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Mammoths and a dwindling food supply

DNA analysis of 50,000-year-old plants preserved in arctic soil has allowed researchers to determine that a change in vegetation was a likely contributor in the extinction of these enormous mammals at the end of the last ice age. The results were published in the scientific journal Nature in 2014.

Landscape from the Pleistocene Epoch in northern Spain with woolly mammoths (Mammuthus primigenius), equidae, woolly rhinoceros (Coelodonta antiquitatis) and Eurasian cave lions (Panthera leo spelaea).. © Wikimedia Commons, Mauricio Antón
By Vincent Niderkorn - Pascale Mollier, translated by Teri Jones-Villeneuve
Updated on 04/03/2014
Published on 03/12/2014

It is widely accepted that herbivorous megafaunal mammals became extinct due to climate change. These animals had survived several interglacial warming periods throughout the Quaternary period, but succumbed to the one after the last ice age, around 10,000 years ago. The study highlighted the importance of food supply in this decline.

Nothing to eat…

Woolly mammoths and rhinoceros, bison, horses – what did these huge animals eat in the cold climate of the Quaternary period? The question posed a quandary for scientists, because until recently, it was thought that the arctic vegetation was a grassy steppe. If this was the case, how could such meagre vegetation provide enough food for such large animals?  However, a study led by a large consortium of thirty research teams from twelve countries around the world does shed some light on the issue. The vegetation at that time was actually a tundra dominated by forbs, herbaceous dicotyledon-type plants with a higher protein content than grasses. The forbs were gradually overtaken by grasses and shrubs around 10,000 years ago, at the end of the last glaciation (Last Glacial Maximal between 25,000 and 15,000 years ago). This coincides with the extinction of much of the herbivorous megafauna. These results led researchers to believe that mammoths and woolly rhinoceros had a difficult time adapting to this new imposed diet, a possible contributing factor in their extinction.

Permafrost: a giant glacier

This study was based on analyses made on DNA extracted from Arctic permafrost. Permafrost is the deep section of the ground that remains frozen, and therefore impermeable. DNA amplification and sequencing were used on plant DNA fragments preserved in permafrost, allowing scientists to identify the plant species and piece together their history over the past 50,000 years. Additionally, samples from the stomachs and intestines of woolly mammoths and rhinoceros, bison and horses preserved in the ice dating from the last ice age revealed changes in their diets.

A special method of DNA analysis

One particular technique, called DNA metabarcoding, was used to identify the plant species. This technique makes it possible to analyse DNA that is in an extremely deteriorated state, which is the case for plant DNA preserved for 50,000 years in ice. INRA’s Herbivore Joint Research Unit in Clermont-Ferrand helped validate the quantitative aspect of this method, in cooperation with the CNRS’s Ecology Laboratory in Grenoble (1).

(1) Project financed through incentive credits from INRA’s Division of Animal Physiology and Livestock Systems - Management.

Contact(s)
Scientific contact(s):

Associated Division(s):
Animal Physiology and Livestock Systems , Social Sciences, Agriculture and Food, Rural Development and Environment.

Reference

Willerslev et al. (2014) Fifty thousand years of Arctic vegetation and megafaunal diet. Nature, 506, 47-51. doi : 10.1038/nature12921.

Alternating periods of freezing and thawing

The Quaternary period, which began around 200 million years ago, has been marked by a series of glaciations, one approximately every 10,000 years or so, which are separated by warmer interglacials. A quarter of exposed land was once covered with ice. The warming that followed the last ice age (120,000 to 10,000 years ago) quickly melted many of these ice caps, especially those covering North America and Europe.