Evolution, stress, and longevity

The disposable soma theory suggests that longevity is determined through th e setting of longevity assurance mechanisms so as to provide an optimal com promise between investments in somatic maintenance (including stress resist ance) and in reproduction. A corollary is that species with low extrinsic m ortality are predicted to invest relatively more effort in maintenance, res ulting in slower intrinsic ageing, than species with high extrinsic mortali ty. We tested this prediction in a comparative study of stress resistance i n primary skin fibroblasts and confirmed that cells from long-lived species are indeed more resistant to a variant of stressors. A widely studied exam ple of within-species variation in lifespan is the rodent calorie restricti on model. Food-restricted animals show elevations in a range of stress resp onse mechanisms, and it has been suggested that this is an outcome of natur al selection for lift: history plasticity. We have developed a theoretical model for dynamic optimisation of the allocation of effort to maintenance a nd reproduction in response to fluctuations in food availability. The model supports the suggestion that the response to calorie restriction may be an evolutionary adaptation, raising interesting questions about the hierarchy of genetic control of multiple stress response systems. The model identifi es ecological factors likely to support such an adaptation that may be rele vant in considering the likely relevance of a similar response to calorie r estriction in other species. Comparative and theoretical studies support th e role of somatic maintenance and stress response systems in controlling th e rate of ageing.