Fig. 1

Location of 24 cave populations of small Arctic charr (Salvelinus alpinus) in the Vindbelgur and Haganes areas, Lake Mývatn northern Iceland. The caves in the Vindbelgur area (V) are clustered into western and eastern locations (W = west; E = east) while those in Haganes (H) can be subdivided into northern, central and southern clusters of caves (N = north; C = central; S = south). One cave (cave 26) is positioned between the H-C and H-S subareas. Lake populations are referred as the generalist (Lake-G) and the Krús morph (Lake-K). Pie charts indicate proportion of individuals affiliated with each genetic cluster according to results from STRUCTURE (K = 5). The contour of lake Mývatn was obtained and modified from the OpenStreet map contributors and the GIS user community. The map of Iceland was obtained and modified from Einarsson et al. 2004