© 2010 Todd Pierson (1 of 21)
Desmognathus wrighti King, 1937
Julian R. Harrison1
1. Historical versus Current Distribution. Pigmy salamanders (Desmognathus wrighti) occur in isolated populations in the high elevation forests of southwestern Virginia, western North Carolina, and eastern Tennessee, at elevations ranging from approximately 762–2,012 m. Pague (1984) reported a slight extension of the range in Virginia, at Pine Mountain, 2.4 km east of Mount Rogers. Pigmy salamanders are especially characteristic of spruce-fir forests, but populations also occur at lower elevations in mesophytic hardwoods; populations found east and south of the present range of spruce and fir may represent post-glacial relicts of a formerly more widespread distribution (Huheey, 1966; Tilley and Harrison, 1969; Rubin, 1971; Bruce, 1977). The historical distribution is unknown.
Crespi (1996) presented evidence that D. wrighti, as currently recognized, is not monotypic but instead a complex of two different allopatric species. She found that populations north of the Black Mountains in North Carolina (Roan, Grandfather, and Whitetop mountains, and Deep Gap, Virginia) differ from the more southwestern populations by fixed alternative alleles at > 1 locus, and a unique morphological characteristic, partial to complete loss of ventral iridophores. A description of the new species is in preparation.
2. Historical versus Current Abundance. The extent to which pigmy salamanders have been affected by the decline of spruce-fir forests at high elevation sites is unknown. Wilson (1995) offered the protection of spruce-fir forests and retention of ground litter in areas occupied by this species as management suggestions. Pigmy salamanders apparently were relatively common in 1936, as the original description was based on 100 carefully examined specimens of which 3/4 were seen in the field; an additional 50 specimens were observed but not collected (King, 1936). Also, Weller (1931) stated that this species (misidentified as a juvenile form of D. fuscus carolinensis) "…was found abundantly only under the tightly fitting bark of stumps or standing trees at high elevations.” In his study of the local distribution and ecology of southern Appalachian plethodontids, Hairston (1949) found most species, including pigmy salamanders, to be abundant. Bogert (1952) noted that pigmy salamanders were relatively abundant in samples of salamanders from high elevations on White Top Mountain (n = 95) and Mount Rogers (n = 94), Virginia, constituting 20% of the sample from each locality. Organ (1961a) collected approximately 7,000 specimens of Desmognathus from Mount Rogers and Whitetop Mountain, Virginia, in the summer of 1957 and the summer, fall, and spring of 1958–'59; none of the five species, including pigmy salamanders, was represented by < 1,000 individuals. Pague and Mitchell (1987) regarded the species as abundant on Whitetop Mountain in Virginia, despite heavy collecting for at least 30 yr. In their study of the effects of timber harvesting on salamanders, Petranka et al. (1993) reported that captures of salamanders in plots from mature forests were five times greater than those from recent clearcuts and that 50–70 yr would be required for populations to return to pre-disturbance levels. Pigmy salamanders were represented by 26 specimens (3% of the total number of salamanders collected) and had a 30% frequency of occurrence in plots. However, Ash and Bruce (1994) questioned the methodology, analysis, and interpretation of the study, suggesting that < 1% of the Desmognathus community may have been sampled (but see Petranka, 1994). Singer et al. (1982) reported no significant difference in numbers of pigmy salamanders and four other salamander species between northern hardwood stands rooted by hogs and stands that were not rooted. However, they did not report that only pigmy salamanders declined significantly as cited by Mathews and Echternacht (1984). Petranka (1998) has observed pigmy salamanders to be common in old-growth deciduous forests at relatively low elevations but uncommon in younger stands.
3. Life History Features.
A. Breeding. Reproduction is terrestrial.
i. Breeding migrations. Unknown.
ii. Breeding habitat. The six nests that are known were found beneath the bank of a creek (Organ, 1961b).
i. Egg deposition sites. Only six nests are known; these were found beneath the bank of a creek at a depth of about 30 cm in a pocket of gravel and mud through which water percolated (Organ, 1961b). Each nest was suspended from a small rock within a small cavity in the mud surrounding the rock and attended by an adult, spent females in the two instances where this could be determined. Courtship of captive adults occurs in both fall and spring (Organ, 1961b). Brooks (1948a), Organ (1961b), Houck (1980), and Verrell (1999) described courtship behavior. Brock and Verrell (1994), Verrell (1997, 2000a), and Verrell and Mabry (2000) presented information concerning courtship pattern.
ii. Clutch sizes. The six known clutches were found in mid October and contained 3–8 embryos in late stages of development (Organ, 1961b); hatching of the eggs occurred 19–25 October.
C. Direct Development. Length of the developmental period is unknown. The terrestrial hatchlings are essentially miniature versions of the adult; there is no aquatic larval stage.
D. Juvenile Habitat. Juveniles are terrestrial and have the same habitat characteristics as adults.
E. Adult Habitat. Typical habitat includes soil surfaces beneath small logs and stones in spruce-fir forests (King, 1936, 1939) and under bark of stumps or standing trees at high elevations (Weller, 1931). Pigmy salamanders are highly terrestrial, characteristic of spruce-fir forests, but present also at lower elevations in mesophytic hardwoods. All the pigmy salamanders observed by Hairston (1949) were in forest habitats with 76% of animals > 61 m from the closest stream. Organ (1961a) confirmed Hairston’s observations but also provided evidence that pigmy salamanders move in late fall into underground seepage areas. When active under conditions of complete darkness and a saturated atmosphere, individuals climb to heights of ≤ 1.2 m (7 ft) on living or dead spruces (Hairston, 1949; Organ, 1961a). On especially damp nights, pigmy salamanders may be found on leaves some distance above the ground (Mathews and Echternacht, 1984).
F. Home Range Size. Unknown.
G. Territories. Unknown. However, males are aggressive toward other males during the courtship season (Organ, 1961a). Larger males always dominate smaller ones. If both are about the same size, usually one male bites and the other flees.
H. Aestivation/Avoiding Dessication. Unknown. Pigmy salamanders are active throughout the warmer and drier parts of the year.
I. Seasonal Migrations. Pigmy salamanders abandon forest habitat in late fall and move into underground seepage areas for hibernation in winter (Organ, 1961a; Bruce, 1977).
J. Torpor (Hibernation). In the fall and spring of 1958–'59, Organ (1961b) removed 649 specimens from a site measuring about 1 m (3 ft) on a side by 30 cm (1 ft ) deep in saturated gravel and mud beneath the bank of a creek. He interpreted this as a hibernating aggregation.
K. Interspecific Associations/Exclusions. Pigmy salamanders occur syntopically with ≤ 4 or 5 different congeners in various parts of its range. These species are segregated ecologically by microhabitat based primarily on distance from open water, though considerable overlap in horizontal distribution occurs. Pigmy salamanders are the most terrestrial desmognathines in this streamside community, occurring exclusively in the forest, especially during the summer. They also exhibit greater scansorial activity than other species when active at night. The ecological differences between pigmy salamanders and their congeners, especially members of the D. ochrophaeus complex (Tilley and Mahoney, 1996), in part also forest species, have been interpreted as a consequence of interspecific competition (Hairston, 1949). Tilley (1968), however, suggested that selection has favored increased terrestrialism in the smaller species because of their susceptibility to predation by the larger ones. Subsequent studies by Hairston (1986, 1987) also pointed to predation rather than competition as the mechanism involved in streamside desmognathine communities. Pigmy salamanders are known to occur sympatrically with seepage salamanders (D. aeneus), an ecologically similar species, at several localities in the southern Nantahala Mountains of southwestern North Carolina (Tilley and Harrison, 1969; Rubin, 1971; Bruce, 1991), but the nature of the association between these two species in that area is unknown.
L. Age/Size at Reproductive Maturity. Males reach sexual maturity at 17–19 mm SVL (to anterior corner of vent), females at 20 mm SVL (Harrison, 1963). According to Organ (1961a), males mature sexually when they are 3.5 yr old and have attained a SVL > 24 mm (to posterior corner of vent); females mature when 4.5 yr old but do not lay eggs until they are 5 yr old.
M. Longevity. Unknown. Males and non-brooding females have a mean annual survival rate of 91% in the early years of life and 29% in the later years (Organ, 1961a).
N. Feeding Behavior. Food items in 10 stomachs examined by Hairston (1949) included springtails, parasitic wasps, moths, beetles, thrips, flies, pseudoscorpions, spiders, and acarine mites, particularly orabatids. All or most of these prey items were species characteristic of the forest-floor habitat. Orabatid mites are abundant and ecologically important components of coniferous forests (Jacot, 1936).
O. Predators. Known predators include spring salamanders (Gyrinophilus porphyriticus) and a carabid beetle (Huheey and Stupka, 1967). Other presumed predators include larger, syntopic species of Desmognathus, small snakes such as ring-necked snakes (Diadophis punctatus), and birds. Of a Pigmy salamander museum sample, 7% had broken tails (Wake and Dresner, 1967).
P. Anti-Predator Mechanisms. When exposed or touched, pigmy salamanders flip and become immobile (Brodie, 1977).
Q. Diseases. Unknown.
R. Parasites. Unknown.
4. Conservation. In North Carolina, pigmy salamanders have been placed in category W5 of that state’s “Watch List,” a species facing “increasing amounts of threats to its habitat, whether or not populations are known to be declining” (LeGrand and Hall, 1995). Their rank in that state is S3, “Rare or Uncommon” (21–100 extant populations). Based on his experience with the species in North Carolina, R.C. Bruce (personal communication) has no reason to believe pigmy salamanders are in any jeopardy in that state, though he has not monitored populations in spruce-fir sites. Kucken et al. (1994) found that in a Great Smoky Mountains stream contaminated by sulfuric acid and heavy metals from the Anakeesta Formation, stream breeders were almost entirely eliminated, while terrestrial breeders, including pigmy salamanders, increased in numbers. Along contaminated sections of the stream where black-bellied salamanders (Desmognathus quadramaculatus) were almost entirely eliminated, pigmy salamanders were about four times more abundant than they were along uncontaminated sections where black-bellied salamanders were present. This was interpreted by the authors as reflecting the absence of predation on the smaller species by the larger one along contaminated sections of the stream.
In Tennessee, pigmy salamanders are considered to be in need of management and are given a rank of S2, “very Rare and Imperiled within the state” (Withers, 1996). Populations of pigmy salamanders in Virginia appear to be viable within their restricted range in the Mount Rogers National Recreation area, but they are considered to be a Species of Special Concern with a rank of S2 because of their limited distribution within the state (Pague, 1991). Logging activities and increased recreational development could threaten portions of this range, particularly at lower elevations (Pague, 1991). J.A. Organ (personal communication) has found that pigmy salamander populations on Whitetop Mountain, Virginia, below 1,525 m (5,000 ft) are stable, but above that elevation they may be declining. Further, there is no evidence of any local extinctions on Whitetop Mountain, Mt. Rogers, Beech Mountain, Bluff Mountain, or Pine Mountain in Virginia during the last half of the twentieth century (Organ, 1993, and personal communication). Organ’s findings were based on intensive quantitative sampling in the Mt. Rogers National Recreational Area in the late 1950s, the late 1960s, 1970, and again in 1989–'92. All the known Virginia localities for the species are situated within the Mt. Rogers Recreational Area, Jefferson National Forest (Mitchell and Reay, 1999).
Based on her recent and extensive experience with pigmy salamanders in the field, Erica Crespi (personal communication) observed that in the Great Smoky Mountains, Plott Balsams, Great Balsams, and southward, populations of pigmy salamanders were patchy in distribution, but that enough of them exist to provide long-term stability. In that part of the range, individuals were abundant in small patches (approximately 20 m x 50 m2), but such patches were difficult to find. In contrast, Crespi noted that the more northern populations of the species (Mt. Rogers, Whitetop Mountain, Roan Mountain, and Grandfather Mountain) are more isolated from one another and exist in fewer patches that are farther apart. In that area, pigmy salamanders were locally common in small patches, but patches were uncommon or rare. Thus, northern populations may be more vulnerable to extinction in the face of environmental change.
1Julian R. Harrison
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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