Many of the articles on the web are polarised against or in favour of white tigers. This article aims to present researched, complete and unbiased information on the breeding of white tigers and the problems resulting from inbreeding. Contrary to popular belief, inbreeding does not inevitably result in deformity. It is inbreeding of genetically unsound animals that results in deformity and health issues. Information has been drawn from as many sources as possible, particularly from scientific or research publications. Family trees showing the inter-relatedness of individual tigers mentioned here are available on the other white tiger pages on this website.
COLOUR RATIOS IN MIXED COLOUR LITTERS
When a white tiger is mated to an orange tiger that carries the white gene, the expected ratio of white-to-orange offspring is 50/50 (this is an average across a number of litters). However, some of the family trees show a skewed ratio where white offspring consistently outnumber orange offspring. There are several possibilities:
If the colour ratio is naturally skewed in favour of white offspring, why did white tigers not historically outnumber orange tigers in the wild?
White tigers grow larger and apparently faster than their orange relatives and this advantage may also be conferred on heterozygous orange (orange-carrying-white) tigers. This size/growth difference might begin in the womb. It is possible that the white colour is just a side-effect of a gene that influences size and growth. If larger size and faster growth is beneficial, this would keep the white gene in the gene pool in spite of the reduced camouflage. White tigers might be less likely to survive to adulthood in the wild, hence their comparitive rarity, but heterozygous orange tigers might have an advantage over homozygous orange tigers.
INBREEDING DEPRESSION IN WHITE TIGERS
Sara Iverson has produced a genealogy showing the two white tiger bloodlines converging in America, with Mohan and Begum on one side and Como Zoo's brother-sister pair of wild caught Amur tigers on the other. Iverson's chart illustrates the critical junctures where the bloodlines intersect, first with Kesari and Tony at Cincinnati Zoo and later Ranjit and Obie in Omaha, like marriages between royal houses. According to "Tigers Of The World", the Indian subspecies was, at one time, represented in North America by five individuals, all siblings highly inbred for white coloration with co-efficients of 0.406. All of this means white tigers have been greatly inbred.
It is not true that infant mortality in white tigers is 80%. This urban legend seems to have originated with opponents of white tigers. Poor husbandry, stressed mothers and feline infectious enteritis (for which a vaccine is now available) played a large part in white tiger cub mortality.
White tigers show a problem called inbreeding depression - continued inbreeding to fix a particular trait (the white colour) shows up other deleterious genes in the population. As a result, white tigers are prone to being cross-eyed and have other problems as noted later. Andy Goldfarb, tiger trainer who worked at MarineWorld in Vallejo, has said that when stressed or confused all white tigers cross their eyes. Inbreeding depression can be overcome by crossing white tigers to unrelated orange tigers; although the offspring will all be orange, they can be bred back to the white parent to produce white cubs. White tigers are now found in numerous zoos, not so much for conservation purposes (since they are essentially "man-made" and most are mongrels of Bengal and Amur tigers), but because they are a hit with the public. Contrary to the claims of zoos, white tigers are not a separate "endangered species"; they are colour morphs of orange tiger which have been bred in the same way domestic cat varieties have been perpetuated. White tigers are often larger than normal Bengal tigers.
The rising number of unusual tigers reported in Similipal suggests that inbreeding is causing recessive genes to surface in that location. Inbreeding in zoos is causing other recessive genes to show up; not just colour variations, but also physical deformities.
Outside of India, the white tigers (and possibly the golden tabby tigers) in captivity are hybrid Bengal/Amur tigers and are prone to cross eyes (strabismus: the nerves of the visual pathways are routed to the wrong side of the brain), "star-gazing" (related to nutritional imbalances possibly associated with hand rearing), a weakened immune system and poor tolerance of anaesthesia. Although "star-gazing" is sometimes seen in white tigers, "Tigers Of The World" notes that this is a nervous disorder unconnected with crossed eyes and not specific to white tigers. Parkinson's syndrome has also been associates with white tigers (Rathore and Khera 1981). Vitamin B-1 deficiency resulting in star gazing has been diagnosed in hand-reared big cats.
Zoo vet David Taylor treated two white tigers, purchased from Cincinatti zoo, at a German safari park (they had salmonella poisoning) and found they reacted strangely to the anaesthetic. "The majority of albinos cannot synthesize an enzyme called tyrosinase, which could conceivably alter the way the body handles injectable anaesthetics" according to Taylor in his book "Vet On The Wild Side". At the time (1987), he had been treating 2 young white tigers with salmonella poisoning at Fritz Wurm's Stukenbrock safari park. However white tigers are not albinos, but chinchillas so this statement is erroneous when applied to the tigers.
Strabismus is evidently associated with the white colour, rather than simply to inbreeding, since normal coloured tigers related to the white strains are rarely cross-eyed. Bhim and Sumita were cross-eyed despite being born to unrelated parents; Ranjit, Bharat, Priya and Peela were bred from a brother-sister mating and were not cross-eyed. It is also associated with Bengal/Amur hybrids since only one pure Bengal white tiger has been reported to be cross eyed, this being Mohini's daughter Rewati. Rewati's younger brother, Moni, was normal eyed. Tony, common ancestor of most North American white tigers, is sometimes claimed to be cross eyed as were the Hawthorn Circus's 2 three quarters Amur white tigers, Bagheera and Frosty. According to Cuneo, Tony (who eventually died of cancer) had normal vision and was not cross-eyed. Frosty was cross-eyed. Selective breeding could reduce or eliminate strabismus in white tigers in the same way it has been eliminated from Siamese cats. The effects of inbreeding don't end with crossed eyes. Selective breeding has eliminated crossed eyes in Cuneo's tigers and, out of around 80 tigers, only a few of his oldest white tigers have this defect. Hawthorn Circus has avoided breeding siblings together or parents to offspring as has happened in zoos. The 2 white males they obtained from the Cincinnati zoo in 1976 (bred from Kesari and Tony) were outcrossed to gold tigers. A white male from that litter, Arjun, apparently went insane and should have been destroyed, but instead was retired in Germany and may have been used for breeding.
Many of the white tigers trained at Ringling Circus by Wade Burck's are claimed to be hard of hearing. One, Bagheera, was reported to be stone deaf. According to Cuneo none of the tigers had any hearing deficit otherwise they could not be used in shows. Trainers often mistake obstinacy for deafness! Three of Burck's tigers are cross-eyed. All are neurotic and easily spooked. One, Silver, is mentally retarded from inhaling placental fluids and suffering oxygen starvation at birth. Silver remained comatose for four months and was tube fed. At 5 years old, Silver roars continuously, bangs his head against his cage bars, swats phantom flies and is afraid of everything including whips, music, meat and Burck. Burck himself was mauled by a white tiger called Frosty during a fight between two tigers. Roychoudhury states that Bagheera and Frosty's paternity is unknown (Thornton 1978), though Thornton's 1978 article in The Journal Of Zoology suggested that the registered Amur tiger originally named Genghis and later called Ural had been their mother's preferred partner during "gang matings" in the Hawthorn Circus. (The tigers trained by Burck at Ringling and Hawthorn were owned by Cuneo).
GENETIC ANOMALIES IN WHITE TIGERS
There has also been interest in white tigers in connection with Chediak-Higashi Syndrome (oculocutaneous albinism). This is similar to albino mutations and has been observed in domestic cats where it causes bluish lightening of the fur colour and is associated with crossed eyes and prolonged bleeding after surgery. Mohini was screened for Chediak-Higashi on arrival at Washington, but was negative. It is not true that Chediak-Higashi Syndrome is widespread in white tigers. It is not known where that urban legend originated. Tests and post mortem examinations have not upheld this claim.
Other deformities include shortened tendons of the forelegs, abnormal kidneys, arched backbone and twisted neck. Reduced fertility and miscarriages were noted by Sankhala and attributed to inbreeding; to reduce mortality rates, fresh blood from tawny tigers must be introduced into white tiger breeding programmes. 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. At New Delhi Zoo, cubs born with arched backs and clubbed feet have had to be euthanased; other defects in the line include crooked spines, sway back and shortened limbs. A white tiger born at the Cincinnati Zoo developed central retinal degeneration at the Milwaukee County Zoo. Ed Maruska noted in "Tigers Of The World", that a couple of white tiger cubs born at Cincinnati Zoo had cataracts. An article published in the children's edition of National Geographic notes that circus people refer (erroneously) to white tigers as "stargazers" due to their strabismus. Following the Mohan/Radha mating, out of 48 subsequent white tiger litters there were 148 cubs. 105 died without reproducing. This represents a high mortality rate among white tigers. However, 33 of those deaths were related to accidents while the remaining 72 deaths may have been due to a combination of genetic anomalies and poor husbandry.
Jack Hanna made the comment in his book about white tigers being prone to physical problems which is why Taj was pulled for hand rearing. She was unable to stand properly on her hind legs and risked becoming deformed or lame on the slick floor of the tiger den. This problem has also been observed by Cuneo. However, some zoos have reported leg problems and juvenile lameness due to over feeding (feeding on muscle meat is another cause; the calcium deficiency affects bone growth). Overfed fed cubs take on the appearance of an English bull dog, though this is reversible if caught early. Some snub nosed white tigers might fall into this category as opposed to having a brachycephaly mutation though tigers the size and shape of bull dogs have been reported in the wild. Many captive tigers, and especially white tigers, die of liver or kidney problems caused by poor diet. On good diets they are long-lived - Sheba III, Bagheera and Frosty's orange mother (not to be confused with Tony's mother, Sheba II), lived to be 26.
In the 1950s, EP Gee noted the wild white tigers of Rewa and adjacent districts were larger than orange tigers, leading sportsmen and naturalists to wonder if it was a separate breed or variety of tiger and whether wild white tigers prefer to mate with white tigers rather than orange ones. By 1959, this could not be answered in the wild due to the lack of white tigers in the wild. He noted that if the gene was a recessive mutant as Haldane advised, then the white tigers were homozygous and a pure-breeding white strain could be perpetuated in captivity at Rewa, but advised against excessive inbreeding as it could lead to deterioration. Gee added "Such a white breed of tiger, if firmly established in India, would, give this country a considerable amount of prestige in the zoological world, as well as provide a fillip for tourism and at a later date a possible economically valuable item of export ‘to foreign countries." This economic viability, not just for India, but also for zoos and circuses would prove genetically disastrous for many of the tigers.
In general, white and golden tigers grow faster than their normal coloured kin. Detailed records from zoos show tht white tigers are born larger and grow faster which could give them an advantage in the wild. Records show that orange tigers that carry the white gene also tend to become larger than average. KS Sankhala wrote "One of the functions of the white gene may have been to keep a size gene in the population in case it is ever needed." My own feeling is that if heterozygous orange tigers grow bigger and have an advantage, this coincidentally kept the white gene in the population (unfortunately trophy hunters generally aimed for the largest tigers, thus depleting the carriers of the white gene).
However, not all white tigers end up larger than their normal-coloured kin, again possibly a result of inbreeding depression and deleterious genes meeting up. One of Alan Gold's troop of performing white tigers included an abnormally small white tiger bred from Hawthorn Circus white tigers; it was possibly one of Taj and Ika's cubs born at the Columbus Zoo.
Sankhala also observed that white tigers are whiter in Rewa and this was related to the temperature. This sounds similar to temperature-dependent albinism in Siamese cats and contributed to early beliefs that the gene involved was a form of albinism. However, white tigers are chinchilla, not albino. The chinchilla gene (colour inhibitor gene) restricts the normal colour to the outer third or quarter of the hair. The longer the fur the more colour there is, hence more heavily furred Bengal/Amur hybrids in cooler climes look darker than the shorter furred white Bengal tigers in India.
Textual content is licensed under the GFDL.
For more information on the genetics of colour and pattern:
Robinson's Genetics for Cat Breeders & Veterinarians 4th Ed (the current version)
Genetics for Cat Breeders, 3rd Ed by Roy Robinson (earlier version showing some of the historical misunderstandings)
Cat Genetics by A C Jude (1950s cat genetics text; demonstrates the early confusion that chinchilla was a form of albinism)
For more information on genetics, inheritance and gene pools see:
The Pros and Cons of Inbreeding
The Pros and Cons of Cloning
For more information on anomalous colour and pattern forms in big cats see
Karl Shuker's "Mystery Cats of the World" (Robert Hale: London, 1989 - some of the genetics content is outdated)
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