Phylogenic maximum likelihood tree based on SSU sequences of the genus Pristionchus. As outgroup the sequence of Koerneria sp. was included as the closest related genus to Pristionchus. A single best tree was obtained using the Kimura 2-parameter model (Kimura 1980) with Ts/Tv = 1,4727, equal base frequencies, and a γ-correction with shape parameter α = 0,2381. Numbers at nodes indicate bootstrap values after 1000 replications. E, species observed in Western Europe; A, species observed in North-America (this study).