Scientists identify likely origins of vertebrate air breathing

30 October 2012 by Liz O'Connell, posted in General

by Marie Thoms

University of Alaska Fairbanks scientists have identified what they think is the ancestral trait that allowed for the evolution of air breathing in vertebrates. They presented their research at the 42nd annual meeting of the Society for Neuroscience Oct. 17 in New Orleans.

“To breathe air with a lung, you need more than a lung, you need neural circuitry that is sensitive to carbon dioxide,” said Michael Harris, a UAF neuroscientist and lead researcher on a project investigating the mechanisms that generate and control breathing.

“It’s the neural circuitry that allows air-breathing organisms to take in oxygen, which cells need to convert food into energy, and expel the waste carbon dioxide resulting from that process,” he said. “I’m interested in where that carbon-dioxide-sensitive neural circuit, called a rhythm generator, came from.”

Harris and colleagues think that air breathing likely evolved in an ancestral vertebrate that did not have a lung, but did have a rhythm generator.

“We try to find living examples of primitive non-air-breathing ancestors, like lamprey, and then look for evidence of a rhythm generator that did something other than air breathing,” Harris said.

Reproduction of an old engraving (anonymous) used as illustration in an article about lamprey (1912) / (F. Barthélemy Les lamproies, Le Cordon Bleu, n° 685, Paris, 15 Décembre 1912)

Lampreys are ancient fish that have characteristics similar to the first vertebrates. They do not have lungs and do not breathe air. As larvae, they live in tubes dug into soft mud and breathe and feed by pumping water through their bodies. When mud or debris clogs a lamprey’s tube, they use a cough-like behavior to expel water and clear the tube. A rhythm generator in their brain controls that behavior.

“We thought the lamprey ‘cough’ closely resembled air breathing in amphibians,” said Harris. “When we removed the brains from lampreys and measured nerve activity that would normally be associated with breathing, we found patterns that resemble breathing and found that the rhythm generator was sensitive to carbon dioxide.”

Air breathing evolved in fish and allowed the movement of vertebrates to land and the evolution of reptiles, birds and mammals. Without a carbon-dioxide-sensitive rhythm generator, the structure that would become the lung might not have worked as a lung.

“The evolution of lung breathing may be a repurposing of carbon dioxide sensitive cough that already existed in lungless vertebrates, like the lamprey,” said Harris.

Harris and collaborators Barbara Taylor, a UAF neuroscientist, and their lab technician Megan Hoffman, also study Sudden Infant Death Syndrome and hope understanding the evolutionary origin of breathing will provide insights into their SIDS research.

 

Find more Arctic science at Frontier Scientists.

ADDITIONAL CONTACTS: Michael Harris, associate professor of integrative physiology and neuroscience, 907-474-7801, mbharris@alaska.edu. Barbara Taylor, associate professor of biology in neuroscience, 907-474-2487, betaylor@alaska.edu. Megan Hoffman, research technician, 907-474-5024, mhoffman2@alaska.edu

ON THE WEB: Society for Neuroscience annual meeting: http://www.sfn.org/am2012/

Institute of Arctic Biology: www.iab.uaf.edu

NOTE TO EDITORS: Michael Harris and Megan Hoffman are attending the Society for Neuroscience meeting in New Orleans. Harris is available via text message at 907-590-7516.

Originally posted at University of Alaska Fairbanks News: Headlines by Marie Thoms on Oct - 15 - 2012 http://uafcornerstone.net/scientists-identify-likely-origins-of-vertebrate-air-breathing/

The video clip below recorded in Harris’ lab shows the difference between gill ventilation and a “cough” in a larval lamprey. The “cough” occurs at about the 9 second mark.


3 Responses to “Scientists identify likely origins of vertebrate air breathing”

  1. Ryan Reply | Permalink

    I thought you were *cough* wryly suggesting something by the way you have the word ‘cough’ surrounded by quotes.

  2. Kmplex Reply | Permalink

    These scientists are taking a specialized behavior from a specialized ancient fish and extrapolating it millions of years and hundreds of apomorphies down the line to lungfish. Sharks are more closely related to lung-breathers than lampreys. There might be some validity to recognizing that breathing air poses certain challenges, like CO2 acidosis, requiring neurobiological adaptations, but there is no reason to look to such a primitive vertebrate for clues about a very derived condition among vertebrates, breathing air with a lung. http://www.nextluxury.com

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