Black Tigers

Black Tigers

Subject – Environment

Context – A team of scientists has resolved the genetic mystery of Simlipal’s so-called black tigers

Concept –

• The study found that a single genetic mutation in these tigers caused black stripes to broaden or spread into the tawny background.
• Tigers have a distinctive dark stripe pattern on a light background of white or golden. A rare pattern variant, distinguished by stripes that are broadened and fused together, is also observed in both wild and captive populations. This is known as pseudo-melanism, which is different from true melanism, a condition characterised by unusually high deposition of melanin, a dark pigment.
• While truly melanistic tigers are yet to be recorded, pseudo-melanistic ones have been camera-trapped repeatedly, and only, in Simlipal, a 2,750-km tiger reserve in Odisha, since 2007.
• Through whole-genome data and pedigree-based association analyses from zoo tigers, the study found that pseudo-melanism is linked to a single mutation in Transmembrane Aminopeptidase Q (Taqpep), a gene responsible for similar traits in other cat species.
• Black tiger sightings have been claimed sporadically at least since 1773 when artist James Forbes painted a watercolour of one shot in Kerala.Similar claims were made from Myanmar (1913) and China (1950s).
• Besides, pseudo-melanism is caused by a recessive (hidden) gene.
• Long before three black tigers were camera-trapped in 2007, Simlipal furnished the first confirmed record of the mutant in 1993 when a tribal youth killed a pseudo-melanistic tigress in self-defence.
• Pseudo-melanistic tigers are also present in three zoos in India — Nandankanan (Bhubaneswar), Arignar Anna Zoological Park (Chennai) and BhagwanBirsa Biological Park (Ranchi) — where they were born in captivity. All of them have ancestral links to one individual from Simlipal.

Natural selection

• Natural selection eliminates the weakest from a gene pool, and the traits of the more successful get passed on.
• Niche modelling, the study said, shows higher frequency of melanistic leopards in darker tropical and subtropical forests than in drier open habitats. Likewise, darker coats may confer a selective advantage in both hunting and avoiding hunters in Simlipal’s tropical moist deciduous and semi-evergreen closed-canopy forest, with a relatively darker understory.
• Meanwhile, India’s northwestern tiger population shows higher mean relatedness between individuals (46%) and lower heterozygosity (22%) than even Simlipal (38% and 28%). While Ranthambhore has been a genetic island for decades, tiger siblings were handpicked from this inbred population for repopulating Sariska. That is another study in the offing.

To know about Simplipal Tiger Reserve, please click here.