8 julio, 2024

White tigers: characteristics, distribution, reproduction, feeding

The white tigers are a genetic variant, product of the mutation of a transporter protein, of the species panthera tigris. This white variant has amazed humanity since its discovery centuries ago in populations located on the Indian subcontinent.

Specifically, the variant occurs only in populations of the subspecies panthera tigris tigrisAlso known as the Bengal tiger. Although some specimens of the subspecies have been reported panthera tigris altaica (Siberian tiger) which are probably the result of crosses between the two subspecies, mediated by man.

At present, all known white individuals and other known color variations of this subspecies are only known from captive animals, as their wild counterparts have either disappeared or no current records are known in the wild.

In nature there are few sightings that occur, as they are quite elusive animals due to how disadvantaged they are with respect to their camouflage in contrast to those individuals that have a typical orange coloration.

The oldest sightings date from the year 1500 in the populations of panthera tigris present in India. Most of the populations of panthera tigris tigris in the Indian subcontinent they are severely fragmented.

The last known specimen in the wild was hunted in 1958 and it is unknown if there are still wild populations with the genetic characteristics that allow the birth of tigers with this mutation.

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General characteristics of the white tiger

White tigers are characterized by the absence of the typical orange color of Bengal tigers. Like the orange tigers, the black spots and stripes remain unchanged unlike other coloration variants such as the all-white tiger or the gold tiger.

For a long time it was thought that the white tiger was albino, however, although phaeomelanin (responsible for the reddish or yellow coloration) is largely absent, eumelanin is still present in the fur of the stripes and in the eyes.

Some white specimens may also present some degree of strabismus due to the decrease in pigment in the epithelium of the retina and the iris during eye development. Also, white tigers are usually slightly larger than tigers of typical coloration.

The stripes on the body are usually dark brown or sepia colouring, the eyes are blue colouring, and the nose is pink colouring, along with the foot pads.

Genetics

White tiger fur is an autosomal recessive trait determined by a white (W) locus whose genotype is (w/w). The genetic basis of the heritability of the coat remains still with very few data.

Recent research indicates that the white variety, although atypical, is viable in the wild because such a mutation is not accompanied by any major physiological abnormalities that affect the tigers’ survival in the wild.

The mutation in the SLC45A2 carrier protein due to a simple change in the amino acid sequence (A477V) is the cause of the acquisition of said coloration in the fur.

Three-dimensional homology models suggest that this change in the amino acid sequence of the protein may partially block the transporter channel, which may affect melanogenesis.

So far, other mammalian color-determining genes have also been evaluated, both in white tigers and those with typical coloration. The MC1R, ASIP, TYR (albino gene), TYRP1 and SLC7A11 genes were evaluated without observing variations associated with the coloration of the white tiger.

The mutation in the SLC45A2 gene affects only pheomelanin pigmentation in the tiger.

State of conservation

the species panthera tigris It is listed as «endangered» (EN) according to the International Union for Conservation of Nature. Of the nine subspecies that existed, three are now officially extinct.

The populations of the subspecies panthera tigris tigris They have declined rapidly due to illegal hunting, the disappearance and destruction of their habitats, as well as the decline in the populations of the prey they consume.

Currently, Bengal tigers have just over 1 million km2 to inhabit. Their populations have decreased by more than 40% in the last two decades and it is expected that in the next three generations of tigers (approximately 21 years) the population trend will continue to decrease.

Many tiger populations are found outside of protected areas, making them more susceptible and fragile. Another of the criteria used to categorize tigers as endangered is the decrease in the number of mature individuals, with an estimated 2,000 to 3,000 reproductive adults in the wild.

Although many places are known to have tiger presence, little evidence exists that they constitute stable breeding populations.

white specimens

All of the white tiger individuals that exist today are in captivity and are highly inbred in order to “preserve the recessive coloration trait”. However, this brings with it a series of diseases such as premature death, the inviability of the litters and the appearance of deformities and frequent occurrence of tumors.

This set of diseases has led to speculation that the white variant of the tiger is nothing more than a genetic anomaly or deformity. However, the death of several white tigers in the wild due to poaching demonstrates that coloration does not greatly affect the survival of individuals.

The last white tiger in the wild was hunted in 1958. There are no recent records of this coloration variant in India, and the frequency of the recessive gene that causes this phenotype in the wild is unknown.

Probably the pressures that this variant suffered in the past were the same that currently exist for normal individuals: uncontrolled hunting, habitat intervention and fragmentation of the same.

Distribution

panthera tigris It is a species with a wide distribution. Originally they stretched from Turkey in the west to the eastern coast of Russia. However, in the last century they have disappeared from much of Central Asia, some Indonesian islands, and large areas of Southwest and East Asia.

Recently they only occupy 6% of their original territory. Breeding populations only exist in Bangladesh, Bhutan, India, Indonesia, Malaysia, Nepal, Russia, and Thailand. Poor and unconfirmed breeding data also exist in China, Myanmar, and North Korea.

panthera tigris it currently has six subspecies distinguished on the basis of molecular markers. Three other subspecies previously established based on taxonomic characteristics are extinct.

Much of the areas where tigers are found suffer from anthropogenic pressure due to land use and poaching.

Reproduction

White tigers originate when the specimens that reproduce are carriers of the recessive gene (w) are heterozygous or homozygous. These tigers are highly sought after in zoos and exotic animal exhibits.

Due to this, and to the non-existence of this variety in nature, a large part of the specimens known today are the product of inbreeding.

The reproductive characteristics are similar to those of tigers in the wild. In general they can reproduce throughout the year. The minimum age for reproduction in the female is around four years and in males up to 5 years. The litters can vary between 2 and 4 puppies.

The pups have a high mortality rate, (up to 50%), however, life expectancy increases as the pups get older. High cub mortality rates, often attributed to human activities, pose a great risk to conservation activities in most tiger ranges.

Similarly, in the case of the white tiger, the mortality of litters as a result of inbreeding puts the conservation of the variety at risk.

Feeding

These cats are purely carnivorous. In their range they feed on buffalo, impala, wild boar, and wild hogs, primates such as langurs, and deer. They can even consume other predators such as the sloth bear, but to a lesser extent, and juvenile elephants.

Tigers prefer to consume large prey with an average weight of between 100 and 114 kilograms. Tigers generally choose and defend territories with high prey availability up to 100 animals per km2. Knowing this, those areas with high prey availability are strategic points for conservation.

On the other hand, when food is scarce they can consume a wide variety of small prey such as amphibians, small rodents and rabbits. Due to the fact that the prey present variations in their populations in the areas of distribution of panthera tigristhe frequency and preference of hunting one prey or another depends on its local abundance.

In areas close to human settlements, they frequently feed on farm animals, constituting up to 10% of their diet. However, the latter results in the selective hunting of “harmful” tigers.

References

Andheria, AP, Karanth, KU, & Kumar, NS (2007). Diet and prey profiles of three sympatric large carnivores in Bandipur Tiger Reserve, India. Journal of Zoology, 273(2), 169-175.
Bagchi, S., Goyal, SP, & Sankar, K. (2003). Prey abundance and prey selection by tigers (panthera tigris) in a semi-arid, dry deciduous forest in western India. Journal of Zoology, 260(3), 285-290.
Chundawat, RS, Khan, JA & Mallon, DP 2011. Panthera tigris ssp. tigris. The IUCN Red List of Threatened Species 2011: e.T136899A4348945. Downloaded on 28 October 2019.
Goodrich, J., Lynam, A., Miquelle, D., Wibisono, H., Kawanishi, K., Pattanavibool, A., Htun, S., Tempa, T., Karki, J., Jhala, Y. & Karanth, U. 2015. panthera tigris. The IUCN Red List of Threatened Species 2015: e.T15955A50659951. Downloaded on 28 October 2019.
Haberstroh, LI, Ullrey, DE, Sikarski, JG, Richter, NA, Colmery, BH, & Myers, TD (1984). Diet and oral health in captive Amur tigers (panthera tigris altaica). The Journal of Zoo Animal Medicine, fifteen(4), 142-146.
Karanth, KU (1995). estimating tiger panthera tigris populations from camera-trap data using capture-recapture models. Biological conservation, 71(3), 333-338.

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