The color of animals can have a pigmentary or structural origin. Pigment color is the color provided by certain chemical compounds, called pigments . On the other hand, structural colors originate from microscopic surfaces that interfere with visible light by physical mechanisms, reflecting certain wavelengths and not others; Frequently, these structural colors—alone, or in combination with pigments, appear in the wings of butterflies or in the feathers of many birds—produce iridescent effects.
If we talk about colors by pigments, there are several among the animals that stand out. Eumelanin , which produces black or brown tones, pheomelanin , which produces yellow and ocher, or carotenoids , which produce orange, pink and red tones.
Given the breadth of coloration in the animal kingdom, the definition of albinism can change from species to species, but, in general, we say that an animal is albino when it has little or no pigmentation in the skin, eyes, and integumentary structures—hair, feathers or scales.
Albinism, a genetic condition
Albinism in animals —including humans— happens due to the inheritance of an altered copy of the gene responsible for regulating the production of pigments . Generally, the presence of a viable allele of that gene is sufficient for pigmentation to occur, so albinism is usually a genetic condition associated with recessive homozygosis , that is, in both copies of chromosomes, for it to occur albinism, the gene must be altered.
This implies not only that the mutation must occur—or be inherited—but that it must occur in both copies of chromosomes, those of paternal and maternal origin. So two individuals with normal pigments can have an albino child—if they both carry a mutated copy of the gene—but two albinos cannot have a normally pigmented child.
The expression of the genes that provide the color of the coat or skin is subject to the functioning of the gene that provides or does not provide the ability to have pigmentation. An albino organism can inherit from its parents the genes that code for a certain color pattern, and not express them because of albinism. And you can pass those genes on to your offspring, and if they’re not albino, they’ll express them normally like their grandparents did. This phenomenon, in which a gene dominates the expression of a different gene, which is not allelic with the previous one, is called epistasis .
The difference between albinism and leucism
Some animals have white fur, but have pigmented eyes, or more pinkish skin than an albino animal. Some forms of eumelanin can become so light that they appear as white pigmentation. This phenomenon is called leucism , and is different from albinism.
In an animal with leucism, pigments are expressed . Only these are so clear, that they come to look white. However, they can present other parts of the body pigmented with other shades —such as an arctic fox, which despite its white fur usually has quite dark eyes and the tip of its black tail.
In an animal with albinism, the coloration is white due to the absence of pigments, which makes it particularly sensitive to solar radiation, since it is the pigments of the skin, hair and eyes that protect us from its harmful effects .
Albino animals are therefore very prone to eye or skin problems.
An animal with leucism, however, does have pigmentation, albeit white, that protects it from sunlight.
Some animals with albinism
In addition to humans, albinism is a condition present in many animal species, although it is rare. Among aquarium fish it is usually more common, due to artificial selection for its particular attractiveness, since in an aquarium, light can be controlled to prevent damage.
Certain cases of particularly striking albinism, such as that of peacocks, are selected for their attractiveness. Cases of albinism have also been observed among reptiles, from crocodiles to pythons.
Among mammals, cases of albinism have been observed in dogs, cats, horses, and other domestic or livestock animals. Cases of albinism have also been found in zebras, porcupines, rats, mice, squirrels, rabbits, hedgehogs, pandas or kangaroos, and there are even cases of albino cetaceans.
Among the primates, there is an albino spider monkey that resides in the Barranquilla Zoo, Colombia, or Alba , the only known albino orangutan, who lives in a protected forest in Borneo.
One of the most famous cases of animals with albinism was Copito de Nieve , a gorilla brought from Río Muni, in Equatorial Guinea, in 1966, to the Barcelona Zoo. He was the only known albino gorilla in the world, and he died of skin cancer in 2003, at an estimated age of 39.
To date, no other gorilla with this condition has been found, not even among the multiple offspring left by Copito de Nieve .
References:
Fertl, D. et al. 2009. Albinism. In WF Perrin et al. (Eds.), Encyclopedia of Marine Mammals (Second Edition) (pp. 24-26). Academic Press. DOI: 10.1016/B978-0-12-373553-9.00006-7
McCardle, H. 2012. Albinism in Wild Vertebrates. NHS. 2020. Albinism. Nhs.Uk.
