Ice Age warmth wiped out lemmings, study finds

Collared lemming (Dicrostonyx torquatus)

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Lemmings became "regionally extinct" five times due to rapid climate change during the last Ice Age, scientists have found.

Each extinction was followed by a re-colonisation of genetically different lemmings, according to the study.

It investigated how Europe's small mammals fared during the era when large numbers of megafauna became extinct.

Previously, experts believed that small mammals were largely unaffected during the Late Pleistocene.

But when the international research team analysed ancient DNA sequences from fossilised remains of collared lemmings (Dicrostonyx torquarus) from cave sites in Belgium, they were surprised by the results.

"What we'd expected is that there'd be pretty much just a single population that was there all the way through," said research team member Dr Ian Barnes from the school of biological sciences at Royal Holloway University in Surrey.

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Instead the tests revealed that genetically distinct populations of lemmings were "present at different points in time" during the Late Pleistocene, 11,700 to around 126,000 years ago, meaning that the lemming population had been wiped out multiple times and then re-colonised some time after, possibly from populations in eastern Europe or Russia.

The study, published in the journal Proceedings of the Natural Academy of Sciences, found that these "regional extinctions" occurred during periods of rapid warming within the last Ice Age.

Scientists suggest such climate fluctuations may have left lemmings unable to adapt to the changes in the vegetation they relied on as a food source.

Although Belgium's lemmings were able to re-colonise after each regional extinction, the population lost much of its genetic diversity during this pattern of events.

"There's an amazing genetic diversity just at this one site in Belgium, compared to the tiny amount of diversity that we see in the modern-day lemmings," said Dr Barnes.

By the end of the Late Pleistocene, western Europe's lemmings had retreated to the Arctic Ocean coast across Siberia where modern collared lemmings are still found.

Megafauna mystery

The team's findings could also shed light on why many of Europe's megafauna, such as woolly mammoths, cave hyenas and cave bears, became extinct during the same period.

For years experts have debated whether the demise of these huge land mammals was mainly due to human predation or environmental changes.

Previous studies have suggested that in Australia, human activity was largely responsible for the extinction of megafauna. But the debate about what caused many of Europe's large mammals to disappear during the Late Pleistocene remains "a reasonably open question", according to Dr Barnes.

The team focused on lemmings as indicators of what may have happened to other land mammal populations during the last Ice Age.

Since such small mammals would not have been hunted by humans, the discovery of this decrease in population size shows that there was a "general pattern of instability" in both large and small mammals during the Late Pleistocene.

According to the study, this pattern supports the theory that environmental changes, rather than human predation, were the main cause of the demise of megafauna in Europe at the end of the last Ice Age.

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