Cephalopods and their incredible color change

Cephalopods, more commonly known as squids, cuttlefish and octopuses are some really incredible and interesting animals. They are pretty smart, they are fast swimmers and they are well known for squirt ink into their environment, and disappear in a blink of an eye. If you have ever tried to catch one, then you would also know they are superb at getting away, even when they are locked in a cage, they can squeeze through all small spaces like between bars or holes that are several times smaller than themselves. The most impressing thing about them though, must be their use of colors and their incredible ability to alter their color in matter of seconds.

What makes cephalopods able to change color?

Their secret lies in some cells they have lying right under their outer skin layer. These are special cells called chromatophores. They are surrounded by layers of muscles that can constrict (temporary state) or expand (relaxed state), and within these cells are pigments. There are only one kind of pigment in each chromatophore, but different chromatophores can have different kinds of pigments. When the muscles constricts, they push pigments from the cell closer to the outer skin layer. More precisely, in constricted state, the cell will have a flattened disc-shape at the top (against the outer skin layer), where the pigments will occupy the space and the color gets more visible. If the muscles returns to relaxing state (expanded), the cell will shrink back to a small blob, and will retract from the outer skin layer. Cephalopods can decide which chromatophores they will constrict and expand, and this makes them capable of showing different colors and patterns (Harris 2001).

Why would a cephalopod want to change colors?

They have several reasons to change color. One is that they uses this to fit perfectly into the environment and be camouflaged well. If the environment changes, then so do they. They can have a broad range of different chromatophores, some have as many as five different ones (Douma 2008), which means they can create several different patterns and combinations, because they can decide exactly which colors they want to show at any time, and this make them capable of hiding or looking less conspicuous with all sorts of backgrounds(Meyer 2013).

Another reason for changing color can be if a predator approaches, then a cephalopod will expand chromatophores to create distinctive color patterns to warn a predator that they might be dangerous or bad for eating, just like other animals that also uses aposematism. They can also use different colors if they mimic something. Some of them are exceptional at mimicking other sea creatures, so with their ability to change color as well, they look even more convincing (Meyer 2013).

A third reason for color change can be communication. Several species have males that can change color to attract females or repel other males. Some might flash colors for a period of time, and this is thought to yield some kind of information that humans know little about (Meyer 2013).

What are pigments?

Pigments are different chemical components you can find in both living organisms and in inorganic matter. There are many different pigments, but what they all essentially do, is absorbing one or several wave lengths from the light spectre and reflect others. Different wave lengths that are reflected, are perceived as different colors.( see: Douma 2008)

Here I have a great video showing how cephalopods can change their colors and use it for different purposes.

  https://www.youtube.com/watch?v=aoCzZHcwKxI, viewed 27 May 2014

References:

Harris, T 2001, HowStuffWorks.com(Discovery communications), Atlanta, US,viewed  7 Mai 2014,<http://animals.howstuffworks.com/animal-facts/animal-camouflage2.htm >

Meyer, F 2013, How Octopuses and Squids Change Color, National Museum of Natural History, Washington DC, US, viewed 7 May 2014,

<http://ocean.si.edu/ocean-news/how-octopuses-and-squids-change-color >

Douma, M, curator, 2008, Cause of Color: Biological Pigments, Viewed 7 May 2014, <http://www.webexhibits.org/causesofcolor/7I.html >

What causes the colors we see in animals?

Animals are showing a wonderful range of colors which make them look very beautiful, and also helps the animals in ways of survival, and in attracting mates. A lot of insects, reptiles and especially birds tend to show many different and wonderful color combinations, but how do they get or create this wide range of colors?

Colors in animals can be created by two different mechanisms, one is by producing pigments, the other on is by producing specific structures that interact with light in a special way that results in different colors.

Pigments

Pigments are chemical substances that individual animals usually can produce themselves. They have genes that code for different precursors and proteins, that are combined in manners that create very specific substances that can absorb different wavelengths. Humans and close relatives see light in the specter from 400 nm to 750 nm, and this is called the visible specter, but other animals can sometimes see shorter and/or longer wavelengths. When light hits a pigment, the pigment will absorb a portion of the light, and reflect the rest. Depending on which portions of the visible light that are reflected from the pigment , we will perceive a certain color. If all light in the visible specter is reflected, we will perceive an object as white, opposite of this is black, when all wavelengths in the specter are absorbed an nothing reflected. Some chemical substances will as an example absorb light in the green and blue part of the specter and reflect most of the red and orange specter, which might make an object look reddish. Different chemical substances put together might absorb different wavelengths, and therefor will the composition of different substances altogether dictate which color we might perceive, depending on the reflection. Different compositions might give different colors. In the animal kingdom melanin is the pigment that is most abundant, but you might find other pigments as well, all though less common. Melanin give rise to colors like black, brown, and reddish brown . Lots of animals show colors that are a result of pigments from their diet, like carotenoids that give animals a yellow, orange and red color, and flavonoids is another example. Birds are a good example of animals that gain red and pink from their diet, this colors are not produced, so to get their beautiful plumage, they need to eat certain types of food that is rich in this pigments. Pigments are usually found in skin and underlying tissue, but can also color gut content, fur, and feathers. Pigments are usually causing the warm colors you find in animals, like red, orange, and yellow, but it is possible to find green and blue pigments as well.

Illustration 1: This lion looks brownish due to melanin in the fur, were different amounts and different types of melanin can cause small changes in the wavelengths that reach the observer, and hence give slightly different colors.

Illustration 2: This finch has a beautiful red color due to pigments from its diet. It consumes berries with carotenoids that give it the strong color.

Structural colors:

These colors are based on interactions between white light and arrays on or in materials. Here is the architecture of the material more important than the chemical makeup of material. Structural colors are due to reflection, refraction, diffraction and scattering of light, but never absorption. Here it is often important that the material are structurally stable and stiff, and are often based on non living materials. Bird's feathers that is showing green and blue colors are often due to specific structures and architectures in the feathers that interact with light in a special way. Structural colors are usually cool colors like, blue, green, violet and ultraviolet. Some times a combinations of pigments and structural colors are used to create new color effects.

Some examples off effects that can cause structural colors: (there are many more effects than explained here, I just talk about two possible structural effects that create different colors)

Scattering effects: Here white light will encounter a cloud or array of molecules, particles or other structures. What happens is that wavelengths will be spread in different directions, including in the direction of the observer. Depending on the wavelength that goes in the observers direction, the observer will see a specific color. Normally, if the structure that scatters the light is bigger than 700 nm, the color perceived will be matte white. A smaller structure around 400 nm will scatter more of the short wavelengths, and less of the long wavelengths, which will only pass through.

Illustration 3: This picture show how light of short wavelengths are scattered while longer wavelengths are just passing through. The scattered light here can as an example be wavelengths in the blue part of the scale, and can then be perceived as Tyndal blue that you find in feathers and in blue eyes.

Interference: Here white light is separated when it reaches a structure, and is then brought back together. When the light does so, some rays will have travelled a longer distance than other rays, and as a result some wavelengths will be in phase and reinforced, while others will be out of phase and chancel out, and this is what gives the brilliant iridescent.

Illustration 4: These hummingbirds are showing structural iridescent colors, where the light is refracted, and depending on the angle of the bird and the observer, the color might change a bit, due to different wavelengths being reflected back after refraction.

References:

Resh, V &Carde, R(eds) 2009,Encyclopedia of insects, second edn, Elsevier Science & Technology, Chicago.

Illustration 1: Viewed 20 May 2014<http://www.webexhibits.org/causesofcolor/7I.html >

Illustration 2: Viewed 20 May 2014<http://www.webexhibits.org/causesofcolor/7I.html >

Illustration 3: From Resh & Carde 2009

Illustration 4: Viewed 20 May 2014<http://www.birds.cornell.edu/AllAboutBirds/studying/feathers/color/document_view >

Albinism in animals:

Have you ever seen an albino animal before? Ever wondered how an animal can end up being this white when every other animal within a certain species is dark? Well, here I will try to explain a little bit about albinism in animals, why they become white, and what effects it might have on the animal that's showing this abnormality.

Albinism is a rather seldom happening, and it is rare to see animals displaying this for several reasons. One of the reasons for this rare event is the fact that this is due to mutations that hardly ever happens, maybe just in 1/ 20000-50000 cases, the rate depends a little bit on what kind of mutation that is causing the albinism(Encyclopædia Britannica 2014). Second, although this condition can be inherited and transmitted to the next generation, this is not very likely, since albino animals usually have lower fitness and less chance of surviving.

So what is actually albinism?

It is a condition that's congenital, and animals that have this are displaying an absence of pigmentation in skin, hair/scales/fur, and also in eyes.This makes the skin pale(more like pink since the blood vessels give the skin some color), and hairs and fur look white. Eyes will also look red, due to lost pigmentation(Encyclopædia Britannica 2014). The reason for this is the absence of the pigment melanin, and this can be due to different things. A common reason for this is likely to be connected with Tyrosinase, an enzyme that catalyzes the process where melanin is synthesized from Tyrosine. With albinism this enzym might be defect or absent, and the result is absence of melanin that normally would give an individual color.(Encyclopædia Britannica 2014). Albinism is normally determined by homozygosity of recessive genes, but can also be determined by genes on the X-chromosomes(Redei 2008)

A bit about melanin production:

(Redei 2008):

During embryonic development precursor cells called melanoblasts move to the surface areas of the skin and become specialized cells called melanocytes.

Melanoblasts→ melanocytes

Melanocytes contain organelles that's called melanosomes were melanin is synthesized:

Melanosomes

↓

(Tyrosinase)

Tyrosine → Melanin.

Sometimes albinism can be a result of other things as well, and does not necessarily have to do with Tyrosinase. It might be that the melanosomes don't mature like they should, or that something else in the tyrosine-melanin pathway is defect. There is more than one enzyme contributing in this pathway, and defects can be found everywhere, because everything is dictated by genes, and genes are susceptible to mutations. But as mentioned, a defect Tyrosinase are very often the cause here(Redei 2008)

Why is albinism often decreasing fitness or making it harder for an individual to survive?

First of all albinism and the absent of pigmentation makes an individual more susceptible to cancer. Pigments acts as a screen against UV radiation, and protects the skin against damage(Encyclopædia Britannica 2014). When the animal doesn't have this protection, the damage caused by sun's radiation increases cancer rates, and rates of survival decreases. Second, some mutations that causes the albinism can also affect the eyes in other ways than just affect the eye's color. Albinism can give different eye diseases, either direct or indirect, that can effect an individuals survival(Witkop jr, 1989). Third, albinism effects defense mechanisms related to color and also camouflage. Imagine a white mouse running on the ground where it is seen against a dark brown background of dirt and leaf litter. It would be spotted hundreds of meters away, compared to a brown mouse with excellent camouflage. This mouse would literally advertise to predators where it is found at all times, and would probably not survive for long(see earlier blogs on this topic). Fourth reason for not seeing to many albinos in the wild can also be related to sexual selection. Sexual selection might exclude some albino animals if they don't show the desired colors that the other sex prefers. Then their chance of reproducing can decrease, and albino genes are then less likely to reach the next generation.

Under is some pictures of animals that are showing albinism.

Picture 1: Elks outside Oslo in Norway. Photo: Arnhild Oien

Picture2: How do you think this peacock do when it comes to impressing the ladies? 

References:

Witkop jr, CJ 1989, 'Albinism', Clinics in Dermatology, vol.7, no.2, pp.80-91, viewed 15 May 2014, <http://www.sciencedirect.com.elibrary.jcu.edu.au/science/article/pii/0738081X8990059X# >

Redei, GP 2008, Encyclopedia of Genetics, Genomics, Proteomics and Informatics, 3^rd edn, Springer, US.

Encyclopædia Britannica 2014, Albinism, Encyclopædia Britannica online, viewed 15 May 2014, <http://www.britannica.com.elibrary.jcu.edu.au/EBchecked/topic/12993/albinism >

Picture 1: Viewed 15 May 2014, http://www.bt.dk/utroligt-men-sandt/royal-albino-elg-faar-kongeligt-navn

Picture 2: Viewed 15 May 2014 http://animalshak.com/2012/09/wordless-wednesday-albino-peacock.html

Thermoregulation and melanistic animals

What I want to highlight today is how environment and temperatures can have an effect on animals coloration. I how talked about how predation can cause a selection pressure on animals, so they respond in developing colors that either warn off predators, or make the prey less visible in their environment. But sometimes there are other things that can create a selection pressure as well. This might include colors that attract a mate, or colors used for thermoregulation. I will dig deeper in to thermoregulation today.

Some animals are what we call ectotherms, they are dependent on the temperature and heat energy around them, to maintain there metabolic rate and for development, growth and movement. These animals need to actively move in to sun to heat up, and to find shade and cooler environments if they get to hot. This is behavioral thermoregulation. In some environments, like high altitude areas, the temperature might not get very high, and the sun might not be up for many hours(for example in the northern hemisphere). This means that animals might have a hard time rising their temperature enough to be active and retain their metabolism, and development and growth will be slow. In these environments the reduced temperature and energy available, might have a bigger impact on selection pressure than mate selection and predation will have, if you compare it to more favorable environments with higher temperatures. This will have an impact on animals coloration, because a small difference in color can make a huge difference in the levels of activity, growth and development, and therefor make an animal more successful. Dark colored animals will obtain more energy from the sun, they heat up faster, and then they have more hours for disposal during a day, and obviously this is an advantage.

Researchers studied a butterfly larva in cold and warm environments, and concluded with some interesting facts(Lindstedt et al. 2009). The larvae they studied showed patterns of orange to deter predators(aposematism- warning colors), and in favorable environments the most successful larvae was the larvae with most conspicuous colors, this because it is easier for predators to see, and more predators avoid them. But in colder environments they found a trade off, because the most successful larvae here, where those with smaller patterns and darker colors. These were more active and developed faster, and showed faster growth. As mentioned in the report:' Benefits of shorter development and growth at faster rates, can be significant, because it decreases the period when a larva is vulnerable to predation and parasitism, and increases the probability of individual surviving until reproductive life stage'.

A researcher from Stellenbosch University in Africa, Susana Clusella-Trullas, studied coloration among lizards in Africa, and published her study in Ecology in August 2009. She found that darker colored lizards in cooler environments where more successful compared to the paler once, because they were able to be longer active during the day. Bellow is a link to an interview with her, where she explains what she found and how she managed to do the research. It is very interesting.

https://www.esa.org/fieldtalk/its-only-skin-deep-melanism-and-thermoregulation-in-lizards/

There is other examples of animals that use color to regulate there temperature as well. There has been research on chameleons(Bennett 2004), where they found that different colors are not just used as camouflage, but also change of color is due to temperatures. When the chameleons are feeling cold and the sun rises in the morning, they will show a dark skin color to heat up faster, and when their favorable temperature is reached, they will change color so they become more pale, and less energy is absorbed. This is a very interesting and fascinating adaption, that truly seems to work well.

I also have some examples from Norway where I live. We have this species of spider in the orb weaver family that is found in coastal habitats as well as high latitudes up in the mountains. It is very common many places in Norway. What is interesting, is how the color changes when you reach higher altitudes. Close to the coast the spider is displaying a white coloration with some black stripes on its legs and some black markings on the abdomen. But up in the mountains, you will find it to be totally black. The temperatures here are much lower compared to the coast, and to survive the spider needs to be able to gain as much energy from the sun and the surroundings as possible. We also have a snake in the wiper family, that normally shows a black zig zag pattern on its back, against a pale background color on the rest of its body. This pattern seems to be less visible on higher altitudes, due to more individuals with darker skin, some are almost entirely black. Zig zag patterns are often believed to act as a warning or to play a part in motion dazzling, but up in high altitudes this becomes less important, and there is a trade of between this pattern that gives decreased predation risk, an being melanistic where the snake can develop and grow faster, and be more active and catch prey easier.

Below is a picture of the snake where the pattern is visible, and the other one is the melanistic type. The species is Vipera berus .

Illustration 1: Normal snake

Illustration 2: Melanistic snake

Below is the spider Larinioides cornutus with different colors.

Illustration 3: Photo: Glenn Halvor Morka

Illustration 3: Photo Jostein Gohliu

References:

Illustration 1: http://no.wikipedia.org/wiki/Hoggorm

Illustration 2: http://no.wikipedia.org/wiki/Hoggorm

Illustration 3: http://www.edderkopper.net/Araneidae.html

Illustration 4: http://www.edderkopper.net/Forum/smf_1-1-11_install/index.php?topic=4308.0

Lindstedt, C, Lindström & L, Mappes, J 2009, 'Thermoregulation Constrains Effective Warning Signal Expression', Evoultion, vol.63, no.2, pp.469-478, viewed 26 April 2014, <http://www.jstor.org.elibrary.jcu.edu.au/ >

Bennett, AF 2004, 'Thermoregulation in African chameleons', International Congress Series, vol.1275, pp.234-241, viewed 26 April 2014, <http://www.sciencedirect.com.elibrary.jcu.edu.au/ >

Seasonal color change in animals

What do Arctic foxes, hares and ptarmigans have in common?

These animals are found up north in Europe and America/Canada, and they have adapted to a life in an environment that is highly affected by changes in weather from one season to another. During summer the sun can be hot, and the environment is composed of green vegetation, soil and rocky layers in between. In winter, the temperatures can go really low over long periods of time, especially in alpine areas. The winter can last for 6 to 8 months and with it comes great amounts of snow that paints the environment in white colors. For an animal living under such changing conditions, having one color throughout the year will make them really vulnerable. These animals mentioned, have together with several other species adapted two types of coats, one for winter and one for summer.

Winter coat is thick, long and white, and gives good protection and isolation against low temperatures and cold arctic winds. It also matches the background perfectly and provides a good camouflage. During summer the environment changes, and the coat also changes to match the background, and to make the animal more comfortable when the temperature rises. This time of year the coat gets more grey or brown depending on the species, and the coat gets shorter(if fur) and not so dense and warm(Harris 2009).

The obvious strategy behind this color change is camouflage and background matching. For example, a brown hare against a white background of snow would be a very easy target for an eagle soaring in the sky. Natural selection seems to favor the animals that match the background best. Animals that have the ability to match the changing background by producing different colors of fur or feathers, have a higher probability of surviving, and will through time reach a higher fitness level because they are less preyed upon. There is a reason why you in arctic climates can find the same color patterns in several very unrelated species of animals. They have all been shaped by the same harsh environment and faced the same challenges when it comes to blending in, so the white winter coat is a result of convergent evolution, an adaption to better fit in.

How and when do the animals change their coat? A research from 1970 on mountain hare in Scotland, gave researchers a clue about which mechanisms that lies beneath the color change. The shedding of fur is thought to be triggered by change in daylight – in other words daylengt(Flux 2009). When the days grow shorter, this will trigger release of hormones(Harris 2001) in the animal that leads to changes in colors and composition of the coat. Temperatures on the other hand will decide how fast this change will occur(Flux 2009). When days grow shorter during fall, the change of color can be postponed if the temperatures are high, and same can happen in spring if the weather are very cold, then the white fur might be shed later. On the other hand, if spring arrives early one year and it is really hot, they can shed their fur in a couple of days, compared to other times where they can use 2-3 weeks. (Flux 2009)

There are several animals that are found in the northern hemisphere that displays distinct winter and summer coats, some examples are: Species of hare and mouse, the barren ground caribou(not fully white winter coat though), the weasel(the ermine), the arctic fox, and the ptarmigan(grouse, bird).

This is a ptarmigan that you can find up in alpine areas in Norway. During winter this bird is displaying a wonderful winter coat. Photo: Per Ivar Somby.

Viewed 30 April 2014, <http://nrksuper.no/super/blog/dyr-i-vinterdrakt/ >

Same bird in summer coat:

Photo: Terje Kolaas

viewed 30 April 2014, <http://www.birdlife.no/naturforvaltning/nyheter/?id=1231 >

The weasel, also found in Norway, have a brown and white summer coat, but entirely white winter coat. Photo: Anne Elliott.

Viewed 30 April 2014, <http://nrksuper.no/super/blog/dyr-i-vinterdrakt/ >

Biography:

Flux, JEC 2009(date of publishing on internet- first ever published 1970), 'Colour change of Mountain hares (Lepus timidus scoticus) in north-east Scotland', Journal of Zoology, vol.162, no 3, pp. 345-358, viewed 30 April 2014, <http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1970.tb01270.x/pdf >

Harris, T 2001, HowStuffWorks.com(Discovery communications), Atlanta, US,viewed 30 April 2014,<http://animals.howstuffworks.com/animal-facts/animal-camouflage2.htm >

Distraction

Colors and patterns for distraction and escape:

Animals put a lot of time and energy trying to avoid being preyed upon, as examples they can camouflage themselves, or trying to make themselves less interesting, or advertise that they are distasteful or poisonous. But we all know that there are predators in these world, they live and they thrive, which means they must get food somehow. So what happens, if in despite of camouflage or other strategies to avoid attack, a predator spots something and decides to attack? Does this mean there is no escape? Of course there might be. Everyone knows that lots of animals have claws, teeth, and other defense mechanisms to fight of a predator physically, and some also chemically, like a bombarding beetle or a skunk. But did you also know that some animals rely on special colors and patterns as a distraction maneuver? Well, here are some ways animals can actually escape an attack without going into physical interactions and without being dangerous.

One of the most famous strategies is startle display(Wilson 2009). This means that an animal being attacked, suddenly show off some powerful and strong colors or patterns that will cause some kind of reaction in the predators behavior. Usually the flashing of color patterns causes the predator to hesitate for a moment, giving the prey some extra time, although maybe just a second or two, but enough to make an escape. Imagine that you are walking past a door, and someone is hiding behind it, and then suddenly jumps out in front of you shouting, the person doesn't need to be dangerous or be a treat to you at all, but you still will display some kind of reaction like freeze for a second or jump to the side to avoid that person. Basically, when something happens fast, which you don't see coming, your brain needs time to adjust and think about what happens and how you should react. This is kind of the same thing that happens when an animal suddenly goes from for example cryptic colors matching the background, til showing of all sorts of colors in a second. This is likely to be extra useful for animals that are slow or clumsy fliers, such as mantises and stick insects, because they need time to prepare for flight(Langridge 2009)

The peacock butterfly has cryptic colors when in a resting position, but if a threat appears, it will open its wings and flash its amazing colors.
From: <http://en.wikipedia.org/wiki/File:Inachis_io_bottom_side.jpg>, viewed 3 April 2014

 From: <http://www.warrenphotographic.co.uk/26028-peacock-butterfly>, viewed 3 April 2014.

Some patterns are proved to be especially good when it comes to creating a hesitation, and can even make the predator retreat. Eye spots are such patterns(Wilson 2009), they seem to be working great, and the pattern is found among many different animals, but is especially abundant among butterflies and moths. These eye spots are found on the wings, and is usually not visible when the butterfly or moth rests. But if in danger, the wings will be spread out, and suddenly a set of 'eyes' appear. The predator, in these cases often birds, will be very surprised and hesitate and might also pull back for a second. Sometimes the predator actually go for a retreat, and this is thought to be because the spots look like the eyes of an owl. And since owls are predators, many smaller animals then back off. Not only moths and butterflies display this pattern, also frogs, octopuses, stick insects, mantises and caterpillars display it, which seems to strengthen the theory of this strategy as being a successful one. It is obviously a feature that has convergently appeared in different groups of animals, and usually if something like this happens, it is because it has an advantage somehow.

This picture shows a Lo moth with eyespots similar to a big animal like an owl.
Picture from: < http://lepcurious.blogspot.com.au/2011/03/defenses-of-butterflies-eyespots.html > viewed 3 April 2014

Another trick some animals use, is displaying some kind of pattern or colors that look similar to a head or at least something that confuses the predator when it comes to which end is which(Wilson 2009). They might also conceal their real eyes in colors or stripes that makes the eyes less visible and this can create more confusion. Butterflies can for example have eyespots, something that looks like antenna, and a shape that may appear as a head on distance. The prinsiple behind this is to make the predator attack the side that is less vulnerable, and it also makes it possible to get away, because the predator will misjudge the direction the prey might be heading for an escape. Lots of animals can survive another day with a lost peace of their tail, but injuries on their anterior side will often be fatal(if they don't get eaten). Butterflies, fishes and centipedes are some animals that uses this technic to confuse predators. An animal that also uses this technic is a caterpillar that has eyespots making it look like a snakes head, fooling a predator in to believing that it is something entirely different than it actually is, which might scare a predator and make it retreat.

This picture show two caterpillars that has patterns on their head making them similar in appearance to a snake.
Picture from: < http://lepcurious.blogspot.com.au/2011/03/defenses-of-butterflies-eyespots.html > viewed 3 April 2014

This fish show a deflection display, drawing attention away from its head towards it's posterior end. Notice how the real eyes are goes almost unnoticed.
Picture from: <http://www.eplantscience.com/index/general_zoology/deflecting_an_attack.php>, viewed 3 April 2014

Although these technics mentioned seem to work in many cases, there are some drawbacks as well(Langridge 2009). If a predator don't use visual cues, like if the predator have bad/no vision or don't see all colors, it might not have any effect at all, so it comes down to which predator that actually hunts a particular prey.

Another effect you can find, is habituation, which means the predator is exposed to the flashing or the pattern several times and over time learn that this doesn't mean anything, or after a while learn to attack the real anterior end after several times of trial and failures. They get used to the display the prey puts up, and then the startling and frightening effect wears off. This means that it probably works best if the predator is a generalist.

Biography:

Wilson, C 2009, Animal behavior: Animal Defenses, Chelsea House, Infobase Publishing, United States.

Langridge, KV 2009, 'Cuttlefish use startle displays, but not against large predators',

Animal Behaviour, Vol.77, No.4, pp. 847-856, viewed 2 April 2014, < http://www.sciencedirect.com.elibrary.jcu.edu.au/ >.

Motion dazzle markings:

Animals have several strategies to avoid predation, and mimicry and camouflage are widely used, and seem to work well for lots of animals. There is one downside using these strategies though, and it is related to movement. When an animal moves, it is exposing itself, making it easy for a predator to spot it. This creates a huge challenge for animals that are moving around to find food sources, and is even more challenging as the animal increases in size, because it is then harder to hide, or make the body blend in with the background. To cope with this, it has been proposed that a good strategy to avoid predation might be something called motion dazzling. So what is this exactly?

Motion dazzle patterns are very bold and visible patterns, that are assumed to create confusion and mislead the predator. During experiments(Stevens, M, Yule, DH, Ruxton, GD 2008) scientists have proved such patterns to be efficient because they make it difficult for the predator to estimate speed, distance and direction. Patterns are proved to be more efficient if the speed increases, so it is likely to be more present in fast moving animals. If a predator- a lion, misjudges the distance to a zebra for example, this might lead to an attack ending in disaster. If a predator misjudges a distance, it might miss the target by centimeters to meters, depending on target, the patterns and the speed, but as long as misjudging is present, there is opportunities for the prey to escape, and this is likely the reason for why these patterns have evolved.

There hasn't been a lot of research on this subject, but there were a couple of researchers that worked with this and got supporting results for motion dazzling being efficient(Stevens, M, Yule, DH, Ruxton, GD 2008). They used a computer program to test if people were more or less likely to hit a target when the target wore stripes and zig- zag patterns, and they found that such patterns made it more difficult to succeed. Since human and vertebrate eyes work pretty much in the same fashion, it is likely that this can be transfered to nature as well.

There are found animals with these dazzling patterns among several taxa, including vertebrates, fishes, reptiles and some insects.

A highly debated animal within this area is the zebra. It has been believed for a long time that the stripes the zebra possesses are a good example of a motion dazzle pattern. Zebras are big animals, that are mostly found on grassland areas with open landscape where there is no place to hide. They have to move a lot during the day, which makes it even easier to detect them. Because camouflage is not really an option for these animals, it would make sense that the stripes would protect them against predators, making it harder to catch them due to misjudging as explained earlier. When they live in a herd, the stripes could even create more confusion. Focusing on one individual will be hard when all zebras have striped patterns that seem to blend in and mix with each other, the outline of an individual will then be hard to see. But one research project found little evidence for this being the case(Caro et al. 2014) when they looked at the distribution of zebras and big predators, and how efficiently the predators were at catching prey.

In general there is a lot of assumptions regarding this area, and little research done. It is hard to conclude if patterns we see are a result of evolution related to motion dazzling, or if there are entirely other reasons for the patterns we see. But it is obvious that some patterns can create confusion and misjugdgment, but if the bold stripes and zig-zag patterns are due to motion dazzle or not, is hard to tell.

The pictures below show examples of animals with bold or high contrast patterns:

Picture from <http://www.youtube.com/watch?v=cgdVVU8tBTQ>, viewed 8 April 2014.

Picture from <http://www.nytimes.com/2008/08/19/science/19obdazz.html?partner=rssnyt&emc=rss&_r=0>, viewed 8 April 2014  

Picture from <http://news.asiantown.net/r/33698/why-do-zebras-have-stripes-distinctive-markings-create-an-optical-illusion-that-dazzles-predators-and-masks-movement > viewed 8 April 2014

Biography:

Stevens, M, Yule, DH, Ruxton, GD 2008, 'Dazzle coloration and prey movement', Proceedings of the Royal Society: Biological science,vol. 275, no. 1651, pp 2639 – 2643, viewed 8 April 2014, <http://rspb.royalsocietypublishing.org/content/275/1651/2639.full >

Caro, T, Izzo, A, Reiner, AC, Walker, H, Stankowich, T 2014, 'The function of zebra stripes', Nature communications, vol. 5, no. 3535, viewed 8 April 2014 <http://www.nature.com/ncomms/2014/140401/ncomms4535/full/ncomms4535.html> 

Mimesis

Mimesis 

  

Although I might actually move a little bit away from my topic, today I will enlighten another part of mimicry. The reason I say it is not all about my topic, is because a part of this mimicry I'm going to write about, will also be related to shape and not just color, but since I have already mentioned mimicry related to warning(batesian and mullerian) I find it natural to say a few words about other ways that mimic can help an animal, not just by advertising. So this time I will dive deeper into Mimesis. 

  

Mimesis is actually related to camouflage, but not in the in way we would normally think about it. Camouflage is as earlier mentioned, a way to blend in so no one can spot you, basically you look like the background, or have a way of not getting detected. Whit mimesis you are detectable, just not as the individual or the species you actually are. The thing here is that an animal don't mind being seen, as long as it is not interesting for the observer, meaning, if a predator is after you, you mimic something the predator don't eat. The animal were a disguise, and in this way, it will be camouflaged in a broad sense. It is not necessarily for these animals to be poisonous or anything, they simply look like something that the observer don't pay attention to. 

  

Often animals that do this type of mimicry will resemble something in their environment that also make them blend in, like a stone, leaf, branch etc. This means other animals will see the mimicking animal, but not actually realize what it is looking at. That is why this is actually a kind of camouflage.  

  

A lot of insects do this kind of camouflaging mimicry, and some examples would be: 

  

• Stick insects: Shaped and colored like a stick. You could easily look at it without ever realizing it is a living animal. 
• Mantists: Some can look like flowers, with beautiful colors so no prey would notice it, and the prey would encounter the predator and realize everything when it is to late. 
• Katidyds: Shaped like a leaf with green colors, or they could look like an ant, so predators would leave it alone. 
• Fish, lobster, and other sea-creatures looking like corals, polyps and sea-grass. 

  

In a broad sense, you could look at mimesis as something that covers almost all kinds of mimicry, because it means resembling something, whether this resemblance has to do with color, shape, sounds, if it mimics a living object or not, and also it could include mimicking of behavior and special kinds of advertisement. This would then included batesian and mullerian mimicry, but in most cases mimesis just implies to being something that is not interesting, something that goes unnoticed, and therefor other types of mimicry is not included here, and would rather be grouped or included elsewhere. 

In this short movie you can see a lot of different animals living in the sea pretending it is something else that would not interest the predator, that is if it is preyed upon, or if it is a predator – pretending it is something that is not dangerous.

https://www.youtube.com/watch?v=ZMNfpb87pe8#t=75
viewed 1 March 2014.

Bibliography:

Wang,
L, Liu, Z, Wang, X, Shih,
C,
Zhao, Y, Engel, MS, & Ren, D 2010,
Ancient pinnate leaf mimesis among lacewings,
Proceedings of the National Academy of Sciences of the United States
of America, viewed 27 March 2014, <
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2941307/ >

Puetz, M 2002,

Mimesis,
The University of Chicago, Illinois, US, viewed 27 March 2014, <
http://csmt.uchicago.edu/glossary2004/mimesis.htm
>