Maternal and paternal sugar consumption interact to modify offspring life history and physiology

Intergenerational effects on offspring phenotypes occur in response to variation in both maternal and paternal nutrition. Because the combined maternal and paternal effects are rarely considered together, however, their relative contributions, and the capacity for interactions between parental diets to shape offspring life history and physiology are not understood. To address this, we altered the sucrose levels of adult fruit flies (Drosophila melanogaster) prior to mating, across two generations, producing parent-parent and parent-offspring combinations that were either matched or mismatched in dietary sucrose. We then measured life span, fecundity, body mass and triglyceride levels in parents and offspring. We reveal complex, non-cumulative interactions, which involve diets of each parent and offspring, shape offspring phenotypes, but the effects were generally not consistent with an adaptive response to parental diet. Notably, we find that interacting parental flies (sires and dams) lived longer when their sucrose treatments were matched, but they produced shorter lived offspring. These results are suggestive of intergenerational conflict over optimal diets, and call for further research into the capacity, and mechanisms, for mismatches in parental environments to enhance offspring phenotype generally. Our study also indicates that studies of maternal and paternal effects will need embrace experimental designs with power to test for interactions between maternal and paternal environments if they are to fully understand the ecological and evolutionary significance of parental effects on offspring fitness. Read the free Plain Language Summary for this article on the Journal blog.