Adaptive consequences of transgenerational inheritance of a predatory mouth-form trait in nematodes

A growing body of evidence suggests that environmentally-induced changes in phenotypes can cross the generation barrier and associated molecular mechanisms are being increasingly identified. Such transgenerational epigenetic inheritance (TEI) is repeatedly considered to be adaptive although experimental support for this claim is often missing. We study the adaptive consequences of TEI in the facultative predatory nematode Pristionchus pacificus, which can form two alternative mouth forms dependent on environmental conditions. The choice of feeding structure in P. pacificus can be manipulated through dietary switching and food reversal. Recent studies showed that certain diets cause the induction of the predatory mouth form, which can result in TEI after food reversal. This memory requires the ubiquitin ligase EBAX-1/ZSWIM8 and the destabilization of clustered microRNAs. To study the adaptive potential of transgenerational memory of the predatory morph, we measured brood size as proxy for fitness. We compared naive worms, with those under dietary induction and food reversal, and found a fitness advantage for animals exhibiting TEI of the predatory morph. Specifically, after food reversal worms had higher lifetime reproductive success for up to three generations when compared to diet-induced or naive worms. These results support the adaptive significance of non-genetic inheritance of the predatory trait.