November 11, 2011
Instant Camouflage Discovered In Two Cephalopods
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Scientists have discovered two deep ocean species of cephalopods, the octopus Japetella heathi and the squid Onychoteuthis banksii, that can go from transparent to opaque in the blink of an eye, a new study finds.
The first predators that the cephalopods must be wary of are creatures that hunt by looking upward for prey silhouetted against the light filtering down through two to three thousand feet of water. Using their transparent skin under these conditions allows the filtered light to pass through them with little trace of their presence.
The second predators that must be considered are fish that use bioluminescence, their own body-driven light source, to attract smaller animals when sunlight is not available which is often the case at the deep levels that such animals inhabit.
“Being pigmented is the best strategy at that point,” Sarah Zylinski, a postdoctoral scientist at Duke University in North Carolina, told LiveScience. “By switching between these two forms, these cephalopods are able to optimize their camouflage in response to the optical conditions at that moment in time.”
Zylinski said studying camouflage gave wonderful insight into how animals perceive their world very differently from humans, Victoria Gill of BBC Nature reports.
The change in color and transparency occurs almost instantaneously due to their color-changing skin cells being under neural control. The squid sees the flash of light and that visual stimulus triggers skin pigments called chromatophores to turn red.
As soon as the light is gone, the pigments vanish, leaving the cephalopods transparent except for their guts and eyes. “This is pretty unique, just in the speed in which it was happening,” Zylinski told LiveScience. “It was so rapid.”
The discovery was made from animals obtained through ocean trawls in the Peru-Chile Trench and Sea of Cortez, with light responses captured on video. The researchers say the study represents the first time to their knowledge that anyone has carried out such ecologically relevant behavioral studies of skin change in cephalopods.
Fifteen to twenty different species of cephalopod were pulled up from the deep by the research ships, but only these two responded to the blue light. “I went through several things I thought would stimulate behaviors,” Zylinski says.
Shallow-water cephalopods will change their body patterns for a shadow or shape passing overhead, but these deeper water animals don´t.
Zylinski next would like to investigate the link between transparency and habitat depth for the Japetella octopus. “Smaller young animals are found higher in the water column and have fewer chromatophores, so they are more reliant on transparency, which makes sense because there won´t be predators using searchlights there.”
The work, which appears this month in the journal Current Biology, was funded by the U.S. Office of Naval Research and the National Science Foundation.
Image Caption: Japetella heathi, an 80 mm octopus found in the mesopelagic zone (600-1000 meters down), can rapidly shift from transparent and reflective to reddish opaque in the presence of light from bioluminescent predators like Diaphus, the headlight fish. Credit: Sarah Zylinski, Duke University
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