Dietary restriction (DR) is a key focus in ageing research. Specific conditions and genotypes were recently found to negate lifespan extension by DR, questioning its universal relevance. However, the conceptual framework of dietary reaction norms explains why DRs effects might not be apparent in some situations. We tested comprehensively the importance of dietary reaction norms by measuring longevity and fecundity on five diets in five genotypes, with and without water supplementation in the fly (N>25,000). We found substantial genetic variation in the reaction norm between diet and lifespan. Environments supplemented with water rescued putative desiccation stress but only at the richest diets. Fecundity declined at these richest diets, but was unaffected by water and is thus most likely caused by nutritional toxicity. Our results demonstrate empirically that any conclusion on the absence of DR is only justified when a range of diets is considered in a reaction norm framework.

中文翻译：

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长寿与饮食之间的关系取决于基因型，并且对干燥敏感

饮食限制（DR）是衰老研究的重点。最近发现特定条件和基因型会否定DR延长寿命，并质疑其普遍意义。但是，饮食反应规范的概念框架解释了为什么DR的影响在某些情况下可能不明显。我们通过测量五种基因型的五种饮食的寿命和繁殖力，全面测试了饮食反应规范的重要性，其中有和没有果蝇补充了水（N> 25,000）。我们发现饮食和寿命之间的反应规范存在重大的遗传差异。补充水的环境可以挽救假定的干燥压力，但仅在最丰富的饮食条件下才可以。在这些最丰富的饮食中，生殖力下降，但不受水的影响，因此很可能是营养毒性引起的。