What causes the color of a mammal's fur?
The color of a mammal's fur are determined by the amount and intensity of melanin that it produces. Melanin is a pigment found in the skin, eyes and hair of mammals that is produced by cells within the skin called Melanocytes, through a process called melanogenesis. There are two types of melanin which are responsible for fur color: eumelanin and pheomelanin. Eumelanin is a dark pigment which results in black or brown colored fur, while pheomelanin is a red pigment which results in red or gold fur. White fur is the result of not producing eumelanin or pheomelanin in the fur.
Wild mammals have adapted specially colored and patterned fur which are the result of producing these pigments in different parts of their pelage and in varying intensities. Some animals produce both pigments in different parts of their body in varying intensities and patterns. For example, wild animals like wild foxes and wild rabbits form bands of brown/grey and red/gold fur. This is called agouti and provides camouflage against the dusty brown environments of their forest habitats (ADW:Hair). These type of camouflage hides them against the backdrop of their natural habitats and aids them in hunting and hiding from predators. Below is a slideshow showing just how well wild animals can blend into their environments.
Now that we know why animals use camouflage and what causes it, we can look into what process actually "tells" the animal to produce melanin in the specific amounts and patterns that they have. Well, this process is Melanogenesis which was mentioned earlier. Melanogenesis occurs within melanosomes of the melanocytes, and it involves the oxidation of the amino acid Tyrosine using the enzyme Tyrosinase into DOPAquinone. Tyrosine comes from the liver where
phenylalanine is converted to tyrosine, catalyzed by phenylalanine hrdoxylase (Melanin
Synthesis Pathway).
In melanogenesis, DOPAquinone then undergoes one of two reactions to produce either Eumelanin, a black pigment, or Pheomelanin, a red pigment. This process occurs in response to genetic instruction from the DNA of the animal (Nasr).
Therefore, we can see that it is the animal’s genes which "tell" the animal to produce a certain pigment, in a certain intensity and in a certain pattern (ADW:Hair).This is done by varying the production of eumelanin and pheomelanin to affect its intensity or using modifying genes to change the color of the pigment. Thereby, the production of eumelanin can result in hair colors ranging from shades of grey to shades of brown and the production of pheomelanin can result in hair color ranging from dark red to gold and even cream. Mammals with white fur either lack the genes which are responsible for the production of melanin (an in albinos), or they have specialized genes which inhibit all or part of the production of pheomelanin, but do not affect the production of eumelanin leaving color in the eyes, whereas albinos have red eyes due to the lack of both types of melanin (Dog Coat Color Genetics).
Special Camouflage
There are mammals which can change color for aided camouflauge in times when their normal fur color would not help them hide. These kinds of mammals largely consist of those which live in cold regions of the world such as the Arctic. Arctic mammals change colors when the seasons change. Normally, during spring and summer, these animals have coats of red, brown, or grey which usually blends in to their environments, but in the winter their coat changes to white to blend in with the snow. Examples of arctic mammals include the arctic hare, and the arctic fox. Because of their genes and hormones, during the winter, these animals stop producing melanin in their fur. Unlike most mammals which have genes which determine the phenotype of their hair for their lifetime, Arctic animals’ have genes that allow their colors to change to adapt to the changing seasons. The melanin inhibiting genes are triggered by hormones which are activated by the lengthening and shortening of the days during the changing seasons. A slideshow of Arctic animals and their color changes are shown below.
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