Biology:White tiger

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A captive white Bengal tiger

The white tiger or bleached tiger is a pigmentation variant of the Bengal tiger, which is reported in the wild from time to time in the Indian states of Madhya Pradesh, Assam, West Bengal and Bihar in the Sunderbans region and especially in the former State of Rewa.[1] Such a tiger has the black stripes typical of the Bengal tiger, but carries a white or near-white coat.

Variation

A tiger at the Madrid Zoo

The white Bengal tigers are distinctive due to the color of their fur. The white fur caused by a lack of the pigment pheomelanin, which is found in Bengal tigers with orange color fur. When compared to Bengal tigers, the white Bengal tigers tend to grow faster and heavier than the orange Bengal tiger. They also tend to be somewhat bigger at birth, and as fully grown 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 and can grow up to 3 meters 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.[2]

For a white Bengal tiger to be born, both parents must carry the unusual gene for white colouring, which only happens naturally about once in 10,000 births.[2] 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.[2] Currently, several hundred white tigers are in captivity worldwide, with about one hundred being found in India. Their unique white color fur has made them popular in entertainment showcasing exotic animals, and at zoos.

Stripeless tigers

A tiger with almost no stripes at The Mirage in Las Vegas, the United States of America

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."[3] Naturalist Richard Lydekker said 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."[4] 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.", and John 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 (Liberec), 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.[5]

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").

Genetics

File:WhiteTiger-TobuZoo2012.ogv

A white tiger's pale coloration is due to the lack of the red and yellow pigments that normally produce the orange color.[6] This had long been thought to be due to a mutation in the gene for the tyrosinase 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 results in selective loss of pheomelanin, the so-called Chinchilla trait, in other mammals. The white phenotype in tigers had been attributed to such a Chinchilla mutation in tyrosinase, and some publications prior to the 1980s refer to it as an albino gene for this reason.[citation needed] However, genomic analysis has demonstrated instead that a mutation in the SLC45A2 gene is responsible. The resultant single amino acid substitution appears to block passage of molecules through this transport protein, and by a mechanism yet to be determined this causes the elimination of pheomelanin expression. This is a recessive trait, meaning that it is only seen in individuals that are homozygous for this mutation.[6] 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. 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.[7] 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."[8] A weakened immune system is directly linked to reduced pigmentation in white tigers.

Defects

Outside of India, inbred white tigers have been prone to crossed eyes, a condition known as strabismus, an example of which is "Clarence the cross-eyed lion",[9] due to incorrectly routed visual pathways in the brains of white tigers. When stressed or confused, all white tigers cross their eyes[10]. 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.[11][12][13]

A deformed tiger

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 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 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.[14]

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.[8] 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.[14] Some 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 was 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 Vegas magician Dirk Arthur.[15] There is a picture of a white tiger which appears to be cross-eyed on just one side in Siegfried & Roy's book Mastering The Impossible. A white tiger, named Scarlett O'Hara, who was Tony's sister, was cross-eyed only on the right side.

A male tiger named 'Cheytan', a son of Bhim and Sumita who was born at the Cincinnati Zoo, died at the San Antonio Zoo in 1992, from anaesthesia complications during root canal therapy. 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.[16] 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.[17]

Mohini was checked for Chédiak-Higashi syndrome in 1960, but the results were inconclusive.[18][19] This condition is similar to albino mutations and causes bluish lightening of the fur color, 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.[18][20] 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."[18] 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."[18]

Inbreeding and outcrossing

A captive tiger in Birmingham, the United Kingdom
A captive tiger in Yerevan Zoo, Armenia

Because of the extreme rarity of the white tiger allele in the wild,[8] 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.[8][21][22] Today there is a large number of white tigers in captivity. A white Amur tiger may have been born at Center Hill and has given rise to a strain of white Amur tigers. A man named Robert Baudy realized that his tigers had white genes when a tiger he sold to Marwell Zoo in England developed white spots, and bred them accordingly.[23] 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.[24] Bharat and Priya were also bred with an unrelated orange tiger from Knoxville 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. ankam Ranjeeth had several mates at the Omaha Zoo.[22]

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.

A Bengal tiger at the Cincinnati Zoo

Siegfried & Roy performed at least one outcross.[25] 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;[26] 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.[26] Siegfried & Roy have bred white tigers in collaboration with the Nashville Zoo.

Because of the inbreeding and resulting genetic defects the Association of Zoos and Aquariums barred member zoos from breeding white tigers, white lions and king cheetahs in a white paper adopted by the board of directors in July 2011. It is noteworthy that the first person to speak out against the displaying of white tigers was William G. Conway, General Director of the New York Zoological Society, which later became known as the Wildlife Conservation Society when he said, "White tigers are freaks. It's not the role of a zoo to show two headed calves and white tigers." He warned AZA in 1983 of the harm to the zoo's credibility in catering to the public's fascination with freaks, but went unheeded until 2008 when AZA issued a request to their members to stop breeding white tigers and then later in July 2011 when the AZA formally adopted that stance as policy. Conway was attacked by Ed Maruska of the Cincinnati Zoo for his observation, but in the end Conway's belief was validated.[27]

A complete scan of the genome led to the discovery that the white tiger’s distinguishing characteristic arises from a single naturally occurring mutation, the substitution of one amino acid for another—valine for alanine—in the protein identified as SLC45A2. The implication of this discovery means that white tigers can be bred from any colored Bengal tiger pair possessing the unique but naturally occurring recessive gene.[28][29]

In 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 town Eskilstuna, 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. In the live action version of Disney's 101 Dalmatians, Cruella de Vil kills a white tiger for its fur. Seto Bagh (or 'White Tiger' in English) is a Nepali language novel by Diamond Shumsher Rana about an encounter with a white tiger. Aravind Adiga's novel The White Tiger won the Man Booker Prize in 2008.[30] 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.

Video games including white tigers include Zoo Tycoon, the Warcraft universe, and Perfect World International. 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. The protector of the mystical world of Shangri-La in Far Cry 4 is a white tiger that allies with the protagonist to defeat demons.[31]

Both the Power Rangers and the Japanese Super Sentai series on which the Power Rangers series is based, have had white tiger themed Rangers and mecha. A trained white tiger from the Bowmanville Zoo in Ontario, Canada, was used in the Animorphs TV series. A superhero named White Tiger appears in "The Justice Friends" in 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. There have been at least four heroes in Marvel comics called "The White Tiger": two gained powers from a group of three mystic amulets that they possessed, one was actually a tigress evolved by the High Evolutionary, and one was given an artificial version of the "Black Panther's Heart Shaped Herb".

Kylie Chan's Dark Heavens series incorporates the four winds of Chinese mythology – including The White Tiger. In Hayate the Combat Butler, Tama, Nagi Sanzenin's pet tiger, is a white tiger. In Colleen Houck's series beginning with the novel Tiger's Curse, one of the main characters, Ren, is shown as a white tiger. In 2013, a white tiger used for an election campaign in Lahore, Pakistan, died of dehydration.[32] A white tiger named Mantecore was used as part of Siegfried & Roy's Siegfried & Roy at the Mirage Resort and Casino magical show. In 2014, Mantecore died at the age of 17 due to illness.

See also

References

  1. ↑ McDougal, C. (1977) The Face of the Tiger. Rivington Books and André Deutsch, London.
  2. ↑ 2.0 2.1 2.2 "White Bengal Tiger". http://www.animalcorner.co.uk/rainforests/bengalwhite.html. 
  3. ↑ Cuvier, Georges (1832). The Animal Kingdom they can grow to as tall as. G & C & H Carvill. 
  4. ↑ Lydekker, R. (1893). The Royal Natural History. Frederick Warne. 
  5. ↑ "Litter of white tigers debuts in Mexico". 6 July 2007. http://msnbc.msn.com/id/19627911. 
  6. ↑ 6.0 6.1 Xu, Xiao; Dong, Gui-Xin; Hu, Xue-Song; Miao, Lin; Zhang, Xue-Li; Zhang, De-Lu; Yang, Han-Dong; Zhang, Tian-You et al. (2013). "The Genetic Basis of White Tigers". Current Biology 23 (11): 1031–5. doi:10.1016/j.cub.2013.04.054. PMID 23707431. 
  7. ↑ Leyhausen, Paul; Reed, Theodore H. (April 1971). "The white tiger: care and breeding of a genetic freak". Smithsonian. 
  8. ↑ 8.0 8.1 8.2 8.3 Sankhala, K. (1997). Tiger! The Story Of The Indian Tiger. Simon and Schuster. ISBN 978-0-00-216124-4. 
  9. ↑ Geringer, Dan (21 July 1986). "Now He's The Cat's Meow". Sports Illustrated 65. 
  10. ↑ Aisling Maria Cronin (30 April 2014). "The Truth About White Tigers and Why Their Breeding Needs to Stop". http://www.onegreenplanet.org/animalsandnature/the-truth-about-white-tigers-and-why-their-breeding-needs-to-stop/. 
  11. ↑ "Cross-eyed tigers". Scientific American 229:43. August 1973. 
  12. ↑ Guillery, R.W.; Kaas, J.H. (22 June 1973). "Genetic abnormality of the visual pathways in a 'white tiger'". Science 180 (92): 1287–9. doi:10.1126/science.180.4092.1287. PMID 4707916. Bibcode: 1973Sci...180.1287G. 
  13. ↑ Bernays, M.E.; Smith, R. (1999). "Convergent strabismus in a white tiger". Australian Veterinary Journal 77 (3): 152–5. doi:10.1111/j.1751-0813.1999.tb11220.x. PMID 10197239. 
  14. ↑ 14.0 14.1 Gorham, Mary Ellen, DVM. Genetic defects do little to mar beauty of India's rare white tigers. March 1986
  15. ↑ Fischer, John (12 December 2017). "Hilo Area Attractions". https://www.tripsavvy.com/hilo-area-attractions-1532636. 
  16. ↑ Bush, Mitchell; Phillips, Lindsay G.; & Montali, Richard J. (1987) "Clinical Management of Captive Tigers", p. 186 in Ronald Lewis Tilson, Ulysses S. Seal (eds.) Tigers Of The World, Biopolitics, Management, and Conservation of an Endangered Species, Noyes Publications, Park Ridge, New Jersey, USA, ISBN:0815511337.
  17. ↑ Taylor, David (1991). Vet On The Wild Side. St. Martin's Press. ISBN 978-0-312-05529-5. 
  18. ↑ 18.0 18.1 18.2 18.3 Maruska, Edward J. (1987) "White Tiger Phantom Or Freak?", Chapter 33, Part IV White Tiger Politics, in Ronald Lewis Tilson, Ulysses S. Seal (eds.) Tigers Of The World, Biopolitics, Management, and Conservation of an Endangered Species, Noyes Publications, Park Ridge, New Jersey, USA, ISBN:0815511337.
  19. ↑ Berrier, H.H.; Robinson, F.R.; Reed, T.H.; Gray, C.W. (1975). "The white tiger enigma". Veterinary Medicine/Small Animal Clinician: 467–472. 
  20. ↑ Beehler, B.A.; Moore, C.P.; Picket, J.P. (1984). "Central retinal degeneration in a white Bengal tiger (Panthera tigris tigris)". Proc. Am. Assoc. Zoo Vet.. 
  21. ↑ Sunquist, Fiona (December 2000). "The Secret Of The White Tiger". National Geographic World: 26. 
  22. ↑ 22.0 22.1 Iverson, S.J. (1982). "Breeding White Tigers". Zoogoer 11: 5–12. 
  23. ↑ "Mutant Big Cats-White Tiger (Page 2)". http://www.messybeast.com/genetics/tigers-white2.htm. 
  24. ↑ Tongren, Sally (1985). To keep them alive. New York: Dembner Books: Distributed by Norton. ISBN 0934878668. 
  25. ↑ Fischbacher, Siegfried; Horn, Roy Uwe Ludwig; Tapert, Annette (1992). Siegfried and Roy: mastering the impossible. New York: W. Morrow. ISBN 0688105513. 
  26. ↑ 26.0 26.1 Rai, Usha (15 March 1987). "Will they outlast this century?". The Times of India (New Delhi). 
  27. ↑ "Welfare and Conservation Implications of Intentional Breeding for the Expression of Rare Recessive Alleles". Association of Zoos & Aquariums. June 2011. http://bigcatrescue.org/wp-content/uploads/2011/12/AZAbansBreedingWhiteTigersLions2011from2008.pdf. Retrieved 21 February 2013. 
  28. ↑ "Save the White Tigers". Scientific American. http://www.scientificamerican.com/article/save-the-white-tigers/. Retrieved 16 October 2014. 
  29. ↑ Bertola, L.D.; Cho, Y.S.; Gadhvi, P.; Harper, C.; Hou, H.; Hu, L.; Jacobs, W.; Jho, S. et al. (2013). "The tiger genome and comparative analysis with lion and snow leopard genomes". Nature Communications 4: 2433. doi:10.1038/ncomms3433. PMID 24045858. PMC 3778509. Bibcode: 2013NatCo...4E2433C. http://repository.up.ac.za/handle/2263/32583. 
  30. ↑ "The Man Booker Prize 2008 — The Winner". The Booker Prize Foundation. http://themanbookerprize.com/fiction/backlist/2008. 
  31. ↑ "Far Cry 4 – The Legend of Shangri-La". Ubisoft Entertainment. 15 August 2014. http://blog.ubi.com/far-cry-4-shangri-la/. 
  32. ↑ Helen Lawson (9 May 2013). "Electioneered to its death: Rare white tiger used as Pakistani campaign mascot dies of dehydration in 30C heat". Daily Mail. http://www.dailymail.co.uk/news/article-2321891/Electioneered-death-Rare-white-tiger-used-Pakistani-campaign-mascot-dies-dehydration-30C-heat.html?ito=feeds-newsxml. 

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