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Jellyfish Rearrange Limbs After Injury

When jellyfish lose limbs, they don't regrow them. Instead, they rearrange their entire bodies to stay symmetrical.

Common moon jellies have an uncommon fix for injuries: When they lose limbs, they don't regrow them. Instead, they rearrange their entire bodies to stay symmetrical despite the loss.

This "symmetrization" is a never-before-seen method of self-repair, and one that probably helps jellies stay alive in the wild. Jellyfish are a favorite snack of sea turtles, and injuries are common. A 2010 study in the journal Integrative and Comparative Biology found that at least a third of marine invertebrates, including jellyfish, are injured at any given time.

Many invertebrates can regrow limbs, but scientists had never observed this sort of rearrangement before, said study researcher Michael Abrams, a graduate student in biology and biological engineering at the California Institute of Technology (Caltech).

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"We've now observed another self-repair mechanism," Abrams told Live Science. "It kind of broadens our definition, a little bit, of self-repair." [See Before and After Images of the Self-Repairing Moon Jellyfish]

Staying symmetrical The discovery of this new self-repair trick was serendipitous. Abrams and his advisor, Caltech biology professor Lea Goentoro, had plans to study the immortal jellyfish (Turritopsis dohrnii), a species that can revert to its immature polyp stage from adulthood, enabling the animal to live indefinitely. The specimens, ordered from Japan, were taking a long time to arrive, Abrams said, and he wanted to practice jellyfish husbandry and experimentation in advance. So he ordered some moon jellyfish (Aurelia aurita) and started testing their ability to self-repair.

Juvenile moon jellies, called ephyrae, look like little snowflakes. They're just a few millimeters in diameter, with eight symmetrically arranged arms. Abrams started doing some amputation experiments on anesthetized ephyrae to see what they could live through.

"Pretty quickly, we realized that they were doing something very different than what anyone had ever talked about before," Abrams said.

Within hours after losing a limb, the juvenile jellies began rotating their remaining arms around their bodies to regain their lost symmetry. A jellyfish with four arms cut off on one side would, within about four days, look like a symmetrical snowflake again - albeit one with half as many arms as before. [Watch the Moon Jellyfish Rearrange Their Limbs (Video)]

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Muscle memory Depending on how many limbs were lost, between 72 percent and 96 percent of jellyfish managed to regain symmetry. And the symmetry was clearly important for survival: Those jellyfish that failed to get in shape would grow oversized mouths and undersized bells, and languish on the tank floor. Jellies that regained symmetry developed with fewer stomachs (they normally have four) and tentacles due to their lost parts, but managed to otherwise mature normally.

The obvious question was how the jellies managed their bodily rearrangement. The researchers first suspected the animals were growing new cells to push their remaining limbs apart so that the arms would be spaced evenly, or perhaps killing off old cells to pull the limbs closer together. But a search for proliferating or dying body cells turned up nothing. And when the researchers prevented cell death and birth, the jellies still managed to become symmetrical.

"We finally got to the point where we just anesthetized the jellyfish in order to get them not to move anymore," Abrams said.

No movement, no symmetry, the researchers found. In fact, it's the muscular movements caused by the jellyfish's regular pulsations that draw the limbs into place around the body.

"It's kind of beautiful that their normal swimming and feeding process leads to this self-repair. It's normal," Abrams said. The process occurs with as few as two remaining limbs and up to seven, he said.

In theory, the findings could inspire self-repairing materials, Abrams said.

"You don't need to rebuild lost parts," he said. "You're just reorganizing what you have."

The researchers reported their findings Monday (June 15) in the journal Proceedings of the National Academy of Sciences.

Original article on Live Science.

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Juvenile moon jellyfish stay symmetrical no matter how many limbs they lose, new research finds.


March 23, 2012 -

Humans may figuratively glow from within, but many species literally emit a natural glow. Here, we celebrate just some of these flashy organisms, such as these fireflies. Photographer Tsuneaki Hiramatsu used slow–shutter speed photos to produce images like this one of firefly signals. "These images show a selection of many extraordinary organisms that produce light, in conjunction with the American Museum of Natural History's upcoming Creatures of Light: Nature’s Bioluminescence exhibition," curator John Sparks of the museum’s Department of Ichthyology, told Discovery News. Bioluminescence refers to organisms that "generate light through a chemical reaction."

Bitter Oyster Mushrooms It’s a little known fact that some common mushrooms glow in the dark. These bitter oyster mushrooms (Panellus stipticus) are bioluminescent. They grow on decaying wood in the forests of eastern North America.

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Dinoflagellates The flickering glow in this photo comes from thousands of live single-celled organisms called dinoflagellates. The species seen here, Pyrocystis fusiformis, is a spindle-shaped cell about one millimeter long -- just large enough to be seen without a microscope, according to Sparks. Tiny particles in each cell, called scintillons, contain chemicals that mix and make light when the water is shaken or stirred.

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Bloody Bay Wall This interactive mural captures a slice of life on Bloody Bay Wall, off Little Cayman Island in the Caribbean Sea. In daylight, creatures on this coral wall can be seen in fine detail. To most observers, this scene might look quite normal, but it takes on an eerie glow at night. Sparks said, "Rare among organisms that live on land, the ability to glow is much more common in the ocean, where up to 90 percent of animals at depths below 700 meters are bioluminescent, including many unknown to science."

Green Fluorescent Protein The brilliant patches of green here come from a compound known as "green fluorescent protein" emitted from certain corals, fishes and sea anemones. The vivid colors only appear when the animals are illuminated by specific wavelengths of light.

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If a different wavelength of light illuminates the same scene, glowing red hues emerge. Orange is yet another color that some glowing organisms can emit. "Like the crystal jelly, whose glow led to a revolution in cellular biology, these animals may hold important clues to essential questions regarding signaling mechanisms, sexual selection, and diversification in the deep sea," Sparks said.

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Scorpions Some scorpions, such as the one seen here, are fluorescent. Certain spiders, insects and minerals glow too. Sparks explained that the luminescent minerals contain fluorescent molecules that glow under ultraviolet light. Andrew Parker, research leader of the Department of Zoology at London’s Natural History Museum, explained that as soon as certain organisms evolved the ability to see, color, light, fluorescence and more all gained greater importance.

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“Since vision evolved, everything has been fully adapted to the presence of a retina, adapted in terms of their color, shape and behavior,” Parker, author of the related book In the Blink of an Eye, told Discovery News. “Prior to the first highly mobile predator with vision, i.e. one that could have an affect on all other cohabitants, the rules would have been much different, and indeed we know from fossils that animal forms and ecology were much different.”

Black Dragonfish The female black dragonfish has a luminous lip that may be used to attract prey. The poor victims would then be chomped to death by the fish’s big, sharp teeth. Both males and females also have tiny light-emitting photophores scattered over their bodies, with larger photophores along the side. Rui Coelho, a shark researcher at the University of Algarve, Portugal, has studied bioluminescent marine animals. He told Discovery News that "photophores may be used to allow individuals to escape from predators or for species recognition, such as during the mating season."

Lanternfish The appropriately named lanternfish conspicuously uses bioluminescence in its ocean habitat. Although virtually all fish are at risk now, due to bycatch threats, pollution and other problems, laternfish account for approximately 65 percent of all deep sea fish, based on ocean trawling counts.

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Danaphos Danaphos is the name of an oceanic ray-finned fish genus. Its more common name is "bottlelights." It, and so many other species, both on land and in the sea, are under threat now. Sparks shared that "scientists are in a race against time as habitats are increasingly threatened by pollution, overfishing, and global climate change." You can, however, non-invasively admire Danaphos and the other glowing species at the new AMNH exhibit, which opens March 31 in New York and runs until Jan. 6, 2013.

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