Modest dietary restriction (DR) prolongs life in a wide range of organisms, spanning single-celled yeast to mammals. Here, we report the use of recent techniques in nutrition research to quantify the detailed relationship between diet, nutrient intake, lifespan, and reproduction in Drosophila melanogaster. Caloric restriction (CR) was not responsible for extending lifespan in our experimental flies. Response surfaces for lifespan and fecundity were maximized at different protein-carbohydrate intakes, with longevity highest at a protein-to-carbohydrate ratio of 1:16 and egg-laying rate maximized at 1:2. Lifetime egg production, the measure closest to fitness, was maximized at an intermediate P:C ratio of 1:4. Flies offered a choice of complementary foods regulated intake to maximize lifetime egg production. The results indicate a role for both direct costs of reproduction and other deleterious consequences of ingesting high levels of protein. We unite a body of apparently conflicting work within a common framework and provide a platform for studying aging in all organisms.diet restriction ͉ geometric framework ͉ longevity ͉ nutrition ͉ aging A nimals that eat less live longer-up to a point. The view that dietary restriction without malnutrition prolongs life has become a central tenet in gerontology (1-3). Yeasts, fruit flies, nematode worms, and mice have become model systems for studying dietary restriction and aging, with some striking commonalities evident at the molecular and cellular levels (1-6). There is growing interest in the relationship between dietary restriction and quality and length of life in humans, although experimental data are lacking and difficult to obtain (7).It is widely held that the life-extending effects of dietary restriction (DR) are due to caloric restriction (CR) (1,8,9), but recently this view has been challenged by experiments suggesting that specific nutrients (proteins and certain amino acids) rather than energy are responsible (10-12). Claims and counterclaims in the debate over the roles of energy and specific nutrients in aging (8,(11)(12)(13)(14) have been hampered by one or more of the following problems (15). First, there is a lack of a suitable concept for baseline energy and nutrient intake, that is, dietary restriction relative to what? Thus, it may be that diet-restricted animals live longer either because eating less extends life, or because the normal nutritional regime in the laboratory is harmfully nutrient-rich in relation to requirements (15-17). Second, there have been too few dietary treatments used within an experiment to allow the effects of nutrients and energy to be partitioned. Hence, data from studies on rodents and Drosophila, which are claimed to prove the primacy of calories in influencing longevity, are open to alternative explanations (15). Finally, in the notable case of Drosophila, no study to date has measured how much flies actually eat throughout their lives. Rather, dietary restriction has been assumed to have occurred after dilution of the di...

Diet affects both lifespan and reproduction [1-9], leading to the prediction that the contrasting reproductive strategies of the sexes should result in sex-specific effects of nutrition on fitness and longevity [6, 10] and favor different patterns of nutrient intake in males and females. However, males and females share most of their genome and intralocus sexual conflict may prevent sex-specific diet optimization. We show that both male and female longevity were maximized on a high-carbohydrate low-protein diet in field crickets Teleogryllus commodus, but male and female lifetime reproductive performances were maximized in markedly different parts of the nutrient intake landscape. Given a choice, crickets exhibited sex-specific dietary preference in the direction that increases reproductive performance, but this sexual dimorphism in preference was incomplete, with both sexes displaced from the optimum diet for lifetime reproduction. Sexes are, therefore, constrained in their ability to reach their sex-specific dietary optima by the shared biology of diet choice. Our data suggest that sex-specific selection has thus far failed fully to resolve intralocus sexual conflict over diet optimization. Such conflict may be an important factor linking nutrition and reproduction to lifespan and aging.

Summary 1.Classic evolutionary models interpret ageing as a cost of reproduction, but evolutionary research has thus far largely neglected the conceptual links between the evolution of ageing and a key mode of selection on male and female reproductive strategies -sexual selection and sexual conflict. 2. We synthesize ideas and evidence linking sex and ageing, and make the case that a focus on this fascinating problem will ultimately lead to a more complete understanding of both the evolution of ageing and the evolution of sexual strategies. 3. The primary and secondary differentiation of male and female reproductive strategies is expected to produce sex-specific optima for traits that affect longevity and ageing rate, often favouring a 'live fast, die young' strategy in males, relative to females, although numerous exceptions to this pattern are observed and sex-differences in ageing rate, in particular, remain poorly understood. 4. Conversely, environmental factors that influence life expectancy or ageing rate can thereby determine the magnitude or even sign of sexual selection. 5. Sexual conflict is expected to displace the sexes from their sex-specific life-history optima through sexually antagonistic interactions, as well as sex-specific selection on loci expressed in both sexes. 6. Despite the availability of interesting and testable hypotheses linking sexual selection and ageing, relevant empirical studies are remarkably sparse, and the complex relation between sex, mortality rate and ageing remains poorly understood.