Impact of late larval nutritional stress on adult metabolic, gut and locomotor phenotypes in Drosophila melanogaster

Dietary quantity and quality are key determinants for insect development from egg to adult. When nutritional deficiency is sub-optimal, development is completed, albeit resulting in an adult insect that is smaller than normal in size. If now fed a normal diet, would the smaller adults be similar to normally developed flies? To begin to answer this question, we characterised a few physiological and musculoskeletal readouts. Larvae were subject to acute starvation in late stages of development, and the resulting adults (Early Life Starved; ELS) maintained on a normal diet, were tested for biochemistry, gut physiology and locomotor activity. In females, no significant difference was observed in biochemical readouts for the whole-body or hemolymph, between control and ELS flies. In males, whole-body glucose and hemolymph trehalose were significantly reduced in ELS flies. Interestingly, ELS flies of both sexes respond with a disproportionally higher accumulation of triacylglycerides (TAGs) when on a high-fat diet. Age-related changes in the adult gut were compared between control and ELS flies: these revealed an increased proportion of ELS flies with loss of gut barrier integrity, deviant number of intestinal stem cells and no difference in enteroendocrine cells. The rate of antimicrobial peptide gene expression to an enteric infection challenge was also slower in ELS flies. For musculoskeletal readouts, climbing and flight behaviour were measured. In population assays, both male and female ELS flies showed climbing deficits. In a fine-scale climbing assay on individual flies, female but not male ELS flies showed higher climbing speed, while males but not females, showed lower geotactic index. This collection of phenotypic assessments show that firstly, larval undernutrition, even when not lethal, continues to impact adult functioning. Secondly, for some phenotypes, a normal diet in adults exposed to early life malnutrition is insufficient to restore optimal functioning. Thirdly, larval dietary loss affects adult insects in a sex-dependent manner. This study lays the framework to uncover the molecular, cellular and hormonal mechanisms that are altered by early life malnutrition. Furthermore, these readouts may be used to develop Drosophila as a high-throughput model for interrogating the efficacy of diet therapies to address malnutrition.