Colonization history of north European field voles (Microtus agrestis) revealed by mitochondrial DNA.

The genetic structure of field vole (Microtus agrestis) populations from northern Europe was examined by restriction fragment length polymorphisms of mitochondrial DNA (mtDNA) in 150 individuals from 67 localities. A total of 83 haplotypes was observed, most of which were rare and highly localized geographically. Overall nucleotide diversity was high (1.34%), but showed a tendency to decrease with higher latitude. Two major mtDNA lineages differing by 2% in nucleotide sequence were identified. A southern mtDNA lineage was observed in field voles from Britain, Denmark and southern and central Sweden, whereas voles from Finland and northern Sweden belonged to a northern lineage. The strict phylogeographic pattern suggests that the present population genetic structure in field voles reflects glacial history: the two groups are derived from different glacial refugia, and recolonized Fennoscandia from two directions. A 150-200-km-wide secondary contact zone between the two mtDNA groups was found in northern Sweden. Distinct phylogeographic substructuring was observed within both major mtDNA groups.