Black and White, the Perfect Combination
By Megan Spofford
Dressed to the nines – penguin countershading
Penguins are often referred to as “wearing tuxedos”; an anthropomorphism that describes how most penguins have black feathers on their back with white on their belly.
The tuxedo look of the penguin is known as countershading in the zoological field. Countershading describes how an animal is darker on the part of their body that faces the sun, and is lighter on the part that faces away from it (an example of this can be seen in the image above). It is important to remember that countershading only describes the coloration pattern of an animal, and not to use the term to define what it does for the animal.
Countershading provides penguin camouflage
The evolutionary purpose of countershading is highly debated, but it is most widely believed to function as a type of crypsis when a penguin is in the water. Crypsis is defined as a type of camouflage that protects an animal from predation. There are arguments for which category of crypsis it may fall under: either self-shadow concealment, or background matching. Self-shadow concealment essentially makes the penguin appear as a flat image, and potentially harder to distinguish from other things typically found in the environment, like rocks or ice. Background matching is where the penguin gets lost in its surroundings, because they look identical.
It might stretch your imagination to think of a penguin being camouflaged in open water, however, marine habitats are the best at providing optimal lighting for a countershaded animal to blend in. When an animal is in the water, the light source is always directly overhead, making lighter colored objects closer to the surface harder to distinguish. When looking downwards, the ocean continually darkens, so dark objects would be obscured in this area. Because many natural penguin predators are strictly marine animals, it would make sense that they evolved feather colors that would make it harder for those predators to see them no matter where they happen to be located in the water. It is also beneficial for the penguin to be countershaded so that they themselves can prey upon fish and crustaceans!
Fossil evidence for the countershading hypothesis
The idea of countershading for camouflage has intrigued zoologists, artists, and militarists (who utilized the concept for weapons and bomber planes) for years. There are some proponents, however that believe the color of penguin feathers may be attributed to other factors, and the evidence for this is based heavily on the findings of a fossil from an extinct penguin in Peru.
Scientists were able to determine the color of feathers of the giant, extinct penguin despite degradation. They did this by examining melanosomes in the feather under a microscope, and it showed that they were a reddish color, instead of black.
Melanosomes are the organelles which create, store, and move melanin pigments in animal tissue. Melanin can come in one of two forms: eumelanin which has an oblong shape and accounts for darker pigmentation, and pheomelanin which is shorter and rounder (like an oval) and accounts for lighter pigmentation. In a comparison of feather color based on melanin, the fossil showed that it was colored by pheomelanin, while existing penguins are colored by eumelanin.
What does melanin do, and what could that have to do with the color pattern of extant penguins?
There are a few different reasons eumelanin might have been triggered to be produced. In order to determine why this occurred in modern day penguins, we have to take a look at the environmental conditions that foster its development.
One that most of us are familiar with is its protective properties from harmful UV radiation. When skin, or feather tissue, is exposed to high levels of UV radiation, eumelanin is produced to block those rays, and thus becomes darker. For penguins that spend time at the equator where UV exposure occurs the most, they would need this melanin protection to keep from developing cancers. Obviously, the ventral (belly) side of a penguin is not exposed to UV radiation while swimming, which is why it would be lighter than the dorsal (back) side that is exposed.
Eumelanin has a molecular structure that is resistant to injury and breakage. Having eumalenain in the majority of your feathers would be beneficial for an animal that moves around on jagged ice formations, or has a high amount of drag load placed on their feathers while swimming speedily, like a penguin.
Further benefits of darker melanin are that it limits blinding glare (when light reflects off of a surface and affects vision), and it helps an animal camouflage into its surroundings in certain types of light (as discussed above!)
So, was eumelanin in feathers adapted mainly for camouflage purposes, or did it become a staple of modern day penguin genetic make-up for one of the other reasons, and it just so happens to also aid in crypsis? Researchers continue to test hypotheses to solve the mystery about the function of the countershaded penguin, so maybe one day soon we will have a definitive answer!
A blend of tuxedo and camo. Penguins are amazing animals. Like this story? Have a story of your own? Leave a comment below. And please help us to continue to provide you with penguin news articles by donating to Penguins International.
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Britannica, The Editors of Encyclopaedia. “Melanin.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., https://www.britannica.com/science/melanin.
Clarke, Julia A., et al. “Fossil Evidence for Evolution of the Shape and Color of Penguin Feathers.” Science, American Association for the Advancement of Science, 12 Nov. 2010, https://science.sciencemag.org/content/330/6006/954.full.
Rowland, Hannah M. “From Abbott Thayer to the Present Day: What Have We Learned about the Function of Countershading?” Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, The Royal Society, 27 Feb. 2009, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2674085/.
Stevens, Martin. “Animal Camouflage.” Google Books, Cambridge University Press, 7 July 2011, https://books.google.com/books?id=10TCvK-9v70C&pg=PA9&lpg=PA9&dq=ssc+camouflage&source=bl&ots=Kwy7skUjOm&sig=ACfU3U0X7ZZMAjFslKA_aAT05Z1-S3IgGA&hl=en&ppis=_c&sa=X&ved=2ahUKEwjzteO38K7lAhVOnJ4KHYYNCeMQ6AEwD3oECAkQAQ#v=onepage&q=ssc camouflage&f=false.