Spatial distribution of the Carpathian and Eastern mtDNA lineages of the bank vole in their contact zone relates to environmental conditions

Abstract

Two maternal lineages of bank vole (Myodes glareolus), the Eastern and the Carpathian, that had originated from different glacial refugia, came to a secondary contact in north-east Poland. We analysed a fragment of mitochondrial DNA (mtDNA) [cytochrome b (cyt b), 424 bp] from 1038 samples of the species to map the contact zone, estimate the mtDNA diversity of bank vole populations, and analyse if the distribution of the two lineages correlates with environmental variables. We found 89 haplotypes of mtDNA: 36 in the Carpathian lineage, 51 in the Eastern lineage and additionally 2 belonging in the Western lineage. The contact zone between lineages varied in width from 45 to 243 km. Nucleotide diversity and haplotype diversity of cyt b were notably higher in the Carpathian lineage than in the Eastern lineage. There was evidence of demographic and spatial expansion in the Eastern lineage. The spatial distribution of bank vole haplotypes belonging to the Carpathian lineage was positively correlated with the number of plant species associated with the Carpathian refugium and the mean temperature of July. The opposite (negative correlations with these two variables) was found for the Eastern lineage. These factors can be related to the different environmental conditions in which the two lineages survived and which affected the current mtDNA diversity.