Vanishing Wars: The Affect of Camouflage in Nature
Biology 342 Fall 2014
What Happens to Camouflage Over an Animal's Lifetime?
The camouflage of an animal can change for a few different reasons
Some animals have camouflage that changes as the animal ages
There are a few different varieties of animal that have a change in camouflage over the course of their lives. One such animal is the Madagascan Pink Winged Stick Insect, and is also know as the pink winged stick insect, (see photo on the left). While still in the egg, the Madagascan Pink Winged Stick Insect looks similar to a seed and can easily be overlooked by someone unfamiliar with the species. Once the egg hatches a small green stick insect emerges without wings. The young feed on the leaves of various plants including blackberries and raspberries. When the young sense danger they may either try to run away from the threat or clasp their front legs together and point them straight forwards along with their antennae while being completely still. Once the danger has passed they will resume their feeding. The stick insect quickly grows into an adult in less than half a year. Once they have finished growing their color changes to a characteristic light brown. It adopts the same defensive positions as the juveniles but is much more reminiscent of an actual stick. They are able to fly quite well and have bright pink wings that are about as long as 70 percent of their body length.
There are other species of walking sticks that have a camouflage pattern that changes significantly throughout the life of the animal. The Giant Prickly Walking Stick has juveniles that go through many different stages of camouflage. When their eggs are first laid ants smell them out as food and bring them to their nest. Once inside the outer layer is eaten away before the rest of the egg is dumped into the waster pile. Once the young hatch they begin to look and act similarly to ants. Because of their swift speed and appearance predators avoid them as they believe them to be obnoxious ants. Once the walking stick grows up it has grown slower and now looks more like a leaf.
Another type of animal that changes their camouflage as they age are flounders. Flounders are a variety of flatfish that live along the ocean floor. The adult flounder has a very distinct camouflage that causes it to appear to be a part of the ocean bottom. When a flounder lies against the bottom only the edges of the fish and eyes able to stand out from the sea floor, (see image on the left). This is a very effective form of camouflage as any predator that is highly dependent on its sight will have a hard time trying to locate these fish. Flounders also partially bury themselves in the sand in order to have a better chance of not being noticed. They are able to do this because the fish themselves have seemingly been turned into cartoon characters hit by a steamroller, even the eyes are now pointing towards the sky rather than against the sides like on most other fish. However flounders, and all flatfishes, do not start out this way. When a flatfish is born it looks like a regular fry, which is to say that it resembles the average fish, one eye on each side of the body. However as a flatfish begins to grow the body starts to flatten and the eyes begin to converge onto one side of the fish as the entire animal undergoes a partial metamorphosis.
Some animals have camouflage that changes with the seasons
In some animals that live in areas that have a high amount of snowfall over the winter there is a tendency for them to have camouflage that changes as the seasons change. One example of this type of camouflage can be found in the snowshoe hare. In the winter snowshoe hairs have a white fur coat that allows them to blend in well with their arctic environment, (see picture on the right). During the summer the snowshoe hare has a brown coloration with the only visible white being its underside. However as the seasons change, the snowshoe hair begins to lose its dark brown coloration and its fur begins to turn white. This ability to change their coat color as the winter approaches allows these rabbits to have an increased ability to hide from predators once the winter snow has fallen. Without this ability the snowshoe hair would easily standout in a snowy forest or field, making it a quick meal for any predator still active during the winter months.
There are a few other animals that have the ability to change color as the winter approaches such as the arctic fox, the ptarmigan and weasels. These animals all utilize this ability to stay hidden during the winter months because they are unable to either migrate to warmer climates or hibernate. This gives them an increased likelihood of surviving during the harsh winter conditions they face when a variety of hugnry mouths are out on patrol.
Some animals are able to change their camouflage at will
While chameleons may be the posterchild for animals that can change their color at will, there are many other species of animal that have the ability to perform this unique feat. One very interesting group of animals that are able to change their camouflage at will are cephlapods, (see photo on the right). Cephalopod means head foot and is an apt description for the animals that make up this class. Squids, octupi, and cuttlefish, and nautiluses are the different kinds of cephalopods that are found in the world's oceans. However the natiluses are unable to change their camouflage. The two main stuctures of a cephalopod are the tentacles and the mantle, which contains the head and vital organs. In squids and cuttlefish there is a hard stucture under the skin. This is referred to as the pen in squids while in cuttlefish it is refferred to as the cuttlebone. Octupi do not have a hard stucture under their skin like a pen or cuttlebone. These predatory animals hunt small fish and crustaceans using their powerful tentacles to hold on and break onry prey. Once prey has been snared it is ripped apart by the parrot like beak of these predatory invertebrates. Cephalopods are some of the most intelligent creatures known to mankind and are able to perform observational learning and can recognize different shapes and some have even been known to break onto fishing boats to eat crabs.
What is most remarkable about these animals, as it relates to our theme, is their ability to adapt their camouflage to virtually any environment. Octupi, squid and cuttlefish all have a unique type of cell known as a chromatophore. Chromatophores are able to change to any color and they allow these animals to blend in with any environment. These animals are able to fluidly change colors from bright reds to sandy tones in just a matter of seconds. (As seen in the photo on the left), cuttlefish can be virtually indistinguishable from their surroundings when they feel threatened or in dange. However both cuttlefish and octopuses are able to go one step further in their camouflage race, they can change the visible texture of their bodies to more closely match those of their surroundings. This is, to put it appropriately, a total game changer. Differently textured materials will have very different visual signatures and having the ability to change their bodies to match the textures of the objects that surround them is an advantage that these creatures have over not just other animals but even our best attempts to create camouflage that can change colors. If chamelons can be thought of as the poster child for the ability to chang camouflage, then cephalopods have to be the brain child behind it.
These figures on the right show how well cuttlefish are able to change their colors to match a background. Cuttlefish were placed into tanks which had their walls and bottoms covered in checkerboard patterns. Each checkerboard pattern had two distinct attributes which were the size of each square and the contrast between the color of each square. Researchers found that cuttlefish had trouble matching a background that had very little contrast between colors and very small squares. The top graph shows the cuttlefish pattern when the squares were at their largest, the middle shows when they were 30% smaller, and the bottom shows when they were 27% smaller than the middle graph. The decimal values show the level of contrast between the squares of a checkerboard background. Larger values indicate that the contrast was more distinct, such as the contrast between black and white is close to 0.80. As can be seen in the bar graphs there were two distinct trends in how the cuttlefish responded to the background. Cuttlefish began to stop attempting to match the different patterns when the squares became too small and when the contrast between the squares became too low, regardless of square size. The line graphs show the spectra, or light absorbance, for the cuttlefish skin across the different contrasts and square sizes. Each line shows cuttlefish patterns that were formed against checkerboards of different contrast values. As can be seen in these graphs, once the area of the skin being analyzed was large enough there was very little difference in the spectra between each checkerboard environment. What this means is that the cuttlefish has to use less energy to produce its pattern as the pattern becomes more grainy. The top graph For more information follow this link, Cuttlefish and Contrast.