Research Spotlight: UConn biologists study tadpoles and ‘bubble-sucking’

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UConn researchers Kurt Schwenk and Jackson Phillips have been looking into ‘bubble-sucking’ tadpoles. They are now researching why and how tadpoles use this action as means of survival.  Photo courtesy of Kurt Schwenk

UConn researchers Kurt Schwenk and Jackson Phillips have been looking into ‘bubble-sucking’ tadpoles. They are now researching why and how tadpoles use this action as means of survival. Photo courtesy of Kurt Schwenk

Researchers at the University of Connecticut recently discovered a previously unstudied phenomenon in tadpoles. Ecology and evolutionary biology professor Kurt Schwenk and graduate researcher Jackson Phillips have been using high-speed video to look into “bubble-sucking,” a mechanism tadpoles use to breathe.  

Schwenk, who usually studies reptiles as opposed to amphibious tadpoles, said the discovery was totally unexpected as the researchers weren’t even originally studying tadpoles.  

“We were keeping tadpoles in the lab as part of a completely different study to look at feeding in these aquatic larval salamanders, and they happened to eat tadpoles,” Schwenk said. 

He explained that he’d been using slow-motion video to study animal behaviors when he and Phillips, then an undergraduate researcher, stumbled on the mechanism. 

“When you have the chance to watch animals closely, you see things that you never expected to see,” Schwenk said. “I observed this unusual behavior where they swam to the surface and did something funny, which I couldn’t tell what it did, and it left this little bubble behind.” 

Schwenk said he researched the mechanism through using slow-motion video of the tadpoles.  

“We were doing high-speed video — high speed means slow motion — so we just got the camera out and filmed it, and sure enough they did something very unexpected. That turns out to be this weird breathing behavior,” Schwenk said. 

Schwenk explained the bubble-sucking is part of how tadpoles breathe.  

“In a nutshell, over the course of looking at five different species of tadpoles, it became apparent that that one or two suctions were clearly respiratory,” Schwenk said. “It forces the air through the glottis, which is the opening of the trachea and it pushes the air into their lungs. We can actually see the lungs inflate.” 


Schwenk found that this was a function of surface tension, which is the same phenomenon that allows insects like water-striders to walk on water.  Photo courtesy of Kurt Schwenk

Schwenk found that this was a function of surface tension, which is the same phenomenon that allows insects like water-striders to walk on water. Photo courtesy of Kurt Schwenk

The question that remained was: Why? What Schwenk and his researchers eventually discovered is that unlike grown frogs, tadpoles can’t break the surface of the water to breathe. 

“What became interesting, apart from the fact that a couple species did it twice as opposed to once, was that we also observed tadpoles swimming up to the surface apparently to breathe, but then literally bouncing off,” Schwenk said. 

He explained this was a function of surface tension, which is the same scientific phenomenon that allows insects like water-striders to walk across the surface of the water. Because the tadpoles couldn’t access the air, they had to suck in air from the surface of the water, replacing it with the air in their lungs. In doing so, the tadpoles left bubbles behind on the surface.  

Schwenk explained that part of the reason the discovery was so interesting was that most people would assume these tadpoles, which have already been extensively studied, wouldn’t have anything else to offer to researchers. 

“Four out of the five species we looked at are just dirt common species that you can find around campus,” Schwenk said. “You would have thought that if there was anything we already knew everything about, it would be these frogs and their tadpoles. Just by virtue of spending some time staring at the animals, we discovered something completely new, completely undescribed, really interesting, unexpected.”  

Because of this, Schwenk’s advice to students interested in research is to keep an open mind to even the most mundane parts of the world around you.  

“If you want to discover new things, you need to spend time ideally outdoors or even indoors, in zoos, with pets, just watch,” Schwenk said. “Watch, and think and ask good questions. Then you’re doing research.”  

Thumbnail photo courtesy of Grace McFadden/The Daily Campus.


Grace McFadden is a campus correspondent for The Daily Campus. She can be reached via email at grace.mcfadden@uconn.edu

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