A
long-standing friend of mine, noted cat geneticist Roy Robinson
, had asked me to collect data on this colour variety which I
was in the process of doing when , sadly, Roy died.
I first
became aware of this colour variety in 1984 or 1985 when on the
television news a Keeper from Columus Zoo, Ohio appeared with an
armful of tiger cubs: two browns, a white, and in the middle one
of these gingery ones. I thought at the time it was one of the most
dramatic visual images I had seen in Zoos.
White
Tigers in the wild have a long history, longer perhaps than many
people realise. On the walls of entrance passageways to ancient
Chinese Tombs, 3,000 or more years of age, are painted the symbols
of the four elemental forces forces of nature - represented amongst
other things by a Green Dragon, and a White Tiger !
The
White Tiger, could, like the Green Dragon have remained solely as
an image, were it not for a number of features:
-
Firstly, China was and still is, well within the natural range
of tigers.
-
Secondly, just like the White Buffalo (Bison) it is inevitable
that white varieties will occur from time to time.
Just how
often these occur is debatable. In the case of the White Buffalo (or
Elephant, for that matter), each instance over the past 2,000 years
has probably been the result of a genuine first mutation.
In
the case of the White Tiger, whilst this might well also have been
the case, and probably on some occasions was, it need not necessarily
have been so.
We
now know that the mutation is inherited as an autosomal recessive.
Thus it is capable of being passed down, without being visible,
from generation to generation until a chance encounter with another
tiger, also carrying this recessive factor, results in a cub or
cubs being born, which visually display the White colouration. Obviously,
the possibility of this happening is far greater in those areas
where the population is significantly " in-bred ". This
does happen naturally, in nature, as Cheetahs have shown, where
two or more " genetic bottlenecks " have occurred in the
last 10,000 or so years. Where for some reason, a population of
tigers is relatively isolated, then it is likely that they will
become in-bred.
Nowadays,
many populations of tigers are extremely dispersed and isolated
as agriculture and population growth forces their numbers down and
confines them to reserves. In recent centuries, whilst this process
had already begun, geographical isolation of a remote valley or
other restriction imposed geographical features would have had the
same effect.
Some
districts in India, became quite celebrated for producing White
Tigers with some regularity. So it was that the Maharaja of Rewa
issued an order that the next White Tiger to be produced was to
be captured alive and brought to him. The story is well known, and
reproduced elsewhere on the WWW. However, a cub, Mohan
duly appeared, was captured, and on maturity was mated to a normal
brown female. One of the brown cubs (the normal brown colour being
the dominant colour) was mated back to her father Mohan
. The theoretical expectation (over 100 matings) was that an average
of 50 of the cubs would turn out to be white. In the first litter
four white cubs were produced!
From
these animals the studbook registered (because they are pure-bred
Indian Tigers) White Tiger strain is descended.
As
a school-boy I dragged my parents and brothers over 100 miles to
see two of these White Tigers which had been purchased by Bristol
Zoo (I still have the post-card souvenir!)
"At the time, we didn't have two farthings to rub together
" said present Director Geoffrey Greed " but those two tigers,
followed by the Okapis re-built the fortunes of Bristol Zoo."
By
1973, when they still hadn't bred successfully I discussed with
Reg Greed, Geoffrey's father ( by then I was Director of Glasgow
Zoo ) the advisability of introducing some fresh blood by means
of an outcross.
"You could always let us have some of the brown cubs, they would
all be browns, but carrying white recessively".
A
few years later a brown male from Edinburgh Zoo was tried with a
white female, I'd have attempted it the other way round, with a
white male to a number of brown females. What did it matter if lots
of brown splits were produced? Anyway, the pairing never reared
any cubs. In retrospect, this was fortunate as the Edinburgh male
was a " non-generic " zoo tiger and these whites were pure-bred
studbook, Indians from a known point of origin in India.
In
the late 1980s, Longleat Safari Park imported a male While Tiger
of the American non-generic strain (the National Zoo in Washington
has individuals of the original Mohan strain). These non-generic
tigers are despised by zoo conservationists, and endangered species
demographics because the contain Siberian Tiger genes. They are
often regarded as a " waste of space ", justified if at
all, by their undoubted visitor appeal.
As
the King-pin amongst a group of 6 to 9 females, this male made an
arresting sight in Longleat Safari Park, fully justifying the decision
to purchase him.
Many
cubs were born in the succeeding years, some of which exhibited
even more variation.The first whites were marked just like the browns
except the stripes were chocolate and their eyes were blue. When
these were bred together in later generations, as might be predicted,
maximum variation started to evidence itself.
In
1994, I saw at Longleat a litter bred from a brown female carrying
White genes mated to a " Ginger Tom " type male. The litter
contained two normally marked browns, another " Ginger Tom
", and a White with absolutely no markings except a few rings around
its tail (this animal is now in Japan).
Butu is from this pairing, although he was hand-reared. He
is one of 7 or 8 examples bred by Longleat (and there are others
in the USA, e.g. Columbus Zoo). They all breed genetically like
White Tigers
Interestingly,
the old natural history books and hunters folk-lore suggests that
White Tigers in the wild are not maladapted and are perfectly capable
of living a full life-span. Both they and their ungulate prey are
seen in tones of grey, although the warning calls of birds and monkeys
are emitted by creatures with acute colour vision..
In
our one acre sloping, naturalistic enclosure, thickly planted with
trees (incidentally , the only tiger enclosure to be so in UK Zoos)
I have seen how White Tigers white tigers with chocolate stripes
can disappear amongst the dappled shadows, with as much facility
as its normal coloured relatives,
Only
man singles such animals out to be shot or captured as trophies.
Centuries ago individual animals probably lived their full allotted
span, and by reproducing, distributed their recessive genetic make-up,
to remain non-visual possibly for hundreds of years, until encounters
with another heterozygous animal caused them to reappear visually
as a White cub again.
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