The
tiger (Panthera tigris) is the largest living catspecies and a member of the genus Panthera. It is most recognisable for its dark vertical stripes on orange-brown fur with a lighter underside. It is an apex predator, primarily preying on ungulates such as deer and wild boar. It is territorial and generally a solitary but social predator, requiring large contiguous areas of habitat, which support its requirements for prey and rearing of its offspring. Tiger cubs stay with their mother for about two years, before they become independent and leave their mother's home range to establish their own.
The tiger was first scientifically described in 1758 and once ranged widely from the Eastern Anatolia Region in the west to the Amur River basin in the east, and in the south from the foothills of the Himalayas to Bali in the Sunda Islands. Since the early 20th century, tiger populations have lost at least 93% of their historic range and have been extirpated from Western and Central Asia, the islands of Java and Bali, and in large areas of Southeast and South Asia and China. Today, the tiger's range is fragmented, stretching from Siberiantemperate forests to subtropical and tropical forestson the Indian subcontinent and Sumatra.
The tiger is listed as Endangered on the IUCN Red List. As of 2015, the global wild tiger population was estimated to number between 3,062 and 3,948 mature individuals, with most of the populations living in small isolated pockets. India currently hosts the largest tiger population. Major reasons for population decline are habitat destruction, habitat fragmentation and poaching. Tigers are also victims of human–wildlife conflict, particularly in range countries with a high human population density.
The tiger is among the most recognisable and popular of the world's charismatic megafauna. It featured prominently in the ancient mythology and folklore of cultures throughout its historic range, and continues to be depicted in modern films and literature, appearing on many flags, coats of armsand as mascots for sporting teams. The tiger is the national animal of India, Bangladesh, Malaysia and South Korea.
Etymology
The Middle English tigre and Old English tigrasderive from Old French tigre, from Latin tigris. This was a borrowing of Classical Greek τίγρις 'tigris', a foreign borrowing of unknown origin meaning 'tiger' and the river Tigris.[4] The origin may have been the Persian word tigra meaning 'pointed or sharp', and the Avestan word tigrhi 'arrow', perhaps referring to the speed of the tiger's leap, although these words are not known to have any meanings associated with tigers.[5]
The generic name Panthera is derived from the Latinword panthera, and the Ancient Greek word πάνθηρ 'panther'.[6] The Sanskrit word पाण्डर pāṇḍ-ara means 'pale yellow, whitish, white'.[7]
Taxonomy and genetics
In 1758, Carl Linnaeus described the tiger in his work Systema Naturae and gave it the scientific nameFelis tigris.[2] In 1929, the British taxonomist Reginald Innes Pocock subordinated the species under the genus Panthera using the scientific name Panthera tigris.[8][9]
Subspecies
Phylogenetic relationship of tiger populations based on Driscoll et al. (2009).
[10]Following Linnaeus's first descriptions of the species, several tiger specimens were described and proposed as subspecies.[11] The validity of several tiger subspecies was questioned in 1999. Most putative subspecies described in the 19th and 20th centuries were distinguished on basis of fur length and colouration, striping patterns and body size, hence characteristics that vary widely within populations. Morphologically, tigers from different regions vary little, and gene flow between populations in those regions is considered to have been possible during the Pleistocene. Therefore, it was proposed to recognize only two tiger subspecies as valid, namely P. t. tigris in mainland Asia, and P. t. sondaica in the Greater Sunda Islands.[12]
Results of craniological analysis of 111 tiger skulls from Southeast Asian range countries indicate that Sumatran tiger skulls differ from Indochinese and Javan tiger skulls, whereas Bali tiger skulls are similar in size to Javan tiger skulls. The authors proposed to classify the Sumatran and Javan tigers as distinct species, P. sumatrae and P. sondaica, with the Bali tiger as subspecies P. sondaica balica.[13]
In 2015, morphological, ecological, and molecular traits of all putative tiger subspecies were analysed in a combined approach. Results support distinction of the two evolutionary groups continental and Sunda tigers. The authors proposed recognition of only two subspecies, namely P. t. tigris comprising the Bengal, Malayan, Indochinese, South Chinese, Siberian and Caspian tiger populations, and P. t. sondaica comprising the Javan, Bali and Sumatran tiger populations. The authors also noted that this reclassification will affect tiger conservation management. The nominate subspecies P. t. tigrisconstitutes two clades:[14]
- a northern clade composed of the Siberian and Caspian tiger populations
- a southern clade composed of all other mainland populations.
One conservation specialist welcomed this proposal as it would make captive breeding programmes and future rewilding of zoo-born tigers easier. One geneticist was sceptical of this study and maintained that the currently recognised nine subspecies can be distinguished genetically.[15]
Description
The tiger has a muscular body with powerful forelimbs, a large head and a tail that is about half the length of its body. Its pelage is dense and heavy, and colouration varies between shades of orange and brown with white ventral areas and distinctive vertical black stripes that are unique in each individual.[51][24] Stripes are likely advantageous for camouflage in vegetation such as long grass with strong vertical patterns of light and shade.[52][53]The tiger is one of only a few striped cat species; it is not known why spotted patterns and rosettes are the more common camouflage pattern among felids.[54] The orangish colour may also aid in camouflage as the tiger's prey are dichromats, and thus may perceive the cat as green and blended in with the vegetation.[55]
A tiger's coat pattern is still visible when it is shaved. This is not due to skin pigmentation, but to the stubble and hair follicles embedded in the skin.[56] It has a mane-like heavy growth of fur around the neck and jaws and long whiskers, especially in males. The pupils are circular with yellow irises. The small, rounded ears have a prominent white spot on the back, surrounded by black.[24] These spots are thought to play an important role in intraspecificcommunication.[57]
The tiger's skull is similar to a lion's skull, with the frontal region usually less depressed or flattened, and a slightly longer postorbital region. The lion skull shows broader nasal openings. Due to the variation in skull sizes of the two species, the structure of the lower jaw is a reliable indicator for their identification.[20] The tiger has fairly stout teeth; its somewhat curved canines are the longest among living felids with a crown height of up to 90 mm (3.5 in).[24]
Size
There is notable sexual dimorphism between male and female tigers, with the latter being consistently smaller. The size difference between them is proportionally greater in the large tiger subspecies, with males weighing up to 1.7 times more than females. Males also have wider forepaw pads, enabling sex to be identified from tracks.[58] It has been hypothesised that body size of different tiger populations may be correlated with climate and be explained by thermoregulation and Bergmann's rule, or by distribution and size of available prey species.[24][59]
Generally, males vary in total length from 250 to 390 cm (8.2 to 12.8 ft) and weigh between 90 and 300 kg (200 and 660 lb) with skull length ranging from 316 to 383 mm (12.4 to 15.1 in). Females vary in total length from 200 to 275 cm (6.56 to 9.02 ft), weigh 65 to 167 kg (143 to 368 lb) with skull length ranging from 268 to 318 mm (0.879 to 1.043 ft). In either sex, the tail represents about 0.6 to 1.1 m (24 to 43 in) of the total length. The Bengal and Siberian tigers are amongst the tallest cats in shoulder height. They are also ranked among the biggest cats that have ever existed reaching weights of more than 300 kg (660 lb).[24] The tigers of the Sunda islands are smaller and less heavy than tigers in mainland Asia, rarely exceeding 142 kg (313 lb) in weight.[27]
Colour variations
White tigers in Haifa Zoo
There are three colour variants – white, golden and stripeless snow white – that now rarely occur in the wild due to the reduction of wild tiger populations, but continue in captive populations. The white tigerhas white fur and sepia brown stripes. The golden tiger has a pale golden pelage with a blond tone and reddish-brown stripes. The snow white tiger is a morph with extremely faint stripes and a pale reddish-brown ringed tail. Both snow white and golden tigers are homozygous for CORIN gene mutations.[60] A black tiger is a colour variant due to pseudo-melanism. They have thick stripes close together so that the background colour is barely visible between stripes.[61]
The white tiger lacks pheomelanin (which creates the orange colour), and has dark sepia-brown stripes and blue eyes. This altered pigmentation is caused by a mutant gene that is inherited as an autosomal recessive trait, which is determined by a white locus. It is not an albino, as the black pigmentsare scarcely affected.[62][60] The mutation changes a single amino acid in the transporter protein SLC45A2. Both parents need to have the allele for whiteness to have white cubs.[63] Between the early and mid 20th century, white tigers were recorded and shot in the Indian states of Odisha, Bihar, Assamand in the area of Rewa, Madhya Pradesh. The local maharaja started breeding tigers in the early 1950s and kept a white male tiger together with its normal-coloured daughter; they had white cubs.[64] To preserve this recessive trait, only a few white individuals were used in captive breeding, which led to a high degree of inbreeding. Inbreeding depression is the main reason for many health problems of captive white tigers, including strabismus, stillbirth, deformities and premature death.[65] Other physical defects include cleft palateand scoliosis.[66]
The Tiger Species Survival Plan has condemned the breeding of white tigers, alleging they are of mixed ancestry and of unknown lineage. The genesresponsible for white colouration are represented by 0.001% of the population. The disproportionate growth in numbers of white tigers points to inbreeding among homozygous recessiveindividuals. This would lead to inbreeding depression and loss of genetic variability.[67]
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