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A team of researchers from McMaster University and elsewhere has carried out a phylogeographic study of the extinct American mastodon (Mammut americanum) based on 35 newly-sequenced mitochondrial genomes. Their findings suggest that American mastodons repeatedly expanded into northern latitudes in response to interglacial warming.

Artistic rendering of American mastodons (Mammut americanum). Image credit: Julius Csotonyi.

Artistic rendering of American mastodons (Mammut americanum). Image credit: Julius Csotonyi.

The American mastodon was an iconic part of wooded and swampy habitats in Pleistocene Americas, with remains recovered from the Central American subtropics to the Arctic latitudes of Alaska and Yukon.

The species went extinct 11,000 years ago during the megafaunal extinctions that took out many of the large mammals such as mammoths, saber-toothed cats and ground sloths.

There has been much speculation about what caused their extinction, though many scientists believe it was a combination of climate change, increasing competition for food sources and overhunting by early humans.

Dramatic and repeated temperature fluctuations occurred routinely on the planet for millions of years — the most dramatic of which over the last 800,000 years — resulting in ice-sheet expansion and retraction and the warming of previously frozen northern regions whose new forests and wetlands provided new food sources for some animals like the mastodon, moose and beaver, but took away grasslands from others like horses, mammoths and bison.

“The genetic data show a strong signal of migration, moving back and forth across the continent, driven, what appears to be entirely by climate,” said senior author Professor Hendrik Poinar, an evolutionary geneticist at McMaster University.

“These mastodons were living in Alaska at a time when it was warm, as well as Mexico and parts of Central America.”

“These weren’t stationary populations, the data show there was constant movement back and forth.”

For the study, Professor Poinar and colleagues teased out and reconstructed DNA from fossilized samples including teeth, tusks and bones.

The analysis shows that mastodons were moving vast distances in response to warming climate conditions and melting ice sheets, from warmer environments, to the northernmost reaches of Alaska and the Yukon.

However, despite these massive increases in territory, northern populations were much less genetically diverse, rendering them more vulnerable to extinction.

“By looking genetically at these animals which lived for the last 800,000 years, we can actually see the make-up of these populations that made it up to the north,” said first author Emil Karpinski, a graduate student at McMaster University.

“It’s really interesting because a lot of species presently, like moose and beaver, are rapidly expanding their range northwards by as much as tens to hundreds of kilometers every century.”

“Analysis of DNA preserved in these fossil mastodon bones gives us so much more information on how these now-extinct beasts lived and died in comparison to what we know based on traditional paleontological approaches,” said co-author Dr. Grant Zazula, a paleontologist with the Government of Yukon.

“These data hold the key to our understanding of how ancient animal communities like mastodons adapted to changes in the past, and provide clues to how arctic ecosystems will respond to future warming scenarios.”

The results were published in the journal Nature Communications.

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E. Karpinski et al. 2020. American mastodon mitochondrial genomes suggest multiple dispersal events in response to Pleistocene climate oscillations. Nat Commun 11, 4048; doi: 10.1038/s41467-020-17893-z

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