Fig. 1

Genetic background and localisation of the parapatric Microtus arvalis populations (crosses) analysed in the hybrid zone between the evolutionary lineages Western and Central. The probability of membership for genetic clusters obtained with Geneland is given in light yellow (>0.9) for the Western and in red (<0.1) for the Central lineage. The distance between the two experimental populations is 8.4 km. Black dots represent other populations included in the admixture analyses but not in tests of partner preferences. The allopatric populations for partner preference tests were localised farther to the west and east of the area shown. The lakes and stream in the valley are represented in blue, while the crests of the valley are the dotted lines