Woolly mammoths suffered genetic 'meltdown' before extinction

Woolly mammoths accumulated multiple harmful mutations in their genome which may have hampered their ability to survive, before the giant animals went extinct thousands of years ago, a new study has found.

Dwindling populations created a "mutational meltdown" in the genomes of the last wooly mammoths, which had survived on an isolated island until a few thousand years ago, researchers said.

Woolly mammoths were one of the most common large herbivores in North America, Siberia and Beringia until a warming climate and human hunters led to their extinction on the mainland about 10,000 years ago.

Small island populations persisted until about 3,700 years ago before the species finally disappeared.

Researchers from University of California, Berkeley in the US compared existing genomes from a mainland mammoth that dates back to 45,000 years ago, when the animal was plentiful, to one that lived about 4,300 years ago.

The recent genome came from a mammoth that had lived in a group of about 300 animals on Wrangel Island in the Arctic Ocean.

The analysis showed that the island mammoth had accumulated multiple harmful mutations in its genome, which interfered with gene functions.

The animals had lost many olfactory receptors, which detect odours, as well as urinary proteins, which can impact social status and mate choice.

The genome also revealed that the island mammoth had specific mutations that likely created an unusual translucent satin coat.

The comparison gave researchers the rare opportunity to see what happens to the genome as a population declines, and supports existing theories of genome deterioration stemming from small population sizes.

The study also offers a warning to conservationists: preserving a small group of isolated animals is not sufficient to stop negative effects of inbreeding and genomic meltdown.

For those interested in wooly mammoth "de-extinction," the study demonstrates that some mammoth genomes carry an overabundance of negative mutations, researchers said.

"Here we got a rare chance to look at snapshots of genomes 'before' and 'after' a population decline in a single species. The results we found were consistent with this theory that had been discussed for decades," said researcher Rebekah Rogers from University of California, Berkeley.

"With only two specimens to look at, these mathematical models were important to show that the differences between the two mammoths are too extreme to be explained by other factors," said Rogers.

The study was published in the journal PLOS Genetics.