Explained: Why ‘black tigers’ sound a warning

What is the news?

Recently, scientists resolved the genetic mystery of Simlipal’s so-called black tigers. Single genetic mutation in these tigers caused black stripes to broaden or spread into the tawny background. 

What is pseudo-melanism? 

Tigers have a 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.

It is a condition characterised by unusually high deposition of melanin, a dark pigment. Truly melanistic tigers are yet to be recorded. 

Why black tigers are rare? 

Firstly, mutants are genetic variations which may occur spontaneously, but not frequently, in nature. Pseudo-melanism is caused by a recessive (hidden) gene. 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.

Secondly, 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. Hence, succession of black tigers is rare. 

What are the recommendations to revive the situation? 

Overall, such populations have a high chance of extinction. Hence, studies like the recent one will provide help in safeguarding the futures of endangered species

Introduction of fresh genes in an isolated pool, depending on the number of migrants, frequency of influx and population size, can also reverse the damage over time.   

Restoring natural connectivity between forests: Due to human-induced habitat fragmentation, populations of tigers become isolated within a particular area, resulting in inbreeding and reduced chances of survival. Hence, we should also focus on restoring or maintaining natural connectivity between tiger forests in the long term.

Source: This post is based on the article “Explained: Why ‘black tigers’ sound a warning” published in The Indian Express on 18^th Sep 2021.