By: Stephanie Pappas, LiveScience Senior Writer
Published: 08/14/2012 07:11 PM EDT on LiveScience
For squid looking to sparkle, extra bling is only seconds away, thanks to a nerve network in the skin that allows these cephalopods to alter their iridescence — the first invertebrate creatures found to have this ability.
A new study finds that electrical stimulation of the nerves in squid skin changes the color and reflectance of tiny platelike structures called iridophores in the skin, allowing changes in hue from red all the way through the color spectrum to blue.
Oddly enough, despite their bright displays, these squid see only in black-and-white, deepening the mystery of why and how they pick a color from their array.
"The cool thing about it is that these animals are colorblind and yet they are producing a color signal," said study researcher Paloma Gonzalez Bellido of the Marine Biological Laboratory (MBL) at Woods Hole, Mass. "It's puzzling to us — even if it isn't for [squid to see], if it is for camouflage, how do you know you're doing this right? You can't see color." [See Video of the Squid Color Changes]
Squid, octopus and other cephalopods have amazing color-changing abilities thanks to specialized structures in their skin called chromatophores. But most squid species also have another set of specialized structures called iridophores, said study researcher Trevor Wardill, a research associate at MBL.
Unlike most colors we see, which are caused by pigments absorbing and reflecting certain wavelengths of light, iridescence is caused by structures interfering with the reflectance of light, causing the wavelengths to interact with one another and creating intense, almost metallic hues. Iridophores are made of complex stacked plates that cause this interference, Wardill told LiveScience.
What wasn't clear is how the iridophores worked. By definition, iridescent color appears slightly different when viewed from different angles, Wardill said, so measuring iridescence changes is tricky.
To figure out the iridophores' secrets, the researchers carefully dissected the skin of dead longfin inshore squid (Doryteuthis pealeii). They traced the nerves of the skin and stimulated them electrically, finding that they could instigate progressive changes in skin color from the at-rest reddish state all the way through the color spectrum to blue.
Unlike the very fast changes seen in chromatophores, the alteration in iridophores moves more slowly, Wardill said, cycling through the rainbow from red to orange to yellow to green to blue over a period of about 15 seconds.
The neural control for the color changes isn't a local reflex, Gonzalez Bellido said; it comes from the central nervous system. The next mystery to solve is how precisely the squid can pick and hold any given color, Wardill said. In the end, the researchers hope to understand how these cephalopods decide without the benefit of color vision what hues they need to display.
"The animals are actually developing color on the skin and they're doing it without pigments, and they potentially have the chance to be picking a certain color," Wardill said. "That would be very exciting, because there are not many examples from any animals that could pick a color and put it on so quickly."
The researchers report their work today (Aug. 14) in the journal Biological Sciences.
- Under the Sea: A Squid Album
- Cuttlefish Cuties: Photos of Color-Changing Cephalopods
- Vision Quiz: What Can Animals See?
Feast For The Eyes
Peeling back layers of the ocean would reveal a feast for the eyes, with brilliant colors and dazzling body forms. These visual delights come to life in the annual underwater photography contest hosted by the University of Miami Rosenstiel School of Marine & Atmospheric Science. In 2012, their panel of experts chose winners from more than 700 entries, with this dashing headshield sea slug photo taken by Ximena Olds (Florida) taking home the "best overall" award. Olds photographed the creature in St. Thomas of the U.S. Virgin Islands.
Phillip Gillette of Florida won second place in the "best student entry" category with his shot of this harlequin shrimp, Hymenocera picta, hiding out in the Similan Islands, Thailand.
Though this animal doesn't look like a tot, indeed the behemoth is just a babe, a juvenile sperm whale (Physeter macrocephalus). The photo, taken in Dominica by Douglas Kahle of Florida took home first place in the animal portrait category.
Davide Lopresti of Spain captured this porcelain crab hanging out on a feathery sea pen in Komodo National Park, Indonesia. The photo won second place in the macro category.
Who you lookin' at? This overdressed scorpionfish, the paddle flap Rhinopias (Rhinopias eschmeyeri) stole the show with its good looks, snagging second place in the "fish or marine animal portrait" category. Rockford Draper of Texas shot the portrait in Bali, Indonesia.
This nudibranch ( Cratena peregrina) won third place in the animal portrait category. It was taken by Nicholas Samaras of Greece in Chalkidiki, Greece. This species is distinguished by two bright-orange marks at the base and tip of each of its tentacle-like structures called rhinophores. C. peregrina is argued to be hermaphrodite.
Matt Potenski of New Jersey took home second place in the wide angle category for his photo of a school of fish swimming in their home of red mangroves (Rhizophora mangle) in South Bimini, Bahamas.
Snagging third place in the Macro category: an Emperor shrimp, Periclimenes imperator taken by Marcello DiFrancesco (Italy) in Ambon, Indonesia.
First place in the Wide Angle category went to this Lionfish, a species in the genus Pterois, in the Red sea, taken by Mark Fuller from Israel.
This amazing jellyfish photograph received nearly half of the 1,221 online votes in the underwater photography contest. The photo was taken by Todd Aki from Florida.
Taking home first place in the Macro category, Canadian Todd Mintz's photo of these cute-as-can-be yellownose gobies, Elacatinus randalli, peering out from bolder brain coral in Bonaire, Dutch Caribbean.