World’s last woolly mammoths were inbred

A new genomic analysis shows the last surviving population of woolly mammoths were inbred, but this low genetic diversity cannot explain their mysterious extinction.

Studying this last population of woolly mammoths could help prevent the extinction of animal species today.

Woolly mammoths first emerged about 300,000 years ago. They were once widespread across the cold tundra of Europe, Asia and North America.

By 10,000 years ago, the world’s last woolly mammoths were isolated to Wrangel Island. The 150km-long island is off the northern coast of far-eastern Siberia. This last stronghold of the iconic Ice Age animals held out until as recently as 4,000 years ago.

Tundra island landscape
Wrangel Island landscape. Credit: Love Dalén.

“We can now confidently reject the idea that the population was simply too small and that they were doomed to go extinct for genetic reasons,” Love Dalén, an evolutionary geneticist at the Centre for Palaeogenetics, a joint collaboration between the Swedish Museum of Natural History and Stockholm University.

Dalén is senior author on the new study which is published in the journal Cell.

“This means it was probably just some random event that killed them off, and if that random event hadn’t happened, then we would still have mammoths today,” Dalén adds.

The study is based on the genomes of 21 woolly mammoths – 14 from Wrangel Island and 7 from the mainland population which pre-dated the genetic bottleneck. The samples provide a window into how mammoth genetic diversity changed over 50,000 years.

Wrangel mammoths showed clear signs of inbreeding and low genetic diversity. The population originated from at most 8 individuals before growing to 200–3000 within 20 generations. But this genetic diversity declined only very slowly over the 6,000 years that the mammoths were on Wrangel Island, suggesting the population size was stable right to the end.

The Wrangel mammoths did show signs of some harmful mutations. But the genetic analysis also showed that they were slowly purging the worst of the mutations.

“What happened at the end is a bit of a mystery still—we don’t know why they went extinct after having been more or less fine for 6,000 years, but we think it was something sudden,” says Dalén.

The researchers hope further genetic analysis of the final 300 years of the species existence – absent in this study – will shed light on how they went extinct.

In the meantime, the scientists say studying the Wrangel Island woolly mammoths could help inform conservation of today’s creatures to prevent extinctions.

“Mammoths are an excellent system for understanding the ongoing biodiversity crisis and what happens from a genetic point of view when a species goes through a population bottleneck because they mirror the fate of a lot of present-day populations,” says first author Marianne Dehasque, also from the Centre for Palaeogenetics.

“It’s important for present day conservation programs to keep in mind that it’s not enough to get the population up to a decent size again; you also have to actively and genetically monitor it because these genomic effects can last for over 6,000 years,” adds Dalén.

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