White tiger
From Wikipedia, the free encyclopedia
For other uses, see White tiger (disambiguation).
The white tiger is a recessive mutant of the Bengal tiger, which was reported in the wild from time to time in Assam, Bengal, Bihar and especially from the former State of Rewa.[1]
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[edit]Color comparison
Compared to normal coloured tigers without the white gene, white tigers tend to be larger, both at birth and as fully grown adults.[2] Kailash Sankhala, the director of the New Delhi Zoo in the 1960s, said "one of the functions of the white gene may have been to keep a size gene in the population, in case it's ever needed."[3] Dark-striped white individuals are well-documented in the Bengal Tigersubspecies, also known as the Royal Bengal or Indian tiger (Panthera tigris tigris or P. t. bengalensis), and may also have occurred in captive Siberian Tigers[citation needed] (Panthera tigris altaica), as well as having been reported historically in several other subspecies.[citation needed]
Currently, several hundred white tigers are in captivity worldwide, with about one hundred being found in India. Nevertheless, their population is on the increase. The modern white tiger population includes both pure Bengals and hybrid Bengal–Siberians, however, it is unclear whether the recessive white gene came only from Bengals, or if it also originated from Siberian ancestors.
The unusual coloration of white tigers has made them popular in zoos and entertainment showcasing exotic animals. German-American magicians Siegfried & Roy became famous for breeding and training two white tigers for their performances, referring to them as "royal white tigers", the white tiger's association with the Maharaja of Rewa.
Rewa Maharaja Martand Singh first observed male white tiger Mohan during his visit to Govindgarh jungle at Rewa, Madhya Pradesh, India. After hunting for months, he was able to capture the first living white tiger seen in nature. With help from official veterinary experts, he unsuccessfully tried to breed the white tiger with colored female tigers. Eventually, however, he succeeded in creating a second generation of white tigers. In time, it expanded around the world.
[edit]White Siberian Tigers
A white tiger is caused by the homozygous occurrence of a recessive allele in the genome. Estimations show that around one in 10,000 wild Bengal tiger births will result in a white tiger. The existence of white Siberian tigers has not been scientifically documented, despite occasional unsubstantiated reports of sightings of white tigers in the regions where wild Siberian tigers live. It may be that the white mutation does not exist in the wild Siberian tiger population: no white Siberian tigers have been born in captivity, despite the fact that the subspecies has been extensively bred during the last few decades (with much outbreeding between the different Siberian lineages for purposes of conservation genetics); a recessive allele should occasionally turn up in a homozygous state during such breeding, and in this particular case yield white tigers from normally-colored parents, but no such animals have been reported.
The famous white Siberian tigers found in captivity are actually not pure Siberian tigers. They are instead the result of Siberian tigers breeding with Bengal tigers. The gene for white coating is quite common among Bengal tigers, but the natural birth of a white Bengal tiger is still a very rare occasion in the wild, where white tigers are not bred selectively.
The white tiger is not considered a tiger subspecies, but rather a mutant variant of the existing tiger subspecies. If a pure white Siberian tiger were to be born, it would therefore not be selectively bred within the tiger conservation programs. It would, however, probably still be selectively bred outside the program in an effort to create more white Siberian tigers. Due to the popularity of white tigers, they are used to attract visitors to zoos.
[edit]Stripeless white tigers and golden tabby tiger
An additional genetic condition can remove most of the striping of a white tiger, making the animal almost pure white. One such specimen was exhibited at Exeter Change in England in 1820, and described by Georges Cuvier as "A white variety of Tiger is sometimes seen, with the stripes very opaque, and not to be observed except in certain angles of light."[4] Naturalist Richard Lydekkersaid that, "a white tiger, in which the fur was of a creamy tint, with the usual stripes faintly visible in certain parts, was exhibited at the old menagerie at Exeter Change about the year 1820."[5]Hamilton Smith said, "A wholly white tiger, with the stripe-pattern visible only under reflected light, like the pattern of a white tabby cat, was exhibited in the Exeter Change Menagerie in 1820.", andJohn George Wood stated that, "a creamy white, with the ordinary tigerine stripes so faintly marked that they were only visible in certain lights." Edwin Henry Landseer also drew this tigress in 1824.
The modern strain of snow white tigers came from repeated brother–sister matings of Bhim and Sumita at Cincinnati Zoo. The gene involved may have come from a Siberian tiger, via their part-Siberian ancestor Tony. Continued inbreeding appears to have caused a recessive gene for stripelessness to show up. About one fourth of Bhim and Sumita's offspring were stripeless. Their striped white offspring, which have been sold to zoos around the world, may also carry the stripeless gene. Because Tony's genome is present in many white tiger pedigrees, the gene may also be present in other captive white tigers. As a result, stripeless white tigers have appeared in zoos as far afield as the Czech Republic, Spain and Mexico. Stage magicians Siegfried & Roy were the first to attempt to selectively breed tigers for stripelessness; they owned snow-white Bengal tigers taken from Cincinnati Zoo (Tsumura, Mantra, Mirage and Akbar-Kabul) and Guadalajara, Mexico (Vishnu and Jahan), as well as a stripeless Siberian tiger called Apollo.[6]
In 2004, a blue-eyed, stripeless white tiger was born in a wildlife refuge in Alicante, Spain. Its parents are normal orange Bengals. The cub was named Artico ("Arctic").
Stripeless white tigers were thought to be sterile until Siegfried & Roy's stripeless white tigress Sitarra, a daughter of Bhim and Sumita, gave birth. Another variation which came out of the white strains were unusually light-orange tigers called "golden tabby tigers". These are probably orange tigers which carry the stripeless white gene as a recessive. Some white tigers in India are very dark, between white and orange.
[edit]Genetics
A white tiger's pale coloration is caused by the presence of a recessive gene. Another geneticcharacteristic makes the stripes of the tiger very pale; white tigers of this type are called snow-white or "pure white". White tigers do not constitute a separate subspecies of their own and can breed with orange ones. Although, assuming the orange parent is heterozygous dominant for the recessive gene, all of the resulting offspring will be heterozygous for the recessive white gene, and their fur will be orange. The only exception would be if the orange parent was itself already a heterozygous tiger, which would give each cub a 50% chance of being either double-recessive white or heterozygous orange. If two heterozygous tigers (or heterozygotes) breed, on average 25% of their offspring will be white, 50% will be heterozygous orange (white gene carriers) and 25% will be homozygous orange, with no white genes. In the 1970s a pair of heterozygous orange tigers named Sashi and Ravi produced 13 cubs in Alipore Zoo, of which 3 were white.[7] If two white tigers breed, 100% of their cubs will be homozygous white tigers. A tiger which is homozygous for the white gene may also be heterozygous or homozygous for many different genes. The question of whether a tiger is heterozygous (a heterozygote) or homozygous (a homozygote) depends on the context of which gene is being discussed. Inbreeding promotes homozygosity and has been used as a strategy to produce white tigers.
White tigers are not albinos: true albino tigers would not have stripes. Even the "stripeless" white tigers have very pale stripes. Confusion has arisen due to the misidentification of the so-called chinchilla gene (for white) as an allele of the albino series[clarification needed]: publications prior to the 1980s refer to it as an albino gene[citation needed]. The mutation is recessive to normal colour, which means that two orange tigers carrying the mutant gene may produce white offspring, and white tigers bred together will produce only white cubs. The stripe colour varies due to the influence and interaction of other genes.
While the inhibitor ("chinchilla") gene affects the colour of the hair shaft, there is a separate "wide-band" gene affecting the distance between the dark bands of colour on agouti hairs.[8] An orange tiger who inherits two copies of this wide-band gene becomes a golden tabby; a white who inherits two copies becomes almost or completely stripeless. Inbreeding allows the effect of recessive genes to show up, hence the ground and stripe colour variations among white tigers.
As early as 1907, naturalist Richard Lydekker doubted the existence of albino tigers.[9] However, we do have a report of true albinism: in 1922, two pink-eyed albino cubs were shot along with their mother at Mica Camp, Tisri, in the Cooch Behar district, according to Victor N. Narayan in a "Miscellaneous Note" in the Journal of the Bombay Natural History Society. The albinos were described as sickly-looking sub-adults, with extended necks and pink eyes.
White tigers, Siamese cats, and Himalayan rabbits have enzymes in their fur which react to temperature, causing them to grow darker in the cold. A white tiger named Mohini was whiter than her relatives in the Bristol Zoo, who showed more cream tones. This may have been because she spent less time outdoors in the winter.[3] White tigers produce a mutated form of tyrosinase, an enzyme used in the production of melanin, which only functions at certain temperatures, below 37 °C (99 °F). This is why Siamese cats and Himalayan rabbits are darker on their faces, ears, legs, and tails (the colour points), where the cold penetrates more easily. This is called acromelanism, and other cats breeds derived from the Siamese, such as the Himalayan and the snowshoe cat, also exhibit the condition.[10] 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."[7] A weakened immune system is directly linked to reduced pigmentation in white tigers.
[edit]Genetic defects
Outside of India, white tigers have been prone to crossed eyes, a condition known as strabismus, an example of which is "Clarence the cross-eyed lion",[11] due to incorrectly routed visual pathways in the brains of white tigers. When stressed or confused, all white tigers cross their eyes[citation needed]. Strabismus is associated with white tigers of mixed Bengal x 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.[12][13][14] The orange littermates 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 called 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 of the 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.[15]
Other genetic problems include shortened tendons of the forelegs, club foot, kidney problems, arched or crooked backbone and twisted neck. Reduced fertility and miscarriages, noted by ”tiger man” Kailash Sankhala in pure-Bengal white tigers were attributed to inbreeding depression.[7] A condition known as "star-gazing", which is associated with inbreeding in big cats, has also been reported in white tigers.[15] Some of the white tigers born to North American lines have bulldog faces with a snub nose, jutting jaw, domed head and wide-set eyes with an indentation between the eyes. However, some of these traits may be linked to poor diet rather than inbreeding.
There is a 450 lb (200 kg) male cross-eyed white tiger at the Pana'ewa Rainforest Zoo in Hawaii, which was donated to the zoo by Las Vegasmagician Dirk Arthur.[16] There is a picture of a white tiger which appears to be cross-eyed on just one side in Siegfried & Roy's bookMastering The Impossible. A white tiger, named Scarlett O'Hara, who was Tony's sister, was cross-eyed only on the right side.
A male white tiger named Cheytan, a son of Bhim and Sumita born at the Cincinnati Zoo, died at the San Antonio Zoo in 1992 from anaesthesia complications during a root canal. It appears that white tigers also react strangely to anaesthesia. The best drug for immobilizing a tiger is CI 744, but a few tigers, white ones in particular, undergo a re-sedation effect 24–36 hours later.[17] This is due to their inability to produce normal tyrosinase, a trait they share with albinos, according to zoo veterinarian David Taylor. He treated a pair of white tigers from the Cincinnati Zoo at Fritz Wurm's safari park in Stukenbrock, Germany, for salmonella poisoning, which reacted strangely to the anaesthesia.[18]
Mohini was checked for Chédiak-Higashi syndrome in 1960, but the results were inconclusive.[19][20] This condition is similar to albino mutations and causes bluish lightening of the fur colour, crossed eyes, and prolonged bleeding after surgery. Also, in the event of an injury, the blood is slow to coagulate. This condition has been observed in domestic cats, but there has never been a case of a white tiger having Chédiak-Higashi syndrome. There has been a single case of a white tiger having central retinal degeneration, reported from the Milwaukee County Zoo, which could be related to reduced pigmentation in the eye.[19][21] The white tiger in question was a male named Mota on loan from the Cincinnati Zoo.
There is a myth that white tigers have an 80% infant mortality rate. However, the infant mortality rate for white tigers is no higher than it is for normal orange tigers bred in captivity. Cincinnati Zoo director Ed Maruska said: "We have not experienced premature death among our white tigers. Forty-two animals born in our collection are still alive. Mohan, a large white tiger, died just short of his 20th birthday, an enviable age for a male of any subspecies, since most males live shorter captive lives. Premature deaths in other collections may be artifacts of captive environmental conditions... In 52 births we had four stillbirths, one of which was an unexplained loss. We lost two additional cubs from viral pneumonia, which is not excessive. Without data from non-inbred tiger lines, it is difficult to determine whether this number is high or low with any degree of accuracy."[19] Ed Maruska also addressed the issue of deformities: "Other than a case of hip dysplasia that occurred in a male white tiger, we have not encountered any other body deformities or any physiological or neurological disorders. Some of these reported maladies in mutant tigers in other collections may be a direct result of inbreeding or improper rearing management of tigers generally."[19]
[edit]Inbreeding and outcrossing
Because of the extreme rarity of the white tiger allele in the wild,[7] the breeding pool was limited to the small number of white tigers in captivity. According to Kailash Sankhala, the last white tiger ever seen in the wild was shot in 1958.[7][22][23] Today, there is such a large number of white tigers in captivity that inbreeding is no longer necessary. A white Amur tiger may have been born at Center Hill and has given rise to a strain of white Amur tigers. The white tiger pictured on the right is at the ZooParc de Beauval in France, and came from Center Hill. A man named Robert Baudy realized that his tigers had white genes when a tiger he sold toMarwell Zoo in England developed white spots, and bred them accordingly.[24] The Lowry Park Zoo in Tampa Bay has four of these white Amur tigers, descended from Robert Baudy's stock.
It has also been possible to expand the white-gene pool by outcrossing white tigers with unrelated orange tigers and then using the cubs to produce more white tigers. The white tigers Ranjit, Bharat, Priya and Bhim were all outcrossed, in some instances to more than one tiger. Bharat was bred to an unrelated orange tiger named Jack from the San Francisco Zoo and had an orange daughter named Kanchana.[25] Bharat and Priya were also bred with an unrelated orange tiger fromKnoxville Zoo, and Ranjit was bred to this tiger's sister, also from Knoxville Zoo. Bhim fathered several litters with an unrelated orange tigress named Kimanthi at the Cincinnati Zoo. Ranjit had several mates at the Omaha Zoo.[26]
The last descendants of Bristol Zoo's white tigers were a group of orange tigers from outcrosses which were bought by a Pakistani senator and shipped to Pakistan. Rajiv, Pretoria Zoo's white tiger, who was born in the Cincinnati Zoo, was also outcrossed and sired at least two litters of orange cubs at Pretoria Zoo. Outcrossing is not necessarily done with the intent of producing more white cubs by resuming inbreeding further down the line.
Outcrossing is a way of bringing fresh blood into the white strain. The New Delhi Zoo loaned out white tigers to some of India's better zoos for outcrossing, and the government had to impose a whip to force zoos to return either the white tigers or their orange offspring.
Siegfried & Roy performed at least one outcross.[27] In the mid-1980s they offered to work with the Indian government in the creation of a healthier strain of white tigers. The Indian government reportedly considered the offer;[28] however, India had a moratorium on breeding white tigers after cubs were born at New Delhi Zoo with arched backs and clubbed feet, necessitating euthanasia.[28] Siegfried & Roy have bred white tigers in collaboration with the Nashville Zoo.
[edit]Popular culture
White tigers appear frequently in literature, video games, television and comic books. Such examples include the Swedish rock band Kent, which featured a white tiger on the cover of their best-selling album Vapen & ammunition in 2002. This was a tribute to the band's home townEskilstuna, as the local zoo in town had white tigers from the Hawthorn Circus as its main attraction. The white tiger has also been featured in the video for the song "Human" by the popular American synth-rock band The Killers. White Tiger is also the name of an American glam metal band from the 1980s.
Aravind Adiga's novel The White Tiger won the Man Booker Prize in 2008.[29] The central character and narrator refers to himself as "The White Tiger". It was a nickname given to him as a child to denote that he was unique in the "jungle" (his hometown), that he was smarter than the others.
Games including white tigers include Zoo Tycoon and the Warcraft universe. The popularity of white tigers has led private users to create mods or game patches for Elder Scrolls IV: Oblivion which changes the Khajit species to possess white tiger aspects, including realistic height and body sizes in relation to the standard orange Khajit. White Tigers are featured as a wild, tamable "pet" companion in Guild Wars Factions. White Tigers are also seen in Heroes of Might and Magic IV, where they are a level 2 unit for the nature alignment.
Both the Power Rangers and the Japanese Super Sentai series from which the Power Rangers series is based on, have used White Tiger themed mecha. A trained white tiger from the Bowmanville Zoo in Ontario, Canada, was used in the Animorphs TV series. A superheronamed White Tiger appears in "The Justice Friends" on Dexter's Laboratory. A white tiger named White Blaze is frequently shown in the anime Ronin Warriors. Tigatron from the animated TV series Transformers: Beast Wars is based on the white tiger.
Kylie Chan's 'Dark Heavens' series incorporates the four winds of Chinese mythology - including the The White Tiger.
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