Spotted Dusky Salamander
© 2012 Todd Pierson (1 of 25)
Country distribution from AmphibiaWeb's database: United States
Desmognathus conanti Rossman, 1958
D. Bruce Means1
1. Historical versus Current Distribution. The geographic distribution of spotted dusky salamanders (Desmognathus conanti) extends south of a line beginning at the confluence of the Cumberland and Ohio rivers on the border of Illinois and Kentucky and continuing southeast through western Kentucky, central Tennessee, and into northwestern South Carolina (Karlin and Guttman, 1986; Petranka, 1998). The species also occurs in a few colonies at the southern tip of Illinois (Smith, 1961). Spotted dusky salamanders occur as far south as southern Mississippi and eastern Louisiana (K. Kozak and colleagues, unpublished data) and may occur in eastern Alabama (Rossman, 1958), but they do not reach western Florida (Means, 1998). Still, many aspects of the southern distributional limits of spotted dusky salamanders presently are unclear. Chaney (1949) did a life history study of six localities in southern Louisiana, believing he was working with a single species he called D. fuscus auriculatus. Later, he conducted additional intensive studies of Louisiana Desmognathus but only considered that he was working with one species, when in fact he may have been working with at least two (Chaney, 1958), including spotted dusky salamanders. Dundee and Rossman (1989) did not question that there were two morphological types in Louisiana, one a ravine dweller with light-colored, heavily patterned adult and larval dorsum and fewer gill filaments in larvae (which could be spotted dusky salamanders), and the other a muckland form with darker coloration and bushy gills (which are probably southern dusky salamanders [D. auriculatus]). They did not, however, reach a conclusion about the taxonomic status of Louisiana Desmognathus. They simply discussed all Louisiana Desmognathus as either "Desmognathus fuscus-auriculatus complex, D. fuscus, or D. auriculatus," with no reference to D. conanti. The ravine-inhabiting form represents either spotted dusky salamanders or some unrecognized species. The only known occurrence of spotted dusky salamanders west of the Mississippi River is a small group of populations on Crowley's Ridge, an isolated gravel ridge in an ancient part of the Mississippi River valley in northeastern Arkansas. These may have been extirpated (Means, 1974; Nickerson et al., 1979; Bonett, 2002; Trauth et al., in preparation).
2. Historical versus Current Abundance. In addition to Crowley's Ridge, where populations seem to have disappeared, population densities in streams near Atlanta, Georgia, were found to be inversely proportional to the degree of stream disturbance associated with urbanization (Orser and Shure, 1972). Siltation and sedimentation of their small stream habitats from runoff following construction and farming probably have extirpated or severely reduced populations of this species throughout its range, but no specific studies have been undertaken to assess historical versus current abundance relationships.
3. Life History Features.
A. Breeding. Reproduction is semi-aquatic.
i. Breeding migrations. Probably do not occur. No breeding migrations have been reported.
ii. Breeding habitat. Desmognathine salamanders are highly territorial and breed in the same habitats in which their eggs are laid.
i. Egg deposition sites. In secretive habits such as the undersides of rocks, leaf mats, moss, and cavities in rotting logs near streams and seeps.
ii. Clutch size. Eggs (13–24) with developing embryos were found in the field from mid July to mid October in Alabama (Mount, 1975), and in the "fall" in northern Mississippi (Brode, 1961). Eggs hatch in 5–7 wk in Alabama (Mount, 1975).
i. Length of larval period. In Alabama, larval development may take ≤ 13 mo in water or is greatly accelerated if on a damp place on land (Mount, 1975). Life history information in Dundee and Rossman (1989) for Louisiana was based upon that of Chaney (1949, 1958), who may have reported mixed data from southern and spotted dusky salamanders. Because of the uncertainty about the taxonomic status and geographic limits of this species (e.g., Dundee and Rossman, 1989; Petranka, 1998), few studies have been undertaken on their life history, reproduction, and development.
D. Juvenile Habitat. Same as for adults, except that choice microhabitats, occupied by the aggressive adult males, are not occupied by juveniles.
E. Adult Habitat. In the deeply shaded, heavily wooded ravines of the Alabama Red Hills where they are syntopic with the Red Hills Salamanders (Phaeognathus hubrichti), spotted dusky salamanders were found on the wetter portions of the stream banks and under the rocks of the stream itself (Brandon, 1966b). Elsewhere in Alabama, Mount (1975) reported them from a variety of damp situations including seepage areas and the edges of small rocky streams, where they were found during the daytime under rocks, damp leaf litter, and in burrows or rotting logs. In Louisiana, populations with boldly patterned individuals that may be spotted dusky salamanders were reported from spring seepages in ravines under logs and debris in shallow water or adjacent to water (Dundee and Rossman, 1989). Smith (1961) reported that spotted dusky salamanders are found in cold springs under wet leaves or rocks at the margin of springs or streams in southern Illinois. In north Georgia, the species was reported from spring-fed streams impacted by different degrees of disturbance from urbanization in and around relieved terrain in Atlanta (Orser and Shure, 1972).
F. Home Range Size. Unknown.
G. Territories. Because some congeners are highly territorial and the species does not migrate, it is probable that adult males, at least, defend territories or choice hiding places, but no studies have been conducted.
H. Aestivation/Avoiding Dessication. Unknown and unstudied.
I. Seasonal Migrations. Unknown. Short movements associated with drought or floods might take place toward or away from the streams along which the species is associated, but as a normal, regular activity, seasonal migrations probably do not exist in this territorial species.
J. Torpor (Hibernation). Unknown.
K. Interspecific Associations/Exclusions. Lake Barkley (Cumberland River) in western Kentucky forms a relatively discrete boundary between northern dusky salamanders (Desmognathus fuscus) and spotted dusky salamanders, with their populations inhabiting tributaries on the eastern and western shores of the lake, respectively (Bonett, 2002). Fine scale examination of populations at the interface of these species revealed only one population that contained few putative hybrid individuals (Bonett, 2002). In Tennessee, populations of dusky salamanders (D. fuscus and D. conanti) previously have been illustrated as continuous across the state (Petranka, 1998), however the well-drained Central Basin Region actually appears to geographically separate the species (see D. fuscus spot map in Redmond and Scott, 1996). Bonett (2002) identified populations of spotted dusky salamanders in northern Alabama and populations of northern dusky salamanders approximately 150 km north in east-central Tennessee; it is unclear if contact between the species exists in the intermediate region. This leaves an ambiguous identification on specimens observed in studies of courtship behavior (Verrell, 1995), reproductive ecology (Hom, 1987), and cover object choice (Hom, 1988) from the Reed Creek drainage of eastern Tennessee, which occurs between the known species boundaries of D. fuscus and D. conanti.
In the Cheaha Mountains of east-central Alabama, spotted dusky salamanders are syntopic with seal salamanders (D. monticola), red salamanders (Pseudotrition ruber), and southern two-lined salamanders (Eurycea cirrigera; Rubenstein, 1969, personal observation). In the Alabama Red Hills, they are found in deep ravines with Red Hills salamanders, seal salamanders, and southern two-lined salamanders (Brandon, 1966b). In southern Mississippi they are found with dwarf salamanders (E. quadridigitata) in leaf packs along swamp edges (R.M.B., personal observations). In southern Louisiana, spotted dusky salamanders may be syntopic with southern dusky salamanders (D. auriculatus; Chaney, 1949; Dundee and Rossman, 1989). In western Tennessee, spotted dusky salamanders were found with long-tailed salamanders (Eurycea longicauda) and southern two-lined salamanders (E. cirrigera; Sites, 1978). Verrell (1995) may not have described the courtship behavior of spotted dusky salamanders because his experimental specimens came from north of the hypothesized "contact zone" in the range of northern dusky salamanders.
L. Age/Size at Reproductive Maturity. Unstudied.
M. Longevity. Unknown.
N. Feeding Behavior. Sites (1978) reported food habits and feeding behavior of animals from three sites in western Tennessee. In the diet he reported amphipods, isopods, pulmonate snails, oligochaetes, chilopods, diplopods, insect larvae, coleopterans, dipterans, collembolans, homopterans, and hymenopterans.
O. Predators. None reported.
P. Anti-Predator Mechanisms. Unstudied.
Q. Diseases. None reported and unstudied.
R. Parasites. Dyer et al. (1980) reported two species of nematodes (Thelandros magnavulvaris, Cosmocercoides dukae), one trematode (Brachycoelium obesum), and unidentified acanthocephalans in the gastrointestinal tracts of 149 (34%) of 442 spotted dusky salamanders from Pulaski County, Illinois.
4. Conservation. With the exception of the studies of Orser and Shure (1972, 1975) on populations in the vicinity of Atlanta, Georgia, no detailed population surveys or studies of the ecology of the spotted dusky salamander have been undertaken. Phylogenetic analyses of Desmognathus based on mitochondrial DNA and morphology suggest many of the characters that have previously been used are labile and can be rapidly acquired when populations enter new adaptive zones (K. Kozak and colleagues, unpublished data). The most urgent study need is the identification of the geographical limits of the species. Unfortunately, spotted dusky salamanders represent one of the most poorly understood amphibians in eastern North America, despite its potentially large geographic distribution.
1D. Bruce Means
2Ronald M. Bonett
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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