Common vole
microtus_arvalis
Interspecific F1 crosses between different species of the common vole demonstrate primary non-random X inactivation. Crosses between M.arvalis and anothe species of «arvalis» group has active X-cromosome from M.arvalis (Zakian et al 1987).
The common vole is hardly restricted in means of distribution and habitat and inhabits large areas of Eurasia. As Microtus arvalis followed human civilisation, primary and secondary habitats can be distinguished. The primary habitats are everything but dense forests, such as meadows, heath lands, and fallow land. The secondary habitats are mainly agricultural fields whereby shallow sloped areas are preferred. The natural food of the common vole is grass, but it also feeds on many agricultural crops (within secondary habitats) and here its reproduction is faster than in primary habitats.
(From Wikipedia)
Systematics of the common voles
Evolution tree of the voles (Mazurok et al 2001)