Of mice and (Viking?) men: phylogeography of British and Irish house mice

Abstract

The west European subspecies of house mouse (Mus musculus domesticus) has gained much of its current widespread distribution through commensalism with humans. This means that the phylogeography of M. m. domesticus should reflect patterns of human movements. We studied restriction fragment length polymorphism (RFLP) and DNA sequence variations in mouse mitochondrial (mt) DNA throughout the British Isles (328 mice from 105 localities, including previously published data). There is a major mtDNA lineage revealed by both RFLP and sequence analyses, which is restricted to the northern and western peripheries of the British Isles, and also occurs in Norway. This distribution of the 'Orkney' lineage fits well with the sphere of influence of the Norwegian Vikings and was probably generated through inadvertent transport by them. To form viable populations, house mice would have required large human settlements such as the Norwegian Vikings founded. The other parts of the British Isles (essentially most of mainland Britain) are characterized by house mice with different mtDNA sequences, some of which are also found in Germany, and which probably reflect both Iron Age movements of people and mice and earlier development of large human settlements. MtDNA studies on house mice have the potential to reveal novel aspects of human history.

Figure 1

Archaeological records of house mice in Britain (see appendix 1 in the electronic supplementary material for further details). Following the chronology by the British and Irish Archaeological Bibliography (http://www.biab.ac.uk/chronology.asp), Bronze Age (black circles) is considered as 2300–700 BC, Iron Age (grey circles; lowland Britain) as 700 BC to AD 43 and Roman (white circles; lowland Britain) as AD 43–450. As most records are from lowland Britain, we retain the chronological framework from lowland Britain when referring to sites elsewhere.

Figure 2

Phylogenetic tree for M. m. domesticus from complete mtDNA d-loop sequences after Bayesian analysis (see text). The tree shows all house mouse haplotypes found in the British Isles together with all available haplotypes from GenBank. All posterior probabilities of 0.60 or greater are shown for branches leading to British haplotypes.

Figure 3

The distribution of haplotypes of the Orkney mtDNA lineage (black circles) and other haplotypes (white circles) among 328 house mice from 105 localities distributed over the (a) British Isles and (b) Orkney and the nearby British mainland. Each pie represents a single collection locality with black circles indicating the proportion of individuals of the Orkney mtDNA lineage. Data taken from complete and partial mtDNA d-loop sequences, and RFLP data from the complete mtDNA genome.