Figure 1.

Map of Switzerland showing the sampling localities of Microtus arvalis samples included in cline analyses of the three transects. Transects are described in Table 1. Localities are designated according to the cytb lineage they harbour (white=Central, grey=Western, black=Italian). The Valais transect along the Rhone valley contains a double transition from the Central through the Western to the Italian lineage. Mixed populations (Figure 2) are indicated by bi-coloured circles. Localities closer than two kilometres to each other were merged for this figure.