Transgenerational inheritance is variable across Caenorhabditis worms

Transgenerational epigenetic inheritance (TEI) allows organisms to express heritable responses to environmental stresses, and can potentially contribute to adaptive evolution. The microbivorous model organism Caenorhabditis elegans is perhaps the best example, as it can learn to avoid pathogenic Pseudomonas bacteria and transmit this learned avoidance to its offspring. However, the extent to which TEI is widespread in nature remains unclear, and therefore our understanding of the generality of this response is limited. To address this, we conducted the first comparative study of TEI across five Caenorhabditis nematode worm species (C. kamaaina, C. elegans, C. tropicalis, C. remanei and C. briggsae). These species differ in RNA interference competence and in the degree of sequence homology between Caenorhabditis worm genes and bacterial RNAs, two factors thought to influence epigenetic responses. We examined transgenerational avoidance of P. vranovensis, a pathogen that reduces fitness in all five species tested. In addition to C. elegans, we found that C. remanei also exhibited transgenerational avoidance of P. vranovensis, whereas neither learning nor inheritance was observed in the other three species. In addition, parental exposure to P. vranovensis also conferred a transgenerational survival benefit upon pathogen encounter in C. elegans, C. remanei and C. tropicalis. Our findings show that TEI of pathogen avoidance extends beyond C. elegans but is not a general response across Caenorhabditis species. This shows that TEI is a species-specific response and highlights the need to understand TEI alongside other responses to environmental variability.