Lack of concordance between mtDNA gene flow and population density fluctuations in the bank vole.

The genetic structure of bank voles Clethrionomys glareolus was determined from analyses of mitochondrial DNA (mtDNA) sequences, and compared with previous data on geographical synchrony in population density fluctuations. From 31 sample sites evenly spaced out along a 256-km transect in SE Norway a total of 39 distinct mtDNA haplotypes were found. The geographical distribution of the haplotypes was significantly non-random, and a cladistic analysis of the evolutionary relationship among haplotypes shows that descendant types were typically limited to a single site, whereas the ancestral types were more widely distributed geographically. This geographical distribution pattern of mtDNA haplotypes strongly indicates that the range and amount of female dispersal is severely restricted and insufficient to account for the previously observed synchrony in population density fluctuations. We conclude that geographical synchrony in this species must be caused by factors that are external to the local population, such as e.g. mobile predators.