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/ >