Today I am going to give you some background information on cephalopods and cuttlefish and their perception. Also types of camouflage, how they work, and the differences in cephalopods and vertebrates.
I am going to start with some information about cephalopods and cuttlefish
First the earth was formed and precambrian time occurred for ~4 billion yearsThen ~500 million years ago came the Cambrian explosion where larger life forms appearedA little bit after that cephalopods branched off from the main group of mollusksAs time went by the species diverged into different forms, which were then wiped out by extinctions. This happened 3 times before the Jurassic period, which is when our current coleoid group formed. Interestingly during each extinction event, the nautiloid group were the only to survive. They have survived to this day with very little change. (So we will ignore them for the rest of the hour)As the coleoid group evolved they had more needs to squeeze into small crevasses and so lost their defensive shells. Some were retained as cartilaginous forms inside the body, but now all of them had soft, vulnerable bodies. They took to hiding and trying to blend in with their surroundings to avoid predators. So over time their modes and mechanisms for camouflage became more and more complex.Now masters of disguise, they can use their abilities to communicate with each other, especially for mating.
Some characteristics of cephalopods areComplex brainAble to live only in salt waterBilateral symmetry which will be talked about laterOne central cavity for organs which is surrounded entirely by the muscle mantleThe name cephalopod comes from 2 greek words meaning “head feet”Their arms & tentacles are attached at the head and lined with suckers and/or hooks used to seize and hold preyThey have a pair of chitinous jaws called a beak to crush shells since they primarily eat their cousins the shelled mollusks and other little critters that run around on the sea floorWith the loss of the shell, muscles were allowed to develop and become more powerful. An organ called a siphon is used for respiration as well as swimming by quickly sucking water in then pushing it out. They are able to jet away quickly by doing thisThey only live for a few years. This is one reason why scientists are so fascinated with the group, because it develops a very complex brain and lives only a short time to use it.
Cuttlefish are solitary animals that live in shallow waters near reef structures which provides places to hide and great camouflage backgroundsThey have lost their external shell, but retain a cartilaginous bone filled with gas for buoyancy, called a cuttlebone CLICK FORWARDThis drawing of a cuttlefish is labeled with all the important body partsThis whole back section is the mantle which holds the cuttlebone and organs. The bottom side is pale due to the lack of coloring organsHere are the 8 arms and 2 specialized tentacles used for reaching. CLICK FORWARDFemales tend to keep these all neatly tucked in to protect her eggs CLICK FORWARDAt the center of the arms and located near the mouth opening is the beakThe fin is attached all the way around the mantle. It flaps in a wave motion as shown to orientate the animal
Now I will move on to perception and neurology which are how the animal determines its camouflage
This two eyes did not come from a common ancestor. Cephalopods diverged far before any eyes had formed, so they must have each evolved within its own linage. This is known as convergent evolution. The 2 eye structures are slightly different from each other. In the vertebrate eye the nerves shown in red run in front of the retina which is in blue andcreate a gap in the retina, resulting in the blind spot because the retina is the layer of tissue that receives light images. Also the way each eye focuses is different. In vertebrates the actual shape of the lens changes while the cephalopod eye has the muscle in green that squeezes the lens in and out.They have two spots ofsensor cells in the retina,one to look more forward, and one to look more backward giving them a larger field of visionNot having the blind spot is important because they receive all of their information visually
When approaching a new environment, visual sensing can start from a distance. If the cuttlefish were to use tactile information to control camouflage, it would require them to make direct contact with several features of the environment. Not only would they have to be close to the features, butthis may visually expose the animal to predators because ofinappropriate postures or movementsduring inspection. Gathering visual information about the surrounding environment is faster, andfor a soft-bodied cephalopod that is advantageousEvidence to support this comes from an experiment conducted by Allen and others showing that cuttlefish rely on visual cues more than on tactile senses. In the experiment they placed cuttlefish in habitats with natural substrate, substrate with glass over it, and a photograph of the substrate. Each type of background was designed to stimulate one of the 3 body patterns known for camouflage.CLICK FORWARDIn the sand and gravel substrates, cuttlefish from each type of background condition displayed similar patterns. The patterns uniform or stipple and mottle are identified by general matching of the background. The disruptive pattern displayed on the rock substrate is used to the fool the predator into seeing a different body outline than that of a cuttlefish. For instance the observer might only see the white triangle or square on its back.
This graph shows quantitative data on the picturesAxis is number of papillae which are bumps on the skin that assist in the camouflage.We can see that within each substrate, the animals engaged similar numbers of papillae which implies that the body pattern for all 3 background conditions were similar. I will discuss papillae in more detail later on.Based on this the authors concluded that tactile observations were not needed to produce the same type of body pattern. The cuttlefish just need to SEE the background not feel it.The rapid ability to change patterns is of intrigue
Scientists believe there is a direct link between the brain and color changing organs in the skin. In the book, Cephalopod Behavior by Hanlon and Messenger, there was an experiment described that helps confirm this idea. Electrical stimulation was applied to different lobes of the brain to observe the response. Stimulation of some lobes but not others resulted in color only on one side or only on the head. If there wasn’t a direct link, the whole body would show the same response. Visual input from the eye is processed in the optic lobe, which selects the appropriate body pattern. This information is then sent to the basal lobe and on to the chromatophore lobes whose axons run without synapses straight out to the chromatophore radial muscles in the skin. Chromatophores will be described in more detail later on, but they are basically what allows the animal’s skin to change color. The basal lobe just checks to make sure that both sides and the anterior and posterior of the cuttlefish are displaying the same pattern. ---Each half of the brain is responsible for controlling one side of the body. Just like humans. For example, lifting one arm but not the other is controlled by the corresponding brain half CLICK FORWARDMost likely this brown one is a female and this one is a male trying to impress her with his colors. The other half however he keeps white to warn other males to stay away.---This picture shows the squid utilizing each half of the brain differently.
This is a drawing of an octopus brain, showing the different lobes here, and the nerves running out to different parts of the body. These 2 kidney beans shapes are the optic lobes. They are huge in comparison with the rest of the brain because they process a lot of information in a small amount of time which is needed for successful camouflage CLICK FORWARD CLICK FORWARDThese high speed camera pictures show how fast all of this actually occursWithin 2 seconds the octopus has changed from completely inconspicuous to its natural pale smooth selfAnother neurological feature of cuttlefish is that they are color blind
Marshall and Messenger support this claim in anarticle on color-blind camouflage. They conducted an experiment to see if cuttlefish would match their skin color to backgrounds of different colors. These are pictures of what the cuttlefish decided to display when on these backgrounds. These are the same backgrounds as seen through a green filter because that is the only wavelength their eye can perceive. As you can see, they did not produce the same colors as the background. They did however produce the correct type of pattern for what they saw. The top one is showing a disruptive pattern because it sees a high contrast background. The second 2 both display a uniform or mottle pattern because the 2 colors used look relatively similar in intensity.Cuttlefish basically only see differences in light intensity. They are also able to perceive polarized light which increases the contrast between colorsBeing color-blind is not a hindrance for cuttlefish because, as we will learn later, the skin can reflect whatever light color is coming off of the substrate
We have already seen the 3 types of body patterns used in camouflage, but there are many more factors that I will soon discuss that effect the quality of the camouflage.
Skin changes and mimicry are the categories that these factors fall intoIncluded in skin changes there are body patterns as observed earlier, different colors that can be created, and papillae changing the texture. Color changes will come up next but right now I will focus on the papillae. Their main goal which is aided by the patterns, is to change the body outline so predators cannot recognize it, but very little is known about how they function.Types of mimicry include posture which is the ways in which cuttlefish hold their arms & movement which is the fashion in which they move or restNow to colors in the human body
Chromatocytes are a type of cell within the dermis that is a sort of vesicle to contain melanin. Melanin is a collection of pigment particles.These cells are responsible for the color of your skin, hair, & eyesThe mechanisms of color change in cephalopods are a little different than coloration in vertebrates
Chromatophores are actually separate organs that function by changing the shape of the pigment sac. There are multiple layers of different types of chromatophores in the thick cephalopod dermis. The organs are stimulated by electrical pulses sent from the brain to the site by a continual axon.On the other hand vertebrates have the chromatocyte cells which are mostly only the one color from melanocytes. These cells squish all the pigment molecules up toward the top layer of skin and are stimulated by chemicals produced from cell signaling.
Cephalopods have 2 types of chromatophores that will help to explain how complete camouflage works
There are pigmented chromatophores which are the same color no matter what angle the light hits them at & are sometimes difficult to distinguish. They include XANTHO- yellow ERTHRO- orange/red MELANO- brown/black CYANO- blue
Chromatophores also come in styles that reflect incoming light. They include IRIDO- which in Messenger’s paper on the neurobiology and natural history of chromatophores he explains well saying ”These are multi-layer stacks of thin chitin platelets alternating with layers of cytoplasm; the platelets function as ‘ ideal ’ quarter-wavelength reflectors and produce spectral colors by constructive interference.” The only wavelengths these reflect are those of blue and green. LEUCO- Are flattened cells that scatter incoming light which usually produces bright white colors. But basically they reflect whatever color is coming in; so in red light, they would display red. They can change orientation to produce visional illusions such as moving stripes. & they only occur in some areas of the skin rather than continuously like the pigments and iridophores do
This cross section through octopus skin shows the organization of the different chromatophore typesThe top part is toward the surface of the skinCP are the Color pigmentedchromatophores where the Blacks are most superficial then the Reds and Yellowsare deepest IP are Iridophoreswhich are producing blues & greens hereLCareLeucophores the broad-band reflectors
This drawing displays a pigmented chromatphore with all of its various partsExtra material that has been folded up until expansion15-25 radial muscle
Here is the chromatophore in its relaxed state CLICK FORWARDThe contraction occurs causing the cytoelastic sac to become flattened and thus produce color from reflecting light through it
Diagram of light rays in a cross section of skinUp is outside & down is inside the skinCh = pigmented chromatophoresLeu = broad band reflecting leucophoresReflect whatever color is coming in; most likely white CLICK FORWARDReflect the color of pigmented chromatophores that are expandedTexture is also needed to create the most accurate body camouflage
Scientists Don’t really know how they workBut papillaecan be raised to various heights as a result of muscle movementSome are located specifically under leucophore areas in order to maximize the broad band reflections and colorClose up of some papillae being accentuated CLICK FORWARDShows the extreme texturing to match the seaweed behind itNow that the skin has been addressed lets look at how some added mimicking may help
Squid looking like what seems to be a sea fan CLICK FORWARDCuttlefish looking like sea weed CLICK FORWARDCuttlefish trying to look like the little plastic tree in the backgroundSome of these postures are pretty good and a study has even been done to determine just how well cuttlefish understand how to position their arms
In this experiment by Barbosa and others cuttlefish were put in front of striped background and arm angles were recorder after the animal had become stationaryInmany trials the second set of arms were raised as well, but at a lower angle than the firstInterestingly the animals were able to hold their position for long periods of time: 20 min
Black dot = outlierAsterisks = extreme outliersThey were in the right range accept for the 45 degree stripesThe data suggests that the cuttlefish have an understanding of how to correctly position their arms
one last idea that might work to evade predatorsNot cuttlefish, but the mimic octopus who is a master at pretending to be an animal other than itself swims along with its arms back to look like a flatfishCLICK FORWARD splays its arms out to look like the venomous spines of a lionfishCLICK FORWARD sticks all but 2 arms into the sand making a linear sea snake impression
Now I will just finish up with some future research ideas
Authors suggested these ideas as future areas of studyIn conclusion cephalopod camouflage is very complex and requires further investigation. The hope is that one day active camouflage could be created for use by the military
Cuttlefish: The Camouflage of Cephalopods Sara Chlebecek
Cephalopod Background• Appeared in the Upper Cambrian – ~500 million years ago• 2 subclasses – Nautiloid: Nautilus – Coleoid: Octopus, squid, & cuttlefish• Camouflage is primary defense• Color change also for social interactions
Cephalopod Characteristics• Complex brain• Salt water only• Bilateral symmetry• Central cavity• Muscle mantle• Well developed head where appendages attach• Arms/tentacles with suckers and/or hooks• Beak• Swim by use of siphon• Short life
Classes of CamouflageSkin changes Mimicry• Pattern • Posture – Uniform – Tentacle positions – Mottle • Movement – Disruptive – Swimming• Color• Texture – Skin papillae • Change body outline • Very little is known
Chromatocytes• Type of cell within the dermis• Vesicle that holds melanin• Melanin – pigment particles• Responsible for color of skin, hair, & eyes
Differences in colorationCephalopods Vertebrates/warm-blood• Chromatophores • Chromatocytes• “phores” – separate organ • “cytes” – type of cell• Shape of pigment sac • Pigment molecules move changes around• Multiple layers of • Flat melanophores near chromatophores in thick surface in thin dermis dermis • Cell signaling• Chromatophore organs hard-wired to brain
Future Research• The behaviors & interactions of cephalopods and their predators in the field• How chromatophores organize and communicate to generate horizontal striped patterns• How background matching is achieved by animals in motion