Scientists have finally understood the reason why some tigers are born white. According to a study appearing in Current Biology the anomaly is due to a single change in a known pigment gene.
Shu-Jin Luo of China’s Peking University, Xiao Xu, Ruiqiang Li, and their colleagues say that although white tigers are now only found in captivity, their color is a completely natural occurrence and white and yellow tigers can both exist in the wild.
“The white tiger represents part of the natural genetic diversity of the tiger that is worth conserving, but is now seen only in captivity,” says Luo.
The researchers mapped the genomes of a family of 16 tigers living in Chimelong Safari Park, including both white and orange individuals. They then sequenced the individual genomes of the three parents in the family.
They found a pigment gene, called SLC45A2 which has already been associated with light colouration in Europeans and also animals like the horses, chicken and fish. This variant present in white tigers inhibits the red and yellow pigments but has no effect on black pigment. Thus, the reason the white tiger still shows its characteristic black stripes.
The researchers believe that a proper captive management program to maintain a healthy Bengal tiger population of both white and yellow tigers should be in place.
Historically, the white tiger has been known to roam the Indian subcontinent since 1500s but the last known free-ranging white tiger was shot in 1958 according to Luo.
He adds that records show many white tigers shot in the wild were adults proving that they are not fit to survive in the wild. In addition, their main prey species deers are color blind, making the predator as fearsome as the common yellow tigers.
The scientists also explains that white tigers in captivity show abnormalities like cross eyes but that is probably because of inbreeding and not because of their faulty genes.
With the genes identified the next step for the researchers is to find and explain the evolutionary mechanism that led to the birth of both white and orange/yellow tigers in the wild.