Figure 5.

Plot of the postzygotic reproductive isolation index against K2P‐corrected distances in cytochrome b gene between hybridizing species. The reproductive isolation index is defined according to Russell's study as follows: 0, both hybrid sexes are fertile; 0.5, one sex fertile, the other sometimes infertile; 1, one sex fertile, the other infertile but viable; 1.5, one sex infertile but viable, the other sometimes still fertile; 2, both sexes viable but infertile; 2.5, one sex viable but infertile, the other sex only sometimes viable; 3, one sex viable, the other missing; 3.5, one sex sometimes viable, the other not; 4, both sexes inviable; 5, hybrids of at least one sex are known to form asexual lineages (highlighted in grey colour). Species pairs where one species occurred more than once in the analysis are indicated by grey triangles (Cobitis taenia), diamonds (Poeciliopsis monacha) and grey squares (Hexagrammos octogramus), respectively