Thursday, February 19, 2015

Cuddle up next to a Cuttlefish....or is that a rock?

By Kara Jew

As much as I would like to tell you how eating cuttlefish will prevent diseases and bring a lifetime of health benefits I can’t. We’re friends (maybe acquaintances), so I won’t lie to you. But hey I’m not going to stop you if you want to eat cuttlefish. It’s your life, and you can do whatever you want. Although my advice: don’t eat it with asparagus…especially when vanilla paste is an option. You’ll upset your stomach and whoever is standing behind you. I’m here to tell you a little more about what the cuttlefish does and how it’s like the Mystique (nerd alert: I’m an X-Men fan) of the ocean.

First off, one of the weird things about the cuttlefish is its eye. Under bright conditions, the cuttlefish pupil resembles of Charlie Brown’s mouth, or in other words, their pupils exhibit a W-shape. Cuttlefish aren't the only ones with peculiar pupils though. Other organisms have a vertical or horizontal pupil such as a Madagascar Velvet Gecko or Yellow Mongoose, respectively.

The eye of a cuttlefish. Look at that W!
It has been suggested that this peculiar shape is restricted to species that spend a considerable amount of time camouflaging on a substrate (or the surface on which an animal or plant lives). A study found that the pupil persists as a W-shape when exposed to bright lights but morphs into a full circle under darkness. Possessing an adjustable pupil allows an organism regulate the amount of light entering the eye thereby avoiding saturation of photoreceptors. They proposed that the W-shaped pupil aids in balancing out light in the natural habitat of the cuttlefish. 
On the left you have the vertical pupil of a Madagascar Velvet Gecko, and on the right the horizontal pupil of the Yellow Mongoose






But enough of eyes! Let’s get to the good stuff. More interesting than the weird eyes of the cuttlefish is their ability to camouflage.

Cuttlefish and the different looks it can take on.
Perhaps the most prominent characteristics of the cuttlefish are their elastic pigmented cells called chromatophores. These are neuromuscular organs, so these cells change with immense flexibility and speed in response to stimuli. In the video below, Backyard Brains, a company dedicated to making neuroscience accessible to everyone, used an iPod to look at the dynamic of a squid's chromatophores. They played the song “Insane in the Membrane” and watched the chromatophores go to town.

 
Chromatophores dancing to "Insane in the Membrane" by Backyard Brains.
 

The chromatophores of cephalopods, like squid, octopi, and cuttlefish, are used for cryptic and social displays. Within each chromatophore is a large pigment-containing compartment, the cytoelastic sacculus, bearing numerous pigment granules that give the chromatophore its color (red, brown, yellow, orange or black). The cytoelastic succulus is surrounded by radial muscles that are controlled by motor neurons in the brain. Cuttlefish can alter its color schemes through contraction or relaxation of these chromatophores. Specifically, contracting the radial muscles causes the cytoelastic succulus to expand and display changes in color. Alternatively, relaxation of the radial muscles leads to the retraction of the sacculus, thus restoring the resting color pattern of the cuttlefish.


A visual to help you understand the chromatophore mechanism. The blue balloon acts as the cytoelastic succulus, and the strings mimic the radial muscles
In order to camouflage with its background, cuttlefish must match with distinctive background characteristics such as the size and spatial frequency of substrate objects, the degree of contrast, texture, color, and pattern. That’s an immense task for any creature to take on, but the cuttlefish is an expert. The distinct body patterns in the cuttlefish due to changes in chromatophores have been partitioned into 3 different patterns:

1. Uniform: Vary in color and brightness, but attributes remain constant
2. Mottle: Characterized by small to moderate light and dark patches (called mottles) that are evenly distributed across the body surface. These patches generally match with corresponding background objects. 
3. Disruptive: Large light and dark components that exist in various shapes, scales, orientations, and contrasts. 

A: Uniform
B: Mottle
C: Disruptive
Can you spot the cuttlefish in the bottom three pictures?


Richard Hammond from the BBC demonstrates the cuttlefish's amazing camouflage capabilities.


These creatures are pretty awesome, right? Hang on though, because things are about to get wild. Get this: cuttlefish are color blind. WHAT?! You may wonder how these creatures are able to perform such drastically different camouflage patterns across a wide array of visual backgrounds. It has been proposed that additional cells in the skin of the cuttlefish aids in camouflage. Aside from chromatophores, the skin of the cuttlefish also contains cells that reflect specific wavelengths of light and ambient light, iridophores and leucophores, respectively. Iridophores are found within a layer underneath the chromatophores. They are stacks of platelets that are responsible for giving cuttlefish and other organisms their metallic green, blue, and gold appearance. Iridophores may change colors slowly in response to hormones. Additionally, leucophores are maintained in a layer beneath both the iridophores and chromatophores. These cells are responsible for white spots that occur on cuttlefish. Leucophores may reflect either white or blue light depending on which is the predominant ambient light. 
Left: Iridophore as seen by the iridescent coloration
Right: Leucophore are the white spots on the skin
In addition to these specialized cells, a study found the opsin gene expressed in the skin of cuttlefish. Opsins, reflective and light-sensitive proteins normally found in the retina of the eye, may also be involved in camouflage. They proposed that these proteins may help the cuttlefish detect reflectance properties of the environment. This would influence chromatophore expansion and aid in matching the brightness of its background. Additionally, opsins may act as filters and convey wavelength information. Unfortunately, the exact function of the skin opsins remains to be determined. 

After all that effort the cuttlefish puts into camouflage, it appears that its ability to evade predators lies in the eyes of the beholder rather than the superpowers of the cuttlefish. Much of the information that allows a predator to differentiate between the cuttlefish and background relies more heavily on the brightness rather than the chromatic aspect of light. Well, hopefully at least you’re impressed with the cuttlefish.

He's out to get you if you don't think he's awesome.

A final fascinating fact about the cuttlefish is the its ability to produce pigmentation patterns called “passing clouds”. It is thought that these cuttlefish possess this ability as a mean to hypnotize their prey. In the passing cloud phenomenon cuttlefish are capable of propagating a distinct dark band across different regions of their body. This band travels at different frequencies as well as region-specific directions on the cuttlefish; however, the bands are synchronized in identical regions. Not much research has been done on the cuttlefish hypnosis attack, but hopefully it’ll be a topic of interest in the near future.

             
 Check out the cuttlefish trying to hypnotize prey.


All in all, would it be too much to say that cuttlefish are the kings of camouflage? No? I didn’t think so either. They’re the color magicians of the deep abyss that we call the ocean.

 Finally, I leave you once again with Ze Frank and his true facts. On today's episode, "True Facts about the cuttlefish". Enjoy.








References:

Chiao, C., J.K. Wickiser, J.J. Allen, B. Genter, R.T. Hanlon. 2011. Hyperspectral imaging of cuttlefish camouflage indicates good color match in the eyes of fish predators. Proceedings of the National Academy of Sciences of the United States of America 108:9148-9153.

Hanlon, R.T., C.C. Chiao, L.M. Mäthger, A. Barbosa, K.C. Buresch, and C. Chubb. 2009. Cephalopod dynamic camouflage: bridging the continuum between background matching and disruptive coloration. Philosophical Transactions of the Royal Society B 364:429-437.

Kelman, E.J., R.J. Baddeley, A.J. Shohet, and D. Osorio. 2007. Perception of visual texture and the expression of disruptive camouflage by the cuttlefish, Sepia officinalis. Proceedings of the Royal Society B 274:1369-1375.

Laan, A., T. Gutnick, M.J. Kuba, and G. Laurent. 2014. Behavioral analysis of cuttlefish traveling waves and its implications for neural control. Current Biology 24:1737-1742.

Mäthger, L.M., R.T. Hanlon, J. Håkansson, and D. Nilsson. 2013. The w-shaped pupil in cuttlefish (Sepia officinalis): functions for improving horizontal vision. Vision Research 83:19-24.

Mäthger, L.M., S.B. Roberts, and R.T. Hanlon. 2010. Evidence for distributed light sensing in the skin of cuttlefish, Sepia officianlis. Biology Letters 6:600-603.

Messenger, J.B. 2001. Cephalopod chromatophores: neurobiology and natural history. Biological Reviews 76:473-528.

Suzuki, M., T. Kimura, H. Ogawa, K. Hotta, and K. Oka. 2011. Chromatophore activity during natural pattern expression by the squid Sepioteuthis lessoniana: contributions of miniature oscillation. PLoS ONE 6:e18244.


Images:


http://www.specialtyexecutives.com/blog/sea-chameleons-pave-way-development-sophisticated-protective-gear

http://www.advancedaquarist.com/blog/scientists-awarded-naval-research-grant-to-study-emulate-cephalopod-camouflage-ability

http://otlibrary.com/cuttlefish/

http://deepseanews.com/2013/10/squittle-day-psa/

http://www.koryoswrites.com/nonfiction/the-functions-of-different-pupil-shapes/

http://www.eyedesignbook.com/ch3/eyech3-f.html

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