August 4, 2009

European Bison Nears Extinction

New research has found that the European bison, Europe's heaviest surviving land animal, is still in danger of extinction, despite heroic conservation efforts. 

Despite the number of wild bison in the herd having steadily risen to about 800, one of the last two wild herds of pure-bred European bison has dwindled down to an effective population of just 25.

The effective population is a measure of the bison's genetic diversity, and can even serve to predict the animal's chances of survival.
This European heavy-weight measures about 10 feet long and are between 6 and 7 feet tall, and can weigh up to 2,000 pounds.

The bison have survived in the wild in two herds that roam both sides of the Bialowieza forest in Belarus and Poland.

Even though European bison can technically be interbred with American bison, they are still basically considered to be separate and individual species with substantial genetic and morphological differences. 

This particular species has a very unfortunate history involving unmitigated poaching that caused the mammal to slowly decline in number.
The European bison was protected for hundreds of years across large areas because it was considered to be "ËœKing's game', which was protected by the monarchy and Russian tsars that conquered Poland.

However, the early 20th Century witnessed people inflicted with great hunger after World War I, who in turn hunted the unprotected bison for meat and hide. By the time 1919 came around, there were no more bison to be found in the wild.

"So in the 1920s, biologists decided to reconstruct the population out of the few individuals left in the public and private collections and zoological gardens," says Malgorzata Tokarska of the Mammal Research Institute of the Polish Academy of Sciences, in Bialowieza, Poland.

A surviving pure-bred population was formed from just four bulls and three cows of the 54 European bison that were remaining in the world at that time. All of their offspring alive today originate from one single bull, meaning 90 percent of all their genes stem from two founders.

Now numbering around 1400, the bison are scattered across the globe. The mere 400 wild bison in existence dwell in the Bialowieza forest on both sides of the border.

In order to quantify the affect of the 20th Century bottleneck, Tokarska and colleagues Agata Kawalko, Jan Wojcik and Cino Pertoldi took genetic samples of 178 individuals at 12 different points in their genome.

The team was able to analyze the bison born each decade beginning in 1950 by testing the skulls and frozen soft tissues of long-dead animals, as well as live animals.

According to the team's report in the Biological Journal of the Linnean Society, the genetic testing has revealed that the herd has an effective population of just 25 animals, despite the increase of actual bison numbers.

The effective population of any group of animals is always lower than the number that actually exist, because of factors like non-breeding individuals or a skewed sex ratio that must be considered.

However, the European bison has obviously never recovered from the genetic bottleneck of the early years of the 20th Century.

To be considered safe from the immediate threat of extinction incurred by the dangerous results of inbreeding or too few genes to adapt to new environments, an effective genetic population of 50 animals is typically required.

"They are highly inbred and closely related and the genetic surveys confirmed that," says Tokarska.

"We could pretend that we have a big plan, but honestly, there's not much we can do. We can not enrich the genetics using breeding methods, since there are no out-bred animals. They all come from the same seven founders."

"Mostly, we can work on maintaining the bison-friendly environment and widen it," she says.

Tokarska has just begun the analysis of the remaining Belarus bison, which may come from the same animals, but the other herd differs a bit genetically.

She says that if researchers are able to confirm that they are from the same animal, it may be possible to bring the two herds together and improve the survival changes of the species.


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