Why do we age?

Kirkwood, Thomas B. L.; Austad, Steven N.

doi:10.1038/35041682

Cited by 1,594 publications

(1,211 citation statements)

References 62 publications

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“…However, assumptions of this model preclude the possibility that senescence can occur in “young” individuals, below a certain “old” chronological age. The “state‐dependent component” (or “age independent,” Martin & Festa‐Bianchet, 2011; also “stage dependent’” in plants, Caswell & Salguero‐Gómez, 2013) of senescence, on the other hand, is based on the idea that the physiological state of an individual, and hence its “biological age,” may better explain late life decreases in performance (Kirkwood & Austad, 2000; McNamara et al., 2009). Thus, “chronologically young” individuals could be considered “biologically old” and also senesce.…”

Section: Introductionmentioning

confidence: 99%

Age, state, environment, and season dependence of senescence in body mass

Kroeger

Blumstein

Armitage

et al. 2018

Ecology and Evolution

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Senescence is a highly variable process that comprises both age‐dependent and state‐dependent components and can be greatly affected by environmental conditions. However, few studies have quantified the magnitude of age‐dependent and state‐dependent senescence in key life‐history traits across individuals inhabiting different spatially structured and seasonal environments. We used longitudinal data from wild female yellow‐bellied marmots (Marmota flaviventer), living in two adjacent environments that differ in elevation and associated phenology, to quantify how age and individual state, measured as “time to death,” affect body mass senescence in different environments. Further, we quantified how patterns of senescence differed between two biologically distinct seasons, spring, and late summer. Body mass senescence had an age‐dependent component, expressed as a decrease in mass in old age. Overall, estimated age‐dependent senescence was greater in females living in the more favorable lower elevation environment, than in the harsher higher elevation environment, and greater in late summer than in spring. Body mass senescence also had a state‐dependent component, captured by effects of time to death, but only in the more favorable lower elevation environment. In spring, body mass gradually decreased from 2 years before death, whereas in late summer, state‐dependent effects were expressed as a terminal decrease in body mass in the last year of life. Contrary to expectations, we found that senescence was more likely to be observed under more favorable environmental conditions, rather than under harsher conditions. By further demonstrating that senescence patterns differ among seasons, our results imply that within‐year temporal environmental variation must be considered alongside spatial environmental variation in order to characterize and understand the pattern and magnitude of senescence in wild populations.

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Section: Introductionmentioning

confidence: 99%

Age, state, environment, and season dependence of senescence in body mass

Kroeger

Blumstein

Armitage

et al. 2018

Ecology and Evolution

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“…Therefore, the findings in this study support the idea of a link between lifespan and reproductive development. Ablation of the reproductive system in worms or insects has been demonstrated to extend lifespan (Rose & Charlesworth, 1980; Hsin & Kenyon, 1999) supporting the disposable soma theory of aging, which reflects the functional interrelationships between the reproductive system and other cells or tissues (Kirkwood & Austad, 2000). One central assumption of that theory is that energetic input in nonreproductive tissues has to be at the expense of cells required for reproduction and vice versa owing to a certain limitation of resources.…”

Section: Discussionmentioning

confidence: 93%

Dissociation of somatic growth, time of sexual maturity, and life expectancy by overexpression of an RGD ‐deficient IGFBP ‐2 variant in female transgenic mice

et al. 2015

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SummaryImpaired growth is often associated with an extension of lifespan. However, the negative correlation between somatic growth and life expectancy is only true within, but not between, species. This can be observed because smaller species have, as a rule, a shorter lifespan than larger species. In insects and worms, reduced reproductive development and increased fat storage are associated with prolonged lifespan. However, in mammals the relationship between the dynamics of reproductive development, fat metabolism, growth rate, and lifespan are less clear. To address this point, female transgenic mice that were overexpressing similar levels of either intact (D‐mice) or mutant insulin‐like growth factor‐binding protein‐2 (IGFBP‐2) lacking the Arg‐Gly‐Asp (RGD) motif (E‐ mice) were investigated. Both lines of transgenic mice exhibited a similar degree of growth impairment (−9% and −10%) in comparison with wild‐type controls (C‐mice). While in D‐mice, sexual maturation was found to be delayed and life expectancy was significantly increased in comparison with C‐mice, these parameters were unaltered in E‐mice in spite of their reduced growth rate. These observations indicate that the RGD‐domain has a major influence on the pleiotropic effects of IGFBP‐2 and suggest that somatic growth and time of sexual maturity or somatic growth and life expectancy are less closely related than thought previously.

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“…In long‐lived species, however, there is a fitness advantage to increased survival. While long‐lived species must allocate resources toward reproduction, they should also allocate resources to systems that enhance adult survival, like telomeres (Kirkwood & Austad, 2000; Kirkwood & Rose, 1991). …”

Section: Introductionmentioning

confidence: 99%

Magellanic penguin telomeres do not shorten with age with increased reproductive effort, investment, and basal corticosterone

Cerchiara

Risques

Prunkard

et al. 2017

Ecology and Evolution

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All species should invest in systems that enhance longevity; however, a fundamental adult life‐history trade‐off exists between the metabolic resources allocated to maintenance and those allocated to reproduction. Long‐lived species will invest more in reproduction than in somatic maintenance as they age. We investigated this trade‐off by analyzing correlations among telomere length, reproductive effort and output, and basal corticosterone in Magellanic penguins (Spheniscus magellanicus). Telomeres shorten with age in most species studied to date, and may affect adult survival. High basal corticosterone is indicative of stressful conditions. Corticosterone, and stress, has been linked to telomere shortening in other species. Magellanic penguins are a particularly good model organism for this question as they are an unusually long‐lived species, exceeding their mass‐adjusted predicted lifespan by 26%. Contrary to our hypothesis, we found adults aged 5 years to over 24 years of age had similar telomere lengths. Telomeres of adults did not shorten over a 3‐year period, regardless of the age of the individual. Neither telomere length, nor the rate at which the telomeres changed over these 3 years, correlated with breeding frequency or investment. Older females also produced larger volume clutches until approximately 15 years old and larger eggs produced heavier fledglings. Furthermore, reproductive success (chicks fledged/eggs laid) is maintained as females aged. Basal corticosterone, however, was not correlated with telomere length in adults and suggests that low basal corticosterone may play a role in the telomere maintenance we observed. Basal corticosterone also declined during the breeding season and was positively correlated with the age of adult penguins. This higher basal corticosterone in older individuals, and consistent reproductive success, supports the prediction that Magellanic penguins invest more in reproduction as they age. Our results demonstrate that telomere maintenance may be a component of longevity even with increased reproductive effort, investment, and basal corticosterone.

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Why do we age?

Cited by 1,594 publications

References 62 publications

Age, state, environment, and season dependence of senescence in body mass

Age, state, environment, and season dependence of senescence in body mass

Dissociation of somatic growth, time of sexual maturity, and life expectancy by overexpression of an RGD ‐deficient IGFBP ‐2 variant in female transgenic mice

Magellanic penguin telomeres do not shorten with age with increased reproductive effort, investment, and basal corticosterone

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