By David Nashed
We have all heard of camouflage, whether it be from an episode of National Geographic, or from our elementary school science teacher. However, despite being a topic of frequent discussion, not many are familiar with how camouflage actually works. In this article, we’ll be taking a look at how camouflage works, as well as how it benefits animals living in the wildlife.
Camouflage is, at its essence, a defence mechanism that living organisms use to better hide themselves within their environment. This is done to mask their location, identity, and movements. However, camouflage is a rather broad term, as there isn’t just one type of camouflage; there are actually two!
The first form of camouflage is the most basic one, and refers to organisms born with natural genetic markings that suit their environment. Arctic hares, arctic foxes, and leafy sea dragons are all great examples of organisms that utilize this type of camouflage. Their natural “skin” (fur and scales) have adapted over time to more suitable colours and patterns for their environment. This case of camouflage is purely genetic, and often takes generations to develop.
Despite its relative simplicity, this form of camouflage is crucial for the survival of the previously mentioned organisms.
Arctic hares use their white pelts to blend into the arctic tundra, which allows them to avoid predators. Leafy sea dragons use their adapted colours to blend in with nearby vegetation and coral for the exact same reason. Arctic foxes are slightly different, as while they do use their camouflage to avoid predators, they also use it to mask their movements while hunting prey.
The second, and much more complex form of camouflage, refers to organisms who constantly change their colour/pattern to suit their current environment. This is a much more active form of camouflage, and is most commonly seen in chameleons and cephalopods (squids, octopi). The science behind this type of camouflage is very intriguing, and relates to physics, biology, and chemistry.
Chameleons have two layers of superposed iridophore cells— iridescent cells that contain pigment and reflect light. These iridophore cells are what allow chameleons to change their colours, seemingly at a moment’s notice. Iridophore cells contain nanocrystals of different sizes, shapes, and organizations, which play a key role in the chameleons' dramatic color shifts.
Essentially, chameleons can change the arrangement of the upper iridophore cell layer by relaxing or exciting their skin, which leads to a change in color.
Michel Milinkovitch, a professor of genetics and evolution at the University of Geneva, said the following: "When the skin is in the relaxed state, the nanocrystals in the iridophore cells are very close to each other — hence, the cells specifically reflect short wavelengths, such as blue."
This changes, however, when the chameleon becomes excited, for the skin becomes excited as well, causing the distance between nearby nanocrystals to increase. As a result of this, the iridophore cells selectively reflect longer wavelengths, such as orange and red.
Chameleons also possess three other cells under their skins; xanthophores which contain yellow pigment, erythrophores which contain red pigment, and melanophores which contain melanin.
These cells release pigment whenever the chameleon needs to produce a new colour. This process is vital for producing colours such as yellow and purple.
Now, let’s move on to cephalopods. Similarly to chameleons, some cephalopods use iridophores to camouflage themselves.
Others however have special cells called chromatophores located under their skin. Every cephalopod has thousands of chromatophores, with each one containing a unique pigment.
These chromatophores are connected to the cephalopod’s nervous system, and can be either contracted or expanded by the cephalopod’s muscular controls. These contractions depend on what colour the cephalopod wants to produce, as the more expanded the cell is, the more visible the pigment is.
For example, if a cephalopod wanted its skin to be red, it would expand the chromatophores that contained red pigment. Once it no longer needed to be red, it would relax those chromatophores.
In conclusion, camouflage is an incredibly interesting biological phenomenon which can be achieved through two different methods. It is an amazing survival tactic which has been developed by dozens of organisms, and has contributed to the survival of said organisms. It also highlights how chemistry, biology, and physics are present in nature itself.
Questions:
Q: What is the main difference between iridophores and chromatophores?
A: Iridophore cells rely primarily on reflecting light to produce wavelengths of different colour. These wavelengths are what give organisms with iridophores, such as chameleons, their colour. Chromatophores on the other hand rely on muscle contractions to increase the visibility of specific pigments, which then give the organism’s skin the desired colour.
Q: How long does it take for organisms to develop natural camouflage?
A: Unsurprisingly, it takes an incredible amount of time for any organism to develop any lasting adaptation. Scientists currently believe that it takes approximately one million years for any species to develop natural camouflage.
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