New DNA evidence suggests when Viking invaders spread through the North Atlantic, they unwittingly brought armies of mice with them. The study, published online in BMC Evolutionary Biology, shows the pattern of Norwegian Viking conquests matches the pattern of a particular DNA marker in the mouse population, and descendents of the stowaway mice still exist in former Viking strongholds.
The house mouse, Mus musculus domesticus, is an opportunistic species whose destiny is linked with that of humans. As their name implies, house mice are often found living among human settlements and may have even co-evolved to live among humans.
Animals like house mice, rats, and even body lice have accompanied human migrations throughout history. It's only recently that scientists have been able to use DNA analyses to see how the spread of their populations is linked to human settlements.
Between the eighth and eleventh centuries A.D., Norwegian Vikings established new colonies in several regions, including Great Britain, Iceland, Newfoundland, and Greenland. Scientists suspected that house mice were able to stowaway in their boats and then make their homes in the settlements, as well. Some evidence for this is the presence of a DNA pattern found only in mice in Norway, from which the Vikings set sail, and northern Britain, which Vikings colonized.
In this new study, scientists analyzed modern and ancient mouse remains from the sites of Viking colonies and found the same pattern. The team took DNA samples from mouse bones found at archaeological digs at Viking settlements in Iceland, Greenland, and Newfoundland, and compared the ancient DNA with samples of modern mouse DNA collected from the same regions. The scientists focused their analysis on a small fragment of mitochondrial DNA, which is passed down unchanged by mothers to their offspring. By looking at this fragment, they could tell which mice were related. With these data, the team figured out how house mice spread across Europe, and showed the mouse family tree matched the pattern of the Vikings' colonization.
This study indicates just how much people can alter the ecosystem in which they live. As we move around and settle in new areas, animals come with us, both unintentionally and purposefully. With animals like house mice, once we humans settle down in a new area, we create a new habitat that perfectly suits our stowaways as well.