Distribution of mitochondrial lineages of grass snakes in southern and western Switzerland (a) and microsatellite clusters according to our STRUCTURE analyses (b). Symbols and colours of mitochondrial lineages correspond to Kindler et al. (2013). Some symbols are slightly shifted from the sampling location, enhancing readability. The four samples in the bottom right corner originate from northern Italy beyond the map sector. Borders within Switzerland denote cantons. Abbreviations for cantons mentioned in the text: BE – Bern, GE – Geneva, SZ – Schwyz, TI – Ticino, UR – Uri, VD – Vaud, VS – Valais. Lake Geneva, mentioned in the text, is located in the southwesternmost part of Switzerland (cantons of Geneva and Vaud) and adjacent France. The maps were created by modifying a Wikimedia map (https://commons.wikimedia.org/wiki/File:Reliefkarte_Schweiz2.png).