Hemidactylium scutatumFour-toed Salamander

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Geographic Range

Hemidactylium scutatum, the four-toed salamander, occurs from Nova Scotia to northern Minnesota, and south to the Gulf of Mexico. It has a discontinuous range and occurs only in small isolated populations in the southern and midwestern states. Its range is more continuous in states along the Appalachian Mountain Range, New England and west to northeastern Minnesota. (Behler and King 1979, Conant and Collins 1998, Lannoo 1998).

Habitat

Four-toed salamanders have specialized habitat requirements which require suitable breeding wetlands within or adjacent to mature forests. They prefer mature, mesic forests with dense canopy cover to preserve body moisture, an abundance of downed woody debris for cover and foraging opportunities, and vernal pools, ponds, bogs, shallow marshes, or other fishless bodies of water for nesting and larval success. Wooded wetlands such as seepage swamps or cedar swamps with many moss mats are ideal. Male adults can be located under leaves, bark, and logs in the upland forest, while females are most often found during the breeding season nesting in moss mats which overhang pools of water. (Harding 1997, Petranka 1998).

Physical Description

The four-toed salamander is a small plethodontid (lungless) salamander only 5 to 10.2 cm (2 to 4 in) in length. It is a rusty brown color or gray-brown color with grayish sides. It is often speckled with black and bluish spots. Unique four-toed hind feet and a constricted ring around the base of its tail easily identify it. They have nasolabial grooves and 13 to 14 coastal grooves (Harding 1997). The tail makes up about 57 percent of its total body length (Petranka 1998).

Female four-toed salamanders have rounded snouts, while sexually active males have more squared (truncated) snouts. Enlarged premaxillary teeth are also evident in sexually active males and can be seen with a closed mouth. The snout-to-vent length (SVL) is approximately 15 percent longer in females than males (Petranka 1998).

Hatchlings are only 11 to 15 mm total body length. They are usually born with toes or toe buds. The larvae are aquatic and a yellowish brown color. A dorsal fin runs from the length of the tail to near the back of the head. Some hatchlings look more like adults but have shorter tails (Petranka 1998).

Development

Reproduction

Mating occurs in the late summer, fall, and possibly into early winter in some places. The male courts the female first by rubbing his nose on the female's nose, then he will circle around her with his tail bend at a sharp right angle. At some point the female straddles the male's tail and presses her snout on the base of his tail. Eventually the male starts moving forward, undulating his tail, and begins depositing spermatophores, while the female follows him at a close distance. The spermatophores are a jelly-like glob that are about 2mm wide at the base and tapers to a thin stalk, which is topped with a yellowish sperm cap. The female picks up the spermatophores and deposits them into her cloaca while pressing her snout against the male's tail. This "straddle walk" lasts for up to 20 minutes (Harding 1997, Petranka 1998).

Female four-toed salamanders migrate to nesting sites primarily from the last week of March through the second week of April, but may wait until as late as early June. Oviposition occurs from mid to late April in Michigan, but can occur as late as February in southern Alabama. Females seek out moss clumps that are just above a pool of water usually in swamps, bogs, marshes, vernal ponds, and slow moving streams. The nesting medium is usually raised clumps of sphagnum moss, but leaf litter, rotting logs, or grass and sedge clumps are also used. The female then locates or constructs a cavity to deposit her eggs, which takes several minutes for each one and may take several hours for the whole clutch. The eggs have a sticky outer coating, which she uses to adhere to the surrounding moss. Fifteen to 80 eggs, each between 2.5 and 3.0 mm in diameter, are laid. More eggs tend to be laid by larger females (Harding 1997, Oliver 1955, Petranka 1998). Females often share nests and as many as 1110 eggs have been found in a single nest (Blanchard 1934). Nest availability is thought to be a factor in this communal nesting behavior (Breitenbach 1982). Often one or more (usually one) female will stay with the nest for a period, but they are usually gone by hatching. Despite a lack of defensive behavior toward invading predators, the female's nest attendance has been found to increase embryo survival (Carreno and Harris 1998). It is believed that the mother's skin secretions may protect the eggs by impeding fungus growth. So far, no beneficial link has been established between joint nesting and embryo survival (Harris and Gill 1980). The incubation period varies from 38 to 62 days depending upon the region and local site conditions. Average survivorship after hatching has been estimted at 9 and 21 percent (Harding 1997, Petranka 1998).

After hatching the larva wiggle from their nest and drop into the nearby water. They are only about 1.1 to 1.4 cm total body length at birth. During this larval stage they feed primarily on zooplankton and other invertebrates. Their larval period lasts between 23-39 days, which is brief compared to other amphibians. At transformation they are only 1.7 to 2.5 cm total body length (Harding 1997, Petranka 1998). The sex ratio of juveniles is nearly equal (Blanchard 1935).

It takes between two and three years for H. scutatum to reach sexual maturity. Captive specimens have lived as long as nine years but it is unknown how long free-ranging individuals may survive (Harding 1997).

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)
  • Average number of offspring
    30
    AnAge
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    912 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    912 days
    AnAge

Lifespan/Longevity

Behavior

Although conspecific behavior other than courtship is not well documented, it is thought that four-toed salamanders may be slightly aggressive toward each other in defense of territories. These territories are no more than small burrows or shelters such as logs or bark.

If molested by humans or predators a four-toed salamander will curl up, hide its head under its tail and become still. At times they may aggressively posture themselves by lifting their head high and swaying the tail while secreting a mild but distasteful skin toxin. They can also voluntarily detach their tails, which continue to wiggle, possibly distracting predators. This autotomization of their tails in unique. The tails of most salamanders must be grasped to come off (Harding 1997, Petranka 1998).

Little is known about their larval interactions, but behavioral studies have shown a lack of schooling behavior, indicating an inability to recognize kin or conspecific individuals from visual or chemical cues. Schooling behavior is a deterrent to predation and increases health by improving the warm of the environment. Thus, the four-toed salamander’s lack of this behavior likely contributes to their low population densities (Carreno, Vess, and Harris 1996).

Four-toed salamanders will share breeding sites with ambystomatid salamanders ("mole salamanders") and they have been found sharing microhabitats with other plethodontids such as the red-backed salamander (Plethodon cinereus), although interactions between these species have not been observed (Easterla 1971, Petranka 1998). In late autumn four-toed salamanders will gather with each other and other amphibians near overwintering sites. As many as two hundred individuals have been found in one site under leaf litter and inside rotting logs in November. It is presumed that they spend the coldest winter periods underground (Petranka 1998).

Food Habits

Few studies have been conducted on the feeding habits of the four-toed salamander, but it is believed their diet consists mainly of insects and their larvae (beetles, flies, ants, bristletails), spiders, mites, worms, and snails (Harding 1997, Petranka 1998).

Economic Importance for Humans: Positive

Forest dwelling salamanders, in general, have been shown to be very important contributers to nutrient cycling and energy flow in forest ecosystems. Therefore, they are important for the health and balance of forest systems as both predator and prey. A study in New Hampshire showed that forest salamanders act as sinks for high quality nutrients such as calcium and their tissue is higher in protein than birds or mammals. Additionally, their collective biomass may be twice that of birds and around the same as small mammals (Burton 1975a, 1975b). While Four-toed salamanders alone are not this abundant, it is likely that they contribute similarly to the food web in many forests where they are plentiful.

Their diet of calcium rich invertebrates makes them nutritious meals for shrews, snakes, birds, fish, and other carnivores which likely feed on four-toed salamanders (Burton 1975b, Harding 1997).

Four-toed salamanders are harmless, slow moving, colorful creatures of our forests and wetlands and are can be an interesing find for the casual naturalist or small child. The asthetic niche these creatures hold makes outdoor recreation more valuable to many.

Economic Importance for Humans: Negative

The four-toed salamander is completely harmless to humans and their interests.

Conservation Status

The four-toed salamander is thought to be in a state of decline throughout its range due primarily to its specialized habitat requirements in conjunction with destruction, degradation, and fragmentation of wetlands and forests. Even in the north and east, where the four-toed salamander's range is more continuous, it only occurs is small isolated colonies where suitable wetland-woodland interfaces exist. Additionally, the low dispersal ability of this salamander hinders it from recolonizing suitable habitat once it has been extirpated from an area (Harding 1997).

Hemidactylium scutatum is currently listed as endangered in Indiana and Minnesota, threatened in Illinios, and has special concern or rare status in Wisconsin, Ohio, and Missouri (Lannoo 1998). To improve conservation efforts, people should be educated on the vulnerability and value of the species.

To improve and increase habitat for the four-toed salamander, mature, closed canopy, mesic hardwood forests should be preserved. Downed woody debris should be left in place or added to these forests. Shallow vernal pools can be created within these woodlands and raised hummucks of earth can be added in and around the pool to promote growth of spagnum moss and sedges (Petranka 1998). The creation of suitable habitat between two populations, or "corridors," could also be investigated where two fragmented populations in close proximity exist.

Individuals are likely killed crossing roads while migrating to and from breeding sites. As a preventative measure, "'critter-culverts" can be installed in areas of high road kill risk to allow salamanders to pass underneath roads to and from their breeding sites.

Other Comments

PLEISTOCENE GLACIATION AND DISJUNCT DISTRIBUTION:

Hemidactylium scutatum occures only in small isolated populations in Illinois, Indiana, Kentucky, Missouri, Arkansas, Oklahoma, Louisiana, Mississippi, Alabama, and Florida. These disjunct populations in the southern and midwestern states are thought to be relict populations left during the post pleistocene glacier retreats. As glaciers moved south during the Pleistocene period the climate cooled and terrestrial animals were gradually forced into warmer refugia in the south. Later, as the glaciers retreated north, barriers such as prairies and deforested areas were created. These barriers stranded populations of animals with low disperal ability and specialized habitat requirements, such as H. Scutatum, and they were left stranded in isolated pockets of suitable habitat. (Lannoo 1998).

EVOLUTION:

The four-toed salamander is a lungless salamander of the Plethodontidae family. All plethodontids are lungless, breathe through their skin, and most are completely terrestrial. However, the four-toed salamander belongs to the tribe Hemidactyliini of the Plethodontinae subfamily. Members of this tribe are the only plethodontids to have an aquatic larval stage and are thought to have split from an earlier line of plethodontids. This suggests the four-toed salamander is a very primitive plethodontid and more closely related to the lunged Ambistomatidae family, or mole salamanders (Wake 1966).

It has been long hypothosized that plethodontid salamanders, evolved in the Appalachian Mountains, slowly losing their lungs in order to reduce buoyancy, become stream-lined, sink easily, and grasp stream bottoms. This allowed them to avoid being carried downstream, away from their habitat, by swift mountain currents.

Due to recent evidence that the Appalachian region was not mountainous at the time of plethodontid evoluion, this hypothesis has been challenged and a debate has developed. Alternative selective mechanisms for lung loss, such as selection for narrower heads and increased prey-capture abilities, have been suggested. The outcome of this debate will be significant in determining the correct phylogenetic relationships of the four-toed salamander and other plethodontids (Beechy and Bruce 1992, Wake 1966).

Contributors

Matthew Gates (author), Michigan State University, James Harding (editor), Michigan State University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

References

Beechy, C., R. Bruce. 1992. Lunglessness in Plethodontid salamanders is consistent witht he hypothesis of a mountain stream origin: A response to Ruben and Boucot. American Naturalist, 149(4): 839-847.

Behler, J., F. King. 1979. National Audubon Society Field Guide to North American Reptiles and Amphibians. New York, NY: Chanticleer Press and Alfred A. Knopf, Inc..

Blanchard, F. 1934. The relation of the female four-toed salamander to her nest. Copeia, 1934: 137-138.

Blanchard, F. 1935. The sex ratio in the salamander Hemidactylium scutatum (Schlegel). Copeia, 1935: 103.

Breitenbach, G. 1982. The frequency of communal nesting and solitary brooding in the salamander, Hemidactylium scutatum. Journal of Herpetology, 16(4): 341-346.

Burton, T., G. Likens. 1975b. Energy flow and nutrient cycling in salamander populations in the Hubbard Brook Experimental Forest, New Hampshire. Ecology, 56: 1068-1080.

Burton, T., G. Likens. 1975a. Salamander populations and biomass in the Hubbard Brook Experimental Forest, New Hampshire. Copeia, 1975: 541-546.

Carreno, C., T. Vess, R. Harris. 1996. An investigation of kin recognition abilities in larval four-toed salamanders, Hemidactylium scutatum (Caudata: Plethodontidae). Herpetologica, 52: 293-300.

Carreno, C., R. Harris. 1998. Lack of nest defense behavior and attendance patterns in a joint nesting salamander, Hemidactylium scutatum (Caudata: Plethodontidae). Copeia, 1998(1): 183-189.

Conant, R., J. Collins. 1998. A Field Guide to Reptiles and Amphibians of Eastern and Central North America, Third ED., Expanded. Boston and New York: Houghton Mifflin.

Easterla, D. 1971. A breeding concentration of fourt-toed slamanders, Hemidactylium scutatum, in southeastern Missouri. Journal of Herpetology, 5: 194-195.

Harding, J. 1997. Amphibians and Reptiles of the Great Lakes Region. Ann Arbor, Michigan: University of Michigan Press.

Harris, R., D. Gill. 1980. Communal nesting, brooding behavior, and embryonic survival of the four-toed salamander *Hemidactylium scutatum*. Herpetologica, 36(2): 141-144.

Lannoo, M. 1998. Status and Conservation of Midwestern Amphibians. Iowa City, Iowa: University of Iowa Press.

Oliver, J. 1955. The Natural History of North American Amphibians and Reptiles. Princeton, New Jersey: D. Van Nostrand Company, Inc.

Petranka, J. 1998. Salamanders of the United States and Cananda. Washington D.C.: Smithsonian Institution Press.

Wake, D. 1966. Comparitive Osteology and Evolution of the Lungless Salamanders, Family Plethodontidae. Los Angeles, California: Anderson, Ritchie and Simon.