Natural variation in the irld gene family affects starvation resistance in C. elegans

Starvation resistance is important to disease and fitness, but the genetic basis of its natural variation is unknown. We developed a synthetic-population (re)sequencing approach using molecular inversion probes (MIP-seq) to measure relative fitness during and after larval starvation in C. elegans. We applied this competitive assay to 100 genetically diverse, sequenced, wild strains, revealing natural variation in starvation resistance. We confirmed that the most starvation-resistant strains survive and recover from starvation better than the most starvation-sensitive strain, MY2147, using standard assays. We performed genome-wide association with the MIP-seq trait data and identified three quantitative trait loci (QTL) for starvation resistance. These QTL contain several members of the Insulin/EGF Receptor-L Domain (irld) family with sequence variation associated with variation in starvation resistance. We used genome editing to show that individual modification of four irld genes increases starvation resistance of MY2147. Modification of irld-39 and irld-52 together increases starvation resistance of the laboratory-reference strain N2. Increased starvation resistance of the irld-39; irld-52 double mutant depends on daf-16/FoxO, and these worms also show increased nuclear localization of DAF-16 during starvation. DAF-16/FoxO is a widely conserved transcriptional effector of insulin/IGF signaling (IIS), and these results suggest that IRLD proteins modify IIS. This work demonstrates efficacy of using MIP-seq to dissect a complex trait, identifies irld genes as natural modifiers of starvation resistance in C. elegans, and suggests that an expanded gene family affects a deeply conserved signaling pathway to alter a fitness-proximal trait.