Amphibians of North Carolina
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NC Records

Desmognathus conanti - Spotted Dusky Salamander


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Taxonomy
Class: Amphibia Order: Caudata Family: Plethodontidae Subfamily: Plethodontinae
Taxonomic Comments: The Spotted Dusky Salamander (Desmognathus conanti) and Northern Dusky Salamander (D. fuscus) as traditionally recognized by herpetologists have a long and complex taxonomic history, with the former originally described as a subspecies of D. fuscus. It was treated as such until genetic studies revealed that it is not closely related to the latter (Beamer and Lamb 2008; Kozak et al. 2005). According to the latest systematic treatment of these species by Pyron and Beamer (2023a) At least 10 other currently recognized species of Desmognathus were either described from populations previously considered to be D. fuscus, described as or later considered to be subspecies of D. fuscus, or later considered to be synonyms of D. fuscus before ultimately being recognized as distinct species. The latest molecular analyses have also revealed extensive cryptic diversity within both D. conanti and D. fuscus as currently conceived, with these two species constituting a polyphyletic assemblages of 13 distinct mitochondrial lineages and perhaps as many as 11 candidate species. Pyron and Beamer (2023a) provide a very comprehensive review of the taxonomic history of this group.

The most recent molecular analyses (Beamer and Lamb 2020, 2022a; Pyron and Beamer 2022b, Pyron et al. 2020, 2022, 2023a, Tilley et al. 2013) indicate that there has been a complex mosaic of hybridization between many of the small Desmognathus species and lineages. Gene exchange has occurred between both phylogenetically sister and geographically adjacent populations, as well as between distantly related and spatially separated groups. In summary, both D. conanti and D. fuscus are now each known to represent polyphyletic assemblages of multiple, geographically well-defined candidate species that are phylogenetically interdigitated with other recognized species. The candidate species include a “mountain dusky”phenotype with smaller, gracile bodies and round tails, a lowland “dusky” type with more robust, larger bodies and keeled tails, and a smaller lowland “dusky” form often associated with ravine streams and adjacent swamps, with slenderer bodies and less heavily-keeled tails.

Pyron and Beamer (2023a) reviewed the information on gene exchange between lineages and noted that some of the candidate species exhibit limited admixture with each other, or with other described forms. In contrast, some other candidate species appear to be genomically exclusive with respect to all other known genetic lineages. After integrating the previous analyses and evaluating the strength of evidence for delimiting additional species within D. conanti and D. fuscus, the authors recognized six additional species based on genetic, geographic, and morphological evidence. They also redefined D. conanti and D. fuscus. The new species are D. anicetus, D. bairdi, D. campi, D. catahoula, D. lycos and D. tilleyi. Among the newly described species, all but D. catahoula occur in North Carolina. Pyron and Beamer (2023a) reported that D. fuscus consists of three genetic lineages and could potentially be further divided into additional species in the future.

As currently recognized, D. conanti presents some taxonomic issues that are not fully resolved. Beamer and Lamb (2020) noted the very close relationship between D. conanti-like forms (see Tilley 19888; Tilley et al. 2013) and D. santeetlah. These forms both occur in the Great Smoky Mountains and vicinity and freely interbreed where they are syntopic. In their analysis, Beamer and Lamb (2020) found that the D. santeetlah clade was nested within a larger group that contained other D. conanti clades. In addition, specimens that phenotypically resemble low-elevation D. conanti (but see Tilley et al. 2013) had haplotypes of D. santeetlah, a feature that likely reflects the widespread hybridization of these forms within the Great Smoky Mountains.

Another taxonomic issue concerns populations of D. fuscus-like and D. conanti-like forms in eastern Tennessee that were studied by Tilley et al. (2013). The authors found several genetic groups in the regions, some of which could be reliably assigned to either D. fuscus or D. conanti, and others that could not and poised major problems with delineating Desmognathus species in the region. The major confounding issues included unexpectedly high levels of lineage divergence in the absence of morphological differentiation and physiographic barriers, discordance between cytB clades and allozyme profiles, and evidence of gene exchange between differentiated lineages. They described complex patterns of discordance among cytB sequences, allozyme patterns, morphology, and reproductive isolation and proposed that several geographic clusters of populations be regarded as “failed species.” These are genetically distinctive lineages that now exchange genes with other forms at levels that compromise their evolutionary independence. Populations of well-defined D. conanti in eastern Tennessee appear to occur no farther north than the Little Tennessee River and vicinity (Tilley et al. 2013), and presumably occur in adjoining areas of western North Carolina.
Species Comments:
Identification
Description: The Spotted Dusky Salamander is a medium-sized and somewhat robust Desmognathus. There are 14 costal grooves and the adults range from 6-13 cm TL. The basal half of the tail is laterally compressed and somewhat triagonal in cross-section, while the terminal half is strongly laterally compressed, triagonal in cross-section, and keeled. Depending on the locale, individuals can range from being rather uniformly dusky or yellowish brown above to being boldly marked with dorsal patterning. Older larvae and young juveniles often have a series of 5-8 dorsal blotches or spots between the front and rear limbs that continue on to the tail, but these become partially fused or develop into a poorly-defined wavy dorsal stripe with age. Older adults may show evidence of having remnants of the dorsal spots and blotches, but others tend towards becoming melanistic and are dark above with little spotting. The venter is cream-colored, with some inividuals having darker speckling, peppering, or reticulated patterning concentrated near the ventro-lateral margins. The underside of the tail of some individuals may have a faint yellowish wash, and the toe tips lack cornifications. As with other Desmognathus, a light line extends from the eye to the angle of the jaw. Adult males have mental glands, enlarged premaxillary teeth, and papillose cloacal lips. This species is variable and can be confused with other Desmognathus. The range, along with the triangular tail, the absence of cornified (dark) toe-tips, and general size and patterning are helpful in identifying specimens in the field.
Online Photos:    Google   iNaturalist
Observation Methods: This species is most easy collected by turning cover objects in the immediate vicinity of small streams.
AmphibiaWeb Account
Distribution in North Carolina
Distribution Comments: As currently defined (Pyron and Beamer, 2023a), the range of D. conanti includes extreme southern Illinois and adjoining areas of western Kentucky, central and western Tennessee, southeastern Louisiana, central and southern Mississippi, the Florida Panhandle, all of Alabama, northwestern Georgia and the Tennessee-North Carolina border region to the Little Tennessee River (see distribution map above).

The exact distribution of D. conanti in North Carolina is poorly documented and genetic markers may be needed to verify many conanti-like specimens in the state. Tilley (1988) reported extensive hybridization between D. conanti and D. santeetlah at their narrow contact zone along an elevational gradient in the western and southwestern section of the Great Smoky Mountains on the Tennessee side. Tilley et al. (2013) found that populations that can be unambiguously assigned to D. conanti appear to occur no farther north in eastern Tennessee than the immediate vicinity of the Little Tennessee River. They presumably occur in nearby areas south of the Little Tennessee River in western North Carolina. Populations studied by Jones (1986) at the northern edge of the Unicoi Mountains in Graham Co. and Monroe Co.,Tennessee are presumably this species (see Tilley et al. 2013). Data to date indicate that this species is found in Graham Co., and presumably in the lowermost tier of counties in southwestern North Carolina (Cherokee; Clay; Macon).
Distribution Reference: Tilley et al. 2013, Beamer and Lamb 2020;
County Map: Clicking on a county returns the records for the species in that county.
GBIF Global Distribution
Key Habitat Requirements
Habitat: The Spotted Dusky Salamander is a semi-aquatic species that is associated with seeps and small streams in many areas of the range (Beane et al. 2010, Tilley and Hugheey 2004). In North Carolina they are confined to lower elevations in the Blue Ridge and can be found in or along the margins of small streams with rocks, logs, mosses and other cover. In the Coastal Plain, D. conanti is sometimes found around the margins of swamps and sluggish, muddy streams (Mount 1975).
See also Habitat Account for Spring Runs and Brooks
Life History and Autecology
Breeding and Courtship: The adults engage in a set of rather stereotypic courtship behaviors that appear to be essentially identical for D. conanti, D. santeetlah, and D. fuscus. The following description of courtship are based on several studies of these species that are summarized by Petranka (1998).

When a male encounters a receptive female, he engages in a 'butterfly walk' in which he approaches while synchronously rotating the forelimbs in a manner that is similar to the butterfly stroke of swimmers. The male may repeatedly jerk his body to-and-fro and undulate his tail during this period. The male eventually places his snout on the female's back, arches his body upward, and raises his belly and forelimbs clear off the ground. The hindlimbs and tail are kept pressed to the substrate, and the snout is pressed downward with considerable force against the female's back. This not only brings the hedonic glands into contact with the female, but also causes tactual stimulation from the enlarged premaxillary teeth of the males. The male then violently snaps his body straight, which often propels him 5-10 cm or more from the female. He then returns and repeats the entire sequence several times. Snapping lacerates the females skin and vaccinates the female with secretions from the male's mental gland. The male may also position himself such that his undulating tail is beneath the chin of the female. From this position, he will also snap the female's dorsum or neck to vaccinate the female. In addition to snapping, a male may slowly pull his teeth across the female's dorsum to vaccinate her. This phase of courtship often lasts for 1-2 hours.

Once the female is fully receptive the male moves forward and undulates his tail as it passes under her chin. The female saddles the male's tail and the courting pair moves forward in a tail-straddle walk. The male eventually begins a series of lateral pelvic rocking movements then deposits a spermatophore. Immediately thereafter, he arches the base of the tail upward and bends the tail sharply to one side. He then violently undulates the tail. The female holds her chin against the base of the bent tail and the courting pair moves forward quickly. As the female passes over the spermatophore, she picks up the sperm cap with her cloacal lips. The animals decouple shortly thereafter.

Jones (1986) found males with the vasa packed with sperm during every month of his study (March - December), suggesting that courtship likely occurs throughout the warmer months of the years when adults are active.
Reproductive Mode: Females lay their eggs beneath rocks, moss mats, or other cryptic microhabitats in or near aquatic sites, often in a constructed depression in the soil that is beneath a cover object. The eggs are deposited in a globular or grape-like cluster that is often suspended to the roof of a cavity or attached to mosses or fibers. The nests are typically located no more than 1-2 meters from the stream edge. Hom (1988) found that females on Chihowee Mountain in eastern Tennessee breed annually and preferred rocks as cover, except during the nesting season when they moved from streams onto stream banks and nested in moss clumps. Jones (1986) found 25 clutches with brooding females during the summer months in the Unicoi Mountains that straddle the NC-TN line. Most were under rocks along the banks of streams or seepages, and most were in contact with the soil. A smaller number were beneath moss mats. All were within 1 meter of the water's edge, and most females appeared to breed annually.

Females brood their eggs through hatching. Hom (1987) reported that 9 of 157 egg clusters in eastern Tennessee did not have attending females and all suffered complete mortality. She estimated a median incubation period of 47 days. The eggs have been found from mid-July to mid-October in Alabama with clutches containing from 13-24 eggs per nest (Mount 1975). Jones (1986) found an average of 23 mature ova (range = 8-37) in 73 gravid females from the Unicoi Mountains of Graham Co., and clutch size increased with female SVL. Hom (1987) also found a positive correlation between female SVL and the number of eggs in nests. Most females in eastern Tennessee oviposit from late June through early August (Hom 1987, Jones 1986). Reproductive success was low in Tennessee populations studied by Hom (1987). The percent of nests in which at least one embryo survived to hatching varied from 24-49% among years and large females hatched a greater percentage of their eggs than small females.
Aquatic Life History: Jones (1986) found that larvae begin to hatch by mid-September. Growth is very slow, and the larvae appear to metamorphose about a year later after growing only a few mm in SVL.
Terrestrial Life History: The juveniles and adults feed predominantly on terrestrial or semiterrestrial invertebrates and appear to be generalists that eat a wide variety of invertebrate prey. As individuals grow, they incorporate larger prey into the diet, but continue to consume large numbers of small prey (Sites 1978). Individuals in western Tennessee fed on terrestrial insects during late summer and early autumn, but showed a tendency to shift towards isopods and other aquatic insects during the spring (Sites 1978). Tiny prey < 1 mm TL were rarely eaten.

About 50% of males that were studied by Jones (1986) in the Unicoi Mountains of Graham Co. reached sexual maturity when around 35 mm SVL, versus 39 mm SVL for females. Males appear to reach sexual maturity when 2 years old, versus 3 years for females. Marynick (1971) reported that females in southern Louisiana reach maturity in two years and lay eggs in their third year, with the smallest egg-laying female being 34 mm SVL. Most females appear to mate earlier in the year and are capable of long-term sperm storage.

Hom (1987) found that most adults remained within a 15 m stretch of stream during a two-year period. Orser and Shure (1975) found that the subadults and adults (> 35 mm SVL) in a population in Georgia moved beneath ground during the winter, with the lowest surface densities occurring in March. Densities were highest in June and July (maximum = 1.12 salamanders/m2) when larvae were metamorphosing, then stabilized at around 0.50/m2 until early autumn. Gravid females were abundant in late-spring, but disappeared by late-July when they presumably moved to nesting sites below the surface. Nocturnal population estimates always exceeded the diurnal estimates and reached a peak of 2.48 salamander/m2 in early July.
General Ecology
Community Ecology: Desmognathus conanti often coexists with other salamanders and could potentially compete for foraging or nesting sites. Means (1975) surveyed steepheads (perennially wet, first-order stream sources that issue from the base of valley headwalls) as well as the lower, low-gradient sections of drainages in the Florida Panhandle for D. conanti and D. auriculatus. He provided evidence that D. conanti excludes D. auriculatus from steepheads and that the latter is only present in steepheads when D. conanti is absent.
Adverse Environmental Impacts
Status in North Carolina
NHP State Rank: [S3]
Global Rank: G5
Environmental Threats: Like many aquatic organisms, dusky salamanders are sensitive to stream pollution and siltation. Orser and Shure (1972) found that densities of D. conanti in streams near Atlanta, Georgia were inversely proportional to the degree of stream disturbance associated with urbanization. Stream scouring, siltation, and loss of ground cover are the most likely reasons for low densities of D. conanti in urban areas.


Status Comments: This is a widespread species in the eastern U.S. that extends into southeastern Tennessee and adjoining Graham County in North Carolina. Additional populations appear to be present in Cherokee, Clay, and Macon counties, but these need to be confirmed with additional collecting and identification using molecular markers.

Photo Gallery for Desmognathus conanti - Spotted Dusky Salamander

1 photo is shown.

Recorded by: Jim Petranka
None Co.
Comment: Map showing the distribution of D. conanti and other members of the D. conanti/fuscus complex.