Pseudo-melanism in Tigers of Simlipal

  Oct 05, 2021

Q Why is it in News ?

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

Q What are Black Tigers?

A 

• 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 characterized by unusually high deposition of melanin, a dark pigment.
• This pseudo-melanism is linked to a single mutation in Transmembrane Aminopeptidase Q (Taqpep), a gene responsible for similar traits in other cat species.

Q Where are they mostly found?

A 

• 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.
• Launched in 2017, the study was the first attempt to investigate the genetic basis for this unusual phenotype (appearance).

Q Why they are rare?

A 

• Mutants are genetic variations which may occur spontaneously, but not frequently, in nature.
• A cub gets two copies of each gene from both parents, and a recessive gene can show up only in the absence of the dominant one.
• So, two normal pattern tigers carrying the recessive pseudo-melanism gene will have to breed together for a one-in-four probability of giving birth to a black cub.
• But recessive genes are rare and it is unlikely that two unrelated tigers will carry the same one and pass it on together to a cub.

Q What is Connection with Simlipal Tiger Reserve ? 

A 

• In an ideal tiger world, where far-ranging individuals are never short of choices for partners, that makes succession of black tigers a rarity.
• Under exceptional circumstances, a black tiger may succeed as part of a very small population that is forced to inbreed in isolation for generations.
• As it turned out, that is what happened at Simlipal.
• Pseudo-melanistic tigers are also present in three zoos in India  Nandankanan (Bhubaneswar), Arignar Anna Zoological Park (Chennai) and Bhagwan Birsa Biological Park (Ranchi)  where they were born in captivity.
• All of them have ancestral links to one individual from Simlipal.

Q What about natural selection?

A 

• 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.

Q What is Project Tiger ? 

A 

• Project Tiger is a tiger conservation program launched in April 1973 during PM Indira Gandhi’s tenure.
• In 1970 India had only 1800 tigers and Project Tiger was launched in Jim Corbett National Park.
• The project is administrated by the National Tiger Conservation Authority (NTCA).
• It aims at ensuring a viable population of Bengal tigers in their natural habitats, protecting them from extinction etc.
• Under this project the govt. has set up a Tiger Protection Force to combat poachers and funded relocation of villagers to minimize human-tiger conflicts.