Larval mannitol diets increase mortality, prolong development, and decrease adult body sizes in fruit flies (Drosophila melanogaster).

Ingestion of the polyol mannitol caused sex-biased mortality in adult Drosophila melanogaster, but larval mortality was not sex-biased. High-sugar diets prolong development and generate smaller adult body sizes in D. melanogaster. We hypothesized that mannitol ingestion would generate similar developmental phenotypes as other high-carbohydrate diets. We predicted concentration-dependent effects on development similar to high-sugar diets when D. melanogaster larvae are fed mannitol, as well as a concentration-dependent amelioration of developmental effects if introduction to mannitol media is delayed past the third instar. Both male and female larvae had prolonged development and smaller adult body sizes when fed increasing concentrations of mannitol. Mannitol-induced increases in mortality were concentration dependent in 0 M to 0.8 M treatments beginning as early as 48 hours post-hatching. Larval survival, and pupation and eclosion times, were normal in 0.4 M mannitol treatments when larvae were first introduced to mannitol 72 hours post-hatching (the beginning of the third-instar); the adverse mannitol effects occurred in 0.8 M mannitol treatments, but at a lower magnitude. Female D. melanogaster adults prefer laying eggs on diets with high sugar concentrations, despite the negative effects on offspring performance. However, when given a choice, female D. melanogaster avoided laying eggs on mannitol-containing media that was otherwise identical to the control media, suggesting females perceived and avoided mannitol. In conclusion, the developmental effects of a larval mannitol diet closely resemble those of high-sugar diets, but adult female oviposition responses to mannitol in laying substrates are distinct from responses to other carbohydrates.