Carolina Mountain Dusky Salamander
© 2010 Dr. Stephen G. Tilley (1 of 15)
Country distribution from AmphibiaWeb's database: United States
Desmognathus carolinensis Dunn, 1916
Carlos D. Camp1
Stephen G. Tilley2
1. Historical versus Current Distribution. Elevated to species status only recently (Tilley and Mahoney, 1996), Carolina mountain dusky salamanders (Desmognathus carolinensis) have a restricted distribution along the Tennessee–North Carolina border in the southwestern Blue Ridge Physiographic Province. They are found on the Blue Ridge, Black, Bald, and Unaka mountains. Their range extends from between Linville Falls and McKinney Gap on the Blue Ridge Divide and the valley of the Doe River on the Tennessee–North Carolina border southwest to the valley of the Pigeon River in North Carolina (Tilley and Mahoney, 1996; Petranka, 1998; Mead and Tilley, 2000). Populations range to the peaks of the highest mountains (approximately 2,000 m) in the Appalachian Mountains (Tilley, 1980). Tilley (1997) speculated that interactions with seal salamanders may have contributed to the isolation and genetic differentiation of units of the D. ochrophaeus complex.
2. Historical versus Current Abundance. Within their restricted range, Carolina mountain dusky salamanders are one of the most common Appalachian salamanders. Petranka and Murray (2001) sampled a cove forest at approximately 1,200 m and estimated the density of this species to exceed 10,000 individuals/ha and 7.5 kg/ha. Petranka et al. (1993) demonstrated that clearcut timber harvesting negatively affects the number of total Desmognathus individuals, including members of the D. ochrophaeus complex. They estimated that, at the rate of clearcutting carried out during the 1980s and early 1990s, the Appalachian forests of North Carolina lost as many as 14 million salamanders of all species each year during that time. However, Ash and Bruce (1994) strongly disagreed with these estimates and did not consider clearcutting to have as strong an impact on native salamanders.
3. Life History Features.
A. Breeding. Courtship occurs on land. Eggs are deposited in or near flowing water.
&nb sp; i. Breeding migrations. Females may move short distances from terrestrial foraging areas into semi-aquatic nesting sites. Closely related Ocoee salamanders (D. ocoee) move to nesting sites several weeks prior to oviposition (Forester, 1981), and Carolina mountain dusky salamanders presumably exhibit similar behavior.
&nb sp; ii. Breeding habitat. Mating occurred among captive individuals during July and September under experimental conditions (Mead and Tilley, 2000). Females apparently breed annually (Tilley, 1973b), similar to other members of the D. ochrophaeus complex (Forester, 1977). Inseminations of females by > 1 male are relatively common, with numbers of multiple inseminations varying among populations (estimated to average 7% of matings; Tilley and Hausman, 1976).
&nb sp; i. Egg deposition sites. Eggs were deposited at several localities on Mt. Mitchell, North Carolina, from late May to early July (Tilley, 1973b). Oviposition during the winter has been inferred from the abundance of small, yolk-laden larvae during the early spring; wintertime clutches were not found during diligent searches, however (Tilley, 1973b). Females that oviposit in summer brood their eggs under moss on rocks and logs associated with seepage areas and small streams. Tilley (1973b) speculated that winter-brooding females may lay their eggs deep below the surfaces of respective seeps. Eggs generally are laid in lacunae hollowed out by the female within or under moss (Martof and Rose, 1963; Tilley, 1973b). Martof and Rose (1963) found clutches on Mt. Mitchell under thick moss beside seepages or in rotting logs in the forest. Eggs are deposited in small, grape-like clusters, each egg attached singly or in twos and threes via respective stalks (Martof and Rose, 1963). As with all amphibians, time to hatching varies with temperature. In laboratory observations, eggs kept at 16 ˚C hatched in 71 d; clutches observed in nature on Mt. Mitchell hatched in 58–69 days (Tilley, 1972). Eggs and/or hatchlings are sometimes consumed by the attending female (Tilley, 1972).
&nb sp; ii. Clutch size. Clutch sizes determined from developing oocytes counted in dissected females ranged from 12–40 eggs (Martof and Rose, 1963). Some females fail to lay their entire clutch complements, and a small number of oocytes may be resorbed (Tilley, 1973a,b); clutch sizes taken from natural nests on Mt. Mitchell ranged from 16–26 (Tilley, 1973b). Clutch size varies with elevation on Mt. Mitchell as a function of variable female body size (Tilley, 1973a). Ova are approximately 3 mm in diameter (Martof and Rose, 1963; Tilley, 1973b). Females brood their eggs (Bishop, 1941; Tilley, 1972). Hatchlings measure 13–18 mm TL and have prominent yolk sacs (Bishop, 1941). Timing of egg laying appears highly variable, with evidence of egg deposition ranging from mid to late fall or winter to late July (Tilley and Tinkle, 1968; Tilley, 1973b).
&nb sp; i. Length of larval stage. Anywhere from 2–8 mo, depending on time of oviposition. Late winter and early spring eggs apparently hatch in 2–3 mo, while eggs laid in the summer may take 4–8 mo (Tilley, 1973b).
&nb sp; ii. Larval requirements.
&nb sp; &nb sp; a. Food. Probably small, aquatic invertebrates.
&nb sp; &nb sp; b. Cover. Larvae inhabit shallow water in seepage areas and water films on vertical rock faces. They may take cover during the day under leaf litter and other detritus in shallow water and seepage areas.
&nb sp; iii. Larval polymorphisms. Individuals that overwinter as larvae reach significantly larger body sizes than those that metamorphose prior to winter (Tilley, 1973b). Variability in dorsolateral stripe configuration is evident in larval specimens (Tilley, 1969).
&nb sp; iv. Features of metamorphosis. SVL of newly metamorphosed animals are typically 10–12 mm (Tilley, 1973a).
&nb sp; v. Post-metamorphic migrations. Juveniles and adults may move into forest-floor habitats.
&nb sp; vi. Neoteny. Neoteny is not known in this species.
D. Juvenile Habitat. Generally similar to adult habitats. Growth rates vary depending on elevation, age, and microhabitat features. Juveniles can grow 8–10 mm/yr in SVL (Tilley, 1973a, 1974).
E. Adult Habitat. Adults are found in seepage areas, on wet rock faces, and in the forest- floor litter in association with streams, particularly headwater seepages (Hairston, 1949; Tilley, 1973a, 1974, 1997). The distribution of this species is directly related to moisture conditions; individuals living at moist, high elevation sites may occur on the forest floor far from streams (Hairston, 1949; Petranka and Murray, 2001). Individuals at low elevations are found in close association with seeps and streams (Hairston, 1949).
Carolina mountain dusky salamanders are largely nocturnal, remaining beneath cover during the day and emerging to feed at night. They may be active during the day when it is heavily overcast. On rainy or foggy nights, Carolina mountain dusky salamanders frequently climb understory plants and tree trunks and perch > 1 m above the forest floor (Hairston, 1949; Petranka, 1998). Activity in members of the D. ochrophaeus complex is directly related to humidity (Feder and Londos, 1984).
F. Home Range Size. Unknown, but probably small. Movements of similar Ocoee salamanders center around a small home range (Huheey and Brandon, 1973).
G. Territories. Adults are aggressive and actively defend space from other Carolina mountain dusky salamanders (Bennett and Houck, 1983; Petranka, 1998).
H. Aestivation/Avoiding Dessication. Unlikely. Individuals are active throughout the summer. Activity levels, however, are directly related to humidity (Feder and Londos, 1984; Petranka and Murray, 2001).
I. Seasonal Migrations. Metamorphosed individuals congregate in seepage areas to escape freezing during winter and disperse into the surrounding forest in the spring (Tilley, 1973b; Petranka, 1998).
J. Torpor (Hibernation). Unknown.
K. Interspecific Associations/Exclusions. Carolina mountain dusky salamanders often occur sympatrically with black-bellied salamanders (D. quadramaculatus), seal salamanders (D. monticola), and pigmy salamanders (D. wrighti; Hairston, 1949). These species are organized similar to other desmognathine communities throughout the southern Appalachian Mountains, where different species predictably sort by body size along the stream–forest interface. Larger species are more aquatic and smaller ones occur more terrestrially. This pattern is evident both along a horizontal gradient from stream–stream bank–forest and along a vertical gradient from stream–seepage–forest (Hairston, 1949). As with other members of the D. ochrophaeus complex, Carolina mountain dusky salamanders are relatively small and occur more terrestrially than most of their sympatric congeners. The observed pattern of desmognathine assortment initially was explained as niche partitioning among competitors (Hairston, 1949; Organ, 1961a). Tilley (1968) and Hairston (1980c), however, suggested that interspecific predation was a more likely cause. A number of studies attempted to determine which was the more probable factor (e.g., Kleeberger, 1984; Carr and Taylor, 1985; Hairston, 1986; Southerland, 1986a,b,d). They generally concluded that some combination of predation and aggressive interference were important factors in interspecific desmognathine interactions. Hairston (1986) made the strongest case for predation with competition being a secondary factor. His statistical methods have been criticized, however (Jaeger and Walls, 1989). Although large desmognathines readily eat small ones in artificial environments, dietary studies have demonstrated that neither black-bellied salamanders nor seal salamanders are important predators of heterospecific congeners (Camp, 1997b). The lack of predation under natural conditions is probably a result of differential habitat selection and behavioral avoidance (perhaps involving chemical cues) of larger congeners by small individuals. Predation by large species may have been important historically in the organization of desmognathine communities. Alternative hypotheses based on abiotic factors, rather than biotic ones such as competition and predation, recently have been proposed to explain patterns of habitat preference among desmognathines (Bruce, 1996; Camp et al., 2000). In forest-floor habitats, Carolina mountain dusky salamanders are often syntopic with Blue Ridge two- lined salamanders (Eurycea wilderae) and several species of woodland salamander (genus Plethodon; Petranka and Murray, 2001).
The Pigeon River forms a southern boundary between Carolina mountain dusky salamanders and the closely related Ocoee salamanders. No such physical barrier exists, however, between Carolina mountain dusky salamanders and Blue Ridge dusky salamanders (D. orestes) to the north. Limited hybridization occurs at points of contact between these two species (Mead and Tilley, 2000). Carolina mountain dusky salamanders exhibit considerable sexual isolation from their sibling, parapatric neighbors (Verrell and Arnold, 1989; Tilley et al., 1990).
L. Age/Size at Reproductive Maturity. Populations on Mt. Mitchell vary in size and age at maturation with elevation. Those at high elevations mature at a relatively late age and large size and reach larger maximum sizes (> 65 mm SVL) than elsewhere in the species’ range (Tilley, 1973a). Adult females at 1,800–1,900 m average 44–48 mm SVL; those at < 1,000 m average 37–38 mm. Populations inhabiting wet rock face versus woodland habitats at the same elevation also differ in size at maturity, with woodland individuals being larger. This difference in maturation size is the result of differential juvenile growth rates (Tilley, 1974).
M. Longevity. Unknown. Similar Ocoee salamanders are known to live at least 7–10 yr (Castanet et al., 1996). Large, dark individuals may be considerably older.
N. Feeding Behavior. Both juveniles and adults are generalists, feeding on stream- and forest- floor-associated invertebrates including pseudoscorpions, snails, annelids, and insects such as beetles, dipteran and lepidopteran larvae, homopterans, and parasitic wasps (Hairston, 1949). Females sometimes cannibalize their own eggs and hatchlings (Tilley, 1972). Bernardo (2002) reported that an adult Carolina mountain dusky salamander ate a Weller’s salamander (Plethodon welleri).
O. Predators. Woodland birds, snakes, and small mammals, particularly shrews (Brannon, 2000), undoubtedly prey on Carolina Mountain dusky salamanders. They may also be preyed upon by spring salamanders (Gyrinophilus porphyriticus). The latter species is a major predator of other members of the D. ochrophaeus complex (Bruce, 1979).
P. Anti-Predator Mechanisms. Unknown. They are probably similar to other desmognathines, i.e., flight, writhing, and biting (Brodie et al., 1989).
Q. Diseases. Unknown.
R. Parasites. Rankin (1937) reported the following parasites from Carolina mountain dusky salamanders in North Carolina: Protozoa—Cryptobia borreli, Eutrichomastix batrachorum, Hexamastix batrachorum, Hexamitus intestinalis, Karotomorpha swezi, Prowazekella longifilis, Tritrichomonas augusta; Trematoda—Brachycoelium hospitale, Cestoda—Crepidobothrium cryptobranchi; Nematoda—Capillaria inequalis, Oxyuris magnavulvaris.
Closely related Ocoee salamanders occupy similar habitats and harbor a helminth fauna that likely is similar to Carolina mountain dusky salamanders and includes nematodes, flukes, and tapeworms (Goater et al., 1987). Leeches occasionally occur on Ocoee salamanders (Goater, 2000).
4. Conservation. Carolina mountain dusky salamanders are among the most common salamanders within their range. Because of their reliance on moist habitats, the greatest potential threat is likely the removal of the protective forest canopy through the harvesting of timber and resulting habitat desiccation. Petranka et al. (1993) estimated that the clearcut logging of Appalachian forests of North Carolina during the 1980s and early 1990s killed millions of salamanders each year, including members of the D. ochrophaeus complex. Ash and Bruce (1993), however, disputed these estimates and considered them to be exaggerations of the actual number killed. Desmognathine salamanders currently are abundant in areas of the southern Appalachians (the Great Smoky Mountains) that have been logged extensively in the past (S.G.T., personal observations). Appalachian seepages occasionally dry up, negatively affecting both reproduction (Camp, 2000) and survival in closely related Ocoee salamanders (C.D.C., unpublished data). It is not known how periodic drought may interact with techniques of timber harvesting to affect populations of Carolina mountain dusky salamanders and other seepage-dwelling salamanders.
1Carlos D. Camp
2Stephen G. Tilley
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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Citation: AmphibiaWeb. 2018. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 12 Dec 2018.
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