animal rights, AZA, conservation, Doc Antle, genetics, HSUS, leucistic, white tiger
White Tigers are NOT Genetically Defective
There is no evidence of a genetic defect inherent in the white color variant of the Royal White Bengal Tiger, notwithstanding the erroneous claims to the contrary by the Humane Society of the United States (HSUS) and the Association of Zoos and Aquariums (AZA). White tigers have a normally occurring, simple recessive genetic color variant known as leucism, much the same as the leucistic (white) deer common to the Carolinas. Leucism and albinism are not the same. White tigers are not albinos and do not carry the genetic weaknesses associated with albinism. According to a recent study published in Current Biology, the gene known as SLC45A2, is a naturally expressed color variant that was common in wild tiger populations prior to extirpation by poachers, hunters and habitat fragmentation in the 1950’s.
White Bengals result from genetic mutations that are part of their natural species diversity, and we have a responsibility to save them”– Shu-Jin Luo and Xiao Xu, Scientific American, 2014.
Leucism, as a simple recessive genetic trait, can be carried by normal (orange) tigers, even though the white color is not visibly exhibited. In humans, Type O blood is a simple recessive trait. This means that in order for a person to have the phenotype for Type O blood, he or she must inherit one Type O gene from each parent. A phenotype is an individual’s observable traits, such as height, eye color, and blood type. The genetic contribution to the phenotype is called the genotype (the genetic ingredients that an animal has, whether or not those traits are visible).
The white gene can be inherited undetected in orange tigers for generations, because a tiger only appears white when each parent in any particular breeding passes the gene for leucism. When two normal colored tigers are bred carrying the recessive leucistic gene, white offspring can occur. The spontaneous occurrence of white tigers in the U.S. population proves that the gene for leucism is widespread in the species.
An animal is heterozygous at a gene locus when it contains two different alleles of a gene. Many orange tigers are heterozygous for leucism, meaning that they carry a dominant gene for the orange color as well as a recessive gene for white. These cats have one of each gene to potentially contribute to offspring, with an equal chance of passing the orange gene or the white gene. When an orange tiger carrying the white gene mates with a white tiger, each of the offspring has a 50% chance of of being white and 100% of the offspring will carry the white gene. If two heterozygous tigers (orange tigers each carrying the recessive white gene and a dominant orange gene) mate, each offspring has a 25% chance of being white; each has a 50% chance of being orange but carrying the white gene, and each has only a 25% chance of being orange and not carrying the white gene. Two visually white tigers bred together will produce only white cubs.
At the Rare Species Fund in Myrtle Beach, we have dedicated ourselves to producing some of the most magnificent and healthy Royal White Bengal Tigers the world has ever seen. The genetic diversity of our breeding stock, combined with hand rearing, good citizen training and unparalleled enrichment opportunities, have enabled us to produce animals of incomparable grace, beauty and genetic vigor.
Genetics or Inbreeding?
William Conway, former director of the Bronx Zoo’s New York Zoological Society, a/k/a Wildlife Conservation Society (WCS), was convinced that white tigers were the victims of a hereditary genetic defect that was isolated and propagated for sideshow exhibits. He actually compared white tigers to “two headed calves.” The comparisons would later be made ad nauseam by the AZA and surrogates for HSUS attempting to set public opinion against white tigers.
White tigers are freaks”– William Conway, Director of the New York Zoological Society (a/k/a WCS).
This flawed argument was formally adopted by the AZA, and focuses on claiming a genetic defect in the white color variant, yet AZA provides no direct examples nor evidence to support the claim; all the while, contradictorily conceding that defects are actually the result of “poor breeding practices.”
Conway’s views held great appeal for animal rights advocates who already considered all animal breeding as “exploitation.” The AZA, one of two trade associations that accredits zoos in the U.S., adopted a policy banning all white tiger breeding in a white paper published in 2011. The irony is, AZA accredited zoos actually pioneered white tiger breeding in the U.S. during the 1960’s and 70’s.
Conway’s apparently limited understanding of white tiger genetics appears to be responsible for his failure to comprehend that the white allele was a naturally occurring simple recessive genetic trait carried by many healthy, normal-appearing Bengal tigers, and at one time was visibly expressed in a healthy wild white population. The trait is not only perfectly normal, but the genetic material catalogued within the DNA “fingerprint” of white tigers is reported to be comparable in diversity to that contained in the orange population.
Notwithstanding, the AZA states that the white gene, “has been clearly linked with various abnormal, debilitating, and, at times, lethal, external and internal conditions and characteristics.” But what they fail to do, is cite any evidence connecting “abnormal” or “debilitating” mutations to anything other than problems more closely related to “breeding practices” than any manifestation of genetic deformities.
Science over Superstition
The best available science recommends saving and strengthening the diversity in the white Bengal tiger, leaving the AZA “no breeding” policy in stark contradiction with the welfare of the species. The facts are simple. The recessive white gene SLC45A2, in and of itself, is not flawed. For example, the gene that makes black leopards black, is also a simple recessive, and AZA zoos do not ban black leopard breeding. The change in policy at AZA seems more correlated to what appears to be an informal alignment with the Humane Society of the United States (HSUS), to protect AZA market share from non-AZA zoos. The policy to ban the breeding of white tigers is an ideological choice, unrelated to science.
Much of the misinformation surrounding white tigers has been proliferated by Carole Baskins of Big Cat Rescue. She has posted her HSUS inspired interpretation of the AZA white paper, along with William Conway’s views, on her website, which in turn has been republished by The Dodo and One Green Planet, and punctuated with horrible photos of inbred tigers. It is worthy of note that Ms. Baskins uses no scientific citations to support her claims of genetic defect. She uses inflammatory rhetoric and shocking images in lieu of facts.
While the original confusion regarding white tiger genetics understandably stemmed from personal opinions derived from a poverty of scientific data, the current anti-white tiger sentiment of AZA/HSUS flies in the face of the best available science. The AZA appears to have aligned themselves with HSUS not only to protect themselves from being targeted by the animal rights industry, but to discredit other legitimate zoological institutions that don’t toe the HSUS/AZA line on captive wildlife policy. It should be interesting to see, as more science becomes available dispelling superstitions about white tiger genetics, if AZA will defy HSUS and adopt a science based policy?
According to Dr. Brian Davis of the Exotic Genome Repository, “There has been no genetic study that has demonstrated a negative biological effect connected to the white variant in tigers. When the white tiger existed in the wild prior to human eradication, adults were common, indicating no decrease in fitness.” Additionally, leucism exists in numerous other species. These traits, erroneously associated with white, are actually strongly linked with inbreeding, regardless of coat color. Contemporary American tiger populations do not need inbreeding to perpetuate the white variant, since the gene is prevalent within the orange population as well other genetic variation that humans have driven extinct in the wild.
There has been no genetic study that has demonstrated a negative biological effect conferred by the white variant in tigers.”– Brian W. Davis, Ph.D., Comparative Genomicist, Exotic Genome Repository
Royal White Bengal Tigers are Magnificent!
Anyone who is interested in seeing what healthy, happy white tigers actually look like, feel free to visit my facility in Myrtle Beach, South Carolina. Our state-of-the-art facility is home to a number of the most fantastic white tigers on the planet today. We didn’t give up on the white tiger. To the contrary, our breeding and enrichment programs are superior to any other zoological facility in the world. Come see white tigers run at full speed through varied terrain. There is not an experience that can compare to seeing these powerful animals do what they were born to do. If you can’t visit in person, watch the video below. Capturing the imagination of millions, the Royal White Bengal Tiger is undeniable in its power as an animal ambassador for conservation, and is a portrait of genetic vigor!
Watch this amazing high speed video footage of perfectly healthy white tigers running at full speed as a part of the Rare Species Fund tiger enrichment program.
Andrew Wyatt said:
Reblogged this on The Last Word and commented:
“An interesting reassessment of white tiger genetics and the politics that surrounding the issue.” — Andrew Wyatt
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Reblogged this on Limitless and commented:
A great article regarding white tigers.
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It is great to see science and common sense being used to explain the realities of white tigers and to combat some of the myths that have proliferated against them. Thank you very much for writing this !
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A good example of misunderstanding how rare, deleterious alleles can become common in small populations and one-sided look with the aim to justify intentional inbreeding and advertise a zoo that probably failed too meet requirements to be an AZA member.
Oh and for the Science I would like to refer to Frankham et al. (2010) for the small populations comment and to Xu et al. 2013 (which is the paper you cite also) for the intentional inbreeding for “pretty” white tigers part, conflicting with your statement on health.
Andrew Wyatt said:
You appear to be glossing over some salient points. The article made it fairly clear that inbreeding has been the problem with the white tiger project. What also appears clear is that, if there is a flaw in the white allele, AZA has failed to make a science based case in support of that hypothesis. As far as the small populations argument, I guess you are saying the entire tiger SSP should be suspended then?
Those white tigers have the vigor of a health beautiful beast.
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To begin, the white variant has not been demonstrated to be deleterious.
“The fact that many white tigers captured or shot in the wild were mature adults suggests that a white tiger in the wild is able to survive without its fitness being substantially compromised. The undesirable traits often associated with captive white tigers are thus most likely due to human-induced inbreeding.” –Xu/Luo 2013
The only tenuous link is strabismus. However, nothing causative has been found, and strabismus is nonexistent in the outbred white tiger population, again pointing towards inbreeding as the culprit rather than the variant. In fact, variation in this gene is found in numerous other species without detriment.
From Xu/Luo 2013:
“Indeed, SLC45A2 mutations in human and chicken worldwide rarely cause phenotypic features other than hypopigmentation. Therefore, we argue that the SLC45A2 A477V substitution in the tiger primarily affects only pigmentation, and that the white tiger morph is a viable natural genetic polymorphism.” –Xu/Luo 2013
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Lastly, the claim that white is perpetuated only by inbreeding is outdated and false. The white allele is now routinely produced by orange-orange or orange-white matings, which eliminates the problem of inbreeding. This should be considered before jumping to false assumptions not based in genetic reality.
In sum, these animals possess diversity that has been driven to extinction in the wild by human stupidity. It is neither scientifically sound, nor rational to fall victim to the same trap by advocating their eradication in captivity. What SHOULD be done (as forward thinking conservationists like Doc and others are doing), is tracking the genetics of each animal, and using the reservoir of genetic diversity that exists in the US to maintain a healthy population. Science, you see.
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