Ancestral diet leads to dynamic transgenerational plasticity for five generations in Drosophila melanogaster

Ancestral exposures can influence phenotypic expression in subsequent generations, which influence diverse biological processes ranging from phenotypic plasticity to obesity. Currently, most transgenerational studies work under the assumption of transgenerational response stability and reproducibility through time and across exposure differences, relying on short-term (i.e. 2-3 generations) single-exposure experiments. Yet, little evidence exists in the literature to validate this assumption, leaving the consistency and reliability of interpretations in question. Additionally, as most studies have focused on proximal mechanistic ( how) rather than ultimate evolutionary ( why) questions, the interpretations of observed responses and broader evolutionary implications remain unclear. In the current study, we begin to address these gaps by analyzing the transgenerational effects of three dietary sugar concentrations (i.e. no, low, and high) relative to controls on body composition (i.e. whole body fat and sugar concentrations) and reproduction (i.e. lifetime fitness) over five generations in both males and females. We found that the changes in ancestral diet led to complex transgenerational body composition and fitness fluctuations relative to control offspring responses, despite the conformity of the treatments to a control diet in the F1-F5 generations. Interestingly, the direction of response frequently changed from generation to generation, and as a function of ancestral exposures and sex. These fluctuating response findings have not been documented previously, and were broadly consistent in both our pilot and main experiments. Our results highlight the dynamic and multifaceted nature of transgenerational plasticity, and provide some of the first evidence that transgenerational response stability may not be universally valid.\n\nSummary StatementAlterations in ancestral dietary sugar transgenerationally influences body composition and fitness in Drosophila melanogaster, leading to fluctuating responses relative to controls over five generations following exposure.