- SAN FRANCISCO - To their amazement, scientists have discovered an octopus that
glows in the dark.
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- Bioluminescence among octopods is rare
enough, but what surprised these investigators even more was the source
of the light the suckers.
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- The unexpected find is helping the researchers
unravel the mystery of how animals evolve the ability to make light, which,
while common in squid and cuttlefish, has previously been documented in
only two octopod species as a glowing ring around the mouths of breeding
females.
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- "What makes the light-producing
abilities of this particular octopus, Stauroteuthis syrtensis, particularly
surprising is that the light comes from the suckers," said Edie Widder,
senior scientist at the Harbor Branch Oceanographic Institution in Fort
Pierce, Fla.
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- "Our first clue that there was something
odd about this octopus came when we brought one into the shipboard laboratory
aboard the R/V EDWIN LINK during a research cruise in the Gulf of Maine."
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- The live specimen was placed in an aquarium.
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- "We noticed its suckers weren't
very sucker-like; they didn't stick to anything," Widder said. "And
did we have a surprise when we turned out the lights! We saw bright blue
light where the suckers should be!"
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- The study of the anatomy and ultrastructure
of the sucker/light organs in another specimen showed although the organs
retain sucker-like traits, many of the muscles usually a prominent feature
of suckers _ are replaced by light-producing cells.
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- "It's a wonderful example of evolutionary
transition," Widder said.
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- While bioluminescence is common in the
oceans, the study of its evolution has been hampered by the lack of a fossil
record, he said.
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- "Light organs such as these that
retain some indication of their previous function therefore offer valuable
insight into evolutionary history," he said, speculating the transformation
may have occurred during the deep-ocean colonization by a creature that
was originally a shallow-water bottom-dweller.
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- Once the suckers were no longer useful
for clinging to the bottom, their only remaining value may have been for
communication, Widder said, noting shallow water species of octopus use
their suckers for visual signaling.
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- To better navigate the dim depths, the
octopus may have first evolved a reflective layer in the back of the suckers,
then further enhanced its visibility with bioluminescence.
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- "These modified suckers may also
aid in attracting the primary prey item found in the stomachs of these
octopods copepods," Widder said. "Like the insects of the sea,
copepods seem an odd food choice for such a large, slow moving animal.
It's like a raccoon trying to live on a diet of mosquitoes."
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- Nevertheless, such eating habits would
make sense if the light organs can act as a lure, attracting the copepods
like moths to a flame, the study authors said.
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- The results were published in the British
journal Nature and in Science News.
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