Bengal Tiger

Verified Timeline

Lore & Background

White tigers have been recorded in India since the 16th century CE. The first white tiger was captured in 1915. A white tiger named Mohan was captured by the king of Rewa, Martand Singh, in 1951 from the forest of Mukundpur, Sidhi district, which is now part of the Sanjay Dubri Tiger Reserve. Many white tigers found in zoos around the world are the offspring of Mohan. According to Kailash Sankhala, the last white tiger ever seen in the wild was shot in 1958. White Bengal tigers are distinctive due to the color of their fur. The white fur is caused by a lack of the pigment pheomelanin, which is found in Bengal tigers with orange fur. When compared to orange Bengal tigers, the white Bengal tigers tend to grow faster and become heavier than the orange Bengal tiger. They also tend to be somewhat bigger, both at birth, and as adults. White Bengal tigers are fully grown when they are 2–3 years of age. White male tigers reach weights of 200 to 230 kilograms (440 to 510 lb) and can grow up to 3 meters (9.8 ft) in length. As with all tigers, the white Bengal tiger's stripes are like fingerprints, with no two tigers having the same pattern. The stripes of the tiger are a pigmentation of the skin; if an individual were to be shaved, its distinctive coat pattern would still be visible. For a white Bengal tiger to be born, both parents must carry the unusual gene for white colouring, which happens naturally only about once in 10,000 births. Dark-striped white individuals are well-documented in the Bengal tiger subspecies (Panthera tigris tigris) as well as having been reported historically in several other subspecies. Currently, several hundred white tigers are in captivity worldwide, with about one hundred being found in India. Their unique colouring has made them popular at zoos, and in entertainment showcasing exotic animals. Their rarity could be because the recessive allele is the result of a one-time mutation, or because white tigers lack adequate camouflage, reducing their ability to stalk prey or survive predation when it is a cub.

In Their Own Story

A white tiger's pale coloration is due to the lack of the red and yellow pheomelanin pigments that normally produce the orange coloration. This had long been attributed to a mutation in the gene for the tyrosinase (TYR) enzyme. A knockout mutation in this gene results in albinism, the ability to make neither pheomelanin (red and yellow pigments) nor eumelanin (black and brown pigments), while a less severe mutation in the same gene in other mammals results in selective loss of pheomelanin, the so-called Chinchilla trait. The white phenotype in tigers had been attributed to such a Chinchilla mutation in tyrosinase, and in the past white tigers were sometimes referred to as 'partial albinos'. While whole genome sequencing determined that such a TYR mutation is responsible for the white lion leucistic variant, a normal TYR gene was found in both white tigers and snow leopards. Instead, in white tigers, a naturally occurring point mutation in the SLC45A2 transport protein gene was found to underlie its pigmentation. The resultant single amino acid substitution introduces an alanine residue that protrudes into the transport protein's central passageway, apparently blocking it, and by a mechanism yet to be determined, this prevents pheomelanin expression in the fur. Mutations in the same gene are known to result in 'cream' coloration in horses, and play a role in the paler skin of humans of European descent. This is a recessive trait, meaning that it is seen only in individuals that are homozygous for this mutation, and that while the progeny of white tigers will all be white, white tigers can be also bred from colored Bengal tiger pairs in which each possesses a single copy of the unique mutation. Inbreeding promotes recessive traits and has been used as a strategy to produce white tigers in captivity, but this has also resulted in a range of other genetic defects. The stripe color varies due to the influence and interaction of other genes. Another genetic characteristic makes the stripes of the tiger very pale; white tigers of this type are called snow-white or "pure white". White tigers, Siamese cats, and Himalayan rabbits have enzymes in their fur which react to temperature, causing them to grow darker in the cold. At Bristol Zoo, a white tiger named Mohini was whiter than her relatives, who showed more cream tones. This may have been because she spent less time outdoors in the winter. Kailash Sankhala observed that white tigers were always whiter in Rewa State, even when they were born in New Delhi and returned there. "In spite of living in a dusty courtyard, they were always snow white." A weakened immune system is directly linked to reduced pigmentation in white tigers.

Reader's Guide

Outside of India, inbred white tigers have been prone to crossed eyes, a condition known as strabismus, due to incorrectly routed visual pathways in the brains of white tigers. When stressed or confused, all white tigers cross their eyes. Strabismus is associated with white tigers of mixed Bengal and Siberian ancestry. The only pure-Bengal white tiger reported to be cross-eyed was Mohini's daughter, Rewati. Strabismus is directly linked to the white gene and is not a separate consequence of inbreeding. The orange litter-mates of white tigers are not prone to strabismus. Siamese cats and albinos of every species which have been studied all exhibit the same visual pathway abnormality found in white tigers. Siamese cats are also sometimes cross-eyed, as are some albino ferrets. The visual pathway abnormality was first documented in white tigers in the brain of a white tiger named Moni after he died, although his eyes were of normal alignment. The abnormality is that there is a disruption in the optic chiasm. The examination of Moni's brain suggested the disruption is less severe in white tigers than it is in Siamese cats. Because of the visual pathway abnormality, by which some optic nerves are routed to the wrong side of the brain, white tigers have a problem with spatial orientation, and bump into things until they learn to compensate. Some tigers compensate by crossing their eyes. When the neurons pass from the retina to the brain and reach the optic chiasma, some cross and some do not, so that visual images are projected to the wrong hemisphere of the brain. White tigers cannot see as well as normal tigers and suffer from photophobia, like albinos. Other genetic problems include shortened tendons of the forelegs, club foot, kidney problems, an arched or crooked backbone and a twisted neck. Reduced fertility and miscarriages, noted by "tiger man" Kailash Sankhala in pure-Bengal white tigers, were attributed to inbreeding depression. A condition known as "star-gazing" (the head and neck are raised almost straight up, as if the affected animal is gazing at the stars), which is associated with inbreeding in big cats, has also been reported in white tigers. There was a 200 kg (450 lb) male cross-eyed white tiger at the Pana'ewa Rainforest Zoo in Hawaii, which was donated to the zoo by Las Vegas magician Dirk Arthur.

Did You Know?

• The white tiger is a leucistic morph of the tiger, typically the Bengal tiger, and has blue eyes.
• The first white tiger was captured in 1915, and a white tiger named Mohan was captured in 1951 by the king of Rewa, Martand Singh.
• For a white Bengal tiger to be born, both parents must carry the unusual gene for white colouring, which happens naturally only about once in 10,000 births.
• The white fur is caused by a lack of the pigment pheomelanin, and a naturally occurring point mutation in the SLC45A2 transport protein gene underlies its pigmentation.
• Outside of India, inbred white tigers have been prone to crossed eyes, a condition known as strabismus, due to incorrectly routed visual pathways in the brain.