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12,871 results for “aging;”
Data from: Evolution of ageing, costs of reproduction and the fecundity–longevity trade-off in eusocial insects
Eusocial insects provide special opportunities to elucidate the evolution of ageing as queens have apparently evaded costs of reproduction and reversed the fecundity-longevity trade-off generally observed in non-social organisms. But how reproduction affects longevity in eusocial insects has rarely been tested experimentally. In this study, we took advantage of the reproductive plasticity of workers to test the causal role of reproduction in determining longevity in eusocial insects. Using the eusocial bumblebee Bombus terrestris, we found that, in whole colonies, in which workers could freely 'choose' whether to become reproductive, workers' level of ovarian activation was significantly positively associated with longevity and ovary-active workers significantly outlived ovary-inactive workers. By contrast, when reproductivity was experimentally induced in randomly-selected workers, thereby decoupling it from other traits, workers' level of ovarian activation was significantly negatively associated with longevity and ovary-active workers were significantly less long-lived than ovary-inactive workers. These findings show that workers experience costs of reproduction and suggest that intrinsically high-quality individuals can overcome these costs. They also raise the possibility that eusocial insect queens exhibit condition-dependent longevity and hence call into question whether eusociality entails a truly reversed fecundity-longevity trade-off involving a fundamental remodelling of conserved genetic and endocrine networks underpinning ageing.
Waterlow score on admission in acutely admitted patients aged 65 and over
<p>834 successively admitted patients aged 65 and over to the acute medical take to a district general hospital had their waterlow score recorded, with subsequent 30-day mortality and length of stay correlated. Admission biochemistry pertaining to sodium, albumin and creatining were also recorded. Records include whether they were a death within 30 days and also their total length of stay. </p>
Data from: Age, experience and sex – do female bulb mites prefer young mating partners?
In species where advancing sire age is associated with decreased progeny fitness, female resistance to mating with old partners can be expected to evolve. In polyandrous species, such resistance may be contingent on female mating experience: virgins should be relatively indiscriminate to ensure egg fertility, whereas non-virgins can be expected to base their re-mating decisions on the age of their previous versus potential new partners, and 'trade up' if previously mated with old males. Here, we tested these predictions using a promiscuous and relatively long-living bulb mite (Rhizoglyphus robini), in which old sire age is associated with decreased fecundity of daughters. In a fully factorial design, we applied two male treatments: young and old, and three female treatments: virgin, previously mated to an old male and previously mated to a young male. Consistent with earlier studies, we observed a reduced mating success of old males. However, we found no support for attributing this result to female discrimination, as female behaviour in response to male mounting attempts was not affected by the age of the suitor, or by its interaction with the age of the female's previous mate. Interestingly, females were passive during 93% of male mounting attempts observed, suggesting that once they are located by a male, they exert little control over copulation. Old males had lower mate searching activity and were less efficient in obtaining matings (lower success rate per mounting attempt), suggesting a decreased mate securing ability due to aging. Overall, our results suggest that in bulb mites, male ability to secure mates declines with age, whereas they do not support the prediction that females actively discriminate against old partners.
Data from: Actuarial senescence in a long-lived orchid challenges our current understanding of ageing
The dominant evolutionary theory of actuarial senescence—an increase in death rate with advancing age—is based on the concept of a germ cell line that is separated from the somatic cells early in life. However, such a separation is not clear in all organisms. This has been suggested to explain the paucity of evidence for actuarial senescence in plants. We used a 32 year study of Dactylorhiza lapponica that replaces its organs each growing season, to test whether individuals of this tuberous orchid senesce. We performed a Bayesian survival trajectory analysis accounting for reproductive investment, for individuals under two types of land use, in two climatic regions. The mortality trajectory was best approximated by a Weibull model, showing clear actuarial senescence. Rates of senescence in this model declined with advancing age, but were slightly higher in mown plots and in the more benign climatic region. At older ages, senescence was evident only when accounting for a positive effect of reproductive investment on mortality. Our results demonstrate actuarial senescence as well as a survival–reproduction trade-off in plants, and indicate that environmental context may influence senescence rates. This knowledge is crucial for understanding the evolution of demographic senescence and for models of plant population dynamics.
Data from: A multigenerational effect of parental age on offspring size but not fitness in common duckweed (Lemna minor)
Classic theories on the evolution of senescence make the simplifying assumption that all offspring are of equal quality, so that demographic senescence only manifests through declining rates of survival or fecundity. However, there is now evidence that, in addition to declining rates of survival and fecundity, many organisms are subject to age-related declines in the quality of offspring produced (i.e. parental age effects). Recent modelling approaches allow for the incorporation of parental age effects into classic demographic analyses, assuming that such effects are limited to a single generation. Does this 'single-generation' assumption hold? To find out, we conducted a laboratory study with the aquatic plant Lemna minor, a species for which parental age effects have been demonstrated previously. We compared the size and fitness of 423 lab-cultured plants (asexually-derived ramets) representing various birth orders, and ancestral 'birth-order genealogies'. We found that offspring size and fitness both declined with increasing 'immediate' birth order (i.e. birth order with respect to the immediate parent), but only offspring size was affected by ancestral birth order. Thus, the assumption that parental age effects on offspring fitness are limited to a single generation does in fact hold for L. minor. This result will guide theorists aiming to refine and generalise modelling approaches that incorporate parental age effects into evolutionary theory on senescence.
Data from: How many cubs can a mum nurse? Maternal age and size influence litter size in polar bears
Life history theory predicts that females' age and size affect the level of maternal investment in current reproduction, balanced against future reproductive effort, maintenance and survival. Using long-term (30 years) individual data on 193 female polar bears (Ursus maritimus), we assessed age- and size-specific variation on litter size. Litter size varied with maternal age, younger females had higher chances of losing a cub during their first months of life. Results suggest an improvement of reproductive abilities early in life due to experience with subsequent reproductive senescence. Litter size increased with maternal size, indicating that size may reflect individual quality. We also found an optimum in the probability of having twins, suggesting stabilizing selection on female body size. Heterogeneity was observed among the largest females, suggesting that large size comes at a cost.
Data from: Evolution of male age-specific reproduction under differential risks and causes of death: males pay the cost of high female fitness
Classic theories of ageing evolution predict that increased extrinsic mortality due to an environmental hazard selects for increased early reproduction, rapid ageing and short intrinsic lifespan. Conversely, emerging theory maintains that when ageing increases susceptibility to an environmental hazard, increased mortality due to this hazard can select against ageing in physiological condition and prolong intrinsic lifespan. However, evolution of slow ageing under high-condition-dependent mortality is expected to result from reallocation of resources to different traits and such reallocation may be hampered by sex-specific trade-offs. Because same life-history trait values often have different fitness consequences in males and females, sexually antagonistic selection can preserve genetic variance for lifespan and ageing. We previously showed that increased condition-dependent mortality caused by heat shock leads to evolution of long-life, decelerated late-life mortality in both sexes and increased female fecundity in the nematode, Caenorhabditis remanei. Here, we used these cryopreserved lines to show that males evolving under heat shock suffered from reduced early-life and net reproduction, while mortality rate had no effect. Our results suggest that heat-shock resistance and associated long-life trade-off with male, but not female, reproduction and therefore sexually antagonistic selection contributes to maintenance of genetic variation for lifespan and fitness in this population.
Data from: Quantifying age-dependent extinction from species phylogenies
Several ecological factors that could play into species extinction are expected to correlate with species age, i.e., time elapsed since the species arose by speciation. To date, however, statistical tools to incorporate species age into likelihood-based phylogenetic inference have been lacking. We present here a computational framework to quantify age-dependent extinction through maximum likelihood parameter estimation based on phylogenetic trees, assuming species lifetimes are gamma distributed. Testing on simulated trees shows that neglecting age dependence can lead to biased estimates of key macroevolutionary parameters. We then apply this method to two real data sets, namely a complete phylogeny of birds (class Aves) and a clade of self-compatible and -incompatible nightshades (Solanaceae), gaining initial insights into the extent to which age-dependent extinction may help explain macroevolutionary patterns. Our methods have been added to the R package TreePar.
Data from: Molecular dating, evolutionary rates, and the age of the grasses
Many questions in evolutionary biology require an estimate of divergence times but, for groups with a sparse fossil record, such estimates rely heavily on molecular dating methods. The accuracy of these methods depends on both an adequate underlying model and the appropriate implementation of fossil evidence as calibration points. We explore the effect of these in Poaceae (grasses), a diverse plant lineage with a very limited fossil record, focusing particularly on dating the early divergences in the group. We show that molecular dating based on a dataset of plastid markers is strongly dependent on the model assumptions. In particular, an acceleration of evolutionary rates at the base of Poaceae followed by a deceleration in the descendants strongly biases methods that assume an autocorrelation of rates. This problem can be circumvented by using markers that have lower rate variation, and we show that phylogenetic markers extracted from complete nuclear genomes can be a useful complement to the more commonly used plastid markers. However, estimates of divergence times remain strongly affected by different implementations of fossil calibration points. Analyses calibrated with only macrofossils lead to estimates for the age of core Poaceae around 51-55 Ma, but the inclusion of microfossil evidence pushes this age to 74-82 Ma and leads to lower estimated evolutionary rates in grasses. These results emphasize the importance of considering markers from multiple genomes and alternative fossil placements when addressing evolutionary issues that depend on ages estimated for important groups.
Data from: Axial length elongation and myopia incidence increase in primary school-age children: 3-year follow-up study
<p>Objective: To investigate the axial length (AL) elongation in primary school-age children during 3-year follow-up period, and evaluate the associations of AL elongation with spherical equivalent (SE), AL at baseline, body height and weight.</p> <p>Design: A 3-year observational cohort study from 2014 to 2017.</p> <p>Setting: Jinshan Hospital of Fudan University in Shanghai.</p> <p>Methods: A total of 452 children successfully completed their measurements in the 3-year follow-up period. Among those children, the mean age was 6.9 ± 0.7 years, ranging from 6 years to 8 years, and 217 (42.7%) were boys. AL was measured with an ocular biometry system. Refractive error was measured using an auto-refractor without cycloplegia.</p> <p>Results: The mean changes of ALs were 0.27 ± 0.28 mm, 0.52 ± 0.40 mm, and 0.89 ± 0.51mm over 1 year, over 2 years and over 3 years, respectively. The mean changes of Spherical equivalents (SEs) were -0.27 ± 0.80 D, -0.56 ± 1.00 D, and -0.95 ± 1.41 D over 1 year, over 2 years and over 3 years, respectively. Multivariate linear regression analysis revealed that mean change of AL was associated with mean change of SE at all points (all P < 0.001). In addition, linear regression analysis revealed that AL elongation in the 3-year follow-up period was associated with AL at baseline (R2 = 0.009, P = 0.045).</p> <p>Conclusions: AL elongation is relatively high in the primary school-age children in Jinshan District, Shanghai. Effect strategies are needed to control AL elongation.</p> <p> </p>
Data from: Theoretical constraints on the precision and age range of rehydroxylation dating
Accurate and precise dating methods are of central importance to archaeology, palaeontology and earth science. This paper investigates the expected precision and age range of rehydroxylation dating, a recently proposed technique for fired clays. An expression for combined measurement uncertainty is presented, which takes into account all significant sources of experimental uncertainty. Numerical simulations are performed for comparison. Combined measurement uncertainties of approximately 5% with respect to the age of the ceramic should be possible given well-designed experiments. In this case, the most significant contribution to combined measurement uncertainty is from effective lifetime temperature. In addition, it is shown that precision should be acceptable for recently fired material (less than 1 year). Mismatch of balance resolution to sample mass results in large variation in combined relative uncertainties, which vary by four orders of magnitude (approx. 1–1160%) across recent experimental studies, rendering some recently reported dates meaningless. It is recommended that this ratio be less than 10−6 for a combined relative uncertainty of less than 1%. The age limits of the technique are set by the value of the rate constant and individual sample mineralogy. This theoretical framework should help future interlaboratory comparison as well as optimizing instrument design.
Data from: Relatedness and age reduce aggressive male interactions over mating in domestic fowl
Altruistic behaviour represents a fundamental challenge in evolutionary biology. It is often best understood through kin selection, where favourable behaviour is directed towards relatives. Kin selection can take place when males cooperate to enhance the reproductive success of relatives. Here, we focus on reduced male–male competition over mating as a case of cooperation, by examining male tolerance of matings by related and unrelated competitors. A suitable model for exploring whether relatedness affects male–male interactions over mating is the domestic fowl, Gallus gallus domesticus. In this species, males form social hierarchies and dominant males commonly interrupt subdominant males' copulation attempts. We investigated whether dominant male fowl differentially direct aggressive interactions towards unrelated and related subordinate males during mating attempts. Dominant male fowl were found to interrupt mating attempts of male relatives less often than those of unrelated males. We further tested whether male age mediates the magnitude of kin tolerance behaviour. However, we found no support for this as both young and old dominant males were less likely to interrupt related, compared to unrelated, subdominant males' copulations during male–male interactions. Our results, consistent with kin selection, provide a rare experimental demonstration of relatedness relaxing male–male competition over mating.
Data from: Offspring provisioning explains clone specific maternal age effects on life history and lifespan in the water flea, Daphnia pulex
Genetic inheritance underpins evolutionary theories of aging, but the role that nongenetic inheritance plays is unclear. Parental age reduces the life span of offspring in a diverse array of taxa but has not been explained from an evolutionary perspective. We quantified the effect that maternal age had on the growth and maturation decisions, life history, rates of senescence, and life span of offspring from three Daphnia pulex clones collected from different populations. We then used those data to test general hypotheses proposed to explain maternal age effects on offspring life span. Three generations of breeding from young or old mothers produced dramatic differences in the life histories of fourth-generation offspring, including significant reductions in life span. The magnitude of the effect differed between clones, which suggests that genetic and nongenetic factors ultimately underpin trait inheritance and shape patterns of aging. Older parents did not transmit a senescent state to their offspring. Instead, offspring from older ancestors had increased early-life reproductive effort, which resulted in an earlier onset of reproductive senescence, and an increased rate of actuarial senescence, which shortened their life span. Our results provide a clear example of the need to consider multiple inheritance mechanisms when studying trait evolution.
Data from: Gene expression changes in male accessory glands during ageing are accompanied by reproductive decline in Drosophila melanogaster
Senescence is accompanied by loss of reproductive functions. Here we studied reproductive ageing in Drosophila melanogaster males and asked whether the expected decline in male reproductive success is due to diminished functionality of the male accessory gland. The male accessory gland produces the majority of seminal fluid proteins (SFPs) transferred to the female at mating. SFPs induce female post-mating changes and are key to male reproductive success. We measured age-dependent gene expression changes for five representative SFP genes in males from four different age groups ranging from one to six weeks after eclosion. Simultaneously, we also measured male reproductive success in post-mating traits mediated by transfer of these five SFPs. We found a decrease in male SFP gene expression with advancing age and an accompanying decline in male post-mating success. Hence, male reproductive senescence is associated with a decline in functionality of the male accessory gland. While overall individual SFP genes decrease in expression our results point towards the idea that the composition of an ejaculate might change with male age as the rate of change was variable for those five genes.
Data from: Reduced lifespan and increased ageing driven by genetic drift in small populations
Explaining the strong variation in lifespan among organisms remains a major challenge in evolutionary biology. Whereas previous work has concentrated mainly on differences in selection regimes and selection pressures, we hypothesize that differences in genetic drift may explain some of this variation. We develop a model to formalize this idea and show that the strong positive relationship between lifespan and genetic diversity predicted by this model indeed exists among populations of Daphnia magna, and that ageing is accelerated in small populations. Additional results suggest that this is due to increased drift in small populations rather than adaptation to environments favoring faster life histories: First, the correlation between genetic diversity and lifespan remains significant after statistical correction for potential environmental covariates. Second, no trade-offs are observed; rather, all investigated traits show clear signs of increased genetic load in the small populations. Third, hybrid vigor with respect to lifespan is observed in crosses between small but not between large populations. Together, these results suggest that the evolution of lifespan and ageing can be strongly affected by genetic drift, especially in small populations, and that variation in lifespan and ageing may often be non-adaptive, due to a strong contribution from mutation accumulation to this variation.
Data from: Sex differences in the effects of juvenile and adult diet on age-dependent reproductive effort
Sexual selection should cause sex differences in patterns of resource allocation. When current and future reproductive effort trade-off, variation in resource acquisition might further cause sex differences in age-dependent investment, or in sensitivity to changes in resource availability over time. However, the nature and prevalence of sex differences in age-dependent investment remain unclear. We manipulated resource acquisition at juvenile and adult stages in decorated crickets, Gryllodes sigillatus, and assessed effects on sex-specific allocation to age-dependent reproductive effort (calling in males, fecundity in females) and longevity. We predicted that the resource and time demands of egg production would result in relatively consistent female strategies across treatments, while male investment should depend sharply on diet. Contrary to expectations, female age-dependent reproductive effort diverged substantially across treatments, with resource-limited females showing much lower and later investment in reproduction; the highest fecundity was associated with intermediate lifespans. In contrast, long-lived males always signalled more than short-lived males, and male age-dependent reproductive effort did not depend on diet. We found consistently positive covariance between male reproductive effort and lifespan, while diet altered this covariance in females, revealing sex differences in the benefits of allocation to longevity. Our results support sex-specific selection on allocation patterns, but also suggest a simpler alternative: males may use social feedback to make allocation decisions, and preferentially store resources as energetic reserves in its absence. Increased calling effort with age therefore could be caused by gradual resource accumulation, heightened mortality risk over time, and a lack of feedback from available mates.
Data from: Age-dependent female responses to a male ejaculate signal alter demographic opportunities for selection
A central tenet of evolutionary explanations for ageing is that the strength of selection wanes with age. However, data on age-specific expression and benefits of sexually selected traits are lacking—particularly for traits subject to sexual conflict. We addressed this by using as a model the responses of Drosophila melanogaster females of different ages to receipt of sex peptide (SP), a seminal fluid protein transferred with sperm during mating. SP can mediate sexual conflict, benefitting males while causing fitness costs in females. Virgin and mated females of all ages showed significantly reduced receptivity in response to SP. However, only young virgin females also showed increased egg laying; hence, there was a narrow demographic window of maximal responses to SP. Males gained significant 'per mating' fitness benefits only when mating with young females. The pattern completely reversed in matings with older females, where SP transfer was costly. The overall benefits of SP transfer (hence opportunity for selection) therefore reversed with female age. The data reveal a new example of demographic variation in the strength of selection, with convergence and conflicts of interest between males and ageing females occurring over different facets of responses to a sexually antagonistic trait.
Data from: Epidemiological survey of the feasibility of broadband ultrasound attenuation measured using calcaneal quantitative ultrasound to predict the incidence of falls in the middle aged and elderly
Objectives: We investigated whether calcaneal quantitative ultrasound (QUS-C) is a feasible tool for predicting the incidence of falls. Design: Prospective epidemiological cohort study. Setting: Community-dwelling people sampled in central western Taiwan. Participants: A cohort of community-dwelling people who were ≥40 years old (men: 524; women: 676) in 2009–2010. Follow-up questionnaires were completed by 186 men and 257 women in 2012. Methods: Structured questionnaires and broadband ultrasound attenuation (BUA) data were obtained in 2009–2010 using QUS-C, and follow-up surveys were done in a telephone interview in 2012. Using a binary logistic regression model, the risk factors associated with a new fall during follow-up were analysed with all significant variables from the bivariate comparisons and theoretically important variables. Primary outcome measures: The incidence of falls was determined when the first new fall occurred during the follow-up period. The mean follow-up time was 2.83 years. Results: The total incidence of falls was 28.0 per 1000 person-years for the ≥40 year old group (all participants), 23.3 per 1000 person-years for the 40–70 year old group, and 45.6 per 1000 person-years for the ≥70 year old group. Using multiple logistic regression models, the independent factors were current smoking, living alone, psychiatric drug usage and lower BUA (OR 0.93; 95% CI 0.88 to 0.99, p<0.05) in the ≥70 year old group. Conclusions: The incidence of falls was highest in the ≥70 year old group. Using QUS-C-derived BUA is feasible for predicting the incidence of falls in community-dwelling elderly people aged ≥70 years.
Data from: Age and sex affect quantitative genetic parameters for dominance rank and aggression in free-living greylag geese
Knowledge of the genetic and environmental influences on a character is pivotal for understanding evolutionary changes in quantitative traits in natural populations. Dominance and aggression are ubiquitous traits that are selectively advantageous in many animal societies and have the potential to impact the evolutionary trajectory of animal populations. Here we provide age- and sex-specific estimates of additive genetic and environmental components of variance for dominance rank and aggression rate in a free-living, human-habituated bird population subject to natural selection. We use a long-term data set on individually marked greylag geese (Anser anser) and show that phenotypic variation in dominance-related behaviours contains significant additive genetic variance, parental effects and permanent environment effects. The relative importance of these variance components varied between age and sex classes, whereby the most pronounced differences concerned non-genetic components. In particular, parental effects were larger in juveniles of both sexes than in adults. In paired adults, the partner's identity had a larger influence on male dominance rank and aggression rate than in females. In sex- and age-specific estimates, heritabilities did not differ significantly between age and sex classes. Adult dominance rank was only weakly genetically correlated between the sexes, leading to considerably higher heritabilities in sex-specific estimates than across sexes. We discuss these patterns in relation to selection acting on dominance rank and aggression in different life history stages and sexes and suggest that different adaptive optima could be a mechanism for maintaining genetic variation in dominance-related traits in free-living animal populations.
Data from: Age, condition and dominance-related sexual ornament size before and during the breeding season in the black grouse Lyrurus tetrix
Male ornaments function as honest cues of male quality in many species and are subject to intra- and intersexual selection. These ornaments are generally studied during peak expression, however their size outside the breeding season may determine ultimate ornament size and costliness, and as such reproductive success. We investigated whether male black grouse Lyrurus tetrix eye comb size was related to age, condition and measures of male dominance before and during the breeding season. Total combined eye comb size began to increase ~70 days before the start of the breeding season. Adult males (aged ≥ 2 years old) had consistently larger eye combs than younger males (1 year old) both before and during the breeding season. Heavier and more dominant adult males (attending the lek more frequently and successfully reproducing) had larger eye combs. For younger males, those that were heavier had larger eye combs. Additionally, males that spent more time on the lek showed increased eye comb size as the breeding season approached. Overall we find that ornament size is positively related to dominance and condition before and during the breeding season. Since dominance is accrued through year-round interactions in many species, the ability to maintain larger signals over prolonged periods,
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