Most tadpoles have to breathe air to survive but hatchlings are too feeble to break the āskinā on a pondās surface caused by water tension ā so they suck air bubbles instead.
While tadpoles have gills, most also develop lungs and frequently surface to breathe air, which is essential for survival in water containing low levels of oxygen.
Kurt Schwenk at the University of Connecticut saw the unusual behaviour by chance while studying salamanders feeding on tadpoles in the lab. āWhat I saw blew my mind. I assumed this had been described before but it hadnāt,ā he says.
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Using high-speed video, Schwenk and Jackson Phillips, a PhD student also at the University of Connecticut, recorded tadpole hatchlings from five frog species swimming to the waterās surface. Due to surface tension they couldnāt break through the surface to gulp air. Instead, they stuck their open mouths to the underside of the waterās surface.
By dropping the floor of the mouth, tadpoles suck at the water surface and create an air pocket that they can pinch off by quickly closing their jaws. This forms a bubble inside the mouth that contains fresh air and a bit of exhaled air. Raising the floor of the mouth squeezes the bubble, forcing air into the lungs. With the lungs full, leftover air is burped out.
A showed that even when tadpoles were older and big enough to breach, those from two species of frog preferred two quick sucks in a row. āThe double bubble-suck could prevent exhaled air being mixed with the fresh air to improve gas exchange efficiency,ā says Schwenk.
Proceedings of the Royal Society B
