Salamanders are amphibians whose respiratory system is highly dependent on the species and its life stage. The group exhibits a diverse range of gas exchange methods, making a simple “yes” or “no” answer to whether they all possess lungs impossible. Some species rely entirely on pulmonary organs, while others have evolved to completely forgo them, using alternative structures for their entire lives.
Salamanders That Use Lungs
Salamanders that possess lungs, such as the aquatic Sirens (family Sirenidae) and the Amphiumas (family Amphiumidae), rely on them for a significant portion of their oxygen intake. These pulmonary structures are simple, sac-like organs that lack the complex internal division found in the lungs of mammals. Because salamanders do not possess a diaphragm, they must use a positive-pressure mechanism known as buccal pumping to move air.
Buccal pumping involves a two-stroke system. The floor of the mouth and throat cavity (buccal cavity) is depressed to draw fresh air through the nostrils, mixing it with expired air from the lungs. The throat muscles then contract to force the mixed air under pressure into the lungs. Species like the Tiger Salamander (Ambystoma tigrinum) use this method, though they still utilize their moist skin for considerable gas exchange, especially when aquatic oxygen levels are low.
The Lungless Salamanders
The lungless salamanders belong to the family Plethodontidae, representing nearly two-thirds of all known salamander species. These species have undergone an evolutionary loss of lungs; the trait regresses through apoptosis before hatching. The complete absence of lungs necessitates an obligate reliance on cutaneous respiration, meaning all gas exchange occurs through the skin and the moist lining of the mouth and throat.
This reliance on skin breathing requires specific anatomical adaptations to maximize oxygen uptake from the environment. Their skin is highly vascularized, containing a dense network of capillaries just beneath the surface to facilitate the rapid diffusion of oxygen and the expulsion of carbon dioxide. Furthermore, the loss of lungs freed up space and structural components in the head, leading to a specialized feeding mechanism.
The Plethodontids possess a highly modified hyobranchial apparatus that powers a projectile tongue. Their tongue is attached to this elastic skeletal structure, allowing them to rapidly fire it out to capture prey. This ballistic projection, sometimes extending up to half their body length, was enabled by the elimination of respiratory demands on the buccal cavity. This group’s biology is fundamentally tied to maintaining a moist environment, as their skin must remain wet for effective gas diffusion.
Gills and Aquatic Respiration
Salamanders also employ branchial respiration, or breathing through gills, particularly during their aquatic phases. Most salamanders hatch as larvae with external, feathery gills that efficiently extract dissolved oxygen directly from the water. These gills are highly visible tufts on either side of the head, packed with blood vessels.
In most species, these gills are lost during metamorphosis as the animal transitions to a terrestrial or semi-terrestrial adult form that relies on lungs and skin. However, a phenomenon called neoteny, or paedomorphosis, occurs in certain species, allowing them to retain their larval features, including the external gills, into adulthood. The Axolotl (Ambystoma mexicanum) and the Mudpuppy (Necturus maculosus) are classic examples of this, becoming sexually mature while remaining fully aquatic and relying heavily on their gills.
The retention of gills in these species is often linked to a lack of response to the thyroid hormones that normally trigger metamorphosis. The Mudpuppy, for instance, is an obligate neotene, retaining its large, maroon-colored gills throughout its entire life. Even these gilled, aquatic adults may still surface to gulp air, using their rudimentary lungs or buccopharyngeal lining if the water’s oxygen content drops too low.
Environmental Factors Shaping Breathing
The efficiency and necessity of a salamander’s chosen respiratory strategy are profoundly shaped by its environment, particularly the levels of dissolved oxygen (DO) in its aquatic habitat. Cold, fast-flowing streams and mountain creeks tend to have high levels of DO, which is an ideal condition for species relying on cutaneous and branchial respiration. The Plethodontidae family, the lungless salamanders, often thrive in these environments because the high DO concentration allows their skin to be a highly effective gas exchanger.
Conversely, warm, stagnant ponds and slow-moving water bodies often experience lower and fluctuating DO levels, sometimes becoming hypoxic. In these conditions, species that possess lungs gain an advantage, as they can supplement their oxygen intake by surfacing to breathe air. This necessity for air-breathing influences the evolution and distribution of different salamander groups, with the presence of lungs offering a buffer against poor water quality.