Anatomical basis for camouflaged polarized light communication in squid


Pygmy Octopus
Nov 21, 2008

Interesting - what do people here think about it?

Camouflage is a means to defeat visual detection by predators, whereas visual communication involves a signal that is conspicuous to a receiver (usually a conspecific). However, most intraspecific visual signals are also conspicuous to predators, so that signalling can lead to the serious consequence of predation. Could an animal achieve visual camouflage and simultaneously send a hidden visual message to a conspecific? Here, we present evidence that the polarized aspect of iridescent colour in squid skin is maintained after it passes through the overlying pigmented chromatophores, which produce the highly evolved—and dynamically changeable—camouflaged patterns in cephalopods. Since cephalopods are polarization sensitive, and can regulate polarization via skin iridescence, it is conceivable that they could send polarized signals to conspecifics while staying camouflaged to fish or mammalian predators, most of which are not polarization sensitive.
This is pretty cool work... it matches what I've assumed, but it's good that they thought to check it. I haven't seen a paper that describes exactly how the iridophores produce variable polarization: are they controlled by muscles that swivel them, or something else?
I'm not sure.... I thought it said something about polarized light being a product of iridescence...

Could it be that the Cephs are luring prey? Most ceph prey can see polarized light, so maybe they are luring certain kinds?
Polarization sensitivity definitely seems to function in communication:
Boal, et al. 2004. Behavioral evidence for intraspecific signaling with achromatic and polarized light by cuttlefish (Mollusca: Cephalopoda. Behaviour. 141, 837-861.

and predation on silvery fishes and translucent crustaceans (as light passing through translucent animals can become linearly polarized).

I think investigating polarized light signaling in coleoids will truly illuminate the complexity in their communication channels. Martin Moynihan thought ceph communication constituted a visual language, but most ceph behaviour researchers disagree, stating the 10-30 body patterns expressed in certain species is insufficient. If there are ritualized polarized light signals in some taxa (S. officinalis, L pealeii, etc.), then the amount of visual signals in a cephs "repertoire" could be much greater than once thought.

I think polarization sensitivity and chemical communication are the future of ceph intraspecific behaviour studies.

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