Trends in lipid and protein contents during medfly aging: an harmonic path to death

Survival and egg-laying trends were investigated in Mediterranean fruit flies (Ceratitis capitata) adults maintained on a sucrose-only diet, or on a full diet that consisted of a 3:1 sucrose and yeast hydrolizate mixture. In addition, we followed the total individual lipid and protein contents of aging flies in a cohort. Survival trends and life expectancy parameters at eclosion for males and females on full diet and for males on sucrose only were very similar. In contrast, the mortality of females on sucrose only was high early in life, but then slowed down. Egg-laying was ten times greater in female flies on full diet than in flies on sucrose only. Lipid contents in males and females on both types of diets were very similar, and harmonically oscillated with an amplitude of approximately 10 days. Successive crests of lipids tended to be smaller with the ageing of the cohort, and lipids contents significantly dropped at very advanced ages and close to the maximal age of the whole cohort. Protein contents of flies maintained on a full diet were high and stayed at a constant level throughout the entire life of the cohort. Protein levels in males and females on sucrose only dropped drastically during the first days of adult life, but then stayed stable at a low level until advanced ages. We propose that the synchronous rhythmic oscillation in lipid contents of male and female flies seems to be independently set by an internal clock. Protein reserves are allocated according to the access to protein food sources and these levels of protein are closely associated to egg production and mortality. Our results are discussed in view of resource allocation during reproduction and senescence.