Larval protein restriction interacts with adult diet to increase fitness in an outbred multiparent population

Developmental conditions including temperature, diet, and parasites can shape adult fitness phenotypes in many species. Studies typically focus on the additive effects of early-life and adult life conditions on life history response in the context of competing models of developmental plasticity (i.e. environmental matching and silver spoon). These models continue to yield mixed results in the same or different species. Here, we characterize interaction effects of larval vs adult diet on lifespan and fecundity in a high diversity outbred population of Drosophila melanogaster . We compare fitness proxies of matched vs mismatched early-to-late nutritional conditions differing in protein content. Diet interactions significantly affected both traits, albeit differently. We find no consistent evidence for either model. Rather, several patterns emerged including age and sex effects, survival differences in the post-median life phase, regime-specific timing of peak fecundity, and substantial fecundities in older post-median flies. Surprisingly, lower adult protein delayed egg-laying by about 2 weeks, compared to treatments with higher protein in adult diet. Our results underscore the extent to which adult life history expression depends significantly on developmental conditions. Results further highlight the need for assessing possible adult life phase patterns which might potentially reveal trade-offs between adult life stages than traits. ### Competing Interest Statement The authors have declared no competing interest.