Amphibians of North Carolina
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Plethodon cinereus - Eastern Red-backed Salamander

Taxonomy
Class: Amphibia Order: Caudata Family: Plethodontidae Subfamily: Plethodontinae
Taxonomic Comments: Populations of a wide-ranging and geographically variable small Plethodon with a reddish dorsal stripe were traditionally thought to comprise a single polytypic species, the Red-backed Salamander (P. cinereus), with three recognized subspecies. Highton and Webster (1976) and Highton and Larson (1979) analyzed protein variation and found that two of the southern forms (P. c. serratus, P. c. polycentratus) differed substantially from a wide-ranging northern form (P. c. cinereus). They documented fixed allelic differences for five loci, and recognized the southern forms as a separate species, P. serratus. Another P. cinereus-like form in northern Virginia, P. shenandoah, was recognized as a separate species by Highton and Worthington (1967), while a second form that is a narrowly endemic to the central Blue Ridge Mountains in Virginia was recognized as P. sherando (Highton 2004).

Studies of geographic patterns of genetic variation in several salamander species have shown that populations in formerly glaciated regions are often less genetically variable than southern populations. This implies that these species have undergone a post-glaciation range expansion northward from southern refugia. Radomski et al. (2020) used both mtDNA and nuclear markers to examine post-glaciation range expansions in P. cinereus. The mtDNA analysis produced six geographically cohesive clades that increased in geographic range size from south to north. Their data suggest that populations may have survived in several glacial refugia, then underwent major range expansions following the last glacial retreat. In contrast to the mtDNA analysis, the nuclear loci revealed little phylogeographic structure. Despite substantial geographic variation within this wide-ranging species as documented by Radomski et al. (2020) and others, populations referable to P. cinereus are considered to constitute a single species.
Species Comments: Plethodon cinereus is a wide-ranging and common salamander that is found in the eastern US. There are hundreds of scientific papers that have documented various aspects of the biology of this species. These include studies of genetic and phenotypic variation, evolutionary biology, general life history, population and community ecology, reproductive and social behavior, and conservation biology. Fisher-Reid et al. (2021) provide a comprehensive review of the literature, and Jaeger et al. (2016) summarize over 50 years of research on the behavioral ecology of this species. Here, we provide a general overview of these studies based primarily on information summarized by Petranka (1998) and Fisher-Reid et al. (2021).
Identification
Description: The Eastern Red-backed Salamander is a small Plethodon that has small legs relative to body size, a rounded tail, and an average of 18-20 costal grooves. Two common color morphs occur in many populations. The striped or 'red-backed' morph has a broad, straight-edged, orangish red or red (rarely light tan) dorsal stripe that extends from the head onto the tail. The sides of the body are dark with whitish speckling, and the region immediately adjoining the dorsal stripe is typically darker and less speckled than the lower sides. The venter is strongly mottled with black and white. The unstriped or 'lead-backed' morph is similar, but lacks the reddish dorsal stripe. This form is uniformly dark on the dorsum and sides except for whitish speckling that tends to be concentrated on the lower sides. In addition to the striped and unstriped morphs, an 'erythristic' morph that has bright crimson red on the back, sides, and legs occurs in some northern populations (Petranka 1998). Other rare color morphs have occasionally been found that likely reflect genetic anomalies (Moore and Ouellet 2014). Both the striped and unstriped morphs occur in North Carolina populations.

Local populations of P. cinereus often contain both striped and unstriped individuals, and numerous studies have documented changes in the proportion of striped and unstriped individuals that occur at different spatial scales (Petranka 1998). Clinal variation is evident in many areas, but pinpointing the factors that maintain these polymorphisms and influence the proportion of striped and unstriped morphs has proven to be difficult. There is a general tendency for striped morphs to prevail in areas with colder climates, but other factors such as local microclimates, local forest types, and differential selection by predators appear to affect the proportion of striped and unstriped morphs in local and regional populations (Fisher-Reid et al. 2021).
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Observation Methods: The juveniles and adults are active on the ground surface during the cooler months of the year. They can be found beneath surface cover objects such as rocks, decaying logs or slabs of bark during the day, and on the forest floor at night.
AmphibiaWeb Account
Distribution in North Carolina
Distribution Comments: The Eastern Red-backed Salamander ranges from southern Quebec and the Maritime Provinces of southern Canada southward along the Atlantic seaboard to central North Carolina. The range extends westward through the Great Lakes region to Minnesota and adjoining areas of southern Canada, and to as far west as eastern Illinois, West Virginia, and northeastern Tennessee farther south. Populations in North Carolina are found primarily in the northern mountains southward to the French Broad River Valley, in the northeastern portion of the Piedmont, and in the northeastern and east-central portions of the Coastal Plain.
Distribution Reference: Beane et al. 2010, Fisher-Reid et al. 2021, Petranka 1998
County Map: Clicking on a county returns the records for the species in that county.
GBIF Global Distribution
Key Habitat Requirements
Habitat: This wide-ranging species has been found in a variety of forest types, including deciduous hardwoods, northern conifer forests, and mixed deciduous-conifer habitats (Petranka 1998). This is primarily a northern species and it is sensitive to excessive heat and drying. Populations in North Carolina and other areas in the southern portion of the range prefer cool, mesic forests, including stands of hardwoods and mixed stands of hardwoods and conifers. Mature forests with a well-developed closed canopy, deep soils, and ample surface cover provide ideal conditions.

Individuals in southern populations are active on the ground surface mainly during the spring and fall which allows them to escape exposure to hot and dry conditions that often occur during the summer months. In North Carolina, populations in the western mountains are buffered from extreme summer heat, but those in the Piedmont are restricted to cool, moist environs. They are often found on steep, north-facing slopes, often in association with rhododendrons and other disjunct, montane species. Coastal Plain populations are prevalent in bottomland forests that are dominated by hardwoods.
Biotic Relationships: This and other small woodland salamanders are preyed upon by a variety of predators, including snakes and birds. Garter snakes are common predators and studies using these show that P. cinereus can use chemical cues to detect garter snakes and threat levels. When exposed to snake fecal cues, individuals often spend more time in hiding and reduce foraging rates (Maerz et al. 2001, Sullivan et al. 2002). When exposed to fecal cues from snakes that were fed either P. cinereus or earthworms, they more strongly avoided the fecal cues from snakes that were fed salamanders (Murray and Jenkins 1999).
See also Habitat Account for General Cool Mesic Forests and Shrublands
Life History and Autecology
Breeding and Courtship: The mating season is prolonged and lasts from autumn through early to mid-spring (Petranka 1998). Local and regional populations often vary in the seasonal peak in breeding. Petranka (1998) noted that mating in a New York population begins during the second week of October, while most mating in southern Michigan populations occurs during the autumn. Females in the Michigan populations had sperm in their cloacae from late October through late April, and females had fresh spermatophores between 31 October and 9 December. In a Tennessee population, females had spermatophores in their cloacae from December through March (Nagel 1977), while in a Maryland population, the vas deferentia were packed with sperm from September-May, and females with spermatophores were observed from 28 October-18 April (Sayler 1966).

The males breed annually throughout the range, but females may breed annually or biennially depending on the geographic locality and their age. Females in most northern populations oviposit biennially, presumably because individuals cannot obtain sufficient energy during the relatively short growing seasons to yolk a clutch. Females that Nagel (1977) studied in eastern Tennessee bred annually, which suggests that many North Carolina populations do the same. Lotter (1978) found that females in a Connecticut population bred every other year when young, but shift to annual breeding after exceeding 44 mm SVL.

Courtship involves a tail-straddle walk that is characteristic of North American plethodontids. Males have enlarged premaxillary teeth with recurved anterior cusps that function to abrade the skin and pass mental gland secretions into the female's circulatory system during courtship (Wilburn et al. 2014, Arnold 1977). Gergits and Jaeger (1990) observed courtship behavior in Virginia and the males appeared to locate gravid females by following pheromone trails.

The following description of courtship is based on a summary by Petranka (1998). After approaching a female, the male moves in front of her to block her movements and sometimes nose-taps the female as he moves forward. Nose-tapping allows chemicals to be drawn into the nasolabial grooves of the male. The male then arches his tail upward just distal to the vent and, with the tip on the ground, wags the tail from side to side. If the female moves away, the male reorients in front of her and wiggles the tail again. The male then rubs his mental gland back and forth on the female's back while moving along the female's body. The enlarged premaxillary teeth abrade the skin at this point and allow mental gland secretions to enter her circulatory system (Wilburn et al. 2014). The male next moves forward and aligns himself along the female's body and wags his tail. The female approaches and places her chin on his dorsum just above the vent and straddles the male's tail. The pair then engages in a tail straddle walk until the male deposits a spermatophore. The male then leads the female forward, and the female picks up the spermatophore after positioning herself above it. The pair separates shortly thereafter.

Gergits and Jaeger (1990) observed courtship in the wild and noted that courting males sometimes break from females and bite approaching males. An intruder male may also bite a courting male and disrupted courtship. Courting females often squash male fecal pellets with their snouts, which appears to be a way to assess the quality of the diets of potential mates (Fisher-Reid et al. 2021, Petranka 1998).
Reproductive Mode: Females lay their eggs after the spring warm-up, and most commonly during June and July. They deposit their eggs in grape-like clusters within natural cavities or crevices. The eggs are usually suspended from the roof of the cavity by a short pedicel, and the female remains coiled about her clutch through hatching (Petranka 1998). Freshly laid ova are pale yellow to yellowish white, 3.0-4.0 mm in diameter, and are surrounded by two jelly envelopes. The entire structure is 3.5-5.0 mm in diameter. In northern or mountainous areas, females often lay their eggs either in crevices within decaying logs or in cavities beneath logs or rocks that are embedded in the soil. In southern populations where surface activity is curtained during the summer months, they presumably oviposit in subsurface retreats. Nagel (1977) was unable to locate any surface nests in a Tennessee population. Subsurface nesting is probably typical of most North Carolina populations.

The females only lay a few eggs, with the average clutch size in local populations varying from 6-9 eggs (Petranka 1998). Clutch size tends to increase with body size, but rarely exceeds 10-12 eggs per female. Females will cannibalize eggs both in the laboratory and in the field, and individuals that drive females from their nests may eat their eggs (Highton and Savage 1961, Piersol 1914). The brooding females will aggressively defend their eggs from marauding conspecifics by biting, snapping, or lunging at them (Bachmann 1984, Tornick 2010). There is one record of a wild-caught female with 3 eggs in her stomach, but almost no information on the extent to which oophagy and nest piracy occur in nature (Petranka 1998). Tornick (2010) found that females were more aggressive when guarding older clutches, but there was no difference in aggressive behavior when females guarded large versus small clutches of eggs. Females of all sizes aggressively defended their clutches. Freshly laid eggs reach the hatching stages in about 6 weeks and the young disperse from the nests within a few weeks after hatching.
Terrestrial Life History: The juveniles and adults remain under cover during the day, but emerge at night to forage and mate when weather conditions are favorable. During dry weather they retreat either into the humus layer and mineral soil or beneath logs or other moist surface cover. Individuals often forage directly of the forest floor, but will also climb low-lying vegetation at night. They are generalist, gape-limited predators that consumed a wide variety of palatable prey, including many types of small insects, snails, slugs, annelid worms, spiders, mites, centipedes, and millipedes. Ants, mites, annelid worms, and springtails are often well-represented in the diets (Fisher-Reid et al. 2021, Petranka 1998).

Local and regional populations differ in their patterns of seasonal surface activity. Populations at northern locales often show a spring and fall peak in activity, while those at mid- or higher elevations in mountainous regions are often most active on the surface during the summer months (Fisher-Reid et al. 2021, Petranka 1998). Individuals in non-mountainous regions at southern locales -- or in the lower valleys in mountainous areas -- are most active from fall through spring. Populations in North Carolina tend to follow the latter pattern, with animals beginning to become active on the ground surface after mid-September then moving underground in mid to late April as hot summer weather arrives. Populations outside of the mountains are often active during the winter months during bouts of warm weather.

The juveniles in most populations reach sexual maturity about 2 years after hatching, but females likely requiring an additional year or more to produce their first clutch. In a Quebec population near the northern limit of the range, males became sexually mature when 3-5 years old and reproduce annually, while females were mostly unable to reproduce until 4-6 years old (Leclair et al. 2008).

Detailed studies of Virginia populations indicate that the adults are territorial and will aggressively defend high quality cover objects such as decaying logs from conspecifics. They mark their territories using both fecal pellets and glandular secretions, and will engage in threatening posturing and outright attacks of intruders that enter a territory. Larger individuals are able to successfully defend their territories from smaller individuals, and males who hold higher quality territories are more likely to attract females.

In addition to territorial adults, many individuals are floaters that are typically smaller animals that do not hold territories. Studies from northern populations suggest that the adults are less aggressive and territorial, perhaps because feeding opportunities on the ground surface are less constrained by weather (Fisher-Reid et al. 2021). Robert Jaeger and colleagues have conducted numerous studies on territoriality and many other aspects of social behavior in this species that are often chemically mediated. This work is summarized in a recent compendium (Jaeger et al. 2016). Petranka (1998) and Fisher-Reid et al. (2021) also provide additional information of social interactions between conspecifics.
General Ecology
Population Ecology: The Eastern Red-backed Salamander is one of the most abundant woodland salamanders in many areas of its range. Surface density estimates have ranged from as few as 0.05 salamanders/m2 to as high as 6.3 salamanders/m2 (Fisher-Reid et al. 2021, Petranka 1998). Some of these may be underestimates because at any given moment many animals are not surface active. In many populations territoriality and agonistic behaviors appear to play an important role in spacing out individuals and may ultimately act to set an upper limit on local population sizes.
Community Ecology: The interactions of P. cinereus with other community members have been studied by several researchers. One is with P. shenandoah which is a rare species that is restricted to areas in or immediate next to talus on three mountains in north-central Virginia (Highton and Worthington 1967). Populations of this species are surrounded by P. cinereus that occupies the adjoining woods. Research by several investigators suggest that this pattern is due to the fact that P. cinereus adults exclude P. shenandoah juveniles from areas outside of talus, while talus slopes are uninhabitable to P. cinereus due to its susceptibility to desiccation (Fisher-Reid et al. 2021, Petranka 1998). Several other studies have examined competitive interactions of P. cinereus with other small Plethodon species, including P. hoffmani, P. nettingi, P. electromorphus, P. hubrichti, as well as larger Plethodon species and Desmognathus species. Summaries of these studies are in Fisher-Reid et al. (2021) and Petranka (1998).
Adverse Environmental Impacts
Effects of Introduced Species/Induced Increases of Native Species: Introduced earthworms that feed in the leaf litter appear to be adversely affecting populations of P. cinereus in many areas. In Michigan, Brunges et al. (2020) found a negative association between salamander numbers and the presence of invasive earthworms. This was likely due to the fact that earthworms consumed the organically-rich O-horizon of the leaf litter layer that P. cinereus depends on for moisture and protection. Similar patterns were found in Virginia by Ransom (2017) where the presence of the invasive earthworm, Octolasion tyrtaeum, reduced the number of P. cinereus. Studies in Ohio (Ziemba et al. 2015, Ziemba et al. 2016) have shown similar adverse effects of introduced earthworms on P. cinereus.
Status in North Carolina
NHP State Rank: S5
Global Rank: G5
Environmental Threats: The Eastern Red-backed Salamander is widespread and locally abundant in many areas and is not threatened. However, several anthropogenic factors can adversely affect local populations. In addition, countless numbers of local populations have been destroyed from the widespread deforestation, urbanization, and industrialization that followed European settlement. Intensive timber harvesting techniques and associated edge effects can greatly depress local numbers (e,g, deMaynadier and Hunter, 1995, Knapp et al. 2003, Rodewald and Yahner 1999), and full recovery may require decades. Wildfires can also reduce or eliminate local populations, presumably due to the loss of leaf litter, organic humus, surface cover, and the tree canopy. Roads are significant barriers to dispersal, and salamander numbers in the general vicinity of roads are usually depressed due to the hotter and drier conditions there. Surface mines and mountain top removal in Appalachia greatly impact salamanders and recovering mines that are in grass or shrub stages have very few plethodontid salamanders, including P. cinereus (Williams et al. 2017, Wood and Williams 2013). Fisher-Reid et al. (2021) provide an excellent review of these and other factors that are adversely impacting this species.
Stewardship: Local populations are best sustained by having large tracts of mature or old-growth forests that provide optimal conditions for these and many other woodland salamanders.

Photo Gallery for Plethodon cinereus - Eastern Red-backed Salamander

12 photos are shown.

Recorded by: David George, Steve Hall, Carol Tingley
Chatham Co.		Recorded by: Pat Momich
Madison Co.
Recorded by: Pat Momich
Madison Co.		Recorded by: Ilona Conolly (reported by Owen McConnell)
McDowell Co.
Recorded by: Jim Petranka and Becky Elkin
Madison Co.		Recorded by: Jim Petranka and Becky Elkin
Madison Co.
Recorded by: L. Osteen
Durham Co.		Recorded by: Steve Hall
Warren Co.
Recorded by: Owen McConnell
Durham Co.		Recorded by: Steve Hall
Orange Co.
Recorded by: Steve Hall
Durham Co.		Recorded by: Steve Hall
Chatham Co.