Dietary tryptophan modifies the effects of developmental predator stress on lifespan in male <i>Drosophila melanogaster</i>

Abstract Environmental stressors and diet both play key roles in shaping animal lifespan, yet their interactive effects remain poorly understood under ecologically realistic predation risk. We experimentally tested how predator-induced stress during early development and dietary tryptophan supplementation affect the lifespan of Drosophila melanogaster males. Tryptophan, an essential amino acid and precursor to multiple physiological pathways including serotonin biosynthesis, influences stress responses and aging-related processes. Using a 2×2 experimental design (predator exposure ± tryptophan supplementation), we found that predator-exposed flies had the shortest lifespans, while those without predators lived longest. Tryptophan supplementation significantly increased lifespan in predator-exposed flies but did not alter lifespan in predator-free conditions. These results suggest that dietary tryptophan can mitigate some consequences of chronic developmental stress, but its effects depend on environmental context and do not imply a general mechanism of serotonergic lifespan extension. Instead, our findings support a broader ecological interpretation in which nutritional inputs interact with early-life stress to shape adult survival. Our results highlight the importance of diet–environment interactions in aging and demonstrate that ecologically relevant predator stress can modify life-history outcomes in a model organism. This study illustrates how nutritional manipulations can modify—but not eliminate—the survival costs of chronic stress.