Fig. 1

Substrate types and sampling sites inside and outside Lake Ohrid. a Bathymetric map of Lake Ohrid with 10 m contour lines. Coloured rectangles represent substrate types for a particular locality classified based on information recorded during field trips (see Methods for details on substrate classification). Sampling sites of Acroloxus are colour-coded according to substrate type, b Map of the Euro-Mediterranean subregion with sampling sites (grey: Balkans; pink: Lake Ohrid; © d-maps.com), c Shell of the littoral A. macedonicus, d Shell of the sublittoral A. improvisus