FT. PIERCE, FL - The discovery of bioluminescence in a deep-sea octopus has been making big news in the scientific world. Appearing on the cover of the March 11 issue of Nature and the March 13 issue of Science News, this octopus is providing new insight into how animals evolve the ability to make light. Finding bioluminescence in any octopus was a big surprise for the co-discoverers, HBOI Senior Scientist Edie Widder and Harbor Branch Postdoctoral Fellow Sönke Johnsen.
Although bioluminescence is common in squid and cuttlefish, it is extremely rare among octopods. Previously the only documented examples were in two species where bioluminescence appears as a glowing ring around the mouths of breeding females - glow-in-the-dark lipstick perhaps?
What makes the light producing abilities of this particular octopus, Stauroteuthis syrtensis, particularly surprising is where the light comes from, the suckers! In fact Widder and Johnsen's first clue that there was something odd about this octopus came when they brought one into the shipboard laboratory aboard the R/V EDWIN LINK during a research cruise in the Gulf of Maine. A live specimen, captured thanks to the skill of Harbor Branch JOHNSON-SEA-LINK submersible pilot Scott Olson, was placed in an aquarium where the researchers noticed that its suckers weren't very sucker-like. They didn't stick to anything! But even more surprising, when they turned out the lights, they discovered bright blue light where the suckers should be.
Another specimen, captured thanks to Harbor Branch JOHNSON-SEA-LINK pilot Phil Santos, was used for an investigation of the anatomy and ultrastructure of the sucker/light organs. This work, carried out by former Smithsonian postdoctoral fellow Elizabeth J. Balser (now at Illinois Wesleyan University) with the assistance of HBOI summer intern Erin Fisher (now a graduate student at Scripps Institution of Oceanography), revealed that although these organs still had sucker-like traits, many of the muscles, which are a prominent feature of suckers, were replaced by light-producing cells.
"It's a wonderful example of evolutionary transition," says Widder. Although bioluminescence is extremely common in the oceans, the study of its evolution has been greatly hampered by the lack of a fossil record. Light organs such as these that retain some indication of their previous function therefore offer valuable insight into evolutionary history. Widder believes that the change from sucker to light organ may have occurred during colonization of the deep open-ocean by a creature that was originally a shallow-water bottom-dweller. Once the suckers were no longer useful for clinging to the bottom, their only remaining value may have been for communication. Shallow water species of octopus display their suckers for visual signaling.
To enhance the effect in the dim depths Widder believes that the octopus may have first evolved a reflective layer in the back of the suckers and then further enhanced their visibility with bioluminescence. These modified suckers may also aid in attracting the primary prey item found in the stomachs of these octopods - copepods. Like the insects of the sea, copepods seem an odd food choice for such a large, slow moving animal. Widder makes the analogy of it being like a raccoon trying to live on a diet of mosquitoes. However, if the light organs can act as a lure, attracting the copepods like moths to a flame, then perhaps this strange diet makes sense.
Harbor Branch Oceanographic Institution, Inc. (HBOI) is one of our nation's premier not-for-profit oceanographic educational and environmental research facilities dedicated to exploring the world's oceans and to the understanding and ecologically sound management of the earth's marine resources.
Journal
Nature