13 September 2008

How to eat slippery octopus if you don't have hands

If you didn't have arms and had to swallow something with eight of them it could get messy. Especially if it was still alive and didn't want to get eaten. Fortunately, if you were a moray eel, you would have a trick up your sleeve, or rather your throat.Like the monster in the movie "Alien", the moray eel uses its second set of jaws to help it swallow wriggly, slippery and very unwilling prey.

Lots of fish have a second set of jaws, but these tend to be hard grinding plates or jaws with little teeth that don't move much. The moray eel's second set of jaws is armed with large, curved teeth and powered by elongated muscles that allow for extreme mobility. These reach forward to seize and drag prey (no doubt kicking and screaming) into the eel's throat.

'Alien' Jaws Help Moray Eels Feed
ScienceDaily 6 Sep 08;
Moray eels have a unique way of feeding reminiscent of a science fiction thriller, researchers at UC Davis have discovered. After seizing prey in its jaws, a second set of jaws located in the moray's throat reaches forward into the mouth, grabs the food and carries it back to the esophagus for swallowing.

"This is really an amazing innovation for feeding behavior for fishes in general," said Rita Mehta, a postdoctoral researcher in the Section of Evolution and Ecology at UC Davis.

The research shows the amazing diversity possible among living things, even in something as fundamental as feeding, Mehta said.

The researcher used a high-speed digital camera to film eels feeding in the laboratory, and was able to capture the rapid movement of these secondary pharyngeal jaws. She also used X-ray and other imaging equipment at the UC Davis School of Veterinary Medicine to work out how the jaws could move.

More than 200 species of moray eels are found in tropical waters worldwide, often living in holes in rocks and coral reefs. In the wild, they can reach 10 feet in length.

Most fish feed by suction. When it comes upon food or prey, the fish rapidly expands its mouth cavity, sucking in water and the food with it. Some fish feed by overtaking prey with their mouth open or grabbing it in their jaws, but most of those fish then use suction to move the food from the mouth to the esophagus.

But moray eels have little ability to generate suction through their mouths, Mehta found. Instead, they first grasp food with their powerful, toothsome outer jaws. Then the pharyngeal jaws, armed with large, curved teeth, reach forward and seize it. At the same time, the outer jaws release the prey and the pharyngeal jaws bring it back for swallowing. The whole process takes just fractions of a second.

Other fish are known to have pharyngeal jaws that can grind or crush food, but "nothing this spectacular," said Peter Wainwright, professor of evolution and ecology at UC Davis and co-author with Mehta on the paper. Only the moray eel seems to have a second, mobile set of jaws that can reach forward and grab prey.

At rest, the pharyngeal jaws sit behind the eel's skull. When they reach forward, they move almost the length of the animal's skull, but do not protrude beyond the powerful outer jaws. The arrangement means that if the eel can sink in a few teeth to hold its prey, it can secure its meal with the pharyngeal jaws, the researchers note.

Mehta compared the eels to snakes, which also have to fit large food items through a relatively narrow mouth into a long, thin body. Snakes solve the problem by "ratcheting:" they can separate the left and right sides of their jaw, and hold onto the food with one side while they work the other side of the mouth round it.

Mehta and Wainwright are now investigating how the morays' extraordinary jaws evolved. Other species of eel, such as the American eel Anguilla, feed by suction. Moray eels may have evolved other methods as a result of hunting in confined spaces, where they could not rapidly expand their heads to create suction.

"Eels are an amazingly diverse and bizarre group of fishes, and not very well known," Wainwright said.

The research is published in the Sept. 6 issue of the journal Nature and was supported by grants from the American Association of University Women and the National Science Foundation.
Moray Eels Grab Prey With "Alien" Jaws
Sara B. McPherson, National Geographic News 5 Sep 07;
Much like the fearsome star of the Alien movies, moray eels have a second set of toothed jaws that drag prey into their throats, a new study has found.

In a series of experiments, scientists at the University of California, Davis, recently discovered that moray eels possess an extremely mobile set of jaws in their throat that they can project forward into their mouth to aid in feeding.

However, unlike the fictitious alien's second mandible, which it menacingly extended toward its prey, the eel's jaws are much more practical, said lead author and evolutionary biologist Rita Mehta. (Get fish pictures, sounds, news, and more.)

"The [jaws] are functionally specialized to grasp large prey and assist in swallowing," Mehta said.

Suction Feeding

Most fish catch their prey using a suction method. When food is within reach, a fish will rapidly open its mouth.

This motion expands the mouth cavity, creating negative pressure and drawing water—and the prey—down their throats.

But, suction feeding has several restrictions. For one, the method limits the size of prey that a fish can draw into its mouth. The technique also requires room around the fish's head to accommodate the space generated when it expands its mouth cavity.

These limitations can pose problems for species such as the predatory moray eel, which resides in the tight spaces and crevices of the oceans' coral reefs.

So instead of suction, the eels rely on strong jaws filled with sharp teeth to bite their prey.

Biting allows morays to feed on larger animals without having to expand their mouth cavity when stuck in the confining quarters of the reefs.

Though scientists understood how moray eels caught their food, exactly how they swallowed it remained a mystery until this recent study.

The findings will be published tomorrow in the journal Nature.

Fancy Forceps

Using high-speed video, Mehta and study co-author Peter Wainwright observed moray eels eating squid and noticed that the eels used a very unique set of secondary, or pharyngeal, jaws to devour their prey.

While most fish use these secondary jaws to manipulate prey and help in swallowing, Mehta and Wainwright noticed an important distinction in the moray's jaws.

"The pharyngeal jaws in their throat exhibit a very different architecture from the jaws of other bony fishes," Mehta said. "[They] look like a fancy pair of forceps with large, sharp recurved teeth."

And unlike most pharyngeal jaws, which have a limited range of motion, the moray's inner mandibles have elongated muscles that allow for extreme mobility.

This unique feature allows the eels to protrude their secondary jaws forward from their throats and into their mouths, where they grasp prey and guide it toward the esophagus.

This dual-jaw system allows morays to maintain a grip on their food at all times, Mehta said.

Mark Westneat is the curator of zoology at the Field Museum of Natural History in Chicago.

"That's what's fascinating about this discovery," he said. "Lots of fish have pharyngeal jaws, but they tend to be hard grinding plates or jaws with little teeth that don't move much".

"What's unusual about the morays' jaws is their ability to drag prey from the mouth back into the throat."


This is somewhat old news, I know and I do apologise. I'll be uploading bits of these here and there, primarily to support the upcoming fact sheets of our marine life. So links to scientific findings don't drop out and die when the hosting website changes urls etc. Sigh, the travails of an ever changing net.

2 comments:

  1. It may be old news, but it certainly never fails to fascinate me, especially considering that moray eels as a whole are widespread and well-known to many.

    Besides, it's another reason why moray eels really should be treated with respect.

    P.S. Is there any way to remove the annoying and unsightly spam comments and the links from spam blogs?

    ReplyDelete
  2. Yes Ivan, I found the X-ray diagrams fascinating. And indeed, we shouldn't mess with morays.

    And sigh, I've deleted the spam comments. Sorry took so long to do it.

    ReplyDelete

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