Genomic meltdown found before woolly mammoths' extinction

Once one of the most common large herbivores in North America, Siberia and Beringia, woolly mammoths' genomes appeared to have experienced a mutational meltdown as their population dwindled, pushing them closer to extinction.

The finding, published this week in the journal PLOS Genetics, was based on comparing genomes from a mainland woolly mammoth that dates back to 45,000 years ago, when the animal was plentiful, to genetic material from one that lived about 4,300 years ago, when the species neared extinction.

A warming climate and human hunters led to the mammoths' extinction on the mainland of North America about 10,000 years ago.

Small island populations persisted until about 3,700 years ago before the species finally disappeared. The islands where they lived are along Beringia, the now-underwater land bridge between North America and Siberia.

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

"We found an excess of what looked like bad mutations in the mammoth from Wrangel Island," said Rebekah Rogers, who led the work as a postdoctoral scholar at the University of California, Berkeley, in collaboration with professor of integrative biology Monty Slatkin, and is now an assistant professor at the University of North Carolina at Charlotte.

The researchers found that the island mammoth had accumulated multiple harmful mutations in its genome, which interfered with gene functions. It had lost many olfactory receptors, which detect odors, as well as urinary proteins, which can impact social status and mate choice.

In addition, they revealed that the island mammoth had specific mutations that likely created an unusual translucent satin coat.

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

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

"There is a long history of theoretical work about how genomes might change in small populations. Here we got a rare chance to look at snapshots of genomes 'before' and 'after' a population decline in a single species," Rogers was quoted as saying in a news release from UC Berkeley.

"The results we found were consistent with this theory that had been discussed for decades." Endit