CT scans help answer question of how fish lungs evolved

February 7, 2013 by Linda B. Glaser
CT scans help answer question of how fish lungs evolved
The vascular system of a sturgeon, with the arteries injected with X-ray opaque barium. The gills, which are serviced by many small blood vessels, are visible.

(Phys.org)—One of the great problems of evolution is to understand how the major features of organisms have changed over great swaths of time. How did limbs evolve from fins? How did bird feathers arise from scales?

The is a major organ of great functional importance for vertebrates (animals with backbones). Since the mid-19th century, most biologists have thought that in living fishes, gas bladders—internal bags of air to which fishes can add or eliminate oxygen to control buoyancy—are simply a modified version of an ancestral pair of lungs. Others think lungs and gas bladders are completely different organs.

New research at Cornell using computed tomography (CT) technology has gone a long way toward showing that lungs and gas bladders really are variations of the same organ.

Watch the QuickTime video of the scan of a Florida gar: down through the spine, out to the inside surface of the interlocking sheath of heavy scales that encases a gar, and then into the central chamber of the gar's swim bladder, traveling all the way to the front of the swim bladder, just behind the head.

By proving that several ray-finned fishes, namely sturgeons and paddlefishes, as well as bowfin, have pulmonary arteries like those that supply the lungs of vertebrates, the researchers show that the of all these fishes must have originally had lungs supplied by a pulmonary artery.

The micro-CT enabled researchers to look at resolutions of 25 microns, about the width of a human hair. "This is biology as we've never been able to see it before," said Amy McCune, co-author of the study and professor and chair of ecology and . "We're studying from the inside out."

The paper's lead author, Sarah Longo '11, a graduate student at the University of California-Davis, began the research for her honors thesis with McCune. Mark Riccio, director of the Cornell Multiscale CT Facility in the Institute of Biotechnology, is also a co-author; the paper was published Feb. 5 in the online version of the Journal of Morphology.

"Using our state-of-the-art, high-resolution X-ray CT scanners, we noninvasively created 3-dimensional datasets that could be examined from multiple perspectives," explained Riccio. By studying the CT scans of blood vessels filled with X-ray opaque barium in lungfishes, bowfin and several other related fishes, the Cornell researchers showed that other fishes in the lineage that includes bowfin actually have tiny vestigial pulmonary arteries, which branch off from a parent vessel in the same way that pulmonary arteries branch in tetrapods and lungfishes. The arteries in gas bladder , therefore, are actually vestigial pulmonary arteries that have been co-opted for new functions. The researchers hypothesize that this evolutionary change occurred either by the loss of respiration or by dorsal shifts in the anatomical structures of these fishes.

Longo points out that scientists have known about the vestigial arteries for a long time, but because traditional dissection and corrosive casting techniques lose detail, no one made the connection with . "One of the great things about this research was that by using a new technique and having an undergraduate look at it with fresh eyes we found something new," says Longo.

Explore further: New scanner takes images inside and out

Related Stories

New scanner takes images inside and out

May 24, 2011

From fossilized brachiopods, fish lungs and iPhones to mouse hearts and habanero chilies, Cornell's micro-CT (computer tomography) scanner provides spectacular and colorful 3-D datasets from the inside out.

Vertebrate jaw design locked 400 million years ago

July 6, 2011

More than 99 per cent of modern vertebrates (animals with a backbone, including humans) have jaws, yet 420 million years ago, jawless, toothless armour-plated fishes dominated the seas, lakes, and rivers. There were no vertebrates ...

Recommended for you

World's smallest tape recorder is built from microbes

November 23, 2017

Through a few clever molecular hacks, researchers at Columbia University Medical Center have converted a natural bacterial immune system into a microscopic data recorder, laying the groundwork for a new class of technologies ...

A possible explanation for how germlines are rejuvenated

November 23, 2017

(Phys.org)—A pair of researchers affiliated with the University of California and Calico Life Sciences, has discovered a possible explanation regarding how human germlines are rejuvenated. In their paper published in the ...


Adjust slider to filter visible comments by rank

Display comments: newest first

Feb 07, 2013
This comment has been removed by a moderator.
4.3 / 5 (6) Feb 07, 2013
These good questions that throw doubt on evolution will never be answered. This is because evolution per se is not scientific, but philosophical. There have been no scientific experiments up until now that have replicated any true evolutional process. And yet so-called evolutionary scientists (a true misnomer) continue to peddle these empty theories.

That is so wrong-headed a statement that it defies comprehension.

What they have discovered --in direct contradiction of your assertion-- is very solid evidence in SUPPORT of Evolution.

5 / 5 (5) Feb 07, 2013
"There have been no scientific experiments up until now that have replicated any true evolutional process."

One very well known experiment immediately comes to mind: http://en.wikiped...periment

verkle, get your head out of your 2000-year old "science" book. It's been updated.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.