Standardized Drosophila Lifespan Experiments

Experimental flies were raised at a standard density of 400–450 eggs per 200-ml bottle [52 ] on standard SY medium (1,000 ml distilled water, 100 g autolysed yeast powder, 100 g sucrose, 20 g agar, 30 ml Nipagin (100 gl^–1), 3 ml propionic acid). Adults were collected over a 24-h period and transferred without anaesthesia to fresh SY food for 48 h and allowed to mate. Females were then collected using light CO₂ anaesthesia and assigned randomly to the food regimes (Table S1). All experiments were done with mated females. Flies were kept on 35 ml of food at an initial density of 100 individuals per 200-ml bottle and transferred without anaesthesia to fresh food every 2–3 d. Deaths were scored 5–6 d a week and initial sample sizes (n₀) were calculated as the summed death and censor observations over all ages. To minimise any density effects on mortality, two bottles within cohorts were merged when the density of flies reached 50 ± 10. To standardise the effects of parental age on offspring fitness [53 (link)], parents of experimental flies were of the same age and reared at a constant density.