Fig. 1.

Maximum clade credibility chronogram inferred from a BEAST dating analysis. Nodes b–j are nodes of interest with gray horizontal bars indicating the 95% highest posterior density interval; node 1 in green circle is used for calibration. Major ancestral range reconstructions are shown below the branches (N, Nearctic; W, West Palearctic; E, East Palearctic), and arrows show main dispersal events. Species names and terminal branches are in red for East Palearctic species, blue for Nearctic species, and black for West Palearctic species. Pink asterisks are nodes (c, f1–f4, and g1–g3) that showed an increase in diversification rate. The blue circle (node b) indicates the saline origin of the genus Gammarus and the red circle (node c) indicates the origin of freshwater species. Outgroups and Baikal amphipods are not shown (Figs. S1 and S2). (Right) Maps correspond to the sampling sites for the adjacent clade.