Drosophila melanogaster females prioritise dietary sterols for producing high quality eggs

Abstract

Limiting calories or specific nutrients without malnutrition, otherwise known as dietary restriction (DR), has been shown to extend lifespan across a broad range of taxa. Our recent findings in Drosophila melanogaster show that supplementing flies on macronutrient-rich diets with additional cholesterol can extend lifespan to the same extent as DR. Macronutrient-rich diets drive high levels of egg production and in doing so deplete the mothers of somatic sterols that are essential for survival. Thus, DR may be beneficial for lifespan because it reduces egg production which in turn reduces the mother's demand for sterols. If this is true, mothers must be prioritising their available sterols, whether from the diet or from their own bodies, to sustain high quality egg production. To test this, we measured the quality of eggs laid by mothers fed either cholesterol-sufficient or cholesterol-depleted diets. We found that even when the mother's diet was completely devoid of cholesterol, high quality egg production persisted. Furthermore, we show that sterol-supplemented flies with long lives continue to lay high quality eggs that give rise to healthy offspring. Thus, in our assays, long life does not require a fecundity cost.

Dietary restriction and lifespan: adaptive reallocation or somatic sacrifice?

“…It is thus conceivable that to protect fecundity, flies can retrieve sterols from their own soma to produce high-quality eggs in such a way that the adults can still survive to the point that extrinsic hazards would have normally killed them. Our data show that this is possible for about 10 days from adult emergence, which is comparable to estimates of life expectancy in wild D. melanogaster and other flies [68][69][70], suggesting that flies might be able to buffer against dietary sterol shortages to take advantage of dietary macronutrient levels that accommodate high egg production [42].…”

“…Specifically, when dietary protein levels are high and there are adequate levels of dietary carbohydrates and metal ions, egg production will be initiated, even when other essential components, such as sterols, are undersupplied [ 40 ]. To make up for this sterol deficit, flies source them from somatic tissue and deliver them to the ovary to ensure the production of high‐quality eggs [ 19 , 41 , 42 ]. In doing so, flies deplete their own sterols, which shortens their lifespan – a strategy that might enhance fitness in natural populations by enabling flies to take advantage of valuable reproductive opportunities.…”