Posts Tagged ‘genetic bottleneck’

Amur tiger cubs

From the BBC:

Approximately 500 Amur tigers actually survive in the wild, but the effective population is a measure of the genetic diversity of the world’s largest cat.

Very low diversity means any vulnerability to disease or rare genetic disorders is likely to be passed on to the next generation.

So these results paint a grim picture for the tiger’s chance of survival.

The findings are reported in the journal Mammalian Biology.

During the early 20th Century, the Amur tiger was almost driven to extinction, as expanding human settlements, habitat loss and poaching wiped out this biggest of cats from over 90% of its range.

By the 1940s, just 20 to 30 individuals survived in the wild. The new study has identified that this recent “genetic bottleneck” – when the breeding population of tigers was so critically low – has decimated the Amur tiger gene pool.

A more genetically diverse population of animals has a much better chance of survival; it is more likely, for example, to contain the genetic resistance to a variety of diseases and less likely to succumb to rare genetic disorders, which can be “cancelled out” by healthy genes.

Scientists in Russia, Spain and Germany worked together to analyse DNA samples from 15 wild Amur tigers in the Russian Far East.

They took blood samples from the animals and screened them for certain “markers” – points in the DNA code that show that an animal had parents that were genetically very different from each other.

The results revealed evidence of the genetic bottleneck during the tigers’ recent history, when the variety of genes being passed on dramatically reduced.

Genetically speaking, the Amur tiger has not recovered from this.

“Our results are the first to demonstrate a quite recent genetic bottleneck in Siberian tigers, a result that matches the well-documented severe demographic decline of the Siberian tiger population in the 1940s,” the researchers wrote in the paper.

“The worryingly low effective population size challenges the optimism for the recovery of the huge Siberian cat.”

Amur tigers are what we used to call Siberian tigers until we learned a bit about Russian geography and learned from the Russians that these tigers aren’t actually found in Siberia.

They may have existed in Siberia at one time, for it turns out that the extinct Caspian subspecies was actually a western population of Amur tigers. Siberia would lie between the ranges of the population from the Caspian Sea region and the population that currently exists in the Russian Far East. It is likely that some tigers did range into parts of Siberia at one time.

The problem isn’t just the deleterious and lethal recessives that are mentioned in this post. The old bugaboo of inbreeding depression looms high, for most cat species do not have very high inbreeding tolerance.

Tigers are also somewhat susceptible to canine distemper.  And Amur tigers commonly hunt dogs that belong to hunters and trappers operating in the region.  Most dogs in the region have not been vaccinated for distemper, which means very bad things for tigers.

My little hope that one day we might be able to restock the Caspian tiger using reintroduced Amur tigers has been fully destroyed. Every Amur tiger is a precious individual, and we can’t risk any of them, even if it is to revive their former western population.

Unless a crossbreeding program can be implemented, as was done when Texas cougars were introduced to Florida panther range, the future is very bleak for the Amur tiger.

And because all other extant tiger subspecies are both critically endangered and native to more or less tropical or subtropical environment, I don’t know how such a program could be implemented practically.

I guess it’s time to enjoy the world’s largest cat while it still lasts.

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