Fig. 2

Crossing strategy applied in this study (a) Experimental evolution was achieved by crossing distantly related medaka lines, the highly inbred (hereafter, Hd-rR) line (from the southern Japanese population), and the wild Teradomari line (from the northern Japanese population). We used two individuals as the F0 generation: an Hd-rR male (yellow DNA) and a Teradomari female (green DNA); the single nucleotide polymorphism (SNP) rate between their genomes is as much as 3.2 % [33]. The F1 generation was then further crossed to obtain the F2 generation, and the evolutionary outcome was evaluated in the F3 generation (illustrated as embryos). The genomic sequence of the F3 individual is expected to be a mix of those of the two original populations (illustrated beneath the embryos). b Geographical distribution of the four medaka populations used in this study. The Hd-rR line was used for evaluating developmental stability. The map is modified from a previous study [39]