Salamanders are amphibians with diverse respiratory adaptations. Their ability to breathe underwater is complex, varying with life stage, species, and environment. Understanding these strategies provides insight into how they thrive in aquatic and terrestrial conditions.
Aquatic Breathing: Gills and Skin
Salamanders employ specialized mechanisms to extract oxygen from water. Many species, particularly during their larval stage, possess external gills. These feathery structures protrude from their head and are rich in blood vessels. As water flows over these filaments, oxygen diffuses into the bloodstream, while carbon dioxide moves out. This high surface area allows for efficient gas exchange in aquatic environments.
Salamanders also rely on cutaneous respiration, or breathing through their skin, while underwater. Their skin is thin, permeable, and richly supplied with capillaries. Oxygen dissolved in the water passes through this moist skin layer into the blood, and carbon dioxide exits. This method is effective for smaller salamanders or in well-oxygenated water, providing a supplementary or primary means of aquatic respiration. Some aquatic species, like the giant salamander, have evolved skin folds to increase this surface area, enhancing oxygen absorption.
Amphibious Respiration: Lungs, Skin, and Life Stages
Salamanders adapt their breathing methods as they transition between aquatic and terrestrial environments. Many species undergo metamorphosis, where aquatic larvae with gills transform into adults that develop lungs. These adult lungs allow for air breathing when the salamander is on land or at the water’s surface.
Skin respiration remains a component of their gas exchange, regardless of habitat. Adult salamanders with lungs absorb oxygen through their moist skin, whether in water or on land. A salamander might use gills as a larva, transition to lungs and skin for air breathing as an adult, and still rely on skin respiration when submerged. The balance between these methods is dictated by their life cycle, with gilled larvae being obligate aquatic breathers and adults relying on a combination of lungs and skin.
Environmental and Species Variations
Environmental conditions influence how salamanders breathe. Colder, well-oxygenated water supports more efficient gill and skin respiration, while warmer, oxygen-poor water may prompt salamanders to surface for air if they possess lungs. Pollution can also reduce water quality and oxygen availability, impacting their ability to breathe effectively underwater.
Salamander diversity includes varied respiratory adaptations. The family Plethodontidae, comprising over two-thirds of all salamander species, are entirely lungless. These salamanders rely solely on cutaneous respiration through their skin and mucous membranes in their mouth and throat for gas exchange, necessitating a constantly moist environment. Other species exhibit neoteny, retaining external gills into adulthood. Examples include the axolotl and mudpuppy, which remain fully aquatic and breathe primarily through their persistent gills.