Amino acid alterations of the avpr1a gene plotted onto a mitochondrial cytochrome b phylogeny of the genus Microtus. Positions and types of changes are labelled as in Figure 2. Bootstrap values > 50 (10'000 replicates) of the maximum likelihood method are shown on the branches. AA alterations in Microtus segregate generally independently of the phylogenetic background except for the closely related sister species M. arvalis and M. rossiaemeridionalis which show two identical changes at the same positions (58, 85). Additionally, a two AA long insertion together with an alteration at position 42 appear in the cluster of M. agrestis together with M. montebelli and M. kikuchii, where the changes seem to have been subsequently lost in M. oeconomus.