Reproduction and preference to macronutrients have different relations to biological or chronological age in Drosophila.

Varied factors and interventions were shown to extend the lifespan. An understanding of the mechanisms behind the beneficial effects might extend our understanding of how interventions work. However, in most studies, groups are compared at distinct time points representing chronological age. This setup does not take into account that organisms of the same chronological age are different biologically. In other words, they have a different biological age that reflects varied physiological traits. We have compared reproduction and consumption of specific macronutrients for flies in according quartiles (Q) of chronological and biological age. Quartiles of chronological age were obtained by dividing the total lifespan of the cohort into 4 parts. Quartiles of biological age were estimated as time points of 75, 50, 25 and 0% survival of the cohort. We found that the decline in carbohydrate or protein consumption was stronger in the case of chronological rather than biological age. However, flies of biological or chronological quartile 4 consumed virtually the same amounts of macronutrients. The decline in reproduction was significantly reduced in relation to biological age. Thus, the decline was about 38-68% when within chronological quartiles 2 and 1 but only 4-31% for biological ones. The reproductive capacity was reduced by 86-93% in flies of chronological Q4 as compared to a 60-77% decrease for those of biological. Starting from quartile 2 biologically aged flies laid significantly higher number of eggs than flies of the same chronological quartile. Our results point out the significant difference in flies of the same biological and chronological quartile and raise the question about the suitability of comparison traits of organisms with different lifespans same chronological age.