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How Irish stoats survived the last great Ice Age

Posted on 5 April 2007

When did the animals and plants of modern day British Isles arrive? Most were wiped out during the last Ice Age and have taken millennia to re-colonise or were introduced by humans. But this is not always the case, as shown by research led by Professor Jeremy Searle, of the Department of Biology at the University of York.

His latest findings are published in Proceedings of the Royal Society B: Biological Sciences in collaboration with scientists from the Academy of Science of the Czech Republic and Queen’s University, Belfast.

They investigated the history of the stoat, a cold-tolerant animal which lives today throughout the northern hemisphere up to the high Arctic. They found startling evidence that stoats survived in Ireland at the coldest point of the last Ice Age, and have been isolated there ever since.

We found stoats to be far less genetically variable in Britain than Ireland, which indicates that the Irish stoat population is older than stoats in Britain

Professor Searle

The current British stoats apparently arrived more recently via a land bridge with Europe, replacing the previous cold-tolerant residents.

Professor Searle said, "Even though the landmass of Britain is 2.5 times larger than Ireland and is closer to continental Europe, we found stoats to be far less genetically variable in Britain than Ireland, which indicates that the Irish stoat population is older than stoats in Britain."

The cold-tolerant stoats followed the retreating ice at the end of the last Ice Age and spread throughout previously glaciated areas in the British Isles. The stoats in Ireland would have become isolated with rising sea level as the ice retreated. Later, the Isle of Man population of stoats would also have become separated from the British. However, Ireland and the Isle of Man would have become islands well before Britain was separated from continental Europe.

The research suggests that a land bridge from Britain to continental Europe would have been available to stoats during the warm periods of the Late Glacial and Postglacial when the climate in Britain would have been similar to today. Therefore, the scientists believe, stoats, adapted to the warm conditions, used the bridge to enter Britain and replace the original cold-tolerant lineage that continues to survive in the isolated populations of Ireland and the Isle of Man.