Of Mice and Vikings

A recent paper from a multinational team of researchers from the UK, USA, Iceland, Denmark and Sweden describes studies of mytochondrial DNA (mtDNA)  in mice to track ancient Viking movements.  The mice genetics confirm the movements of the Vikings some 1000 years ago to Britain and Greenland and Iceland. They do not however provide any confirmation of the fleeting Viking presence in Newfoundland.

Viking movements: map from bbc.co.uk

“Modern house mouse populations were sampled across Iceland (9 localities), at Narsaq in Greenland (near the Viking Age ‘Eastern Settlement’) and in the north-west of Newfoundland (near the Norwegian Viking archaeological site at L’Anse aux Meadows, 4 localities).  Ancient DNA was obtained from archaeological house mouse bones. In Greenland, these were from the Norwegian Viking ‘Eastern Settlement’ (3 individuals) and ‘Western Settlement’ (2 individuals), dating from between 1015– 1165 AD. In Iceland, these were from four archaeological sites in the north of Iceland, three of which date to the 10th C (1 individual per site) and one of which dates to the Medieval period or later (1477–1717 AD; 2 individuals”.

E P Jones, K Skirnisson, T H McGovern, M TP Gilbert, E Willerslev, J B Searle. Fellow travellers: a concordance of colonization patterns between mice and men in the North Atlantic regionBMC Evolutionary Biology, 2012; 12 (1): 35 DOI: 10.1186/1471-2148-12-35

Abstract

Background: House mice (Mus musculus) are commensals of humans and therefore their phylogeography can reflect human colonization and settlement patterns. Previous studies have linked the distribution of house mouse mitochondrial (mt) DNA clades to areas formerly occupied by the Norwegian Vikings in Norway and the British Isles. Norwegian Viking activity also extended further westwards in the North Atlantic with the settlement of Iceland, short-lived colonies in Greenland and a fleeting colony in Newfoundland in 1000 AD. Here we investigate whether house mouse mtDNA sequences reflect human history in these other regions as well.

Results . House mice samples from Iceland, whether from archaeological Viking Age material or from modern-day specimens, had an identical mtDNA haplotype to the clade previously linked with Norwegian Vikings. From mtDNA and microsatellite data, the modern-day Icelandic mice also share the low genetic diversity shown by their human hosts on Iceland. Viking Age mice from Greenland had an mtDNA haplotype deriving from the Icelandic haplotype, but the modern-day Greenlandic mice belong to an entirely different mtDNA clade. We found no genetic association between modern Newfoundland mice and the Icelandic/ancient Greenlandic mice (no ancient Newfoundland mice were available). The modern day Icelandic and Newfoundland mice belong to the subspecies M. m. domesticus, the Greenlandic mice to M. m. musculus.

Conclusions: In the North Atlantic region, human settlement history over a thousand years is reflected remarkably by the mtDNA phylogeny of house mice. In Iceland, the mtDNA data show the arrival and continuity of the house mouse population to the present day, while in Greenland the data suggest the arrival, subsequent extinction and recolonization of house mice – in both places mirroring the history of the European human host populations. If house mice arrived in Newfoundland with the Viking settlers at all, then, like the humans, their presence was also fleeting and left no genetic trace. The continuity of mtDNA haplotype in Iceland over 1000 years illustrates that mtDNA can retain the signature of the ancestral house mouse founders. We also show that, in terms of genetic variability, house mouse populations may also track their host human populations.

Science Daily:

… Modern samples of mouse DNA were collected and compared to ancient samples dating mostly from the 10th to the 12th century. Samples of house mouse DNA were collected from nine sites in Iceland, Narsaq in Greenland, and four sites near the Viking archaeological site, L’Anse aux Meadows, in Newfoundland. The ancient samples came from the Eastern and Western settlements in Greenland and four archaeological sites in Iceland.

Analysis of mouse mitochondrial DNA showed that house mice (M. m. domesticus) hitched a lift with the Vikings, in the early 10th century, into Iceland, either from Norway or the northern part of the British Isles. From Iceland the mice continued their journey on Viking ships to settlements in Greenland. However, while descendants of these stowaways can still be found in Iceland, the early colonizers in Greenland have become extinct and their role has been filled by interloping Danish mice (M. m. musculus) brought by a second wave of European human immigrants. ..

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