Yes, indeed it is true that some, in fact most, amphibians can respire, or breathe, through their skin!
Amphibians include the frogs and toads (Anura, 4800 living species worldwide), salamanders (Caudata, 520 species), and tropical caecilians (Gymnophiona, about 170 species). Caecilians are legless and live underground or in the water. Most amphibians have delicate skin that must maintain a certain level of moisture or the amphibian will become dehydrated and die. Exceptions to this include toads, which have a tougher skin and usually are found further away from water sources or moisture leaf litter. It is the nature of this delicate skin that allows amphibians to absorb oxygen straight from the environment into their cells.
Most animals need oxygen to survive. They breathe (or absorb) oxygen into the blood stream in the gills, lungs, or at the skin surface. The cells of the body use the oxygen during cellular respiration, or the time when cells make energy for the body to function. A by-product is carbon dioxide, which is released from the animal and, in turn, used by plants to produce energy and release oxygen.
Because amphibians are a large and diverse group (over 5500 species in total), there are many forms of respiration. Different methods include using the skin, as discussed above, the use of lungs, and the use of gills.
When many frogs and toads and salamanders hatch from their egg, they are in a larval form called a tadpole (or pollywog in some areas). Tadpoles have gills because they live submersed in water where they feed on algae. Oxygenated water flows over the gills and the tadpole can extract the oxygen from the water. When the tadpole metamorphoses into an adult they develop lungs (in most cases) and then breathe oxygen using this option (in addition to respiring through their skin). There also is a relatively rare salamander, called an axolotl, which does not metamorphose into an adult that leaves the water. It maintains its gills throughout its entire life. These animals can be found in scientific laboratories and pet stores but exist in the wild in only a couple of places in Mexico.
Interestingly, there are some salamanders, which belong to the family Plethodontidae (270 living species), which do not have lungs or gills! These small salamanders are very abundant and speciose in the Appalachian Mountains in the eastern United States (although members of the family around found in other areas, including in the tropics of Latin America and the Pacific Northwest). They live in moist areas, commonly found under rocks or logs. They will come out on moist evenings and sit on tuffs of moss or above the leaf litter. These salamanders breathe completely through their skin! They absorb oxygen directly to the cells. Although many frogs absorb oxygen through the skin, they also have lungs. This group of salamanders is very interesting biologically!
The ability to breathe through the skin seems like a really neat ability. The amount of use that the adaptation receives depends on the species of amphibian and the conditions of the environment at any given time. Some species breathe regularly though their skin while others may seldom need to use the adaptation (for example, frogs that spend a lot of their time in the water).
One negative aspect of the ability to breathe through the skin has recently come to light, especially in the cool montane regions of the tropics. A disease called Chytridiomycosis has been spreading among species of amphibians. It has been reported in Austrailia, Central and South America, and now even is in the United States! A fungus coats the skin of the amphibian, particularly frogs and salamanders (little is known about the biology of caecilians so it is unclear to what extent they are being affected). The fungus reduces the ability of the frog to respire through its skin. As the frog becomes stressed it elevates its body up (much liking holding up your body during push-ups) to allow more airflow to the delicate ventral (stomach) surface. Eventually the frog cannot get enough oxygen and dies. Chytridiomycosis is being studied, but much remains to be understood as to why it affects amphibians and how the amphibian, especially if it has lungs, cannot get enough oxygen to survive. As you may imagine, the frogs and salamanders depending most on respiring through their skin are greatly affected by this disease! Once Chytridiomycosis hits a site upwards of 60% of the individuals and the species are killed within just a couple of months. Currently research does not show promise of many species recovering from these great population crashes.
Amphibians, with their great species diversity, utilize all sorts of methods for respiration. Some include gills, lungs, and absorption right through the skin. Many species employ more than one method, either throughout their life (gills as larvae and lungs as adults) or at the same time (lungs and respiration through the skin). Amphibians are indeed a very interesting group!
Photos taken by Julie M. Ray and Andrew Hein
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