Fig. 3.

a Sampling sites of Gasterosteus aculeatus in the eastern Pacific basin and northern Europe. The extent of Fig. 1a is bounded with black lines. The configuration of ice sheets at the last glacial maximum [102] is shown with white shading. The map was created with rnaturalearth ver. 0.1.0 (https://github.com/ropensci/rnaturalearth) and sf ver. 0.9-0 (https://r-spatial.github.io/sf/). b Maximum likelihood phylogenetic tree of native non-hybrid individuals from western and eastern basins of the Pacific and northern Europe based on 3717 concatenated SNPs. Individuals from Japanese freshwater populations of G. aculeatus are highlighted in blue. Bootstrap values (> 60%) are shown