Amphibians
Lungless Salamander
Plethodontidae · also called plethodontid
The most successful salamanders on Earth got that way by giving something up. The lungless salamanders have no lungs at all — they breathe entirely through their skin and the lining of their mouths — and that single trade, made by a stream-dwelling ancestor, produced a family of around 500 species, two thirds of all salamanders.
Overview
Lungless salamanders are the family Plethodontidae, around 500 species, concentrated in the Americas with a few in southern Europe and one genus in South Korea. All are carnivores of cool, damp microhabitats — forest floor, leaf litter, rotting logs, seeps, streamsides, and caves. Many fire a projectile tongue to catch prey in a few thousandths of a second, one of the fastest feeding strikes of any vertebrate.
Breathing through the skin
Adults have no lungs. Oxygen dissolves in the moisture on the skin and the mouth lining and diffuses into blood vessels just beneath — which only works because the animals are small, cool, and permanently damp. It is thought the family’s ancestor lost its lungs to solve a buoyancy problem in fast mountain streams, and the trait was never reversed.
Free of the water
Many lungless salamanders lay a few large eggs on land, often guarded by the female, that hatch straight into miniature salamanders with no aquatic larval stage — so they need no pond or stream at all.
An Appalachian explosion
The southern Appalachian Mountains hold the greatest concentration of salamander species anywhere on Earth, almost all lungless, many restricted to a single mountain or valley. Woodland species are often 5 to 12 cm long, may live their whole lives in a few square metres, and can reach 10 to 25 years.
Status
Lungless salamanders as a family are Not Evaluated, trend decreasing. Many North American species are common, but a large share of the tropical American species are Endangered or Critically Endangered from deforestation and a warming climate, and the salamander skin fungus Bsal, devastating in Europe, would be catastrophic if it reached the Americas.
Lungless Salamander: common questions
How does a salamander breathe with no lungs?
Through its skin and the lining of its mouth and throat, a process called cutaneous respiration. Oxygen from the air or water dissolves in the film of moisture on the skin and diffuses across into a dense network of tiny blood vessels just beneath the surface, while carbon dioxide passes out the same way. This works because lungless salamanders are small, with a high ratio of surface area to body volume, and because they keep their skin permanently moist and their metabolism low. The limitation is severe. The skin must stay wet and the animal must stay cool, since warmth raises its oxygen demand faster than skin breathing can supply, which is why these salamanders retreat underground in dry or hot weather.
Why did they lose their lungs in the first place?
The leading explanation is that the ancestor of the family lived in cold, fast, highly oxygenated mountain streams, where lungs were more of a liability than an asset. Air-filled lungs make a small animal buoyant, which is a problem for something trying to stay wedged among stones in a current, and in cold oxygen-rich water skin breathing alone is enough. Losing the lungs removed the buoyancy problem. Once gone, lungs were never regained, and the lungless body plan turned out to be highly successful on land as well, as long as the animal stayed in damp, cool places, which is why the family went on to become the largest and most diverse group of salamanders.
Where do lungless salamanders live, and why are the Appalachians special?
They live in cool, moist places across the Americas and a few other regions, but the southern Appalachian Mountains of the eastern United States are the world capital of salamander diversity, with dozens of species, almost all of them plethodontids, packed into a relatively small area. The reasons are a long, stable history of moist forest, a complex topography of ridges and valleys that isolates populations on individual mountains, and a lifestyle that keeps salamanders from dispersing far, all of which let many closely related species evolve and persist side by side. Some are found on a single mountaintop and nowhere else.
Are lungless salamanders endangered?
As a whole family, no, since many North American woodland species are still abundant, and a single hectare of good Appalachian forest can hold thousands of individuals. But a large number of individual species are in trouble, especially the tropical climbing and cave species of Mexico and Central America, many of which are Endangered or Critically Endangered from deforestation and a warming, drying climate that shrinks the cool damp zones they need. There is also serious concern about a salamander-specific skin fungus, Batrachochytrium salamandrivorans, which has devastated salamanders in Europe and, if it reaches the Americas, could be catastrophic for this family.