Food presentation modifies longevity and the beneficial action of dietary restriction in Drosophila
Introduction
The relationships between diet and longevity are of increasing interest. The observation that flies fed on dilute sources of food are long lived has suggested that dietary restriction promotes longevity (Partridge et al., 2005, Piper and Partridge, 2007). This conclusion assumes that flies ingest nutrients in proportion of their concentrations in their food. Recent papers have challenged this view. First flies respond to specific macronutrients such as protein and carbohydrates and not to the calorie content of the food (Mair et al., 2005, Min et al., 2007, Vigne and Frelin, 2007a, Vigne and Frelin, 2007b, Skorupa et al., 2008). Second flies can change their feeding behaviour in response to changes in their diet (Carvalho et al., 2005, Ja et al., 2007). Feeding behaviour by small insect has long been difficult to analyze. It can now be assessed using the capillary feeding assay (Ja et al., 2007). This assay has recently been used to show that caloric restriction per se does not promote longevity of flies (Lee et al., 2008).
We previously reported that aged, 30-day-old, flies do not respond to dietary restriction by an increased longevity (Vigne and Frelin, 2007a). Whether their unresponsiveness is due to a modified feeding behaviour or to a modified sensitivity to nutrients was not defined. This study uses a capillary feeding assay to analyze the feeding behaviour of flies and its possible alterations with ageing. The results indicate that the feeding behaviour of flies is more complex than previously thought. They suggest that feeding behaviour must be carefully defined when considering the relationship between nutrition and longevity.
Section snippets
Fly stocks
w1118 flies (Bloomington stock Center) were reared in 300 ml bottles filled with 30 ml of standard food medium (8.2% cornmeal, 6.2% sucrose, 1.7% heat inactivated baker’s yeast and 1% agar supplemented with 3.75 g/l methyl 4-hydroxybenzoate) in humidified, temperature controlled chambers at 25 °C and 60% relative humidity and under a 12:12 light:dark cycle. Experiments were performed using male flies. Young flies were 1-day-old. Aged flies were 10-, 20- or 30-day-old. During ageing, flies were
Influence of ageing on feeding behaviour
The feeding behaviour of ageing male flies was analyzed using a capillary feeding assay. Four age classes were selected: 1, 10, 20 and 30 days. Flies were exposed to a pure sucrose solution, to a mixed sucrose/yeast solution or to independent sources of sucrose and yeast. Fig. 2 compares sucrose intakes by flies exposed to rich diets (10S, 10S10Y or 10S-10Y) or to poorer, 2-fold diluted diets (5S, 5S5Y or 5S-5Y). Under all conditions, we observed that flies on the diluted diet consumed larger
Discussion
This study analyses the feeding behaviour and feeding preferences by male Drosophila and their relationships to longevity.
In a key paper, Lee et al., 2008 showed that female flies regulate their intake of proteins and carbohydrates separately. Under self selection conditions, they select a low yeast diet that maximises fitness. This study shows that male flies have a similar behaviour. Male flies have a 3- to 5-fold preference for sucrose when sucrose and yeast are presented separately. When
Conclusions
This study shows that the feeding behaviour of Drosophila is far more complex than usually considered. Flies sense sucrose and yeast nutrients independently and adapt to changes in the quantity and presentation of their foods. This study, together with recent studies (Lee et al., 2008, Skorupa et al., 2008, Wong et al., 2009) stresses that a careful analysis of feeding behaviour is necessary before drawing any conclusion the relationship between diet and longevity.
Acknowledgements
This study was funded by the INSERM, ANR and the University of Nice Sophia Antipolis. We are grateful to anonymous reviewers for their comment of on a previous version of this paper.
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