Hemidactylium scutatum larvae, lungless salamander native to eastern North America Credit: Zachary R Lewis |
Lungs are essential to many vertebrates including humans. However, four living amphibian clades have independently eliminated pulmonary respiration and lack lungs, breathing primarily through their wet skin. Little is known of the developmental basis of lung loss in these clades.
In a new study in Science Advances researchers in the Department of Organismic and Evolutionary Biology and the Museum of Comparative Zoology at Harvard University examined the Plethodontidae, a dominant family of salamanders, all of which are lungless as adults, and find they actually do develop lungs as embryos shedding light on the evolution of lung loss over millions of years.
The lungless salamander family Plethodontidae is the most species-rich family of salamanders accounting for more than two-thirds of existing salamander diversity. All adult plethondontids are lungless, breathing entirely through nonpulmonary tissues, mainly the skin and the mucus membranes in the mouth and throat. Lung loss has occurred independently at least four times among distantly related amphibians and there are other instances of lung reduction or loss in both amphibians and some vertebrates. The developmental reason for this loss, however, remains a mystery.
“Clearly lungless salamanders do fine without lungs given that they make up about two-thirds of all salamander species,” said lead author Zachary R. Lewis, former doctoral candidate (PhD ’16), “perhaps losing lungs enabled, rather than hindered, this remarkable evolutionary success.”