© 2011 Todd Pierson (1 of 66)
Country distribution from AmphibiaWeb's database: United States
Desmognathus monticola Dunn, 1916
Carlos D. Camp1
1. Historical versus Current Distribution. Seal salamanders (Desmognathus monticola) range throughout the central and southern Appalachians from western Pennsylvania to central Alabama. Disjunct populations occur in the coastal plain of southern Alabama and the Florida Panhandle (Rose and Dobie, 1963; Means and Longden, 1970; Mount, 1975; Caldwell and Folkerts, 1976). Seal salamanders are most commonly found below elevations of 1,219–1,372 m, although they occur as high as 1,555 m (Hairston, 1949; Organ, 1961a). Seal salamanders are commonly used as fish-bait in the southern Appalachians. In a recent survey of bait shops in northern Georgia, seal salamanders made up 67% of salamanders sold as “spring lizards” (Jensen and Waters, 1999). The introduction of other desmognathines into uninhabited areas has been attributed to the bait trade (Martof, 1953b). Because of the widespread use of seal salamanders as bait, this species may have been introduced into new areas by anglers.
2. Historical versus Current Abundance. It is likely that certain populations of seal salamanders have suffered due to collection for fish bait and other human activities. One technique of bait collection, which may have a negative effect, involves pouring liquid bleach into small, high-gradient streams to drive out salamanders. Because salamanders thus collected have low survivabilities, wholesale purchasers (i.e., owners of bait shops) generally do not buy salamanders from such collectors more than once, and this attitude may restrict usage of the bleach (Jensen and Waters, 1999). Acidification of streams due to mine drainage may affect seal salamanders. Roudebush (1988) showed that feeding rates were depressed in salamanders exposed to low pH levels. Petranka et al. (1993) demonstrated that clearcut timber harvesting negatively affects the number of total Desmognathus individuals, including seal salamanders. 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. No significant change in abundance was noted in 20 yr of seal salamander surveys carried out in undisturbed habitats in the Appalachian Mountains of southwestern North Carolina (Hairston, 1996).
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Seal salamanders are not known to migrate. Mating occurs in the fall and spring in Virginia (Organ, 1961a). Brock and Verrell (1994) observed mating in July–November in specimens collected in southwestern North Carolina. Organ (1961a) suggested a biennial breeding cycle in females; his conclusions of biennial oogenic cycles in desmognathines have been questioned, however (Tilley, 1968, 1977; Tilley and Tinkle, 1968). Eggs have been found from mid June to August (Pope, 1924; Organ, 1961a; Folkerts, 1968; Bruce, 1990; Camp, 1997a).
ii. Breeding habitat. Mating presumably occurs in the same areas that are optimal for non-reproductive activities. Adult male and female seal salamanders have been observed occupying common refugia during late summer in Georgia (C.D.C., personal observations). Mating involves orientation of the male to the female, chemical and tactile stimulation of the female by the male, and the “tail-straddle walk” characteristic of other plethodontids (Organ, 1961a; Brock and Verrell, 1994).
i. Egg deposition sites. Eggs are attended by females and are laid in or near running water. Eggs may be buried in nests in streambeds (Bruce, 1990) > 30 cm below ground (Organ, 1961a). Petranka (1998) reports finding eggs in leaf clumps. Egg clutches have been found in seepages flowing under rocks (Folkerts, 1968), under moss next to flowing water (Pope, 1924), and in crevices in wet cliffs (Camp, 1997a). Eggs are attached, typically to the underside of a rock, in either a monolayer or in a loose group, 2–3 eggs thick (Pope, 1924; Folkerts, 1968).
ii. Clutch size. Egg numbers range from 13–39 (Pope, 1924; Organ, 1961a; Folkerts, 1968; Camp, 1997a). Clutch sizes determined from eggs collected in the field averaged 27 and 22 in Virginia (Organ, 1961a) and Alabama (Folkerts, 1968), respectively. Clutch sizes determined from the numbers of developing oocytes are independent of female size (Tilley, 1968). Eggs range in diameter from 4.0–4.8 mm (Bruce, 1989; Camp, 1997a). Incubation time is 1–2 mo, and hatching occurs at 11–12 mm SVL (Folkerts, 1968; Bruce, 1990).
i. Length of larval stage. Larvae overwinter and metamorphose in either the spring or early to mid summer, suggesting a larval period of 8–13 mo (Organ, 1961a; Juterbock, 1984; Bruce, 1989).
ii. Larval requirements.
a. Food. Unreported. Larvae probably feed on small aquatic arthropods.
b. Cover. Larvae typically occur along small gravelly bars and rocky seepage areas in streams (Folkerts, 1968).
iii. Larval polymorphisms. Larvae of this species do not exhibit distinct polymorphisms.
vi. Features of metamorphosis. Metamorphosis occurs at approximately 14–16 mm SVL (Organ, 1961a; Folkerts, 1968; Juterbock, 1984; Bruce, 1989, 1990, 1995; Bruce and Hairston, 1990).
v. Post-metamorphic migrations. This species is not known to migrate.
vi. Neoteny. This species is not known to exhibit neoteny.
D. Juvenile Habitat. Metamorphosed seal salamanders are nocturnal, emerging from under rocks, logs, or stream-bank burrows (Brandon and Huheey, 1971; Shealy, 1975; Hairston, 1986). Juveniles and adults use different microhabitats based on cover size, moisture levels, and coarseness. Adults are found under larger, moister, coarser objects; juveniles appear to avoid adults, and thus these sites (Krzysik and Miller, 1979; Colley et al., 1989). Juveniles shift their choices of substrates in the presence of adults (Colley et al., 1989). Intraspecific competition for cover objects may occur (Brandon and Huheey, 1971; Kleeberger, 1984). Juveniles are located closer to water in streambeds, on average, than adults (Hairston, 1986). Immature seal salamanders occasionally are found wandering on the faces of wet cliffs (C.D.C. and S.G.T., personal observations).
E. Adult Habitat. Seal salamanders most commonly are found in hardwood forests in association with small- to medium-sized streams containing cool, well-aerated water (Petranka, 1998). Seal salamanders are found under cover objects in association with streambanks and uninundated portions of streambeds, rather than in the stream channel proper (Hairston, 1949; Organ, 1961a; Krzysik, 1979). They are also common in seepages (Organ, 1961a), although they typically do not occur as close to the headwaters of seeps as members of the D. ochrophaeus complex (C.D.C. and S.G.T., personal observations). Seal salamanders occasionally use crevices associated with wet cliffs as refugia (Tilley, 1980; Camp, 1997a). Adult males have been observed to share crevices in wet cliffs with adult females (Camp, 1997a; C.D.C., personal observations).
Following heavy rains, seal salamanders may temporarily leave streams and stream banks and forage in surrounding forest (Kleeberger, 1985), occasionally climbing on tree trunks 1–2 m above the ground (Petranka, 1998).
F. Home Range Size. Generally small, estimated to be 0.07–0.45 m2 in one study (Kleeberger, 1985) and 8.4 m2 in another (Hardin et al., 1969).
G. Territories. Seal salamanders defend cover sites from conspecifics of either sex (Keen and Sharp, 1984; Keen and Reed, 1985). They defend feeding cover sites significantly more than they do non-feeding cover sites. Individuals of this species move among refugia, defending whichever refugia they happen to inhabit. Therefore, Keen and Sharpe (1984) suggested that seal salamanders possess mobile territories. A similar pattern is seen in black-bellied salamanders that move among a small set of favored refugia, functionally maintaining a constant territory through a combination of aggressive defense and pheromonal advertisement (Camp and Lee, 1996). Camp (2003a) reports an instance of intraspecific aggression in seal salamanders.
H. Aestivation/Avoiding Dessication. Unlikely. Surface activity peaks in April and declines with summer. Winter rains may trigger additional surface activity (Shealy, 1975; Petranka, 1998). Individuals are active at the surface in the southern part of their range during periods of warm temperatures throughout the winter (C.D.C., personal observations).
I. Seasonal Migrations. This species is not known to migrate.
J. Torpor (Hibernation). Unknown.
K. Interspecific Associations/Exclusions. Seal salamanders are sympatric with a variety of combinations of congeners throughout their range. Over much of their range, seal salamanders are syntopic with members of the dusky salamander (D. fuscus) and/or mountain dusky salamander (D. ochrophaeus) complexes. Members of monticola-fuscus-ochrophaeus assemblages in Pennsylvania assort positively by body size and substrate-particle size. Seal salamanders, being the largest members, choose the coarsest substrates. They are also the most aquatic species among this group, preferring moister substrates than either of their two sympatric congeners (Krzysik, 1979). Likewise, seal salamanders are more aquatic than their smaller, sympatric counterparts (Ocoee salamanders [D. ocoee] and D. conanti [spotted dusky salamanders]) in Alabama (Folkerts, 1968). Seal salamanders and Ocoee salamanders segregate spatially and temporally in the Piedmont of South Carolina, with seal salamanders being more aquatic and diurnal than Ocoee salamanders (Shealy, 1975). In experimental, laboratory-based trials, seal salamanders are more aggressive toward dusky salamanders than to conspecifics (Keen and Sharp, 1984). Choices of substrate moisture and sizes of cover objects by either of these two species were not affected by the presence of the other, although activity of dusky salamanders was depressed by presence of seal salamanders (Keen, 1982). Tilley (1997) speculated that interactions with seal salamanders may have contributed to the isolation and genetic differentiation of units of the D. ochrophaeus complex.
Throughout much of the southern Appalachian region, seal salamanders are sympatric with at least two congeneric species. They often occur syntopically with black-bellied salamanders (D. quadramaculatus) and members of the D. ochrophaeus complex. They additionally may occur with shovel-nosed salamanders (D. marmoratus) and seepage salamanders (D. aeneus), as well as dusky salamanders. Except for the completely aquatic shovel-nosed salamander, these species assort by body size along the stream-forest interface with larger species being more aquatic and smaller ones occurring 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 (Organ, 1961a). Seal salamanders are intermediate in both body size and habitat preference, occurring along stream banks, in uninundated parts of streambeds, and seepages. 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 either black-bellied salamanders or seal salamanders are significant predators of heterospecific congeners (Camp, 1997b). Nevertheless, some researchers hold that 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, have recently been proposed (Bruce, 1996; Camp et al., 2000). 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. The activity levels of dusky salamanders are depressed by the presence of larger seal salamanders (Keen, 1982), and both activity levels and substrate choices of seal salamanders are altered by the presence of larger black-bellied salamanders in experimental tanks (Carr and Taylor, 1985; Roudebush and Taylor, 1987a). Seal salamanders avoid chemical extracts of black-bellied salamanders under experimental conditions (Southerland, 1986a; Roudebush and Taylor, 1987b; Jacobs and Taylor, 1992). Keen (1985), however, suggested that interspecific aggression between these two species may not be more important than intraspecific interactions. The presence or absence of black-bellied salamanders did not affect the dispersion of seal salamanders in a study by Grover (2000).
L. Age/Size at Reproductive Maturity. Adult size varies among populations. Bruce and Hairston (1990) reported size data on two populations in southwestern North Carolina. Adult males at Wolf Creek averaged 57 mm (range = 46–72) SVL, and those from Coweeta averaged 67 mm (range = 48–80) SVL. Adult females averaged 59 mm (range = 53–65) and 64 mm (range = 52–76) SVL, respectively, at the same two sites. Castanet et al. (1996) and Bruce et al. (2002) aged individuals of these same populations using skeletochronology. They found that males and females at each site mature at 4-6 yr and 5-7 yr, respectively. Bruce et al. (2002) showed, however, that more individuals at Coweeta matured at later ages than those at Wolf Creek. Adults measured from northern Alabama had respective average SVLs for males and females of 64 mm and 57 mm; those from the Alabama Coastal Plain averaged 68 mm and 59 mm for males and females, respectively (Folkerts, 1968). Duncan (1967) reported maximum sizes for seal salamanders in Virginia to be 78 mm for males, 67 mm for females. Series of salamanders examined from Kentucky and North Carolina indicated that maturity was reached at 42 mm in males, 48 mm in females (Juterbock, 1978).
Adult seal salamanders exhibit male-biased sexual size dimorphism. Although males mature at smaller sizes and earlier ages than females, males reach larger maximum sizes than females. This results from females having more depressed post-maturation growth rates than males (Bruce, 1993; Castanet et al., 1996).
M. Longevity. Castanet et al. (1996) and Bruce et al. (2002) aged individuals using skeletochronological techniques and reported that females live at least 9 yr and males live at least 11 yr. Bruce and Hairston (1990) suggested greater potential longevity for animals in a population characterized by delayed maturity and larger body size.
N. Feeding Behavior. Nocturnal. Animals emerge from daytime retreats under logs and rocks or from stream-bank burrows to forage. Juveniles actively move about to forage, whereas adults are more likely to sit in the entrances to their burrows and wait for prey (Brandon and Huheey, 1971; Kleeberger, 1985; C.D.C., personal observations). Surface activity peaks around midnight, with a second bout of activity near sunrise (Hairston, 1949, 1986; Shealy, 1975). Both juveniles and adults feed on aquatic and terrestrial invertebrates including true bugs, stoneflies, caddisflies, lepidopterans, beetles, mayflies, dipterans, wasps, ants, odonates, millipedes, and earthworms (Hairston, 1949; Duncan, 1967; Krzysik, 1979; Kleeberger, 1982). Larger animals eat larger prey items (Krzysik, 1979). Seal salamanders have been reported to occasionally eat other salamanders (Shealy, 1975; Bernardo, 2002); however, evidence from dietary studies suggests that predation on other salamanders occurs rarely under natural conditions (Camp, 1997b). Brown et al. (2003) report a seal salamander taking an especially large (35 mm, 74.5% of the salamander's SVL) hesperiid lepidopteran larva.
O. Predators. Natural predators are not reported (Petranka, 1998). Spring salamanders (Gyrinophilus porphyriticus) feed regularly on other salamanders (Bruce, 1979) and may prey on larval and juvenile seal salamanders. In Georgia, seal salamanders occasionally occur along the edges of streams with potentially predaceous fish (e.g., Cottus carolinae, Nocomis leptacephalus, Semotilus atromaculatus). Snake species known to feed on amphibians (e.g., Nerodia sipedon, Diadophis punctatus) have been seen foraging at night in streams inhabited by seal salamanders (C.D.C., personal observations). Predation pressure and/or intraspecific aggression may be high. Wake and Dresner (1967) report that 11% of a museum sample had broken tails.
P. Anti-Predator Mechanisms. Seal salamanders apparently use chemical cues to avoid contact with, and thus possible predation by, black-bellied salamanders (Roudebush and Taylor, 1987b; Jacobs and Taylor, 1992). Choices of egg-deposition sites may, in part, mitigate the effects of predation on eggs. Egg-attendance by maternal females apparently prevents at least some predation on egg clutches. Removal of a 65 mm female from her clutch resulted in the predation on the unattended eggs by a 67 mm female conspecific within 10 min (Camp, 1997a).
Q. Diseases. Unknown.
R. Parasites. Goater et al. (1987) reported the occurrence of six adult nematode species (Capillaria inequalis, Thelandros magnavulvaris, Omeia papillocauda, Desmognathinema nantahalaensis, Falcaustra plethodontis, and Cosmocercoides dukae) and one larval nematode species (an ascaridoidid) in seal salamanders. They found mature forms of three species of trematode (Brachycoelium elongatum, Gorgoderina bilobata, and Phyllodistomum solidum) and one species of tapeworm (Cylindrotaenia americana). They also found larval tapeworms (proteocephalan plerocercoids) and one species of larval acanthocephalan (Centrorynchus conspectus). Goater (2000) found a much lower incidence of leeches (Oligobdella biannulata) in seal salamanders than in the more aquatic black-bellied salamander. He similarly found low infection rates of trypanosomes, blood parasites that presumably use leeches as vectors, in seal salamanders.
4. Conservation. Seal salamanders remain abundant in areas of preferred habitat over much of their geographic range. In 20 yr of surveys of seal salamanders carried out in undisturbed habitats in the Appalachian Mountains of North Carolina, Hairston (1996) found no significant changes in abundance. There may be local threats to viable populations, however. Stream acidification as a consequence of mine drainage may negatively affect some populations. Roudebush (1988) showed that low pH depressed feeding rates, but salamanders did not die when exposed to a pH of 3.5 for 3 wk.
Certain populations of seal salamanders may have experienced declines due to exploitation as fish bait. In a recent survey of bait shops in northern Georgia, this species made up 67% of salamanders sold as “spring lizards” (Jensen and Waters, 1999). The collecting technique of pouring liquid bleach into small, high-gradient streams to drive out salamanders may be particularly harmful to this and other species of streamside salamanders. Because salamanders collected using this method have low survivabilities, bait shops owners often refuse to purchase salamanders from such collectors more than once (Jensen and Waters, 1999).
Optimal habitats for seal salamanders are seepages and small- to medium-sized streams containing cool, well-aerated water, located within mesic, hardwood forests (Organ, 1961; Petranka, 1998). The greatest threat to populations of this species, therefore, may be timber harvesting techniques (e.g., clearcutting) that increase rates of evaporative water loss through the removal of the protective canopy. Petranka et al. (1993) argued that clearcut timber harvesting negatively affects the number of total Desmognathus individuals, including seal salamanders; and estimated that clearcutting killed millions of salamanders from the Appalachian forests of North Carolina during the 1980s and early 1990s. Ash and Bruce (1993), however, disputed these estimates and considered them to be exaggerations of the actual numbers lost. Desmognathine salamanders currently are abundant in areas of the southern Appalachians (the Great Smoky Mountains) that have been extensively logged in the past (S.G.T., personal observations). Appalachian seepages occasionally dry up (Camp, 2000), and it is not known how periodic drought may interact with techniques of timber harvesting to affect populations of seal and other seepage-dwelling salamanders. Because of restricted ranges/population sizes, inherently warmer climates, and intensive silviculture in the Coastal Plain, timber harvesting may be a greater threat to Coastal Plain populations of seal salamanders than to Appalachian populations.
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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