Amphibians of North Carolina
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Hemidactylium scutatum - Four-toed Salamander


Taxonomy
Class: Amphibia Order: Caudata Family: Plethodontidae Subfamily: Hemidactyliinae
Taxonomic Comments: The Four-toed Salamander (Hemidactylium scutatum) is a member of one of the most genetically distinctive and ancient lineages within the family Plethodontidae. Based on complete mtDNA sequencing, Mueller (2006) estimated that the Hemidactylium lineage arose about 107-108 million years ago. The Four-toed Salamander also has the largest geographic range of any plethodontid salamander and contains a series of highly disjunct and isolated populations in the western and southern portions of its range. A recent molecular analysis of mtDNA (Herman and Bouzat 2016) documented deep sequence diverges within the species and provided very strong support for the recognition of five regional monophyletic clades within Hemidactylium (Clades B-F). A sixth clade was also recognized (Clade A) had less statistical support. The oldest clade was estimated to have arisen over 2 million years ago, which suggests that Hemidactylium likely contains more than one species. Three of the clades recognized by Herman and Bouzat (2016) occur in North Carolina, and one (Clade E) is an ancient lineage that has a very limited distribution in the western mountains and adjoining areas of northwestern South Carolina. This and perhaps other lineages may eventually be recognized as separate species. At present, the Four-toed Salamander is being treated as a single species with complex genetic structure.
Species Comments:
Identification
Description: The Four-toed Salamander is a small plethodontid that has several distinctive features, including only four toes on each hind foot, a constriction around the base of the tail, and a white venter with bold black spots or blotches. The dorsum has a dark brown ground color that is overlain with rusty orange blotches that are more prominent on the top of the tail and the upper limbs. The sides of the body are grayish. The tail of adults comprises about 57% of the total length on average, and is proportionately shorter in females (Petranka 1998). Sexually active males have truncated snouts (more rounded in females) and enlarged premaxillary teeth. The adults range from 5-10 cm TL, and females average about 15% longer than males.

The hatchlings vary from 11-15 mm TL and have front limbs with well-formed toes and rear limbs with toe buds (Petranka 1998). The larvae have a broad tail fin that extends along the back to near the head. They have a mottled yellowish brown dorsum, a slender build, prominent eyes, and well-developed gills. Small juveniles generally resemble the adults but have proportionately shorter tails.
Online Photos:    Google
Observation Methods: Four-toed Salamanders are commonly encountered during the fall and spring months when adults are present around breeding sites.
AmphibiaWeb Account
Distribution in North Carolina
Distribution Comments: This species has a very large range that extends from Nova Scotia westward through extreme southern Canada to the Great Lakes region in Ontario and into eastern Minnesota in the US. From there, the range extends southward through much of the forested regions of the eastern US to the Florida Panhandle and the Gulf Coast regions of Alabama, Mississippi, and Louisiana. Populations are disjunct in many areas in the southern and southwestern portions of the range. In North Carolina, populations occur in all three physiographic provinces, but are relatively uncommon in the mountains and Coastal Plain.
Distribution Reference: Beane et al. (2010); Petranka (1998)
County Map: Clicking on a county returns the records for the species in that county.
Key Habitat Requirements
Habitat: The juveniles and adults live in forests that surround breeding sites such as bogs, marshes, vernal ponds and seepage runs. The females breed in fish-free habitats and typically lay their eggs in moist moss clumps along the margins of aquatic sites. Populations in North Carolina can be found in both hardwood and mixed pine-hardwood forests that have fish-free habitats with suitable nesting habitat. The nesting sites need to remain moist during the incubation period, and the pools and seepage runs must have water that persists until mid to late summer in order to support the aquatic larvae (Beane et al. 2010, Petranka 1998).

Biotic Relationships: The larvae usually share breeding ponds with predators such as Ambystoma larvae, newts, and predaceous insects. Eastern newts prey on the larvae, and other aquatic predators such as the larvae of odonates, dytistid beetles, and mole salamanders likely do also. The larvae lack defenses against fish, which explains why populations are strongly associated with seasonal ponds (Kats et al. 1988). The adults will assume a defensive posture in the presence of a predator, and have a variety of defenses against predators such as small snakes or shrews (Brodie 1977). The skin produces noxious secretions and exposure of the boldly marked belly may function as warning coloration. Individuals will often raise and undulate the tail in the presence of a predator, and will autotomize the tail if sufficiently provoked. The wiggling autotomized tail acts to detract predators from the head and body.
See also Habitat Account for Hardwood Forests with Isolated Pools
Life History and Autecology
Breeding and Courtship: In most populations the adults appear to mate in the fall and possibly the early winter months before migrating to the breeding sites. Most of our information on breeding is based on studies of northern populations (Petranka 1998). Blanchard (1933a) found females with spermatozoa in their cloacae in late October and November in Michigan, and adults collected in September and October courted soon after being returned to the laboratory. Other specimens that were collected in Michigan in early November deposited spermatophores through early December (Branin 1935). The mating season of more southern populations is poorly documented. In North Carolina the adults become active on the ground surface in late summer and fall and presumably mate during this period. Kilpatrick (1997) provided evidence that mating may occur in West Virginia populations during both the autumn and early spring based on when sperm was present in the vasa deferentia, but direct observations of mating were not observed.

The adults engage in a tail-straddle walk as seen in other plethodontids. Courtship behavior has not been described in detail, but the following general account is based on observations by Branin (1935) and summarized by Petranka (1998). The male initiates courtship by showing heightened activity that is characterized by the active nosing of conspecifics. A male that encounters a female during this stage will often circle about with the tail bent sharply at a right angle to his body. The female eventually straddles the male's tail and presses her chin against the dorsal surface of the base of his tail. The male then moves forward and undulates his tail from side to side. The female follows while maintaining her same relative position and tracks the movement of the tail with her chin. The tail straddle walk may lasts for 20 minutes. Branin (1935) observed females pausing over spermatophores for several minutes, but did not witness spermatophore pickup. The spermatophore consists of an expanded, gelatinous disk about 2-2.3 mm broad that tapers upward into a 1 mm diameter stalk which supports a pale yellowish sperm cap. The entire spermatophore is around 2.5 mm tall (Blanchard 1933a). Males have enlarged premaxillary teeth that protrude from the lip and are likely used to scratch the female's skin and introduce hedonic gland secretions.
Reproductive Mode: The males remain in forest-floor habitats after mating, but the females migrate to and from breeding sites. Movements to ponds typically occur shortly before the females begin ovipositing in late winter or spring. However, females in Arkansas have been observed migrating from October-March (Petranka 1998). Local migrations typically occur in association with the spring warm-up and females begin nesting shortly after arriving at the breeding sites. This typically is in late March through early May in northern populations and a month or more earlier in southern populations (Petranka 1998). Nesting in North Carolina populations is usually well underway by early to mid-March. Harris and Ludwig (2004) found that some females in Virginia breed annually, while others skip one or more years before breeding again. This likely reflects food limitations and the inability of some females to consume enough food to yolk a clutch annually.

After arriving at a breeding site the females select nesting sites that are next to the water's edge but above the water line. They most commonly lay their eggs in moss mats near the water's edge or in raised moss mats on islets within ponds. They occasionally use other microhabitats such as clumps of grasses, rushes, and sedges, or mounds of pine needles. Cool, shaded microsites such as steep banks and the moss-covered bases of trees or shrubs at the water's edge are often preferred. These provide shading and help keep the moss mats moist during the incubation period. Sphagnum mosses are commonly used for nesting, but other mosses that form thick mats or carpets such as species of Thuidium, Mnium, and Climacium are also used (Petranka 1998). The latter are frequently used in North Carolina, along with Sphagnum that is often present at breeding sites in the mountains.

The females construct crude cavities within moss mats or other nesting material and lay their eggs singly in a loose clump. The freshly laid eggs are 2.5-3.0 mm in diameter, have faint light gray pigmentation above, and are surrounded by two envelopes (Petranka 1998). Most females lay from 15-60 eggs, and clutch size is often positively correlated with female SVL. The level of egg brooding by females appears to vary locally. When nesting singly, the majority of females in some local populations brood their eggs through hatching, while most females in other populations abandon the eggs prior to hatching. The embryos develop slowly and typically take 6-10 weeks to reach the hatching stages (Kilpatrick 1997, Petranka 1998).

Although females in a local population often nest individually and brood their eggs, a substantial percentage often nest communally and produce nests that contain clutches from more than one female. One communal nest in Michigan contained 1110 eggs, and was estimated to be the product of around 30-35 females (Blanchard 1934). One unusual feature of the brooding behavior is that only one or two females typically remain with the eggs in a communal nest, while the remainder deposit their eggs and leave shortly thereafter.

Researchers in Virginia (Harris and Gill 1980, Harris et al. 1995) found that most communal nests had a single brooder, which is most commonly the first female to arrive at the nesting site. The brooding female incurs an energetic costs since she apparently feeds very little during this time. The authors found that brooding enhanced the survival of the embryos in both single and communal nests, but survival did not differ among the two types that were brooded. Nesting females were not aggressive to one another and there was little evidence of oophagy. This suggests that brooding in communal nests may reflect kin selection where a brooding female guards the eggs of close relatives. However, there is little evidence that the females aggressively defend the eggs from predators or intruders (CarreƱo and Harris 1998).

In another study Banning et al. (2008) found that embryos in communal nests tended to have higher survival than those in single nests. In addition, at least one female in a communal nest was more likely to have higher levels of a skin bacteria that inhibits a fungus that attacks eggs compared with females in single nests. Brooding females appear to be able to transmit antifungal bacteria to the developing embryos in their nests. This may be one of the major advantages of brooding.
Aquatic Life History: Shortly after hatching, the gilled larvae wiggle through moss mats or other nesting material and enter the pond or seep where they complete the larval stage. The larvae feed on small zooplankton and other invertebrates and have very brief larval periods relative to most plethodontid salamanders. The larval period in Michigan populations lasts about 6 weeks, with transformation occurring in July when larvae reach 18-24 mm TL (Blanchard 1923). Kilpatrick (1997) estimated the larval period to last 9 to 10 weeks in West Virginia, with transformation occurring in mid-August when larvae averaged 13.3 mm SVL and 16.6 mm TL. Other estimates for the length of the larval period are 39 days and 21 days for natural populations (Petranka 1998).

Berger-Bishop and Harris (1996) designed experiments to examined the effects of larval density and food level on growth parameters in Virginia larvae. They found that food level and larval density have little effect on relative tail length at any developmental stage. Larvae established at low and high experimental densities did not differ in relative tail length, SVL at metamorphosis, mass at metamorphosis, or length of the larval period. As in natural populations, the larval period was very brief (means of 23-27 days and 38-39 days for two experiments) and the larvae transformed on average when only 11-14 mm SVL and 17-25 mm TL.

Larvae are not strongly aggressive, and rarely bite or lunge at one another. Behavioral trials suggest that the larvae have the ability to recognize kin (Harris et al. 2003).
Terrestrial Life History: Females return to their summer forest-floor retreats shortly after leaving the nests. The juveniles also disperse away from breeding ponds within a few weeks after transforming and live in the surrounding forests until sexually mature (Petranka 1998). Movements generally occur on warm nights with misty or rainy weather. The juveniles and adults subsist on small invertebrates that are found in the leaf litter and beneath cover objects. Bishop (1919) found beetles, lepidopterans, spiders, mites, and bristletails in transformed New York specimens. Individuals tend to be inactive on the ground surface during the warmest summer months.

Adults maintained in the laboratory are only weakly aggressive towards conspecifics and probably do not defend burrows or cover objects during the warmer months of the year (Grant 1955). Both the adults and juveniles have been found congregating in late autumn in or near overwintering sites. Blanchard (1933b) found 18 Hemidactylium in November in and adjacent to a rotten log, and over 200 in cavities or depressions under leaf litter in an area that was less than four square meters. Specimens at northern locales are rarely found during the colder months after mid-November, and presumably spent the winter in subsurface retreats.

In Michigan, both sexes become sexually mature about 28 months after hatching when males reach 49-57 mm TL and females reach 62-68 mm TL (Blanchard and Blanchard 1931). In Virginia populations, individuals sexually mature about 2 years after hatching (Wood 1953b). Sex ratios of a large series of juveniles collected in Michigan were close to 1:1, with females slightly outnumbering males (Blanchard 1935).
General Ecology
Population Ecology: Local populations are centered around the breeding sites and tend to be patchily distributed across landscapes, particularly in the southern portion of the range. Factors that regulate the sizes of local populations are poorly known. Individuals do not appears to be strongly territorial and females do not appear to defend nesting habitats from conspecifics. Local populations tend to be small, with most probably having fewer than 100-200 adults.
Community Ecology: The larvae often share breeding ponds with other amphibians such as the Eastern Newt, several species of mole salamanders (Ambystoma spp.), and the Wood Frog. Interactions with these and other community members are largely unstudied. Nesting above the water line may have evolved as a way to avoid aquatic egg predators such as newts and Wood Frog tadpoles.
Adverse Environmental Impacts
Status in North Carolina
NHP State Rank: S3
Global Rank: G5
Status in North Carolina: SC
Environmental Threats: The Four-toed Salamander has specialized niche requirements that make it vulnerable to habitat disturbance. Key habitat requirements for sustaining local populations include seasonal, fish-free aquatic habitats, adequate moss-covered nesting sites along wetland margins, and sufficient forest habitat to sustain the juveniles and adults. Populations thrive in areas with mature hardwood forests that contain suitable breeding sites. A canopy of mature deciduous trees helps retain moisture on the forest floor and encourages the growth of moss mats around breeding sites. Mature forests also have large amounts of fallen woody debris and organic soils that offer optimal habitats for juveniles and adults outside of the breeding season. Although poorly documented, this species has undoubtedly declined markedly throughout its range because of the loss of vernal ponds, bogs and other wetlands associated with land clearing and development (e. g., Daniel 1989). Many populations in the southern portion of the range are geographic disjuncts and lack connectivity with nearest neighbors. Climate change may eliminate many populations in the future as hotter conditions prevail.
Status Comments: Hemidactylium populations in North Carolina consist of three evolutionary lineage, including Clade E of Herman and Bouzat (2016) that is a 2 million year old lineage that may eventually be recognized as a separate species. Clade E has a very limited range, and only a few extant populations are known to exist. Individuals who determine state and global ranks need to better integrate knowledge about genetic lineages within recognized species when determining ranks.
Stewardship: Viable populations of pond-breeding amphibians cannot be maintained unless there is sufficient habitat for both the aquatic and terrestrial stages of the life cycle. Scientists have obtained information on the use of terrestrial habitats by pond-breeding amphibians from radiotelemetry and radioactive tagging studies of adults and juveniles, and the use of drift fence arrays that were established at different distances from ponds. Semlitsch and Bodie (2003) reviewed and summarized data on movements of salamanders from ponds, and Rittenhouse and Semlitsch (2007) estimated the distances that species migrate from ponds based on statistical models. Rittenhouse and Semlitsch (2007) concluded that 95% of individual salamanders moved < 245 m from pond edges.

Data on the movements and terrestrial habitat use by Hemidactylium is largely lacking. Males remain in forested habitats year-round, while females undergo migrations to and from ponds during the late winter and early spring. Three animals in Massachusetts were found 152 m, 198 m, and 201 m from the nearest nesting habitat, while one animal was found 72 m from the nearest nesting site in Quebec (Meyer 2008). These anecdotal accounts suggest that the distances that Hemidactylium moves from breeding sites are similar to those of ambystomatid salamanders.

Land managers or land owners who are interested in constructing seasonal ponds to protect local populations of Hemidactylium should consider adding raised hummocks of earth in ponds, or raised hills along pond margins to encourage the growth of moss mats and sedges. Of course, none of these efforts will be successful without maintaining or creating an extensive forest buffer around the breeding sites.

Photo Gallery for Hemidactylium scutatum - Four-toed Salamander

12 photos are shown.

Recorded by: L. Osteen
Orange Co.
Recorded by: Steve Hall and Allison Weakley
Orange Co.
Recorded by: Billy Hartness, Joel Jakubowski
Rockingham Co.
Recorded by: J. A. Anderson
Surry Co.
Recorded by: F. Williams, S. Williams
Gates Co.
Recorded by: F. Williams, S. Williams
Gates Co.
Recorded by: Owen McConnell & Simpson Eason
Durham Co.
Recorded by: Steve Hall
Montgomery Co.
Recorded by: Steve Hall
Montgomery Co.
Recorded by: Chris McGrath, Jeff Humphries, Lori Williams (NC WRC), Ed Corey
Rockingham Co.
Recorded by: NC PARC Meeting
Rockingham Co.
Recorded by: FKW, SBW
Gates Co.