Description

DESCRIPTION: (A description of species morphology as if you had the amphibian in your hand, typically starting with the snout-vent length, then focusing from the head to the body and extremities)

Hemidactylium scutatum is a small plethodontid salamander with only four toes on each hind foot, unlike most other salamanders which have five. Female snout-vent length ranges from about 29 - 72 mm, while female total lengths range from 62 - 92.8 mm (see Variation). Males have a total length range of about 50 - 54 mm (Lannoo 2005). The tail is about 57% of the total body length and its base is noticeably constricted (Gates 2002). The snout is short and rounded (Florida Natural Areas Inventory 2001). There are 13 - 14 costal grooves (Gates 2002).

DIAGNOSIS: (How this species is differentiated from similar species)

Unlike most other salamanders, H. scutatum have four toes on each hind foot instead of five. Dwarf salamanders in the Eurycea quadridigitata complex also have four toes, but have a yellowish belly with a lateral stripe (Florida Natural Areas Inventory 2001).

Unlike other plethodons, H. scutatum are not direct-developing and have a larval stage (Lanoo 2005, Wahl et al. 2008).

COLORATION: (In life and/or in preservative)

In life, the dorsum is rusty brown to black and has black dots. The lateral surfaces are grayish while the venter is bright white with bold, black spots (Florida Natural Areas Inventory 2001).

VARIATION: (if known)

Size at reproductive maturity varies greatly among females. In the George Washington National Forest in Virginia, where the elevation is 1,000 m, the average snout-vent length at reproductive maturity is 42.0 mm and the average total length is 92.8 mm. In lowland Virginia, mature females have snout-vent lengths ranging from 29 - 33 mm, while lowland Michigan females can reproduce when they have total lengths between 62 - 72 mm (Lannoo 2005). Females have a snout-vent-length that is about 15% longer than in males (Gates 2002). Males reach maturity at about 54 mm in total length in Michigan, but can be as small as 50 - 52 mm. Reproductive maturity in Michigan is estimated to occur at 2.3 years old, while lowland Virginia populations are estimated to reach reproductive maturity at 22 months (Lannoo 2005).

Sexually active males have snouts that are more square and truncated than those of females. Sexually active males also have enlarged premaxillary teeth that are visible when the mouth is closed (Gates 2002).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Canada, United States

U.S. state distribution from AmphibiaWeb's database: Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Massachusetts, Maryland, Maine, Michigan, Minnesota, Missouri, Mississippi, North Carolina, New Hampshire, New Jersey, New York, Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, Tennessee, Virginia, Vermont, Wisconsin, West Virginia

Canadian province distribution from AmphibiaWeb's database: New Brunswick, Nova Scotia, Ontario, Quebec

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (7 records).

The species range is from southeastern Canada to the Gulf of Mexico via the United States, extending westward to Wisconsin, Illinois, Missouri, and Oklahoma. In the southwest parts of this range, the species populations are disjunct. Adults generally inhabit coniferous or hardwood forests that surround still waters like ponds, bogs, and swamps, which are necessary for larvae (Lannoo 2005). The Northeastern parts of the species range are characterized by coniferous bogs. In the western areas of the species range, the habitat is composed of oak-hickory mixed hardwoods such as oak-hickory-sweetgum (Quercus-Carya-Liquidambar spp.) in Missouri. In the southern parts of the range, the species occupies forests with various oaks and pines (Meyer 2008).

Life History, Abundance, Activity, and Special Behaviors

In winter, H. scutatum can be found in high densities in holes and crevices in the ground with other amphibians (Lannoo 2005).

Adults mate in autumn on land and females migrate from woodlands to ponds, bogs, or streams for oviposition in spring (Lannoo 2005). Males begin courting females by rubbing his nose on the female’s, then encircling her with his tail bent at a right angle. While undulating his tail and releasing spermatophores, the male advances forward and the female follows. The female presses her snout against the male’s tail while placing the spermatophores into her cloaca. This behavior may last for up to 20 minutes (Gates 2002).

Migration to nesting sites occurs at different times depending on altitude, with lowland Virginia salamanders migrating between February and mid-April, compared to salamanders in montane Virginia, lowland Michigan, and New York migrating from April to mid-May. Some populations may migrate as late as early June (Readel and Phillips 2006, Lannoo 2005, Gates 2002).

Breeding and nesting occurs on the edges of wetland areas like ponds and springs, most often in Sphagnum moss (Maley Berkey 2010, Chalmers 2004). Hemidactylium scutatum also nests in Climacium, Thuidium, and Mnium mosses. Nests are usually located in moss but can also be found in sedges, liverworts, loose bark, pine needle mounds, rotten wood, stumps, logs, upturned roots, under branches, under rocks, or in aquatic grass tufts (Wahl et al. 2008, Chalmers 2004). In Maine, nests have been observed from late April to early July (Chalmers 2004). Females lay eggs a few inches above water and prefer steep banks, which help larvae reach the water when they hatch and improve their chance of survival. Females also prefer nesting sites where vegetation has a lower pH, as pH of vegetation has been observed to have an inverse relationship with embryonic survival rates (Wahl et al. 2008). Generally one female solitarily broods a nest (Lannoo 2005).

Nests may have as many as 100 eggs, but average clutch sizes generally range from 4 to 80 eggs, and nests with over 40 eggs are thought to be communal (Chalmers 2004, Lannoo 2005). Joint or communal nests may be formed by multiple females. Generally, communal nests only have one brooding female, and females may alternate brooding a nest. One communal nest in Michigan was observed to have about 1,100 eggs and was likely made by around 20 females (Lannoo 2005). Since egg-laying occurs at different times in joint nests, groups of eggs in joint nests may be in different developmental stages. Following nest flooding by heavy rain, it is common for females to desert nests. The embryonic survival of deserted nests is significantly lower than that of brooded nests, as has been observed in other salamanders (Harris and Gill 1980). Nests have been observed to be reused for 2 - 3 years (Chalmer 2004).

As has been observed in other salamanders that brood eggs, oophagy occurs in H. scutatum. It is possible that females eat fungal-infested eggs to protect the others from infestation, as in Desmognathus ochrophaeus, or that an intruding female will eat eggs in a nest before laying her own to attain nutrition without leaving her clutch (Harris and Gill 1980). However, in general, brooding females do not eat (Lannoo 2005).

The embryonic period is 45 days with 28 distinct stages (Hurney et al. 2015). Upon hatching, the egg jelly loses its firm consistency and oozes (Chalmers 2004) before larvae wriggle into the water (Lannoo 2005, Readel and Phillips 2006).

Hemidactylium scutatum are thought to be aggressive toward each other when defending their territory, which usually only encompass small shelters in logs or bark (Gates 2002). When disturbed by predators, H. scutatum may curl up, hide its head under its tail, and stay still. Adults may also display a defensive posture to predators like ring-necked snakes. The dorsal surface of the tail has a glandular concentration. The tail may be raised and undulated. There is aposematic coloration on the venter and the skin produces mildly noxious secretions. The tail has autotomy and can be voluntarily shed, unlike most other salamanders whose tails must be grasped before falling off (Lannoo 2005, Illinois Natural History Survey, Gates 2002). Hemidactylium scutatum lack defenses against introduced predatory fish (Illinois Natural History Survey).

Predators of H. scutatum include beetles like Pterostichus spp., centipedes (Chilopoda), and other amphibians such as Eastern newts (Notophthalmus viridescens). Beetles have been observed to have a preference for other salamander eggs, such as those of Desmognathus ocoee, over H. scutatum eggs (Illinois Natural History Survey, Lannoo 2005).

Adult H. scutatum consume various calcium-rich terrestrial invertebrates, while larvae consume small aquatic invertebrates (Hammerson and Jackson 2014, Gates 2002).

Females likely have long lives and may be able to live over 9 years (Lannoo 2005).

Hemidactylium scutatum occurs with other pond-breeding amphibians in the United States, such as Eastern newts (Notophthalmus viridescens), spotted salamanders (Ambystroma maculatum), smallmouth salamanders (A. texanum), tiger salamanders (A. tigrinum), an 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) (Lannoo 2005).

Larva
Hatchlings have a black pupil, a bronze- or gold-flecked iris, and an eye line on both sides of the eye. On the forehead, there is a Y-shaped marking between the eyes. The gills become brown or orange-red. The ventral surface is cream or white, which is distinct from the tan, latticed, and spotted dorsum (Chalmers 2004).

The embryonic period is 45 days with 28 distinct stages (Hurney et al. 2015). Upon hatching, larvae wriggle into the water (Lannoo 2005, Readel and Phillips 2006). The larval period is about 20 - 40 days, which is relatively short compared to other plethodontids (Lannoo 2005, Wahl et al. 2008). Larvae metamorphose in the summer after about 1.5 - 2 months and reach reproductive maturity in 18 more months (Lannoo 2005).

Larvae need still water such as bogs, swamps, or ponds, without fish (Lannoo 2005).

Larvae are able to recognize their kin (Lannoo 2005).

Larvae feed on planktonic organisms and small worms (Lannoo 2005).

Larval ambystomatids, naiads, and fish likely feed on H. scutatum larvae. Larvae have lower levels of activity when predators are present, reducing the growth rate (Lannoo 2005).

Trends and Threats
Hemidactylium scutatum is considered of "Least Concern" on the IUCN Red List (IUCN 2022). While H. scutatum populations are abundant in protected areas like Great Smoky Mountains National Park and the George Washington and Jefferson National Forest, the loss of vernal summer ponds and draining of wetlands raises concerns for populations in the eastern United States (Lannoo 2005). Wetlands are vulnerable to habitat loss and degradation by fragmentation, pollution from agricultural runoff, and introduced predatory fish, which H. scutatum lack defenses against (Maley Berkey 2010, Meyer 2008). In Illinois, where H. scutatum is listed as "Threatened", subpopulation surveys have shown that the species has high levels of heterozygosity and an inbreeding coefficient of effectively 0, indicating healthy levels of genetic diversity (Maley Berkey 2011). Despite its rarity, H. scutatum populations are stable (Hammerson and Jackson 2014).

Hemidactylium scutatum have a short larval period and females tend not to lay eggs annually, which, combined with their secretive nature, likely cause underestimations of population size (Lannoo 2005).

Fungus may infest eggs, and it is possible that oophagy occurs to protect other eggs from infestation. It is unknown if this occurs via secondary infection. Small nematodes have been observed in egg jelly and protozoan parasites have been seen in adults (Lannoo 2005).

Recommended conservation actions include upholding the ecological integrity of streams and surrounding upland areas. Activities that cause sedimentation should be avoided, and the hardwood canopies in floodplains areas should be protected (Florida Natural Areas Inventory 2001). These canopies allow mosses to grow, which H. scutatum build nests on (Meyer 2008). Feral hogs disrupt habitats and may eat salamanders, so they should be eliminated or controlled (Florida Natural Areas Inventory 2001). Additionally, decreases in pond pH, increases in water temperature, and sedimentation can negatively affect larvae (Meyer 2008).

Comments

PHYLOGENETIC RELATIONSHIPS:

Bayesian inference and Maximum Parsimony analysis on mtDNA of cytochrome oxidase gene co1 from H. scutatum supports the hypothesis that plethodontid salamanders originated from the Appalachians. These analyses also showed the divergences of regional monophyletic clades, with higher diversity in southern parts of the species range compared to northern areas. Two of these clades have a wide range across most of the known range of H. scutatum. These two clades are further divided to form five geographic subclades: Southwest, Teays, Ouachita, Northeast, Ozark, and Midwest (Herman 2009).

OTHER INTERESTING INFORMATION:

References
Chalmers, R.J. (2004). Wetland and Nest Scale Habitat Use by the Four-toed Salamander (Hemidactylium scutatum) in Maine, and a Comparison of Survey Methods. [Masters Thesis, The University of Maine]. Electronic Theses and Dissertations. [link]

Florida Natural Areas Inventory. (2001). Four-Toed Salamander Hemidactylium scutatum. Reference Natural Communities Geodatabase. https://www.fnai.org/PDFs/FieldGuides/Hemidactylium_scutatum.pdf. Accessed 23 January 2024.

Gates, M. (2002). Hemidactylium scutatum. Animal Diversity Web. https://animaldiversity.org/accounts/Hemidactylium_scutatum/. Accessed 25 January 2024.

Hammerson, G., Jackson, D.R. (2014). Hemidactylium scutatum. NatureServe Explorer. https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.101408/Hemidactylium_scutatum. Accessed 25 January 2024.

Harris, R. N., and Gill, D. E. (1980). Communal Nesting, Brooding Behavior, and Embryonic Survival of the Four-Toed Salamander Hemidactylium scutatum. Herpetologica, 36(2), 141–144. [link]

Herman, T.A. (2009). Range-wide phylogeography of the four-toed salamander (Hemidactylium scutatum): out of Appalachia and into the glacial aftermath. [Masters Thesis, Bowling Green State University]. OhioLINK. [link]

Hurney, C.A., Babcock, S.K. Shook, D.R., Pelletier, T.M., Turner, S.D., Maturo, J., Cobgill, S., Snow, M.C. Kinch, K. (2015). “Normal table of embryonic development in the four-toed salamander, Hemidactylium scutatum.” Mechanisms of Development, 136, 99-110. https://doi.org/10.1016/j.mod.2014.12.007.

Illinois Natural History Survey. (n.d.) Four-Toed Salamander. INHS Herpetology Collection, University of Illinois Urbana-Champaign. https://herpetology.inhs.illinois.edu/species-lists/ilspecies/four-toed-salamander/. Accessed 23 January 2024.

IUCN SSC Amphibian Specialist Group. (2022). Hemidactylium scutatum. The IUCN Red List of Threatened Species 2022: e.T59285A193374453. https://dx.doi.org/10.2305/IUCN.UK.2022-1.RLTS.T59285A193374453.en. Accessed 14 November 2023.

Lannoo, M. (2005). Amphibian Declines: The Conservation Status of United States Species. (Lannoo, M., Ed.) University of California Press.

Larson, A., Wake, D., Devitt, T. (2006). Plethodontidae. Lungless Salamanders. Tree of Life Web Project Version 26 September 2006 (under construction). http://tolweb.org/Plethodontidae/15441/2006.09.26 http://tolweb.org/. Accessed 1 February 2024.

Macey, J.R. (2005). Plethodontid salamander mitochondrial genomics: A parsimony evaluation of character conflict and implications for historical biogeography. Cladistics, 21, 194-202. [link]

Maley Berkey, A.J. (2010). Surveys for nesting sites of the four-toed salamander at Middle Fork SFWA. Illinois Natural History Survey. Obtained from https://dnr.illinois.gov/content/dam/soi/en/web/dnr/grants/documents/wpfgrantreports/2009029w.pdf. Accessed 16 November 2023.

Maley Berkey, A.J. (2011). Genetic Variation in Populations of the four-Toed Salamander at the Middle Fork State Fish and Wildlife Area: To collect tissue samples for individual populations and use genetic analyses to estimate the genetic variation within each population. Illinois Natural History Survey. https://dnr.illinois.gov/content/dam/soi/en/web/dnr/grants/documents/wpfgrantreports/2011017w.pdf. Accessed 16 November 2023.

Meyer, Rachelle. (2008). Hemidactylium scutatum. Fire Effects Information System, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. https://www.fs.usda.gov/database/feis/animals/amphibian/hesc/all.html. Accessed in January 2024.

Natural Heritage & Endangered Species Program. (1994). Four-toed salamander. Massachusetts Division of Fisheries and Wildlife https://www.mass.gov/doc/four-toed-salamander/download#:~:text=Etymology%3A%20The%20specific%20name%20Hemidactylium,and%20sides%20of%20the%20body. Accessed 29 January 2024.

Readel, A.M. and Phillips, C.A. (2006). A survey of the reptiles and amphibians of Kickapoo State Park and the Middle Fork State Fish and Wildlife Area (MFSFWA). Illinois Natural History Survey. https://dnr.illinois.gov/content/dam/soi/en/web/dnr/grants/documents/wpfgrantreports/2006032w.pdf. Accessed 16 November 2023.

Wahl, G. W., Harris, R. N., and Nelms, T. (2008). Nest site selection and embryonic survival in four-toed salamanders, Hemidactylium scutatum (Caudata: Plethodontidae). Herpetologica, 64(1), 12–19. [link]

Species Account Citation: AmphibiaWeb 2024 Hemidactylium scutatum: Four-toed Salamander <https://amphibiaweb.org/species/4069> University of California, Berkeley, CA, USA. Accessed Nov 23, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 23 Nov 2024.

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