Ecological stoichiometry and adult fat reserves suggest bet-hedging in Drosophila melanogaster development

The elemental composition of organisms relates to a suite of functional traits that change during development in response to environmental conditions. It may be a part of a phenomenon known as developmental programming, which hypothetically creates phenotypes that are better adapted to their environments. However, associations between developmental speed and elemental body composition are not well understood. We compared body mass, elemental body composition, food uptake and fat metabolism of Drosophila melanogaster Oregon-R male fruit flies across the time gradient of their larval development. The results showed that flies with intermediate and rapid developmental speeds were heavier than slowly developing flies. Slowly developing flies had higher body carbon concentration than rapidly developing and intermediate flies. Rapidly developing flies had the highest body nitrogen concentration, while slowly developing flies had higher body nitrogen levels than flies with intermediate speed of development. The carbon-to-nitrogen ratio was therefore lower in rapidly developing flies than in slow and intermediate flies. Feeding rates were lowest in the slowly developing flies. The amount of storage fats was highest in the intermediate group. This means that the growth of rapidly developing flies is not suppressed by stress and they actively convert the food they consume into growth with less emphasis on storage build-up, suggesting bet-hedging in the larval development. In contrast, flies in the intermediate developmental group had the greatest fat reserves which optimize fitness under many climatic conditions. Low food intake may slow down development and the accumulation of body fat reserves in slowly developing flies. However, at the cost of slower growth, their phenotype conceivably facilitates survival under higher stochasticity of their ephemeral environments spoiled by metabolic waste due to high density of conspecifics. Overall, this study suggests that bet-hedging may be a common developmental strategy in fruit flies to cope with environmental uncertainty.