'Viking mouse' invasion tracked

Humans and mice have been close companions for thousands of years

Scientists say that studying the genes of mice will reveal new information about patterns of human migration.

They say the rodents have often been fellow travellers when populations set off in search of new places to live - and the details can be recovered.

A paper published in a Royal Society journal analyses the genetic make-up of house mice from more than 100 locations across the UK.

It shows that one distinct strain most probably arrived with the Vikings.

Rodents from Orkney are among those helping the scientists. It has been shown that mice from the islands have a DNA signature similar to their Scandinavian relations.

But these house mice (Mus musculus domesticus) were also found in areas around the Atlantic coast of Europe reached by the Norse explorers, said Professor Jeremy Searle, from York University.

"If we look at the genetic patterning of the mice, we find they have patterning that very much relates to human history; and so we get a particular genetic type of mouse that is found in the region where the Norwegian Vikings operated," he told BBC News.

"What this suggests to us is that the Norwegian Vikings were taking these mice around and they were taking a particular genetic type; because there are all sorts of genetic types and the particular type that happened to be where the first Vikings picked them up is the one that got spread around."

Abundant food

Much of Britain has another strain with genetic similarities to a type in Germany.

It is thought this rodent probably arrived from continental Europe with Iron Age people.

The humble house mouse has its origin as a species in Asia and migrated on foot to the Middle East, becoming firmly established in the first agricultural settlements - no doubt enjoying the abundant food to be found in grain stores.

"Interestingly, [the house mice] didn't migrate into Europe at the same time as agriculture, about 8,000 years ago," Professor Earle explained.

"They only migrated in about 3,000 years ago. And the reason for this is that it wasn't until the Iron Age that we got the development of large settlements in western Europe. The house mouse needs these large settlements in order to survive and out-compete the local field mouse."

Professor Searle said future studies with mice could help document more fine-scale Viking movements such as the colonisation of different parts of Faroe, Iceland and even North America.

Professor Searle and colleagues publish their research in Proceedings of the Royal Society B: Biological Sciences.