White tiger's coat down to one change in a gene

Records of sightings in the wild on the Indian sub-continent date back to the 1500s

Chinese scientists have acquired new insights into how white tigers get their colouration.

The researchers have traced the cause to a single change in a gene known to drive pigmentation in a host of animals, including humans.

White tigers are a rare variant of the customary orange Bengal sub-species.

Today, they are found exclusively in captive programmes where the limited numbers are interbred to maintain the distinctive fur colour.

Shu-Jin Luo of Peking University and colleagues report in the journal Current Biology how they investigated the genetics of a family of tigers living in Chimelong Safari Park in Panyu, Guangzhou Province.

This ambush of tigers included both white and orange individuals.

The study zeroed in on the pigment gene called SLC45A2, which has long been associated with the light colouration seen in some human populations, and in a range of other animals including horses, chickens, and fish.

The team identified a small alteration in the white-tiger version of SLC45A2 that appears to inhibit the production of red and yellow pigments. This change has no effect on the generation of black pigment - explaining why the whites still have their characteristic dark stripes.

A number of the white tigers found in zoos have health issues, such as eyesight problems and some deformities.

However, Luo and colleagues say these deficiencies are a consequence of inbreeding by humans and that the white coats are in no way indicative of a more general weakness in the Bengal variant.

Establishing this fact means that re-introducing them to the wild under a carefully managed conservation programme might be worth considering.

"The last known free-ranging white tiger was shot in 1958, before which sporadic sightings were made in India," the researchers write.

"Reasons for the extinction of wild white tigers were likely the same as those accounting for the dramatic decline in wild tigers in general: uncontrolled trophy hunting, habitat loss, and habitat fragmentation.

"However, the fact that many white tigers captured or shot in the wild were mature adults suggests that a white tiger in the wild is able to survive without its fitness being substantially compromised."