PORTLAND, OREGON—Almost all land animals need lungs to survive. The world’s largest group of salamanders is a rare exception. Now, researchers know how these amphibians came to breathe through their skin instead. A copy of a key lung gene shifted where it is active, rendering skin capable of efficient gas exchange, they reported here this week at the annual meeting of the Society for Integrative and Comparative Biology. The loss of lungs represents major evolutionary change, one expected to limit the size, lifestyle, and whereabouts of any species. But the 448 species of a family of salamanders called plethodontids must not have gotten that message, as they roam across the Western Hemisphere, South Korea, and Italy; range from 25 millimeters to 27 centimeters long; and call burrows to tree tops home. So evolutionary developmental biologists tracked embryonic development of one of these species, the dusky salamander (Desmognathus fuscus), and discovered that although lungs do start to form, they never fully develop. Instead, this species produces extra blood vessels to the skin. Studies of gene activity in this and other vertebrates also revealed that there is a key gene in the vertebrate lung that exists in two copies in salamanders. That gene is active just in the lungs of lunged salamanders, but in lungless species is active in the skin, mouth, and throat as well. It codes for a protein that helps membranes be more receptive to gas exchange, and its presence in the skin and mouth helps explain why some salamanders don’t need lungs at all. Called a surfactant protein, this newly discovered protein may prove useful for treating breathing problems in people, the researchers note.
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