Intergenerational effects of dietary changes on trait means and variance

Environmental stress can alter not only trait means but also trait variances—an often-overlooked yet evolvable feature with ecological and evolutionary relevance. Here, we examine how dietary stress affects both the mean and variance of morphological and reproductive traits across two generations in clonal Daphnia. Using a factorial design, we manipulated maternal and offspring environments with high- (algae) or low-quality (cyanobacteria) diets, measuring eye size, body size, and reproductive output in eight genotypes. Morphological trait means showed consistent treatment-by-generation interactions: low-quality diets reduced trait size, with partial recovery upon re-exposure to high-quality food. Reproduction was determined largely by current conditions, while eye and body size showed legacy effects of maternal environment. Trait variance patterns were trait-specific and not uniformly linked to mean responses: eye size variance declined under stress, body size variance increased across generations, and reproductive variance peaked in offspring released from maternal stress. We also developed a conceptual framework that specifically considered roles for condition transfer, anticipatory plasticity, and diversified bet-hedging as potential mechanisms underlying these intergenerational impacts on traits and variances. Although no single mechanism explained all outcomes, our findings support condition transfer and suggest potential co-occurrence of multiple strategies. This data and script supports the associated article and contains all the relevant information to replicate the study.