Ice Age 6: the genomic meltdown of the woolly mammoth

If the Ice Age animated film franchise were to follow the descendants of Manny the mammoth for a few thousand years or so, viewers would see the species suffer a ‘mutational meltdown’ as a result of its dwindling and increasingly isolated populations.

Woolly mammoths were one of the most common large herbivores in North America, Siberia and Beringia until a warming climate and hunters led to their extinction on the mainland about 10,000 years ago, though small island populations persisted for another 6300 years or so. Now, the genomes of mammoths from two very different periods in history have been examined by Rebekah Rogers and Montgomery Slatkin of the University of California, Berkeley.

The researchers 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 4300 years ago. The latter came from a mammoth that had lived in a group of about 300 animals on Wrangel Island in the Arctic Ocean, where mammoths subsisted with a population size more than 43-fold lower than previous populations.

Published in the journal PLOS Genetics, 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 provided 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.

“There is a long history of theoretical work about how genomes might change in small populations,” said Rogers. “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.”

Image courtesy of Timothy Neesam under CC BY-NC-ND 2.0