APPALACHIAN NATURE: An Entree’ of Salamanders
If you tend to lift rocks or logs in our forests, you’ve undoubtedly uncovered red-backed salamanders. The Appalachians are known for their salamanders, especially red-backed salamanders. Various studies have found densities of red-backed salamanders surpassing 1,000 per acre! Put another way, one study revealed that the biomass of red-backed salamanders was equal to the biomass of all other study area vertebrates (birds, reptiles, mammals, fish, frogs and toads), while another study found their biomass equaled all small mammals in its study area. Such significant figures underline the strategic role of the red-backed salamanders in the energy budget of our Appalachian forests.
There are five families of salamanders that inhabit our Appalachian forests, all of which are carnivorous. Three of these families are represented by only one species; the red-spotted newt (aka red eft), the hellbender, and the mudpuppy. What we normally find under rocks are either the large mole salamanders (usually spotted or marbled, with a few rare localized Jefferson and tiger populations) or, 19 out of 20 times; the ubiquitous lungless salamanders, most likely the red-backed.
Certainly, the lungless salamanders can be found in numbers and species not equaled anywhere else in the world. In fact, the Great Smoky Mountains National Park claims it contains the most varied and abundant salamander fauna in the world (including 24 species of lungless salamanders). Of the world’s total of 586-odd species of salamanders, red-backed salamanders represent one of the more than 395 species of lungless salamanders in the Plethodontidae family. Within the Appalachians, there are nearly 50 species in the Plethodontidae family, of which 18 are endemic (live nowhere else in the world), and within the Plethodon genus, there are 35 species and nine endemics (actual numbers are subject to active scientific discussion). Almost all Plethodontidae species are restricted to southern Canada south to Bolivia and Brazil (one genus of six species exists in Europe and one species was recently found in Korea).
The Plethodon salamanders presumably have originated within the Southern Appalachians. The common ancestors of today’s species go back 2 – 5 million years ago (Pliocene Epoch) when five lineages formed the basis of four species groups that constitute the current population of eastern North American Plethodons. The four species groups include the red-backed salamander group (P. cinereus – 7 species), the Weller’s salamander group (P. welleri – 4 species), the Wehrle’s salamander group (P. wehrlei – 2 species) and the slimy salamander group (P. glutinosus – 22 species). Two of the five ancestral lineages went into the Weller’s salamander group.
While most Plethodontidae salamanders are terrestrial, they occupy a great diversity of adaptive zones ranging from strictly aquatic ones to strictly terrestrial and even arboreal ones. Being amphibians, even the terrestrial species (including the red-backed salamander) must lay its eggs in water. However, these terrestrial species have evolved the ability to lay their eggs within a water-encapsulated case. Thus, the aquatic larval stage develops in this watery enclosure, and undergoes metamorphosis to adult form prior to emergence from the direct-developing egg. Other terrestrial species, such as the common dusky salamander, lay its eggs on land and creates a trench to water, so that the newly hatched larvae can squirm down to the water. Many others simply go into the water to mate and lay eggs.
So, what accounts for this Southern Appalachian salamander hotspot? For one, there are numerous valleys and ridges with high peaks which tend to isolate populations; the basis of speciation. Also, as the regional climate has warmed and cooled during the Pleistocene Epoch (the past 2 million year glacial ice age); the waxing and waning of habitats have isolated suitable habitats, enabling more species diversity. Since the last glacial maximum of 22,000 years ago, northern spruce/fir forest habitats have become isolated on numerous Appalachian mountaintops. Such ‘relic’ habitats create refugium for boreal salamander species, which, over hundreds of years of breeding and mutational adaptations, have become separate species. Our own Shenandoah National Park is home to the Shenandoah salamander, known to exist nowhere in the world but on the rocky northern talus slopes of Stony Man, Hawksbill and Pinnacles Mountains. Two other endemic Appalachian species; the Cheat Mountain and Peaks of Otter salamanders, are similarly limited to high summits, penned in by the encroachment of the ubiquitous red-backed salamander. Other endemics of the Appalachians, such as the Hoffman’s and ravine salamanders have been able to successfully compete with the red-backed and coexist sympatrically in limited forest habitats.
While many plethodons have limited habitats, the red-backed salamander has been able to spread far and wide, including much of the glaciated north, up to Nova Scotia.
Science had widely accepted the hypothesis that early ancestors of today’s lungless salamanders were lunged aquatic salamanders who, due to the buoyancy of the lungs, found it advantageous to evolve smaller lungs to help maintain their position in fast-moving waters, ultimately losing their lungs completely. However, this concept is now subject to competing hypotheses. Nonetheless, lungless they are, and, with a need for all body cells to access moisture and air through the skin, a slimy skin surface, along with a long, narrow tube-like body shape, have evolved. (Even the massive hellbenders of the Ohio River basin that can reach upwards of 27” in length, survive only on account of substantial fleshy folds of skin along its sides that aid in oxygen and water absorption.)
The taxonomy of the Plethodon genus is highly debated due to the lack of morphological differences along with the common adoption of two or more color morphs of the same species (for example, the red-backed salamander has a lead phase that looks quite different). Only through nuclear and mitochondrial DNA studies have many of the species been isolated. Additionally, among similar species with overlapping ranges, many species have been known to hybridize, further complicating the identification of species.