About Desmognathus fuscus (Rafinesque, 1820)
Taxonomy and Common Name
Desmognathus fuscus, commonly called the northern dusky salamander, is a small but sturdy lungless salamander in the family Plethodontidae.
Dorsal and Ventral Coloration
Its upper body ranges in color from reddish-brown to gray or olive, with a white or grey underside. The body is sparsely covered in dark spots or mottling that is most concentrated on the sides.
Dorsal Stripe Patterns
It may have a light dorsal stripe or two dark stripes that continue onto the proximal part of the tail. Juveniles have five to eight pairs of dorsal spots or blotches between their front and hind legs, while older individuals tend to be uniformly dark brown or black.
Diagnostic Facial Stripe
Like all dusky salamander species, both juveniles and adults have a single pale black-outlined stripe that extends from the eye diagonally to the back of the jaw.
Morphological Traits
Both juveniles and adults also have 14 costal grooves, larger hind limbs than forelimbs, and a keeled knife-like tail that is triangular in cross-section and laterally compressed at its base.
Tail Characteristics
The tail is shorter than half the salamander’s total body length and is typically lighter in color than the body.
Adult Size
Adults can grow up to 14 cm in total length; the average adult length is 9.4 cm for males and 8.6 cm for females.
Respiratory Adaptations
As a plethodontid salamander, this species is lungless and absorbs oxygen through its skin, plus membranous tissue in the mouth and throat.
Sensory Adaptations
It also has a naso-labial groove that improves its sense of smell, helping it locate mates and prey by scent.
Global Distribution
This species is native to North America, found across central-eastern Canada and the United States, ranging from southern New Brunswick, southeastern Quebec and southern Ontario south to South Carolina. Populations found further south than this range are now considered to belong to other species that were previously synonymized with D. fuscus, such as D. conanti.
Canadian Range Proportion
Approximately 5% of the species’ global range falls within Canada.
Canadian Habitat Preference
Within its Canadian range, the northern dusky salamander most often occurs in forested habitat along high-elevation low-order streams.
Canadian Designatable Units
Two distinct designatable units exist for the species in Canada: the Quebec/New Brunswick unit and the Carolinian unit in Ontario.
Ohio Population Research
A comprehensive review of D. fuscus populations in Ohio was published in the 2013 work Amphibians of Ohio.
Michigan Isolated Population
An isolated breeding population exists in eastern Michigan, though it is unknown whether this population is natural or introduced.
Northern Range Habitat
At the northern edge of the species’ range, the northern dusky salamander lives in saturated soil in the riparian zone near springs, seepages, and small tributaries of small headwater streams.
Optimal Habitat Conditions
Optimal habitat occurs in undisturbed watersheds with running or trickling water and abundant forest cover. Forest cover keeps water cool and well oxygenated, and maintains the moisture and temperature levels the salamanders need to survive.
Southern Range Habitat
In the southern part of its range, the species can be found in upland streams, as well as floodplains, sloughs, and muddy sites.
Population Genetic Structure
Due to their limited mobility, many populations of this species are genetically distinct.
Breeding Season and Courtship
Breeding happens on land annually, in either spring or fall, and involves elaborate courtship rituals.
Reproductive Male Traits
Sexually active adult males have papillose cloacal lips and a small mental gland that becomes enlarged when reproductive.
Reproductive Female Traits
Females do not have a mental gland, and have folded cloacal lips.
Mating Behavior
During mating, the male rubs his snout, cheeks, and mental gland on the female’s snout; the female typically responds by picking up the male’s spermatophore.
Fecundity and Body Size
A female’s fecundity increases with her body size.
Clutch Characteristics
Females usually lay between 10 and 30 eggs under streamside logs, moss, or rocks where the soil is water-saturated. Clutch size varies geographically, and can be as large as 45 or as small as 8.
Egg Incubation
Females stay with their eggs during the 6 to 10 week (45 to 60 day) incubation period to protect eggs from desiccation and predation.
Hatchling Traits
When larvae hatch, they are fully aquatic and approximately 1.5 cm long.
Metamorphosis Size
Larvae eventually metamorphose into semi-terrestrial adults; newly metamorphosed juveniles measure 2.8 to 4.4 cm in length.
Life Cycle Structure
This species has a biphasic life cycle: larvae remain aquatic for 7 to 16 months before transitioning to a semi-terrestrial adult stage.
Maturity and Lifespan
Northern dusky salamanders reach sexual maturity at around 3 to 4 years of age, and have a life expectancy of 10 to 15 years.
