Oscheius tipulae, a widespread hermaphroditic soil nematode, displays a higher genetic diversity and geographical structure than Caenorhabditis elegans.

The nematode Oscheius tipulae belongs to the same family (Rhabditidae) as the model species Caenorhabditis elegans. Both species reproduce through self-fertilizing hermaphrodites and facultative males. Recent studies have shown that the self-fertile C. elegans and C. briggsae displayed a 20-fold lower genetic diversity than the male-female species C. remanei. Several explanations have been put forward to account for this difference, including their mode of reproduction and dynamic population structure. Here, we present the results of extensive worldwide sampling of O. tipulae, which we previously used as a laboratory organism for developmental genetics. We found that O. tipulae is much more widespread and common in soil throughout the world than Caenorhabditis species. We analysed 63 O. tipulae isolates from several continents using amplified fragment length polymorphism (AFLP). We found that O. tipulae harbours a 5-fold higher genetic diversity than C. elegans and C. briggsae. As in C. elegans, a high proportion of this diversity was found locally. Yet, we detected significant geographical differentiation, both at the worldwide scale with a latitudinal structure and between three localities in France. In summary, O. tipulae exhibited significantly higher levels of genetic diversity and large-scale geographical structure than C. elegans, despite their shared mode of reproduction. This species difference in genetic diversity may be explained by a number of other differences, such as population size, distribution, migration and dynamics. Due to its widespread occurrence and relatively high genetic diversity, O. tipulae may be a promising study species for evolutionary studies.