Leucism (a.k.a. achromia) is a state of reduced pigmentation that can occur in individuals of almost all species of animals. Leucistic animals can display a range of colors, depending on whether they lack the pigment eumelanin, which is black or brown, and/or phaeomelanin which is yellow or red.
The animal's skin may appear pigments or pink; its fur, feathers or scales may be red, orange, beige, blond or pure white. However leucistic animals always have normally colored eyes--which is the easiest way to distinguish pale leucistic animals from albinos.
Leucism is produced by the expression of a single recessive gene. Partial expression of leucism, where some parts of the animal have normal coloring, can lead to an animal having a pied or spotted appearance.
Overall leucism tends to be a disadvantage to an animal. They lose the function advantages of coat marking such as camouflage. Leucistic zebra finch chicks lack the 'gape marking' that encourages the parents to feed them, leading the parents to favor normally colored chicks when food sources are limited.
Below is a collection of some of the more interesting sightings of leucistic animals shoing how it effects almost all species and produces a range of different patterns and coloration.
- Perhaps the first leucistic elepphant seal reported was seen on Prion Island (South Georgia) in 2003.
- In 2004 another presumed leucistic pale-colored female was sighted at Marion Island.
- A number of leucistic Antarctic fur seals have been spotted, including one that was piebald--as described in this report (2008). Single leucistic specimen of the same species had been previously reported in South Georgia and the sub-Antarctic Marion island. The individuals seen are often juveniles which suggests that they rarely survive to maturity.
- The young female elepant seal pictured to the right was spotted in 2009.
- White lions are described being first sighted variously in 1928 or the 1940s. They are popular exhibits in zoos. Some groups are advocating protection of white lions in the wild, but they are not recognized as a species and so cannot be given most designations of protection separate from other color morphs.
- White lion cubs have been reported in a number of African wildlife reserves, but they rarely survive into adulthood. This may be because their pale color makes them less effective hunters (Turner et al 2015).
- White tigers (who retain their black stripes) are not a separate species, but another case of leucistic coloring.
In birds leucism is defined as a lack (or partial lack) of eumelanin and phaomelanin in the feathers, although the soft tissues are often at least partially pigmented.
- A number of the barnacle geese of the Solway Firth (United Kingdom) display leucanism.
- This Adele penguin (see right, native of Antartica, sighted 2008) is one of many penguins from a range of species that display leucism.
- This leucistic sandhill crane was photographed in 2008 at Ewing Bottoms, Indiana.
Other examples of leucistic birds include:
- American Robin (Ontario, 2007)
- Blue tit
- Prairie Chicken (2012)--Particularly striking with its distinct orange markings.
- Puffin (UK, 2010)
- Ruby-throated hummingbird
Leucistic animals retain pigment to different degrees. Partial leucism can lead to specific areas of the body being white and others retain full normall coloration such as with the crow shown right, or this squirrel who is whie colored only on the tail.
While sometimes a harmless variation, leucism is generally something of a disadvantage to the affected animals. These paler animals are normally more visually conspicuous and may lack important species-specific patterns, Therefore leucism may expose them to predators or sunburn, and or put them at a disadvantage in hunting or attracting mates.
On this basis, the evidence that leucism is becoming more common is concerning. Leucism is an indicator associated with inbreeding, and may be an indications that many wild species are dwindling in number and become less genetically heterogeneous, and perhaps less robust in their health and ability to adapt to changes in their environment and climate. As such it may be a precursor to sudden crashed in the populations of wild animals when new challenges exceed their ability to adapt.
Acevedo, J., Torres, D., & Aguayo-Lobo, A. (2009). Rare piebald and partially leucistic Antarctic fur seals, Arctocephalus gazella, at Cape Shirreff, Livingston Island, Antarctica. Polar Biology, 32(1), 41-45.
de Bruyn, P. N., Pistorius, P. A., Tosh, C. A., & Bester, M. N. (2007). Leucistic antarctic fur seal Arctocephalus gazella at marion island. Polar Biology, 30(10), 1355-1358.
Hofmeyr, G. G., Bester, M. N., & Kirkman, S. P. (2005). Leucistic Antarctic fur seals at Bouvetøya. Polar Biology, 29(1), 77-79.
Turner, J. A., Vasicek, C. A., & Somers, M. J. (2015). Effects of a colour variant on hunting ability: the white lion in South Africa. Open Science Repository Biology, (open-access), e45011830.
van Grouw H (2006). Not every white bird is an albino: sense and nonsense about colour aberrations in birds. Dutch Birding [pdf]