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Biology

Seeing with skin: the secret to octopus camouflage

The Paper: Ramirez, M. D., & Oakley, T. H. (2015). Eye-independent , light-activated chromatophore expansion ( LACE ) and expression of phototransduction genes in the skin of Octopus bimaculoides. The Journal of Experimental Biology, 2015(218), 1513–1520. doi:10.1242/jeb.110908

Introduction: Octopuses are true masters of disguise. By changing the coloration, patterns, and even texture of their skin, octopuses are able to camouflage with their surrounding environment. They are so good at these optical illusions that within seconds, octopuses can entirely disappear as they transform into rocks, algae, or other features around them (Fig 1). To see just how incredible octopus camouflage is, watch this short video.

Figure 1: Can you see the octopus in the first image? Watch as these images reveal an octopus hidden in an algae covered rock. The octopus unveils itself in a little over 3 seconds! Source: http://academic.reed.edu/biology/professors/srenn/pages/teaching/web_2007/armmil_site/mechanism.html

Figure 1: Can you see the octopus in the first image? Watch as these images reveal an octopus hidden in an algae covered rock. The octopus unveils itself in a little over 3 seconds! Source: academic.reed.edu

So how exactly are octopuses able to disguise themselves so masterfully? Structures in their skin, called chromatophores, are largely responsible for changes in pigmentation and patterning. Chromatophores are pigment containing, light reflecting cells controlled by muscles. Muscles contract or relax causing chromatophores to alter the pigment expression (Fig 2).

Figure 2: Schematic showing how chromatophores are able to change color by contracting to reduce skin pigmentation (left image) and expanding to increase pigmentation (right image). Source: Wang, et al., 2014. Cephalopod-inspired design of electro-mechano-chemically responsive elastomers for on-demand fluorescent patterning. Nature Communications. 5(4899) doi:10.1038/ncomms5899-

Figure 2: Schematic showing how chromatophores are able to change color by contracting to reduce skin pigmentation (left image) and expanding to increase pigmentation (right image). Source: Wang, et al., 2014. Cephalopod-inspired design of electro-mechano-chemically responsive elastomers for on-demand fluorescent patterning. Nature Communications. 5(4899) doi:10.1038/ncomms5899-

While we know that the chromatophores allow octopuses to change their skin color, it is still a mystery as to how the octopuses determine what background they need to blend in to, especially in such a short time frame. Experiments have shown that octopuses rely upon their well-developed, camera-like eyes to mediate their camouflage, matching their bodies to the surrounding environment based on features such as light intensity and contrast of object edges (interestingly, octopuses are color blind!). So they are likely not utilizing color information to guide their pigmentation patterns. However, when pieces of octopus skin are removed from the animal (so they no longer have contact with the eyes or the brain), chromatophores still respond when exposed to light! How is the skin independently responding to light cues when the brain and eyes are not telling it how to respond?! In an attempt to answer this question, researchers tried to unveil the mechanism behind the octopus’ disguises.

The Methods: Researchers at the University of California Santa Barbara studied how skin reacted to light in the California two-spot octopus (Octopus bimaculoides; Fig. 3). Researchers sequenced the genes present in the skin and used antibody staining to reveal what genes could be controlling the light-activated changes to the skin. Additionally, pieces of skin were dissected from octopuses, severing any nervous connection. The skin was then placed under different wavelengths to see which wavelengths elicited the greatest light-activated change to skin pigmentation.

Figure 3: The California two-spot octopus (Octopus bimaculoides). Source: scienceblogs.com

Figure 3: The California two-spot octopus (Octopus bimaculoides). Source: scienceblogs.com

What allows skin to respond to light? The researchers found a pretty amazing explanation for how the skin is able to respond to light without visual sensory input: the skin itself is able to act like an eye! No, the octopus is not some monster from the black lagoon covered in a million tiny creepy eyes- so no need to freak out. Turns out that the same genes present in the eyes responsible for light detection (called opsin genes, specifically r-opsin in this case) are also found expressed in the skin (Fig. 4). Furthermore, other genes necessary for vision in the eye are expressed in the skin (including some genes called G-protein α(q) and phospholipase C). The genes in the skin are, in fact, nearly identical to those in the eye. And the skin samples the scientist analyzed were most sensitive to the same wavelengths of light that the well-developed octopus eyes are specialized to see. Okay, this is pretty cool… you can freak out now.

Figure 4: A)Octopus bimaculatus. Skin from the region within the yellow box is shown magnified in B. B) Antibody staining of the skin reveals that r-opsin (white) is expressed in the skin cells.

Figure 4: A)Octopus bimaculatus. Skin from the region within the yellow box is shown magnified in B. B) Antibody staining of the skin reveals that r-opsin (white) is expressed in the skin cells.

Conclusion: Other mollusks have been shown to have skin that is reactive to light. For example, clams and other bivalves are able to sense and move towards light. Cephalopods, however, have taken skin light-sensing to a new level, using this trait to entirely shift their appearance in the blink of an eye. Although, not a fully formed eye, the skin is utilizing essentially the same mechanisms that underlie light sensing in the eyes themselves. This light-sensing ability allows the octopus to create optical illusions, disappear into its surroundings, and become invisible to predators- talk about one crazy defense mechanism!

 

Do you think that this finding could be applied to new technology? Tell us how in the comment section!

Discussion

Trackbacks/Pingbacks

  1. […] can change their color or skin pattern to match their current background (or for signaling). Octopus skin has light-sensing capabilities that allow it to change color even when the skin is removed from the […]

  2. […] Regardless of size or shape, all organisms in the ocean face the same three basic challenges: find a mate, find food and avoid being eaten in the process. Avoiding predation can be tricky because the ocean is full of many large predators and suitable hiding places are limited. However, over time organisms have evolved different ways to avoid predation. In the case of cephalopods, such as squid, cuttlefish and octopus, this evolution has resulted in some extraordinary camouflage techniques. Cephalopods are able to match the color and texture of their background to render themselves nearly invisible to potential predators (for more on camouflage, check out this post!). […]

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