A perplexing mystery: why salamanders will lose their lungs?

Their findings were recently published in the journal Science Advances.


Lungless salamanders are the most species-rich salamander family, accounting for more than two-thirds of all salamander diversity today.All adult lungless salamanders lack lungs and breathe only through non-lung tissues, mainly the skin and mucous membranes of the mouth and throat.Lung loss has occurred independently in distant amphibians at least four times, with more cases of lung reduction or loss in amphibians as well as in some vertebrates.However, the developmental explanation for this loss is unknown.

"Given that lungless salamanders make up about two-thirds of all salamander species, it is clear that lungless salamanders are doing well," said study lead author Zachary, a former doctoral student"Perhaps the loss of the lung enabled, rather than hindered, this remarkable evolutionary success," said R. Lewis.

This research builds on Lewis' doctoral work in the lab of senior author Professor James Hanken.Lewis, Hanken and co-author Associate Professor Ryan Kerney of Gettysburg College used histology and micro-CT to examine the morphology of lung development in salamanders with and without lungs.They found that the lungs of lungless salamanders develop in the same way as other species' lungs during embryonic development.The researchers then used in situ hybridization and RNA-sequencing techniques to demonstrate that the structures produced during lungless salamander embryonic development were not only morphologically similar to lungs, but also in terms of the molecules expressed.


Researchers believe that lung development stalls in these species due to a lack of cues that maintain lung development in the tissue that surrounds the developing lung - the lungInterstitial.

"We put the interstitium from the lunged salamander into the lungless salamander embryo and let it develop," Lewis said, "and it resulted in a lung-like, provides some evidence that lungless salamanders are still capable of continuing to develop lungs."

The study also confirms Amy Grace Mekeel's 1936 doctoral thesis, which challenged biologists' leading theory that a slight fold in the adult pharynx is a residualLungs, which have been present since the initial loss of the lungs in the axolotlidae family.Mekeel describes a "lung precursor" that forms in the embryo but disappears by the time it hatches.

"Lung precursors appear and disappear before hatching in lungless salamander embryos, as described by Mekeel," Kerney said. "This work demonstrates Mekeel's earlydiscourse and dispel the original adult relic hypothesis.”

This study shows that although there has been no functional adult lung for at least 25 million years and possibly more than 60 million years, the developmental-genetic pathway of the lung is at leastPartially conservative.Understanding the evolution of lung loss in pneumocystis can also shed light on organ loss in other vertebrates.

Lewis said: "In the future, if these genetic mechanisms are revealed, we will gain a more complete understanding of how evolution eliminated organs like the lung, which has long been thought to be critical forAchieving life on land is essential."

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