Graphic representation of differences in the ITS2 region between and within Caenorhabditis species as branch lengths of a tree for 50 Caenorhabditis strains. Branch length was determined by maximum parsimony (see Methods). With one exception (* C. sp. 8), the differences between strains of the same species (blue boxes) are smaller than the smallest differences between the two most closely related species pairs (orange boxes). In all cases, the differences separating any pair of species is much greater than the differences separating strains of the corresponding species. **The differences between C. remanei strains are larger than the differences seen within other species. Recently, however, hybrid breakdown has been observed in matings between strain VX0088 from China and several strains from Ohio, congruent with the long ITS2 branch of the Chinese isolates (Asher Cutter and Alivia Dey, pers. comm).
Kiontke et al. BMC Evolutionary Biology 2011 11:339 doi:10.1186/1471-2148-11-339