© 2005 John White (1 of 61)
Country distribution from AmphibiaWeb's database: Canada, United States
Hemidactylium scutatum Temminck and Schlegel, 1838
Reid N. Harris 1
1. Historical versus Current Distribution. The current knowledge of distribution of four-toed salamanders (Hemidactylium scutatum) is summarized in Petranka (1998); four-toed salamanders range from southeastern Canada south to the Gulf of Mexico and west to Oklahoma, Missouri, and Wisconsin. Populations appear to be disjunct in the southern and western parts of this range.
2. Historical versus Current Abundance. No published population-size data exist. In a study spanning 23 yr (1979–'83 and 1994–2002; unpublished data) in the George Washington National Forest (GWNF), Virginia, the number of ovipositing females at one montane pond in Virginia fluctuated between 15 and 177; at another nearby pond, numbers fluctuated between 15 and 91. The highest number of females oviposited at both ponds in 1980, and numbers of females between 1994–2002 have averaged 48.31 (SD = 37.42, CV = 0.77) at one pond and 48.5 (SD = 23.94, CV = 0.49) at another. The population density of adult eastern newts (Notophthalmus viridescens) increased dramatically during the study period, and because adult newts prey on larval four-toed salamanders, the failure of the population to approach numbers seen in 1980 may be due to prey–predator dynamics. Surveys of apparently similar nearby ponds have revealed few nesting females.
Early concern was expressed by Wright (1918), who stated that four-toed salamanders were vanishing in New York due to draining of wetlands. Four-toed salamanders are considered Rare in Florida (Means, 1992d) and southern New England (Klemens, 1993), and worthy of Special Concern in Maine (Burgason, 1999) and Minnesota (Moriarty and Jones, 1997). Populations exist in fairly substantial numbers in the Great Smoky Mountains National Park (GSMNP; C.K. Dodd, personal communication), but their overall conservation status is unknown due to their secretive nature, scattered distribution, short larval period, and propensity to brood early in the season (Dodd, 1997; C.K. Dodd, personal communication). Based on reports from two protected areas (GWNF and GSMNP), it appears that populations are doing well in these habitats in the upland south (see above). However, J.W. Petranka (personal communication) feels that current abundance is likely to be much lower than historical abundance due to loss of vernal ponds and other small wetlands across the eastern United States (see also Mitchell et al., 1999).
Inventories of four-toed salamanders will need to consider the following aspects of their biology, which will tend to lead to an underestimate of population size: a short larval period, secretive nature of adults, and a propensity of adult females to skip years of reproduction.
3. Life History Features.
A. Breeding. Insemination and brooding are terrestrial; larvae are aquatic.
i. Breeding migrations. Only females migrate from woodlands to the banks of ponds, bogs, or streams to oviposit. Migration date is related to altitude and latitude, occurring from mid February to mid April in lowland Virginia (Wood, 1955), and from April–mid May in montane Virginia (Harris and Gill, 1980), lowland Michigan (Blanchard, 1934b), and New York (Bishop, 1941b).
ii. Breeding habitat. In Michigan, mating occurs on land from September–November (Blanchard, 1933a; Branin, 1935).
i. Egg deposition sites. Females prefer relatively steep banks, presumably to facilitate larvae making it from land to water. Nests are often found in moss, although nests are also found in grass and sedges and even inside rotted logs (Wood, 1955; Harris and Gill, 1980). It is frequently assumed that Sphagnum moss is preferred; however, females readily nest in other species of moss, such as Thuidium (Gilbert, 1941; Wood, 1955; Easterla, 1971; Petranka, 1998). Large differences in population sizes at apparently similar ponds in the GWNF suggest habitat preferences may be complex (unpublished data).
ii. Clutch size. Average clutch sizes based on dissection and counts of large ova range from 4–80 (Blanchard, 1936; Wood, 1953b). Joint nests are usually formed by two females; as many as 1,110 eggs have been found in one joint nest in Michigan, which suggests that about 20 females contributed eggs (Blanchard, 1934a; Harris et al., 1995). Females often skip years of reproduction (R.N.H. and P.M. Ludwig, unpublished data).
Females may lay eggs in a solitary nest and brood them. Alternatively, females may accept eggs from another female into her nest (Blanchard, 1934a; Harris and Gill, 1980; Breitenbach, 1982). Typically, joint nests have only one brooder (Blanchard, 1934a; Harris et al., 1995), meaning that some females desert their eggs. Females that desert their eggs in joint nests tend to be smaller (unpublished data). The percentage of females involved in joint nests can be over 70% (Blanchard, 1934a; Harris et al., 1995).
C. Larvae/Metamorphosis. For a plethodontid, four-toed salamanders have a short length of larval period of between 20–40 d (Blanchard, 1923; Berger-Bishop and Harris, 1996; O'Laughlin and Harris, 2000). Larvae require still waters (ponds, bogs, swamps, or sluggish streams) that are free of fish. Larvae have the ability to recognize kin (Harris et al., 2003).
D. Juvenile Habitat. Same as adult habitat.
E. Adult Habitat. Adults are found in forests that surround larval habitats. These can include mature hardwood or coniferous forests (Blanchard, 1923; Bishop, 1941b; Wood, 1955). Females have been found to nest in ponds that are near, but not directly adjacent to, a forest (Bishop, 1941b).
F. Home Range Size. Unknown.
G. Territories. Although reported as weakly territorial by Grant (1955), Hemidactylium has not been shown to defend an area. Carreno and Harris (1998) reported no aggressive defense by brooding females against conspecifics.
H. Aestivation/Avoiding Dessication. Aestivation is unknown; animals likely avoid dessicating conditions by moving under cover objects or into burrows.
I. Seasonal Migrations. Unknown.
J. Torpor (Hibernation). During the winter, males and females have been found in high density with conspecifics and other amphibians in holes, channels, and crevices in the ground (Blanchard, 1933b).
K. Interspecific Associations/Exclusions. The species is often assumed to be associated with Sphagnum moss for nesting and hardwood forests for juvenile and adult habitat, but see "Egg deposition sites" and "Adult Habitat" above. Four-toed salamanders co-occur with most of the pond-breeding amphibians of the east central and northeastern United States. For example Minton (1998) notes that in east-central Indiana, four-toed salamanders co-occur with eastern newts (Notophthalmus viridescens), spotted salamanders (Ambystoma maculatum), smallmouth salamanders (A. texanum), tiger salamanders (A. tigrinum), a unisexual Ambystoma hybrid, chorus frogs (Pseudacris triseriata complex), spring peepers (P. crucifer), northern cricket frogs (Acris crepitans), green frogs (Rana clamitans), and northern leopard frogs (R. pipiens).
L. Age/Size at Reproductive Maturity. Considerable geographic variation appears to exist in size at reproductive maturity for females. In montane populations in GWNF (1,000 m elevation), average SVL at reproductive maturity is 42.0 mm (SD = 11.3, n = 49); average total length is 92.8 mm (SD = 6.9, n = 45; R.N.H., unpublished data). In lowland Virginia populations, females can reproduce at SVLs of 29–33 mm (Wood, 1953b). In lowland Michigan populations, females can reproduce at total lengths of 62–72 mm (Blanchard and Blanchard, 1931).
For males in Michigan, individuals can mature as small as 50–52 mm total length, with maturity typically occurring at sizes of at least 54 mm total length (Blanchard and Blanchard, 1931).
Age at reproductive maturity is estimated as 2.3 yr in Michigan (Blanchard and Blanchard, 1931) and 22 mo in lowland populations of Virginia (Wood, 1953b). These estimates are based on analyses of size-frequency histograms and not on longitudinal studies or skeletochronology. As such, these estimates may be underestimated.
M. Longevity. Females appear to be long-lived. Based on longitudinal study in GWNF, a female first captured in 1992 as a breeding adult was recaptured in 1999, although it may have reproduced prior to 1992 (unpublished data). Using a minimum estimate of age at first reproduction as 2 yr, females can live to at least 9 yr of age.
N. Feeding Behavior. Larvae eat small planktonic organisms and small worms (personal observation). Adults also eat arthropods and worms (Bishop, 1919; personal observation). Brooding females do not eat (Wood, 1953b; unpublished data).
O. Predators. Eastern newts prey on larvae (Wells and Harris, 2001; Harris et al., 2003). It is likely that an array of other species prey on larvae, such as larval ambystomatids and naiads. Adult four-toed salamanders will assume a defensive posture in the presence of ring-necked snakes, and skunks may prey on adults (personal observation).
P. Anti-Predator Mechanisms. Brodie (1977) has observed the following anti-predator mechanisms in adults: a glandular concentration on the tail dorsum; tail raised and undulated in the presence of a predator; body can flip or coil; the venter can be exposed; immobility; aposematic coloration; noxious skin secretions; and tail autotomy. Larvae are palatable to newts (Wells and Harris, 2001) and fish (Kats et al., 1988). Predator presence causes larvae to lower their activity level, thereby lowering their growth rate (Wells and Harris, 2001). Eggs are unpalatable to insect predators, such as carabid beetles (Hess and Harris, 2000).
Q. Diseases. Unknown.
R. Parasites. Fungus is known to infest the eggs (Harris and Gill, 1980), although it is not known if the fungus is a secondary infection. Small nematodes have been observed in the egg jelly (Bishop, 1919). A protozoan parasite has been reported in adults (Blanchard and Blanchard, 1931; Blanchard, 1934c).
4. Conservation. Early concern was expressed by Wright (1918), who stated that four-toed salamanders were vanishing in New York due to draining of wetlands. Four-toed salamanders are considered Rare in Florida (Means, 1992) and southern New England (Klemens, 1993), and worthy of Special Concern in Maine (Burgason, 1999) and Minnesota (Moriarty and Jones, 1997). C. K. Dodd (1997, personal communication) reports populations in fairly substantial numbers in the Great Smoky Mountains National Park (GSMNP), but considers their overall conservation status as unknown due to their secretive nature, scattered distribution, short larval period, and propensity to brood early in the season. Based on reports from two protected areas (GWNF and GSMNP), it appears that populations are doing well in protected habitats in the upland south (see above). However, J.W. Petranka (personal communication) feels that current abundance is likely to be much lower than historical abundance due to loss of vernal ponds and other small wetlands across the eastern United States (see also Mitchell et al., 1999).
Inventories of Hemidactylium will need to consider the following aspects of their biology, which will tend to lead to an underestimate of population size: a short larval period, secretive nature of adults, and a propensity of adult females to skip years of reproduction.
1Reid N. Harris
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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