Evolutionary history of Caenorhabditis elegans inferred from microsatellites: evidence for spatial and temporal genetic differentiation and the occurrence of outbreeding.

Although diverse biological disciplines employ the nematode Caenorhabditis elegans as a highly efficient laboratory model system, little is known about its natural history. We investigated its evolutionary past using 10 polymorphic trinucleotide and tetranucleotide microsatellites, derived from across the whole genome. These microsatellites were analyzed from the 35 previously available natural isolates from different parts of the world and also 23 new strains isolated from northwest Germany. Our results highlight that C. elegans lineages differentiate genetically with respect to geographic distance and, to a lesser extent, differences in the time of strain isolation. The latter indicates some turnover of strain genotypes at specific locations. Our data also demonstrate the coexistence of highly diverse genotypes in the population from northwest Germany, which is best explained by recent migration events. Furthermore, selfing is confirmed as the primary mode of reproduction for this hermaphroditic nematode in nature. Importantly, we also find evidence for the occurrence of occasional outbreeding. Taken together, these results support the previous notion that C. elegans is a colonizer, whereby selfing may permit rapid dispersal within new habitats even in the absence of potential mates, whereas occasional outcrossing may serve to compensate for the disadvantages of inbreeding. Such information about the natural history of C. elegans should be of great value for an in-depth understanding of the complexity of this organism, including its multifaceted developmental, neurological, or molecular genetic pathways.