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White & White – Animals without Colour
Whether you’re predator or prey, standing out in a crowd is probably Not A Good Thing. So why do some individuals lack the coloration that is the norm for their species?
The underground lifestyle of mole-rats enables them to escape many of the afflictions of albinism. Conspicuous coloration is of little consequence to their survival, and problems associated with poor vision are of no concern in the dark corridors they traverse.
According to mole-rat expert Nigel Bennett of the University of Pretoria, albinism in these rodents is very rare indeed. In his many years of research he’s come across only five cases, of which three – two common mole-rats and a Cape dune mole-rat – were caught in the Darling area of the Western Cape. He’s also aware of an albino highveld mole-rat snared by a greenskeeper at a Pretoria golf course and an albino Damara mole-rat that was born in captivity. “They seemed well integrated within their colonies,” says Bennett, “and all appeared to be in good physical condition.”
The Ancient Greeks had a word for white: leukos. Applied to animals, the modern English derivation, leucistic, describes them as white, or lacking the pigmentation that makes them immediately recognisable. That is probably why, when faced with an animal without colour, some people think they have discovered a new species.
Leucism is a general term for a wide range of conditions associated with an absence of pigmentation. As Sue Kidson, a professor at the medical school at the University of Cape Town, South Africa, explains, “there are at least 75 genes that play a role in pigmentation, and many variants. So there are a multitude of conditions that can cause a reduction in pigmentation.” In some cases, pigment cells may not be manufactured normally across the whole animal, resulting in an entirely white coat. In others, the pigments fail to develop properly only in patches, giving rise to a blotchy, piebald effect. Such conditions can be inherited but the results are unpredictable, either from one generation to another or in offspring of the same litter.
Leucism is a general term for a wide range of conditions associated with an absence of pigmentation.
The Romans, too, had a word for white: albus. The modern term ‘albino’ refers to animals that lack pigmentation in their skin, eyes or hair. Albinism is a recognised medical condition caused by a defect in the biochemical process that makes the skin pigment melanin. The characteristic eyes of albino animals resutt from the absence of melanin from both the iris and the cornea. Normally black, they appear red or pink because the underlying retinal blood vessels show through. Albinism occurs in two broad types: oculocutaneous, which affects pigmentation of the skin, hair and eyes; and ocular, which affects pigmentation only of the eyes.
Any vertebrate – mammal, bird, fish, reptile or amphibian can be an albino. In humans, the prevalence of albinism varies from about one in 4 000 to one in 15 000 throughout Africa, although in certain areas of Zimbabwe it affects as many as one in 1 000. Rates in other animals are poorly described. There is for example, only one recorded case of an albino gorilla. Named Snowflake, he was born in Equatorial Guinea and achieved fame during his years at Barcelona Zoo.
The white coloration in albino animals acts as a flag, almost certainly compromising the chances of survival for both predators and prey (although this is difficult to prove, as there are so few of them). The lack of pigmentation also causes problems with vision and increases the likelihood of skin cancer.
Text and Photo by Tim Jackson. Taken from the September 2009 editon of Africa Geographic.
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