Blue Ridge Dusky Salamander
© 2016 Dr. Joachim Nerz (1 of 40)
Country distribution from AmphibiaWeb's database: United States
Desmognathus orestes Tilley and Mahoney, 1996
Carlos D. Camp1
1. Historical versus Current Distribution. Recently described Blue Ridge dusky salamanders (Desmognathus orestes; Tilley and Mahoney, 1996) occur in the Blue Ridge Physiographic Province from southwestern Virginia (Floyd County) into northwestern North Carolina (southward to Burke and Mitchell counties) and northeastern Tennessee (Unicoi County; Tilley and Mahoney, 1996; Mead and Tilley, 2000). This species is currently considered to comprise two genetically distinct groups of populations (Tilley and Mahoney, 1996; Tilley, 1997; Mead and Tilley, 2000; Mead et al., 2002).
Like other members of the D. ochrophaeus complex, Blue Ridge dusky salamanders are strongly associated with the headwaters of first-order streams (Tilley, 1997). This species occurs to the tops of the highest mountains within its range (Organ, 1961a; Tilley, 1968; Petranka, 1998). Tilley (1997) speculated that interactions with low elevation seal salamanders may have contributed to the isolation and genetic differentiation of units of the D. ochrophaeus complex.
2. Historical versus Current Abundance. Blue Ridge dusky salamanders are abundant in seepages, beds and banks of headwater streams, and wet cliffs. In mesic, high elevation forests, individuals may disperse widely into forest-floor habitats (Tilley, 1997). 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.
i. Breeding migrations. Adult females of the closely related Ocoee salamander (D. ocoee) have been shown to be philopatric with regard to oviposition sites (Forester, 1977) and move to nesting sites several weeks prior to oviposition (Forester, 1981). Blue Ridge dusky salamanders presumably exhibit similar behaviors and may repeatedly return to headwater streams to lay eggs (Tilley, 1997). Mating occurs throughout the warmer months by individuals held in captivity for 1–2 d (Organ, 1961a).
ii. Breeding habitat.
i. Egg deposition sites. Females lay eggs and brood them in small chambers under moss, rocks, or logs in sites from which larvae can easily enter shallow water (Organ, 1961a; Tilley, 1997; Petranka, 1998). Eggs may be attached to the undersides of rocks ≤ 25 cm beneath stream banks in underground seepages (Organ, 1961a). Eggs have been observed in the field from June–October (Organ, 1961a).
ii. Clutch size. Three recently laid clutches averaged 11 eggs/clutch (Organ, 1961a). Clutch size determined from the dissection of specimens with developing oocytes averaged 14–16 (Martof and Rose, 1963). Clutch size is strongly related to female body size (Martof and Rose, 1963; Tilley, 1968). Eggs hatch after an incubation period of about 2 mo (Organ, 1961a).
Organ (1961a) hypothesized a biennial female reproductive cycle. This conclusion has since been questioned (Tilley, 1968, 1977; Tilley and Tinkle, 1968). Females probably are capable of nesting annually (Tilley and Tinkle, 1968), similar to other members of the D. ochrophaeus complex (Forester, 1977; Tilley, 1980).
i. Length of larval stage. Organ (1961a) determined an 8–9 mo larval period.
ii. Larval requirements.
a. Food. They presumably feed on small, aquatic invertebrates.
b. Cover. Similar to other members of the Desmognathus ochrophaeus complex, larvae are found in shallow water associated with seepages, small streams, and wet rock faces (Huheey and Brandon, 1973; Tilley, 1997).
iii. Larval polymorphisms. Variability in dorsolateral stripe configuration is evident in larval specimens of the related Carolina mountain dusky salamanders (D. carolinensis; Tilley, 1969).
iv. Features of metamorphosis. Metamorphosis occurs at 10–12 mm SVL (Organ, 1961a).
v. Post-metamorphic migrations. Similar to other members of the D. ochrophaeus complex, individuals disperse into forest habitats when temperature and moisture conditions are conducive to overland movement. In mesic, high elevation forests, they become functional components of the forest-floor salamander community during warm months (Hairston, 1949; Tilley, 1997; Petranka, 1998; Petranka and Murray, 2001).
vi. Neoteny. Neoteny is not known in this species.
D. Juvenile Habitat. Similar to adults, they are commonly associated with seepages of headwater streams where they may be found on stream banks, in streambeds, and on wet rock faces (Organ, 1961a; Martof and Rose, 1963).
E. Adult Habitat. Blue Ridge dusky salamanders are found associated with wet rock faces, seepages, and forest-floor habitats in the vicinity of streams and seeps (Organ, 1961a; Martof and Rose, 1963; Tilley, 1997). Adults are nocturnal, spending the day under cover objects. Animals sometimes are active during the day under overcast conditions (Petranka, 1998).
F. Home Range Size. Home ranges are presumably small, similar to those of Ocoee salamanders (Huheey and Brandon, 1973).
G. Territories. Territorial behavior has not been studied in this species. Individuals of other members of the D. ochrophaeus complex exhibit intraspecific aggression (Jaeger, 1988; Verrell and Donovan, 1991).
H. Aestivation/Avoiding Dessication. Unlikely. Blue Ridge dusky salamanders are active throughout the summer (Organ, 1961a).
I. Seasonal Migrations. Individuals may move from streams into forest-floor habitats during warmer months when and where conditions are sufficiently moist. They aggregate in seepages, presumably to overwinter (Organ, 1961a).
J. Torpor (Hibernation). In winter, adults migrate to seepages and springs, or underground retreats (Organ, 1961a).
K. Interspecific Associations/Exclusions. Blue Ridge dusky salamanders often occur sympatrically with black-bellied salamanders (D. quadramaculatus), seal salamanders (D. monticola), dusky salamanders (D. fuscus), and pigmy salamanders (D. wrighti; Organ, 1961a). These species are organized like desmognathine communities throughout the southern Appalachians, where different species predictably assort by body size along the stream-forest interface. Larger species are more aquatic, smaller ones more terrestrial. 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; Organ, 1961a). As with other members of the D. ochrophaeus complex, Blue Ridge dusky salamanders are relatively small and occur more terrestrially than most of its sympatric congeners. The observed pattern of desmognathine assortment was explained initially 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, there is no evidence from extensive dietary studies that large desmognathine 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, Blue Ridge dusky salamanders may be syntopic with Blue Ridge two-lined salamanders (Eurycea wilderae) and several species of woodland salamanders (genus Plethodon). In and around seepages, they may be syntopic with Blue Ridge two-lined salamanders, red salamanders (Pseudotriton ruber), and spring salamanders (Gyrinophilus porphyriticus; Organ, 1961a). Spring salamanders are known to prey on other salamanders in the D. ochrophaeus complex (Bruce, 1979).
A 25-km wide valley
forms a northern boundary between Blue Ridge dusky salamanders and the closely related
Allegheny mountain dusky salamanders (D. ochrophaeus). No such
physical barrier exists, however, between Blue Ridge dusky salamanders and Carolina
mountain dusky salamanders (D. carolinensis) to the south.
Limited hybridization occurs at points of contact between these two species (Mead and
Tilley, 2000; Mead et al., 2002). Blue Ridge mountain dusky salamanders exhibit
considerable sexual isolation from their sibling, parapatric neighbors (Verrell and
Arnold, 1989; Tilley et al., 1990) and from northern dusky salamanders (D.
fuscus; Uzendoski and Verrell ).
M. Longevity. Closely related Ocoee salamanders can live up to at least 10 yr (Castanet et al., 1996), and maximum life spans are probably considerably more than that (Tilley, 1977).
N. Feeding Behavior. According to Petranka (1998), no information is available on diet. Blue Ridge dusky salamanders probably feed heavily on small arthropods, as do the other members of the species complex (Hairston, 1949; Fitzpatrick, 1973; Keen, 1979; Krzysik, 1980b).
O. Predators. Blue Ridge dusky salamanders probably are eaten by various species of vertebrate predators, including birds, small mammals, snakes, and predatory salamanders such as spring salamanders (Petranka, 1998).
P. Anti-Predator Mechanisms. Undescribed. They are presumably the same as in other desmognathines, i.e., flight, writhing, biting, and tail autotomy (Labanick, 1984; Brodie et al., 1989; Hileman and Brodie, 1994).
Q. Diseases. Unknown.
R. Parasites. Unreported. Closely related Ocoee salamanders occupy similar habitats and harbor a helminth fauna that includes nematodes, flukes, and tapeworms (Goater et al., 1987). Leeches occasionally occur on Ocoee salamanders (Goater, 2000).
4. Conservation. Blue Ridge dusky salamanders are abundant at high elevation sites. Because of their reliance on moist habitats, the greatest potential threat is probably the removal of the protective forest canopy through the harvesting of timber and the resulting desiccation of habitats. 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, including members of the D. ochrophaeus complex, each year. Ash and Bruce (1993), however, disputed these estimates and considered them to be exaggerations of the actual number killed. Petranka et al. (1994) indicated that populations of this species at low elevations may take many years to recover from intensive timber harvesting. However, 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 the closely related Ocoee salamanders (C.D.C., unpublished data). It is not known how periodic drought may interact with timber harvesting to affect populations of Blue Ridge dusky and other seepage-dwelling salamanders. Populations of Blue Ridge dusky salamanders that occupy high elevation sites in the southern Appalachians may also be vulnerable to the effects of acid precipitation.
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 24 Jun 2018.
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