Sex and ageing

Live fast, die old: no evidence of reproductive senescence or costs of mating in a damselfly (Odonata: Zygoptera)

Recent examples of actuarial senescence in wild insect populations have challenged the long-held assumption that the brevity of wild insect life spans precludes senescence. We investigate age-related patterns in mating behaviour in adults of a short-lived damselfly, Coenagrion puella and the implications of this mating. Using capture histories for 1033 individuals over two field seasons, we conduct both pooled and stratified analyses of variations in breeding activity. Pooled analyses suggest that there is strong age-related variation in the probability of being present at the mating rendezvous. However, no age-related variation was observed in the probability of mating. Stratified approaches confirmed a general pattern of age-related declines in survival probability, but provided only equivocal evidence of an effect of age on transition between temporary breeding states. Mating males and females showed greater survival than non-mating individuals, possibly as a consequence of higher body condition. Older males that were not currently breeding were less likely to commence breeding on the next day, but showed no patterns in breeding cessation. Overall, transitions between both breeding states declined with age, suggesting that males that breed tend to continue breeding while those that do not breed continue to be unsuccessful. Female mating rates were consistently high across all ages with no age-related decline apparent. While previous research has demonstrated actuarial senescence in this population, as does this study, we find little evidence of either age-related declines in reproductive behaviour or breeding-related declines in survival, which might indicate functional senescence or costs of mating, respectively. Indeed, the greater survival in mating individuals of both sexes suggests that variations in individual quality may mediate both reproductive success and longevity. Contrary to recent studies, we found no compelling evidence for reproductive senescence or a cost of mating in an important and well-studied model odonate. The possible link between condition and ageing suggests that individual quality needs to be taken into account when studying senescence. We recommend the use of multistrata models for the future investigation of these phenomena.

Evolution of aging and death: what insights bacteria can provide

Several unresolved issues, paradoxes, and information voids characterize the field of evolution of aging. The recent discovery of aging-like phenomenon in Escherichia coli, marked by asymmetric segregation of damaged components, particularly protein aggregates, has created a number of new possibilities that remain underexplored. Bacterial systems can potentially throw light on issues such as: whether evolution of aging and evolution of death are different phenomena; whether aging is inevitable for life or is an evolved strategy; whether there could be selection for aging or aging is a pleiotropic effect of some other selection; what are the possible mechanisms of antagonistic pleiotropy, if any; and whether there are mechanisms of aging that are conserved throughout the hierarchy of life. Bacterial aging itself is underexplored and least understood as of now, but even scratching the surface appears to reveal things that may compel us to revise some of the classical concepts about evolution of aging. This warrants more focused and innovative inquiry into aging-like processes in bacteria.

Oxidative stress in testis of animals during aging with and without reproductive activity

The free radical theory of aging postulates that an imbalance between reactive oxygen species (ROS) and reactive nitrogen species (RNS) and antioxidant defenses is important in senescence. To address this issue and gain insight into the aging process, we have evaluated the antioxidant defenses and have assessed oxidative damage in testis tissues in aging male rats. In order to relate aging and reproduction, animals with and without reproductive activity were studied. In reproductive animals the results showed a progressive increase in antioxidant enzyme activity until 12 months of age followed by an abrupt fall at 24 months. In non-reproductive animals, antioxidant activity was stable through 12 months of age, but again, fell abruptly at 24 months of age. In addition, increased aconitase activity and increased testosterone levels were found among reproductively active animals. The data demonstrate the existence of metabolic differences in testis of reproductively experienced animals and reproductively naïve animals.

The rise and fall of women's advantage: a comparison of national trends in life expectancy at age 65 years

The female advantage in life expectancy (LE) is found worldwide, despite differences in living conditions, the status of women and other factors. However, this advantage has decreased in recent years in low-mortality countries. Few researchers have looked at the gender gap in LE in old age (age 65) in a longer historical perspective. Have women always had an advantage in LE at old age and do different countries share the same trends? Life expectancy data for 17 countries were assessed from Human Mortality Database from 1751 to 2007. Since most of the changes in LE taking place today are driven by reductions of old age mortality the gender difference in LE was calculated at age 65. Most low-mortality countries show the same historical trend, a rise and fall of women’s advantage in LE at age 65. Three phases that all but two countries passed through were discerned. After a long phase with a female advantage in LE at 65 of <1 year, the gender gap increased significantly during the twentieth century. The increase occurred in all countries but at different time points. Some countries such as England and France had an early rise in female advantage (1900–1919), while it occurred 50 years later in Sweden, Norway and in the Netherlands. The rise was followed by a more simultaneous fall in female advantage in the studied countries towards the end of the century, with exceptions of Japan and Spain. The different timing regarding the increase of women’s advantage indicates that country-specific factors may have driven the rise in female advantage, while factors shared by all countries may underlie the simultaneous fall. More comprehensive, multi-disciplinary study of the evolution of the gender gap in old age could provide new hypotheses concerning the determinants of gendered differences in mortality.

Consequences of artificial selection on pre-adult development for adult lifespan under benign conditions in the butterfly Bicyclus anynana

The genetic architecture underlying the regulation of lifespan is shaped by evolutionary history, thus, including selection in past environments. In particular, the developmental environment is important, because selection pressure for survival is highest during development. From this life-history point of view, the ageing phenotype is the outcome of these factors, and links between the developmental and adult life stage are expected. In this study, we specifically address whether genetic variation in pre-adult traits affects adult lifespan. We use lines artificially selected for divergence in development time, pupal mass or egg size, thus, exploiting the standing genetic variation in pre-adult traits present in natural populations of Bicyclus anynana. We then reared individuals from each line and the unselected base population in a common environment, and recorded each selected trait and adult longevity. In general, differences in adult lifespan across selection lines were small. This is not surprising given the benign conditions used here. The minor differences in adult survival were only partially the result of environmental influences, as indicated by low phenotypic correlations. However, significant genetic correlations point to possible intrinsic mechanisms involved in lifespan regulation. Genetic variation in egg mass or pupal mass did not contribute to variation in lifespan. However, we found a negative genetic correlation between developmental time and lifespan, suggesting a genetic coupling of faster development with a longer adult lifespan in this species. A follow-up study with an identical set-up that introduces stress during development should give a more detailed insight into the role of development in the regulation of lifespan.

Predictors of mortality in the old-old in Israel: the Cross-sectional and Longitudinal Aging Study

OBJECTIVES

To examine whether well-known predictors of mortality change their predictive power over time, being reduced or even reversed in the old-old.

DESIGN

A multidimensional survey of the Cross-Sectional and Longitudinal Aging Study conducted from 1989 to 1992 with follow-up of mortality after 6, 8, 10, and 12 years since 1989.

SETTING

Israel.

PARTICIPANTS

Participants (N=1,369) were drawn from a national sample of the Jewish Israeli population aged 75 to 94.

MEASUREMENTS

Data included sociodemographic factors and measures of health, physical condition, cognitive performance, and depression.

RESULTS

The results showed that age, sex, disability, self-rated health, and marital status predicted mortality and that their predictive power changed over 9 years.

CONCLUSION

In the old-old, predictors of mortality changed over time, and their predictive effect eventually diminished. The predictors found to be most significant (age, sex, disability, and self-rated health) support the common cause theory.

Heritability of death from coronary heart disease: a 36-year follow-up of 20 966 Swedish twins

OBJECTIVE

The aim of the present study was to evaluate and distinguish between environmental and genetic effects for death from coronary heart disease (CHD) as well as to determine whether the importance of genetic influences is changing with age.

DESIGN

A cohort study with a follow-up time of 36 years.

SUBJECTS

The cohort drawn for the present study includes 20 966 twins born in Sweden between 1886 and 1925 where both twins within a pair still lived within the country in 1961.

METHODS

Concordances and correlated gamma-frailty model were used to assess and distinguish between genetic and environmental influences as well as to evaluate age-related changes in genetic influences.

RESULTS

A total number of 4007 CHD-deaths (2208 males, and 1799 females) was observed. The probability of dying from CHD given that one's twin partner already has died from CHD decreased with increasing age, particularly amongst males. The genetic variation in susceptibility to death from CHD was moderately large, and decreased slightly across time, particularly amongst males. The heritability was 0.57 (95% CI, 0.45-0.69) amongst male twins, and 0.38 (0.26-0.50) amongst female twins.

CONCLUSIONS

The genetic contribution to the variation in CHD-mortality was moderate both in females and males. Furthermore, although genetic effects appeared to be greater at younger ages of death, our findings clearly suggest that genetic factors are in operation throughout the entire life span.

Aging is a deprivation syndrome driven by a germ-soma conflict

Evolution through natural selection can be described as driven by a perpetual conflict of individuals competing for limited resources. Recently, I postulated that the shortage of resources godfathered the evolutionary achievements of the differentiation-apoptosis programming [Rev. Neurosci. 12 (2001) 217]. Unicellular deprivation-induced differentiation into germ cell-like spores can be regarded as the archaic reproduction events which were fueled by the remains of the fratricided cells of the apoptotic fruiting body. Evidence has been accumulated suggesting that conserved through the ages as the evolutionary legacy of the germ-soma conflict, the somatic loss of immortality during the ontogenetic segregation of primordial germ cells recapitulates the archaic fate of the fruiting body. In this heritage, somatic death is a germ cell-triggered event and has been established as evolutionary-fixed default state following asymmetric reproduction in a world of finite resources. Aging, on the other hand, is the stress resistance-dependent phenotype of the somatic resilience that counteracts the germ cell-inflicted death pathway. Thus, aging is a survival response and, in contrast to current beliefs, is antagonistically linked to death that is not imposed by group selection but enforced upon the soma by the selfish genes of the "enemy within". Environmental conditions shape the trade-off solutions as compromise between the conflicting germ-soma interests. Mechanistically, the neuroendocrine system, particularly those components that control energy balance, reproduction and stress responses, orchestrate these events. The reproductive phase is a self-limited process that moulds onset and progress of senescence with germ cell-dependent factors, e.g. gonadal hormones. These degenerate the regulatory pacemakers of the pineal-hypothalamic-pituitary network and its peripheral, e.g. thymic, gonadal and adrenal targets thereby eroding the trophic milieu. The ensuing cellular metabolic stress engenders adaptive adjustments of the glucose-fatty acid cycle, responses that are adequate and thus fitness-boosting under fuel shortage (e.g. during caloric restriction) but become detrimental under fuel abundance. In a Janus-faced capacity, the cellular stress response apparatus expresses both tolerogenic and mutagenic features of the social and asocial deprivation responses [Rev. Neurosci. 12 (2001) 217]. Mediated by the derangement of the energy-Ca(2+)-redox homeostatic triangle, a mosaic of dedifferentiation/apoptosis and mutagenic responses actuates the gradual exhaustion of functional reserves and eventually results in a multitude of aging-related diseases. This scenario reconciles programmed and stochastic features of aging and resolves the major inconsistencies of current theories by linking ultimate and proximate causes of aging. Reproduction, differentiation, apoptosis, stress response and metabolism are merged into a coherent regulatory network that stages aging as a naturally selected, germ cell-triggered and reproductive phase-modulated deprivation response.

Does functional depletion of stem cells drive aging?

The regenerative power of stem cells has raised issues about their relation to aging. We focus on the question of whether a decline in the function of stem cells may itself be a significant feature of aging. The question is implicitly two-fold: does functional depletion of stem cells affect the accumulation of aging-related deficits, and--whether or not depletion is significant--can activation of stem cells alleviate deficits? Two types of system are considered: 1) the exhaustible pool of ovarian follicles. The depletion of follicles leads to the aging-related phenomenon of menopause; and 2) the reserve of hematopoietic stem cells. Substantial numbers are sustained throughout life, but in mouse models, endogenous replicative activity has been shown to decline sharply with age. We discuss the possible implications of these observations for the rate of aging and the prospects for intervention.