Aging, life span, and energetics under adult dietary restriction in lepidoptera

Stressful conditions can affect resource allocation among different life-history traits. The effect of dietary restriction (DR) on longevity and reproduction has been studied in many species, but we know little about its effects on energetics, especially in flying animals that have high energy demand. We assessed the effects of DR on metabolic rate throughout the entire adult life span in two butterfly species, Colias eurytheme and Speyeria mormonia. We cut the food intake of adult females in half and measured resting metabolic rate (RMR) and flight metabolic rate (FMR) together with body mass repeatedly throughout life. In both species, DR reduced body mass, but mass-corrected FMR was not affected, indicating that flight capacity was retained. DR lowered RMR and reduced fecundity but had no effect on life span. FMR declined with age, but the rate of senescence was not affected by DR. In contrast, aging had a strong negative effect on RMR only in control females, whereas food-restricted females had more stable RMR throughout their lives. The results suggest that flight capacity is conserved during nutritional stress but that investment in flight and survival may negatively affect other important physiological processes when resources are limited.