Soil fauna actively change their diet to survive stress.

Animals are expected to choose foods that optimize their growth, reproduction and survival, but their dietary choice changes when suffering stress. Here, we provide the first report of nematode stress resulting from exposure to earthworm-produced cyclic peptides, and confirm that this stress changes the dietary choice of the model animal Caenorhabditis elegans and other soil-dwelling bacterial-feeding nematodes. When allowed free choice in a stress-free environment, nematodes prefer feeding on high-quality bacteria to support a higher reproduction and a shorter lifespan, supporting a reproduction-dominated energy allocation pattern. However, they feed less on preferred food (high-quality bacteria) and include more unpreferred food (low-quality bacteria) in the diet when stressed by the toxic cyclic peptides. Nematodes that eat more unpreferred bacteria appear to shift towards a survival-dominated energy allocation pattern. Specifically, limited resources obtained from low-quality bacteria are preferentially allocated to repair cyclic peptide-induced damage of their DNA and complete their lifespan, although at significantly reduced reproduction level. Our results demonstrate that nematodes can actively change their dietary strategy to maintain survival at the cost of reproduction when they experience acute stress. This stress-driven adjustment of dietary choice may be the key to understand feeding ecology and food web structure. • Earthworm mucus changed the 'normal' feeding preference of soil nematodes. • Earthworm mucus caused DNA damage of soil nematodes. • Cyclic peptides were responsible for changing nematode dietary choice. • Nematodes chose more unpreferred food when exposed to cyclic peptides. • Nematodes reallocated energy resource to somatic repair at the cost of reproduction. [ABSTRACT FROM AUTHOR]