Evolution, stress, and longevity

Abstract

The disposable soma theory suggests that longevity is determined through the setting of longevity assurance mechanisms so as to provide an optimal compromise between investments in somatic maintenance (including stress resistance) and in reproduction. A corollary is that species with low extrinsic mortality are predicted to invest relatively more effort in maintenance, resulting in slower intrinsic ageing, than species with high extrinsic mortality. We tested this prediction in a comparative study of stress resistance in primary skin fibroblasts and confirmed that cells from long-lived species are indeed more resistant to a variant of stressors. A widely studied example of within-species variation in lifespan is the rodent calorie restriction model. Food-restricted animals show elevations in a range of stress response mechanisms, and it has been suggested that this is an outcome of natural selection for life history plasticity. We have developed a theoretical model for dynamic optimisation of the allocation of effort to maintenance and 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 identifies ecological factors likely to support such an adaptation that may be relevant in considering the likely relevance of a similar response to calorie restriction in other species. Comparative and theoretical studies support the role of somatic maintenance and stress response systems in controlling the rate of ageing.

Enhanced protein repair and recycling are not correlated with longevity in 15 vertebrate endotherm species

“…A key observation is that inter-and intraspecies differences in cellular stress resistance are present in young adults, suggesting that longevity is associated with enhanced stress resistance over the lifespan rather than becoming evident only with advanced age. The positive correlation between cellular stress resistance and MLSP is consistent with the disposable soma theory of lifespan, which suggests that the extent of the investment made in cellular maintenance will be determined by selective pressures to extend lifespan (Kirkwood et al 2000).…”

Successful ageing: from cell to self

“…Here, it is interesting to note that species with a short lifespan have generally a higher fertility rate (Williams 1966). This trade-off between life expectancy and reproductive capacity has led to the disposable soma theory (Kirkwood 1977;Kirkwood & Holliday 1979), which comprises three major premises. The first is that in natural populations (with the exception of humans), most deaths generally occur accidentally.…”

Do reef corals age?

“…To understand why ageing should have evolved in those species where it is found, it has long been recognised that the central point is that the force of natural selection -that is, its ability to favour or discriminate against alternative alleles -diminishes with increasing age (Hamilton, 1966;Kirkwood & Holliday, 1979). This is because the force of selection at any age is proportional to the fraction of an individual's expected lifetime reproductive output that still remains in its future, which will decline as a consequence of prevailing mortality if nothing else.…”