Squid skin reveals hidden messages

In the animal world, squid are masters of disguise. Pigmented skin cells enable them to camouflage themselves—almost instantaneously—from predators. Squid also produce polarized skin patterns by regulating the iridescence of their skin, possibly creating a “hidden communication channel” visible only to animals that are sensitive to polarized light.

In research published today in the journal Biology Letters, MBL (Marine Biological Laboratory) researchers Lydia Mäthger and Roger Hanlon present evidence that the polarized aspect of the skin of the longfin inshore squid, Loligo pealeii, is maintained after passing through the pigment cells responsible for camouflage.

While the notion that a few animals produce polarization signals and use them in communication is not new, Mäthger and Hanlon’s findings present the first anatomical evidence for a “hidden communication channel” that can remain masked by typical camouflage patterns. Their results suggest that it might be possible for squid to send concealed polarized signals to one other while staying camouflaged to fish or mammalian predators, most of which do not have polarization vision.

Mäthger notes that these messages could contain information regarding the whereabouts of other squid, for example. “Whether signals could also contain information regarding the presence of predators (i.e., a warning signal) is speculation, but it may be possible,” she adds.

Mäthger and Hanlon maintain that the mechanism behind the transmission of polarized light through squid pigment cells warrants further study. Likewise, investigation of this masked polarization signaling system in squid and other cephalopods in natural environments would provide insight into animal camouflage mechanisms and may uncover similar examples in other species.

From Marine Biological Laboratory

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September 20, 2006