 yr before returning to ponds to breed. Terrestrial adults will return to ponds to breed. The timing of migration varies by gender (Hurlbert, 1969). Males migrate earlier than females in the spring and have a more concentrated migration in the fall. Migrations also vary by latitude and local climate/weather conditions. Hurlbert (1969) found that spring and fall migrations occur during rain episodes when air temperatures exceed 4.4 ˚C. Newts will migrate out of drying breeding ponds in summer (Hurlbert, 1969). The seasonal point of emigration and immigration is similar at many breeding ponds (Hullbert, 1969). Stein (1938) reported a spectacular fall migration of red efts, consisting of thousands of animals, in Massachusetts. As many as 20 animals were picked up in a single scoop of the hand; 100 animals were collected in 30 min, 1,200 animals were collected from a 5 m2 area. Newts use a specialized magnetoreception system to guide homing and migration (Phillips and Borland, 1994).
J. Torpor (Hibernation). Little is known about the hibernacula of newts. Cooper (1956) found newts hibernating in floodplain puddles. An aggregation of newts, lesser sirens (Siren intermedia), bullfrog tadpoles (Rana catesbeiana), and a musk turtle (Sternotherthus odoratus) was found in 1.5 ˚C ice-free water in January in Illinois (Cagle and Smith, 1939). During January in a Massachusetts stream, Morgan and Grierson (1932) found newts both singly in tangles of decaying macrophytes and in groups of 20–40 clustered beneath flat rocks. Bothner (1963) excavated two efts, together with a spotted salamander (A. maculatum), from the hibernaculum of short-headed garter snakes (Thamnophis brachystoma) 43 cm below the surface.
In permanent, deep waterbodies, adult eastern newts may remain aquatic and active throughout the year (Smallwood, 1928; Morgan and Grierson, 1932; George et al., 1977; Pitkin and Tilley, 1982). Although food intake will decrease during the winter, feeding and molting continue, indicating an active metabolism (Morgan and Grierson, 1932; Pitkin and Tilley, 1982).
In populations where the breeding pools are shallow or seasonal, adults migrate out of ponds in summer or autumn (August–September), overwinter on land, and return the following spring to breed (Hurlbert, 1969; Gill, 1978; Massey, 1990).
K. Interspecific Associations/Exclusions. Given both their terrestrial and aquatic life history stages, eastern newts interact with a wide variety of eastern U.S. aquatic and terrestrial amphibians. As well, unlike many North American amphibian species, eastern newts will occupy water bodies containing predaceous fishes (M.J.L., unpublished observations; Gates and Thompson, 1982; see also Kesler and Munns, 1991).
L. Age/Size at Reproductive Maturity. Size and time to sexual maturity vary depending on life history and location. Onset of sexual maturity is size specific rather than age specific (Healy, 1974; Caetano and Leclair, 1996). Populations with efts take a longer time to reach sexual maturity than populations with neotenic adults (Noble, 1929b; Healy, 1974; Harris, 1987a). Red-spotted newts from western North Carolina are larger than individuals from this subspecies found elsewhere (Bishop, 1943), averaging nearly 10 mm TL larger at the time of sexual maturity than New York specimens (Chadwick, 1944). The smallest sexually mature newts from western North Carolina could have been 85–90 mm TL (Hurlbert, 1969), while the smallest males found in north coastal populations were 51–64 mm (Noble, 1926, 1929b).
Neotenic adults and adults that skip the eft stage mature at 7 mo (Harris, 1987a). On Cape Cod and coastal Massachusetts, adults transforming to the eft stage mature at 2 yr (Harris, 1987a). Females appear to mature later than males and at a larger body size (Caetano and Leclair, 1996).
M. Longevity. As with all eastern newt life history features, longevity varies. Most adults are 3–8 yr old and maximum age in populations varies from 9–15 yr (Petranka, 1998). Forester and Likens (1991) found adults from 4–9 yr old in Maryland. Adults in Québec ranged from 2–13 yr (Caetano and Leclair, 1996). Gill (1978, 1985) reported maximum ages of 15 yr for males and 12 yr for females in Virginia. Female survivorship between years appears to be lower than males (Gill, 1978, 1985; Massey, 1990). This results in a greater number of reproductive seasons for males (Gill, 1978). Morin (1983a) reported high mortality rates during periods of drought accompanied by subfreezing temperatures in North Carolina.
N. Feeding Behavior. Similar to larvae, adults are carnivorous, feeding on any available, palatable prey they can swallow whole. Newts rely on visual and chemical cues to locate food (Martin et al., 1974). Prey include zooplankton, amphipods, mayflies, stoneflies, dipterans, hemipterans, lepidopterans, coleopterans, odonates, oligochaetes, leeches, snails, clams, small fishes, fish eggs, anuran eggs and tadpoles, ambystomatid larvae, conspecific embryos and larvae, and shed skins (Hamilton, 1932; Morgan and Grierson, 1932; Bishop, 1941b; Behre, 1953; Wood and Goodwin, 1954; Ries and Bellis, 1966; Walters, 1975; Burton, 1977; George et al., 1977; Gill, 1978; Morin, 1981, 1983a; Pitkin and Tilley, 1982; Morin et al., 1983; Taylor et al., 1988; Wilbur and Fauth, 1990; Fauth and Resetarits, 1991). Adults exhibit a diel feeding pattern, but most feeding occurs in the early morning and is not influenced by the presence of sunfish (Centrarchidae; Kesler and Munns, 1991). Gut passage times vary from 33 h (25 ˚C) to > 15 d (5 ˚C; Jiang and Claussen, 1993). Eastern newts aggregate in vegetation near shorelines but will forage at depths of 9–13 m (George et al., 1977).
Because newts feed opportunistically on seasonally abundant prey, they can influence the relative abundance of zooplankton, insect, and amphibian populations, as well as community structure (Morgan and Grierson, 1932; Morin, 1983a,b; Morin et al., 1983; Fauth and Resetarits, 1991). Morin (1983a) found that the competition with newts leads to decreased size at metamorphosis for tiger salamander (A. tigrinum) larvae. Newt predation on the eggs of A. tigrinum can lead to the exclusion of larvae from breeding ponds (Morin, 1983a). Predation by newts has been documented to influence anuran community composition (Morin, 1983b; Morin et al., 1983; Fauth and Resetarits, 1991), reducing the size of some populations while freeing others from competition.
O. Predators. Many animals are known to feed on eastern newts, despite their anti-predator defenses (see "Anti-Predator Mechanisms" below). In experimental trials, efts and adults were initially rejected by potential predators (e.g., Hurlbert, 1970a). Hurlbert (1970a) found newts to be less acceptable to diurnal terrestrial predators than they were to aquatic and nocturnal terrestrial predators. Adult newts have been found in the stomachs of smallmouth bass (Micropterus dolomieu) in New Hampshire (Burton, 1977). Larvae are taken by sunfish (Lepomis gibbosus; Kesler and Munns, 1991). Snakes, such as hog-nosed snakes (Heterodon sp.) will occasionally eat newts (Uhler et al., 1939). Brodie (1968) found eastern garter snakes (Thamnophis s. sirtalis) and northern water snakes (Nerodia s. sipedon) to have some resistance to newt toxicity, but will not feed consistently on newts. Chelonian predators can include snapping (Chelydra serpentina) and painted turtles (Chrysemys picta). Hamilton (1932) reported newts in the diet of mudpuppies (Necturus maculosus) from New York. Lesser sirens (Siren intermedia intermedia; Fauth and Resetaris, 1991), marbled salamanders (A. opacum; Walters, 1975), and in controlled studies, tiger salamanders (Morin, 1983a) feed on eggs and larval newts. In laboratory studies bullfrogs (Rana catesbeiana) readily consumed newts (Brodie, 1968; Hurlbert, 1970a); however, habitat differences likely limit encounters in the wild (Hurlbert, 1970a). Some eastern newt adults cannibalize embryos (Wood and Goodwin, 1954) and larvae (Gage, 1891; Morgan and Grierson, 1932; Burton, 1977).
Raccoons (Procyon lotor) are the main mammalian predator on eastern newts (Hurlbert, 1970a). Shure et al. (1989) found efts that were decapitated and eviscerated by an unspecified predator in North Carolina. Ross (1933) also reported decapitated efts in New York. In Virginia, leeches appear to be a major source of adult mortality (Gill, 1978).
P. Anti-Predator Mechanisms. The skin of newts contains tetrodotoxin, a neurotoxin (Mosher et al., 1964; Wakeley et al., 1966; Brodie, 1968a; Brodie et al., 1974b). Most of this toxin is concentrated on the dorsal surface. The skin of efts is ten times more toxic than the skin of adults (Brodie, 1968a). This skin toxicity of efts and newts make them unpalatable to many species of crayfish, mammals, birds, fish, reptiles, amphibians, and insects (Hamilton, 1951; Webster, 1960; Brodie, 1968a; Hurlbert, 1970a; Brodie and Brodie, 1980; Brodie and Formanowicz, 1981a; Formanowicz and Brodie, 1982; Kats et al., 1988). In most accounts of predation on adult newts and efts, predators eviscerate the newts after decapitation or puncturing the midventral region, thus avoiding the more toxic dorsal skin (Ross, 1933; Hurlbert, 1970a; Shure et al., 1989). Brook trout (Salmo fontinalis) force-fed newts died within hours (Webster, 1960). Brodie (1968a) achieved similar results in trials with American toads (Bufo americanus), and many species of reptiles. Garter snakes (T. sirtalis) exhibit mouth gaping and rubbing after predation attempts on newts and efts (Hamilton, 1951; Hurlbert, 1970a). Crayfish (Cambarus diogenes and Orconectes propinquus) and beetle larvae (Dytiscus verticalus and Lethocerus americanus) also exhibited agitated mouth part movements after attempts to prey upon newts at metamorphosis (Formanowicz and Brodie, 1982). Because of the effectiveness of the skin toxins, many animals have a learned avoidance to newts (Brodie and Brodie, 1980; Brodie and Formanowicz, 1982). Pough (1974) speculated that it is a compound other than tetrodotoxin that causes four species of leeches, Batracobdella phalera, Mooreobdella fervida, Haemopis marmorata, and Helobdella stagnalis, to avoid parasitizing adult newts.
The bright red color of efts is widely considered to be aposematic—warning off potential predators. The cryptic green-brown coloration of adults helps them to avoid predation. Eft coloration is such an effective anti-predator mechanism that red salamanders (Pseudotriton ruber), mud salamanders (P. montanus), and the erythristic morph of the red-backed salamander (Plethodon cinereus) represent examples of Batesian mimicry in areas where these species occur with newts (Howard and Brodie, 1970; Brodie and Howard, 1972; Huheey and Brandon, 1974; Brodie and Brodie, 1980). Newt subspecies with bright coloration maintain diurnal activity and have a longer eft stage (Huheey and Brandon, 1974). The cryptic colored central newt (N. v. louisianensis) has a shorter eft stage and exhibits more cryptic behavior; this occurs despite the fact that central newts are as toxic as the red subspecies (Brandon et al., 1979a).
The unken posture in newts, first described by Neill (1955), is defined as an upward bending of the head and tail until they nearly touch, and it has been described from observations in the wild (Neill, 1955; Petranka, 1987) and laboratory studies (Brodie and Howard, 1972) of adult newts. This posture exposes the brighter, aposematic coloration of the ventral surface. The unken posture is rarely displayed by efts (Brodie and Howard, 1972). Instead, efts will raise their tail laterally or occasionally in a vertical display when threatened. This may be coupled with an elevation of the hindlimbs (Ducey and Brodie, 1983). Observed behaviors in the wild are similar to laboratory experiments (Brandon et al., 1979b; Ducey and Brodie, 1983).
Newts also exhibit an avoidance response to the tissue of damaged conspecifics (Marvin and Hutchison, 1995; Woody and Mathis, 1997).
Q. Diseases. Unknown.
R. Parasites. The parasites of eastern newt larvae were detailed by Rankin (1937) as follows: Protozoa—Hexamastix batrachorum, Hexamitus intestinalis, and Tritrichomonas augusta; Trematoda—Plagitura sp., intestinal wall metacercariae; Nematoda—Camallanus sp.
The parasites of eastern newt adults were detailed by Rankin (1937) as follows: Protozoa—Cryptobia borreli, Cytamoeba bacterifera, Entamoeba ranarum, Euglenamorpha hegneri, Eutrichomastix batrachorum, Hexamastix batrachorum, Hexamitus batrachorum, Hexamitus intestinalis, Karotomorpha swezi, Myxobolus conspicuus, Nyctotherus cordiformes, Prowazekella longifilis, and Tritrichomonas augusta; Trematoda—Plagitura sp., intestinal wall metacercariae.
Adults in Virginia are affected by parasitic leeches (B. picta) which transmit Trypanosoma diemyctyli, a blood endoparasite (Gill, 1978). In response, adults leave the water to rid themselves of leeches.
4. Conservation. Among U.S. salamanders, eastern newts are second only to tiger salamanders in the extent of their distribution. Their current distribution most likely resembles their historical distribution, with losses of local populations. Eastern newts are good colonizers and will utilize suitable habitat created by beavers and farm pond initiatives (Petranka, 1998). Eastern newts are benefiting from reforestation, which is occurring throughout much of their range (Skelly et al., 1999). Their abundance may vary within and between years (Harris et al., 1988).
Eastern newts are listed as Threatened in Iowa and Kansas, and the potential exists for populations to be impacted in the future by climate change, particularly in regions where drought conditions may persist.
1Todd W. Hunsinger
2Michael J. Lannoo
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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