Genome-wide association and environmental suppression of the mortal germline phenotype of wild C. elegans

The animal germline lineage needs to be maintained along generations. However, some Caenorhabditis elegans wild isolates display a mortal germline phenotype, whereby the lineage becomes sterile after several generations at 25{degrees}C. We used a genome-wide association approach to study the genetic basis for this phenotype in C. elegans populations. We detected a significant peak on chromosome III around 5 Mb, which was confirmed using introgression lines. These results indicate that a seemingly deleterious genotype is maintained at intermediate frequency in the species. Environmental rescue is a likely explanation and we indeed find that naturally associated bacteria and microsporidia suppressed the phenotype. The tested bacteria also suppressed the temperature-sensitive mortal germline phenotype of mutants in small RNA inheritance (nrde-2) and histone modifications (set-2). Even Escherichia coli strains of the K-12 lineage suppressed the phenotype compared to B strains. By shifting a strain cultured on E. coli K-12 back to E. coli B, we found that C. elegans can keep over several generations the memory of the suppressing conditions. Thus, the mortal germline phenotype of wild C. elegans is lin part revealed by laboratory conditions and may represent variation in epigenetic inheritance and environmental interactions. This study also points to the importance of non-genetic memory in the face of environmental variation.