The role of parental age effects on the evolution of aging

Maternal age effects on offspring lifespan and reproduction vary within a species

Across diverse taxa, offspring from older mothers have decreased lifespan and fitness. Little is known about the extent to which maternal age effects vary among genotypes for a given species, however, except for studies of a few arthropod species. To investigate the presence and degree of intraspecific variability in maternal age effects, we compared lifespan, reproductive schedule, and lifetime reproductive output of offspring produced by young, middle-aged, and old mothers in four strains of rotifers in the Brachionus plicatilis species complex. We found significant variability among strains in the magnitude and direction of maternal age effects on offspring life history traits. In one strain, offspring of young mothers lived 20% longer than offspring of old mothers, whereas there were no significant effects of maternal age on lifespan for other strains. Depending on strain, advanced maternal age had positive effects, negative effects, or no effect on lifetime reproductive output. Across strains, older mothers produced offspring that had higher maximum daily reproduction early in life. The effects of maternal age on offspring vital rates could not be explained by changes in trade-offs between lifespan and reproduction. This study documents intraspecific variability in maternal age effects in an additional clade. Investigating intraspecific variability is critical for understanding the ubiquity of maternal age effects and their role in the evolution of life history and aging.

Parental age effect on the longevity and healthspan in Drosophila melanogaster and Caenorhabditis elegans

Several studies have investigated the effect of parental age on biological parameters such as reproduction, lifespan, and health; however, the results have been inconclusive, largely due to inter-species variation and/or modest effect sizes. Here, we examined the effect of parental age on the lifespan, reproductive capacity, and locomotor activity of genetic isogenic lines of the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster. We found that the progeny of successive generations of old parents had significantly shorter lifespans than the progeny of young parents in both species. Moreover, we investigated the fertility, fecundity, and locomotor activity of C. elegans. Interestingly, both the shorter lifespan and deteriorated healthspan of the progeny were significantly improved by switching to only one generation of younger parents. Collectively, these data demonstrate that the detrimental effect of older parental age on the longevity of the progeny can be reversed, suggesting the existence of a beneficial non-genetic mechanism.

Advanced maternal age has negative multigenerational impacts during Drosophila melanogaster embryogenesis

Increasing maternal age is commonly accompanied by decreased fitness in offspring. In Drosophila melanogaster, maternal senescence negatively affects multiple facets of offspring phenotype and fitness. These maternal effects are particularly large on embryonic viability. Identifying which embryonic stages are disrupted can indicate mechanisms of maternal effect senescence. Some maternal effects can also carry-over to subsequent generations. We examined potential multi- and transgenerational effects maternal senescence on embryonic development in two laboratory strains of D. melanogaster. We categorized the developmental stages of embryos from every combination of old and young mother, grandmother and great grandmother. We then modelled embryonic survival across the stages and compared these models among the multigenerational maternal age groups in order to identify which developmental processes were most sensitive to the effects of maternal effect senescence. Maternal effect senescence has negative multigenerational effects on multiple embryonic stages, indicating that maternal provisioning and, possibly epigenetics, but not mutation accumulation, contribute to decreased offspring survival. This study shows the large, early and multi-faceted nature of maternal effects senescence in an insect population.

Evidence of maternal and paternal age effects on speed in thoroughbred racehorses

Effects of parental age on offspring viability have been reported in a wide range of species. However, to what extent parental age influences offspring traits beyond viability remains unclear. Moreover, previous research has primarily focused on maternal age effects. The purpose of this study was to test for paternal and maternal age effects on offspring speed in thoroughbred racehorses. We analysed over 900 000 race performances by over 100 000 horses on British racecourses between 1996 and 2019. With knowledge of the age of all 41 107 dams and 2 887 sires at offspring conception, we jointly modelled maternal and paternal age effects using a 'within-individual centring' approach. Within-parents, we identified a significant effect of maternal age on offspring speed of -0.017 yards s^-1 yr^-1 and a corresponding paternal age effect of -0.011 yards s^-1 yr^-1. Although maternal age effects were stronger (more negative), the existence and magnitude of paternal effects is particularly noteworthy, given thoroughbred sires have no involvement in parental care. Our results also suggest that the selective disappearance of both sires and dams is ongoing. These findings could potentially be used to optimize thoroughbred racehorse breeding decisions, and more generally, add to the increasing body of evidence that both maternal and paternal age affect a range of offspring characteristics.

Evidence of maternal and paternal age effects on speed in thoroughbred racehorses

Effects of parental age on offspring viability have been reported in a wide range of species. However, to what extent parental age influences offspring traits beyond viability remains unclear. Moreover, previous research has primarily focused on maternal age effects. The purpose of this study was to test for paternal and maternal age effects on offspring speed in thoroughbred racehorses. We analysed over 900 000 race performances by over 100 000 horses on British racecourses between 1996 and 2019. With knowledge of the age of all 41 107 dams and 2 887 sires at offspring conception, we jointly modelled maternal and paternal age effects using a 'within-individual centring' approach. Within-parents, we identified a significant effect of maternal age on offspring speed of -0.017 yards s^-1 yr^-1 and a corresponding paternal age effect of -0.011 yards s^-1 yr^-1. Although maternal age effects were stronger (more negative), the existence and magnitude of paternal effects is particularly noteworthy, given thoroughbred sires have no involvement in parental care. Our results also suggest that the selective disappearance of both sires and dams is ongoing. These findings could potentially be used to optimize thoroughbred racehorse breeding decisions, and more generally, add to the increasing body of evidence that both maternal and paternal age affect a range of offspring characteristics.

Evidence of maternal and paternal age effects on speed in thoroughbred racehorses

Effects of parental age on offspring viability have been reported in a wide range of species. However, to what extent parental age influences offspring traits beyond viability remains unclear. Moreover, previous research has primarily focused on maternal age effects. The purpose of this study was to test for paternal and maternal age effects on offspring speed in thoroughbred racehorses. We analysed over 900 000 race performances by over 100 000 horses on British racecourses between 1996 and 2019. With knowledge of the age of all 41 107 dams and 2 887 sires at offspring conception, we jointly modelled maternal and paternal age effects using a 'within-individual centring' approach. Within-parents, we identified a significant effect of maternal age on offspring speed of -0.017 yards s^-1 yr^-1 and a corresponding paternal age effect of -0.011 yards s^-1 yr^-1. Although maternal age effects were stronger (more negative), the existence and magnitude of paternal effects is particularly noteworthy, given thoroughbred sires have no involvement in parental care. Our results also suggest that the selective disappearance of both sires and dams is ongoing. These findings could potentially be used to optimize thoroughbred racehorse breeding decisions, and more generally, add to the increasing body of evidence that both maternal and paternal age affect a range of offspring characteristics.

Triparental ageing in a laboratory population of an insect with maternal care

Parental age at reproduction influences offspring size and survival by affecting prenatal and postnatal conditions in a wide variety of species, including humans. However, most investigations into this manifestation of ageing focus upon maternal age effects; the effects of paternal age and interactions between maternal and paternal age are often neglected. Furthermore, even when maternal age effects are studied, pre- and post-natal effects are often confounded. Using a cross-fostered experimental design, we investigated the joint effects of pre-natal paternal and maternal and post-natal maternal ages on five traits related to offspring outcomes in a laboratory population of a species of burying beetle, Nicrophorus vespilloides. We found a significant positive effect of the age of the egg producer on larval survival to dispersal. We found more statistical evidence for interaction effects, which acted on larval survival and egg length. Both interaction effects were negative and involved the age of the egg-producer, indicating that age-related pre-natal maternal improvements were mitigated by increasing age in fathers and foster mothers. These results agree with an early study that found little evidence for maternal senescence, but it emphasizes that parental age interactions may be an important contributor to ageing patterns. We discuss how the peculiar life history of this species may promote selection to resist the evolution of parental age effects, and how this might have influenced our ability to detect senescence.

Separating the effects of paternal age and mating history: Evidence for sex-specific paternal effect in eastern mosquitofish

Paternal age and past mating effort by males are often confounded, which can affect our understanding of a father's age effects. To our knowledge, only a few studies have standardized mating history when testing for effects of paternal age, and none has simultaneously disentangled how paternal age and mating history might jointly influence offspring traits. Here, we experimentally manipulated male mating history to tease apart its effects from those of paternal age on female fertility and offspring traits in the eastern mosquitofish (Gambusia holbrooki). Male age did not affect female fertility. However, males with greater past mating effort produced significantly larger broods. Paternal age and mating history interacted to affect sons' body size: sons sired by old-virgin males were larger than those sired by old-mated males, but this was not the case for younger fathers. Intriguingly, however, sons sired by old-virgin males tended to produce fewer sperms than those sired by old-mated males, indicating a potential trade-off in beneficial paternal effects. Finally, neither paternal age nor mating history affected daughter's fitness. Our results highlight that variation in offspring traits attributed to paternal age effect could partly arise due to a father's mating history, and not simply to his chronological age.

Evidence of Paternal Effects on Telomere Length Increases in Early Life

Offspring of older parents in many species have decreased longevity, a faster ageing rate and lower fecundity than offspring born to younger parents. Biomarkers of ageing, such as telomeres, that tend to shorten as individuals age, may provide insight into the mechanisms of such parental age effects. Parental age may be associated with offspring telomere length either directly through inheritance of shortened telomeres or indirectly, for example, through changes in parental care in older parents affecting offspring telomere length. Across the literature there is considerable variation in estimates of the heritability of telomere length, and in the direction and extent of parental age effects on telomere length. To address this, we experimentally tested how parental age is associated with the early-life telomere dynamics of chicks at two time points in a captive population of house sparrows Passer domesticus. We experimentally separated parental age from sex effects, and removed effects of age-assortative mating, by allowing the parent birds to only mate with young, or old partners. The effect of parental age was dependent on the sex of the parent and the chicks, and was found in the father-daughter relationship only; older fathers produced daughters with longer telomere lengths post-fledging. Overall we found that chick telomere length increased between the age of 0.5 and 3 months at the population and individual level. This finding is unusual in birds with such increases more commonly associated with non-avian taxa. Our results suggest parental age effects on telomere length are sex-specific either through indirect or direct inheritance. The study of similar patterns in different species and taxa will help us further understand variation in telomere length and its evolution.

Female reproductive aging in seven primate species: Patterns and consequences

Age-related changes in fertility have increasingly been documented in wild animal populations: In many species the youngest and oldest reproducers are disadvantaged relative to prime adults. How do these effects evolve, and what explains their diversity across species? Tackling this question requires detailed data on patterns of age-related reproductive performance in multiple animal species. Here, we compare patterns and consequences of age-related changes in female reproductive performance in seven primate populations that have been subjects of long-term continuous study for 29 to 57 y. We document evidence of age effects on fertility and on offspring performance in most, but not all, of these primate species. Specifically, females of six species showed longer interbirth intervals in the oldest age classes, youngest age classes, or both, and the oldest females also showed relatively fewer completed interbirth intervals. In addition, five species showed markedly lower survival among offspring born to the oldest mothers, and two species showed reduced survival for offspring born to both the youngest and the oldest mothers. In contrast, we found mixed evidence that maternal age affects the age at which daughters first reproduce: Only in muriquis and to some extent in chimpanzees, the only two species with female-biased dispersal, did relatively young mothers produce daughters that tended to have earlier first reproduction. Our findings demonstrate shared patterns as well as contrasts in age-related changes in female fertility across species of nonhuman primates and highlight species-specific behavior and life-history patterns as possible explanations for species-level differences.

A genome-wide test for paternal indirect genetic effects on lifespan in Drosophila melanogaster

Exposing sires to various environmental manipulations has demonstrated that paternal effects can be non-trivial also in species where male investment in offspring is almost exclusively limited to sperm. Whether paternal effects also have a genetic component (i.e. paternal indirect genetic effects (PIGEs)) in such species is however largely unknown, primarily because of methodological difficulties separating indirect from direct effects of genes. PIGEs may nevertheless be important since they have the capacity to contribute to evolutionary change. Here we use Drosophila genetics to construct a breeding design that allows testing nearly complete haploid genomes (more than 99%) for PIGEs. Using this technique, we estimate the variance in male lifespan due to PIGEs among four populations and compare this to the total paternal genetic variance (the sum of paternal indirect and direct genetic effects). Our results indicate that a substantial part of the total paternal genetic variance results from PIGEs. A screen of 38 haploid genomes, randomly sampled from a single population, suggests that PIGEs also influence variation in lifespan within populations. Collectively, our results demonstrate that PIGEs may constitute an underappreciated source of phenotypic variation.

The role of maternal age, growth, and environment in shaping offspring performance in an aerial conifer seed bank

PREMISE

Maternal effects have been demonstrated to affect offspring performance in many organisms, and in plants, seeds are important mediators of these effects. Some woody plant species maintain long-lasting canopy seed banks as an adaptation to wildfires. Importantly, these seeds stored in serotinous cones are produced by the mother plant under varying ontogenetic and physiological conditions.

METHODS

We sampled the canopy seed bank of a highly serotinous population of Pinus pinaster to test whether maternal age and growth and the environmental conditions during each crop year affected seed mass and ultimately germination and early survival. After determining retrospectively the year of each seed cohort, we followed germination and early survival in a semi-natural common garden.

RESULTS

Seed mass was related to maternal age and growth at the time of seed production; i.e., slow-growing, older mothers had smaller seeds, and fast-growing, young mothers had larger seeds, which could be interpreted either as a proxy of senescence or as a maternal strategy. Seed mass had a positive effect on germination success, but aside from differences in seed mass, maternal age had a negative effect and diameter had a positive effect on germination timing and subsequent survival.

CONCLUSIONS

The results highlight the importance of maternal conditions combined with seed mass in shaping seedling establishment. Our findings open new insights in the offspring performance deriving from long-term canopy seed banks, which may have high relevance for plant adaptation.

Exploring the effects of birth order on human lifespan in Polish historical populations, 1738–1968

While the relationships between birth order and later outcomes in life, including health and wealth, have been the subject of investigation for several decades, little or no data exist regarding the relationship between birth order and life expectancy in the Polish population. The aim of this study was to explore the link between birth order and lifespan in Polish historical populations. We obtained 8523 records from a historical dataset that was established for parishioners from the borough of Bejsce, including 4463 males and 4060 females. These data pertain to the populations that lived over a long period in a group of localities for which parish registers were well preserved. The Mann-Whitney U test, the Kruskal-Wallis ANOVA and ANCOVA were run. The results strongly suggest that birth order affects male longevity. However, no such association was found for females. On balance, the hypothesis that first-born boys live longer because they are born to relatively younger parents has received some empirical support and deserves further study. We hypothesise that the effects of birth order on human health and lifespan might be overshadowed by other factors, including educational attainment, socioeconomic status and lifestyle.

Beneficial cumulative effects of old parental age on offspring fitness

Old parental age is commonly associated with negative effects on offspring life-history traits. Such parental senescence effects are predicted to have a cumulative detrimental effect over successive generations. However, old parents may benefit from producing higher quality offspring when these compete for seasonal resources. Thus, old parents may choose to increase investment in their offspring, thereby producing fewer but larger and more competitive progeny. We show that Caenorhabditis elegans hermaphrodites increase parental investment with advancing age, resulting in fitter offspring who reach their reproductive peak earlier. Remarkably, these effects increased over six successive generations of breeding from old parents and were subsequently reversed following a single generation of breeding from a young parent. Our findings support the hypothesis that offspring of old parents receive more resources and convert them into increasingly faster life histories. These results contradict the theory that old parents transfer a cumulative detrimental 'ageing factor' to their offspring.

Should females prefer old males?

Whether females should prefer to mate with old males is controversial. Old males may sire offspring of low quality because of an aging germline, but their proven ability to reach an old age can also be an excellent indicator of superior genetic quality, especially in natural populations. These genetic effects are, however, hard to study in nature, because they are often confounded with direct benefits offered by old males to the female, such as experience and high territory quality. We, therefore, used naturally occurring extra‐pair young to disentangle different aspects of male age on female fitness in a natural population of collared flycatchers because any difference between within‐ and extra‐pair young within a nest should be caused by paternal genetic effects only. Based on 18 years of long‐term data, we found that females paired with older males as social partners experienced an overall reproductive advantage. However, offspring sired by old males were of lower quality as compared to their extra‐pair half‐siblings, whereas the opposite was found in nests attended by young males. These results imply a negative genetic effect of old paternal age, given that extra‐pair males are competitive middle‐age males. Thus, offspring may benefit from being sired by young males but raised by old males, to maximize both genetic and direct effects. Our results show that direct and genetic benefits from pairing with old males may act in opposing directions and that the quality of the germline may deteriorate before other signs of senescence become obvious.

The effects of parental age difference on the offspring sex and fitness of European blackbirds

Background

Many studies of birds have indicated that offspring sex ratios can vary with environmental and parental traits. On the basis of long-term research, we first evaluated the possible influence of parental age difference and brood characteristics on offspring sex and fitness in multi-brooded Blackbirds Turdus merula.

Methodology

The study was conducted in the city-centre Stefan Żeromski Park in Szczecin, NW Poland, where the local population of Blackbirds has been studied since 1996. Data on the offspring sex and fitness were collected in five years, 2005-2007 and 2016-2017. During the breeding season we inspected the study area to locate the pairs' territories and to track their nests and clutches.

Results

We found that the overall sex ratio did not differ statistically from 50:50, but that younger females bonded with older mates did tend to produce more sons, probably because of the greater fitness of male descendants. Accordingly, the sons' breeding success increased with the father's age, but this relationship was close to non-linear, which may indicate that the transgenerational effect of paternal senescence could negatively affect progeny fitness despite the high-quality of older fathers. Older females mated with younger males produced more daughters, which could have been due to the lesser attractiveness of the males and the mothers' poorer condition caused by accelerated senescence. We found that neither offspring hatching sequence nor hatching date or clutch sequence were significant for sex determination.

Conclusions

We consider that in our Blackbird population, parental age could make a more significant contribution to shaping offspring sex and reproductive success.

Heterogenous effects of father and mother age on offspring development

Maternal age has long been described to influence a broad range of offspring life-history traits, including longevity. However, relatively few studies have tested experimentally for the effects of paternal age and even fewer the potential interactive effects of father and mother age on offspring life-history traits from conception to death. To tackle these questions, I performed a factorial experimental design where I manipulated the age of both male and female field crickets (Gryllus bimaculatus) and subsequently assessed their effects over the offspring’s entire lifetime. I found that, despite coming from larger eggs, the embryos of old females grew up at a slower rate, took more time to develop, and showed lower hatching success than those of young females. Offspring postnatal viability was unaffected by female age but, at adulthood, the offspring of old females were bigger and lived shorter than those of young females. Male age effects were mostly present during offspring postnatal development as nymphs sired by old males having increased early mortality. Moreover, father age strongly influenced the development of offspring adult personality as revealed by the shyer personality of crickets sired by an old male. My results indicate that father and mother age at reproduction have different effects that affect offspring traits at different stages of their development. The results further suggest that father and mother age effects could be mediated by independent mechanisms and may separately influence the evolution of aging.

Paternal age negatively affects sperm production of the progeny

Parental age has profound consequences for offspring's phenotype. However, whether patrilineal age affects offspring sperm production remains unknown, despite the importance of sperm production for male reproductive success in species facing post-copulatory sexual selection. Using a longitudinal dataset on ejaculate attributes of the houbara bustard, we showed that offspring sired by old fathers had different age-dependent trajectories of sperm production compared to offspring sired by young fathers. Specifically, they produced less sperm (-48%) in their first year of life, and 14% less during their lifetime. Paternal age had the strongest effect, with weak evidence for grandpaternal or great grandpaternal age effects. These results show that paternal age can affect offspring reproductive success by reducing sperm production, establishing an intergenerational link between ageing and sexual selection.

Pathogen Dynamics across the Diversity of Aging

AbstractReproduction, mortality, and immune function often change with age but do not invariably deteriorate. Across the tree of life, there is extensive variation in age-specific performance and changes to key life-history traits. These changes occur on a spectrum from classic senescence, where performance declines with age, to juvenescence, where performance improves with age. Reproduction, mortality, and immune function are also important factors influencing the spread of infectious disease, yet there exists no comprehensive investigation into how the aging spectrum of these traits impacts epidemics. We used a model laboratory infection system to compile an aging profile of a single organism, including traits directly linked to pathogen susceptibility and those that should indirectly alter pathogen transmission by influencing demography. We then developed generalizable epidemiological models demonstrating that different patterns of aging produce dramatically different transmission landscapes: in many cases, aging can reduce the probability of epidemics, but it can also promote severity. This work provides context and tools for use across taxa by empiricists, demographers, and epidemiologists, advancing our ability to accurately predict factors contributing to epidemics or the potential repercussions of senescence manipulation.

Sex-specific plasticity across generations I: Maternal and paternal effects on sons and daughters

Intergenerational plasticity or parental effects-when parental environments alter the phenotype of future generations-can influence how organisms cope with environmental change. An intriguing, underexplored possibility is that sex-of both the parent and the offspring-plays an important role in driving the evolution of intergenerational plasticity in both adaptive and non-adaptive ways. Here, we evaluate the potential for sex-specific parental effects in a freshwater population of three-spined sticklebacks Gasterosteus aculeatus by independently and jointly manipulating maternal and paternal experiences and separately evaluating their phenotypic effects in sons versus daughters. We tested the adaptive hypothesis that daughters are more responsive to cues from their mother, whereas sons are more responsive to cues from their father. We exposed mothers, fathers or both parents to visual cues of predation risk and measured offspring antipredator traits and brain gene expression. Predator-exposed fathers produced sons that were more risk-prone, whereas predator-exposed mothers produced more anxious sons and daughters. Furthermore, maternal and paternal effects on offspring survival were non-additive: offspring with a predator-exposed father, but not two predator-exposed parents, had lower survival against live predators. There were also strong sex-specific effects on brain gene expression: exposing mothers versus fathers to predation risk activated different transcriptional profiles in their offspring, and sons and daughters strongly differed in the ways in which their brain gene expression profiles were influenced by parental experience. We found little evidence to support the hypothesis that offspring prioritize their same-sex parent's experience. Parental effects varied with both the sex of the parent and the offspring in complicated and non-additive ways. Failing to account for these sex-specific patterns (e.g. by pooling sons and daughters) would have underestimated the magnitude of parental effects. Altogether, these results draw attention to the potential for sex to influence patterns of intergenerational plasticity and raise new questions about the interface between intergenerational plasticity and sex-specific selective pressures, sexual conflict and sexual selection.

Mapping the past, present and future research landscape of paternal effects

BACKGROUND

Although in all sexually reproducing organisms an individual has a mother and a father, non-genetic inheritance has been predominantly studied in mothers. Paternal effects have been far less frequently studied, until recently. In the last 5 years, research on environmentally induced paternal effects has grown rapidly in the number of publications and diversity of topics. Here, we provide an overview of this field using synthesis of evidence (systematic map) and influence (bibliometric analyses).

RESULTS

We find that motivations for studies into paternal effects are diverse. For example, from the ecological and evolutionary perspective, paternal effects are of interest as facilitators of response to environmental change and mediators of extended heredity. Medical researchers track how paternal pre-fertilization exposures to factors, such as diet or trauma, influence offspring health. Toxicologists look at the effects of toxins. We compare how these three research guilds design experiments in relation to objects of their studies: fathers, mothers and offspring. We highlight examples of research gaps, which, in turn, lead to future avenues of research.

CONCLUSIONS

The literature on paternal effects is large and disparate. Our study helps in fostering connections between areas of knowledge that develop in parallel, but which could benefit from the lateral transfer of concepts and methods.

Do the ages of parents or helpers affect offspring fitness in a cooperatively breeding bird?

Age-related changes in parental phenotypes or genotypes can impact offspring fitness, but separating germline from nongermline transgenerational effects of ageing is difficult for wild populations. Further, in cooperatively breeding species, in addition to parental ages, the age of 'helpers' attending offspring may also affect juvenile performance. Using a 30-year study of a cooperative breeder with very high rates of extra-pair paternity, the superb fairy-wren (Malurus cyaneus), we investigated the effects of maternal, paternal and helper ages on three measures of offspring performance: nestling weight, juvenile survival to independence and recruitment to the breeding population. Mothers with a longer lifespan had offspring with higher juvenile survival, indicating selective disappearance, but the effect of maternal age on juvenile survival was of similar magnitude but negative. For extra-pair offspring, there was no evidence of any effect of the ages of either the genetic sire or the cuckolded 'social' father. However, for within-pair offspring, there was a positive effect of paternal age on juvenile survival, which we suggest may be driven by sexual selection. There were positive associations between the average age of helpers attending a nest and two of the three aspects of offspring performance; these effects were stronger than any of the effects of parental age. In general, the multiple associations between offspring fitness and the ages of adults around them appeared to be driven more by age-related changes in environmental effects than by age-related changes in the germline.

Reproductive senescence and parental effects in an indeterminate grower

Reproductive senescence is the decrease of reproductive performance with increasing age and can potentially include trans-generational effects as the offspring produced by old parents might have a lower fitness than those produced by young parents. This negative effect may be caused either by the age of the father, mother or the interaction between the ages of both parents. Using the common woodlouse Armadillidium vulgare, an indeterminate grower, as a biological model, we tested for the existence of a deleterious effect of parental age on fitness components. Contrary to previous findings reported from vertebrate studies, old parents produced both a higher number and larger offspring than young parents. However, their offspring had lower fitness components (by surviving less, producing a smaller number of clutches or not reproducing at all) than offspring born to young parents. Our findings strongly support the existence of trans-generational senescence in woodlice and contradict the belief that old individuals in indeterminate growers contribute the most to recruitment and correspond thereby to the key life stage for population dynamics. Our work also provides rare evidence that the trans-generational effect of senescence can be stronger than direct reproductive senescence in indeterminate growers.

Intergenerational Transfer of Ageing: Parental Age and Offspring Lifespan

The extent to which the age of parents at reproduction can affect offspring lifespan and other fitness-related traits is important in our understanding of the selective forces shaping life history evolution. In this article, the widely reported negative effects of parental age on offspring lifespan (the 'Lansing effect') is examined. Outlined herein are the potential routes whereby a Lansing effect can occur, whether effects might accumulate across multiple generations, and how the Lansing effect should be viewed as part of a broader framework, considering how parental age affects offspring fitness. The robustness of the evidence for a Lansing effect produced so far, potential confounding variables, and how the underlying mechanisms might best be unravelled through carefully designed experimental studies are discussed.

Age of Both Parents Influences Reproduction and Egg Dumping Behavior in Drosophila melanogaster

Trans-generational maternal effects have been shown to influence a broad range of offspring phenotypes. However, very little is known about paternal trans-generational effects. Here, we tested the trans-generational effects of maternal and paternal age, and their interaction, on daughter and son reproductive fitness in Drosophila melanogaster. We found significant effects of parent ages on offspring reproductive fitness during a 10 day postfertilization period. In daughters, older (45 days old) mothers conferred lower reproductive fitness compared with younger mothers (3 days old). In sons, father’s age significantly affected reproductive fitness. The effects of 2 old parents were additive in both sexes and reproductive fitness was lowest when the focal individual had 2 old parents. Interestingly, daughter fertility was sensitive to father’s age but son fertility was insensitive to mother’s age, suggesting a sexual asymmetry in trans-generational effects. We found the egg-laying dynamics in daughters dramatically shaped this relationship. Daughters with 2 old parents demonstrated an extreme egg dumping behavior on day 1 and laid >2.35× the number of eggs than the other 3 age class treatments. Our study reveals significant trans-generational maternal and paternal age effects on fertility and an association with a novel egg laying behavioral phenotype in Drosophila.

Transgenerational maternal age effects in nature: Lessons learnt from Asian elephants

IN FOCUS

Reichert, S., Berger, V., Jackson, J., Chapman, S. N., Htut, W., Mar, K. U., & Lummaa, V. (2019). Maternal age at birth shapes offspring life-history trajectory across generations in long-lived Asian elephants. Journal of Animal Ecology, 89, 996-1007. Parental age can have strong effects on offspring life history, but the prevalence and magnitude of such effects in natural populations remain poorly understood. Using a multigenerational dataset of semi-captive Asian elephants, Reichert et al. (2019) studied the effects of maternal and grandmaternal age on offspring performance and found that offspring from old mothers have lower survival, but higher body condition and reproductive success than offspring from younger mothers. Importantly the observed consequences on survival are long-lasting and span more than one generation, with grand-offspring of old grandmothers also showing reduced survival. These findings suggest that persistent transgenerational effects of maternal age on fitness can shape the individual variation in ageing patterns in nature and ultimately the evolution of life histories.

Maternal age at birth shapes offspring life-history trajectory across generations in long-lived Asian elephants

Advanced maternal age at birth can have pronounced consequences for offspring health, survival and reproduction. If carried over to the next generation, such fitness effects could have important implications for population dynamics and the evolution of ageing, but these remain poorly understood. While many laboratory studies have investigated maternal age effects, relatively few studies have been conducted in natural populations, and they usually only present a "snapshot" of an offspring's lifetime. In the present study, we focus on how maternal age influences offspring life-history trajectories and performance in a long-lived mammal. We use a multigenerational demographic dataset of semi-captive Asian elephants to investigate maternal age effects on several offspring life-history traits: condition, reproductive success and overall survival. We show that offspring born to older mothers display reduced overall survival but higher reproductive success, and reduced survival of their own progeny. Our results show evidence of a persistent effect of maternal age on fitness across generations in a long-lived mammal. By highlighting transgenerational effects on the fitness of the next generation associated with maternal age, the present study helps increase our understanding of factors contributing to individual variation in ageing rates and fitness.

Occurrence of human astrovirus associated with gastroenteritis among Congolese children in Brazzaville, Republic of Congo

INTRODUCTION

Acute viral gastroenteritis is a major public health concern, especially among children younger than 5 years of age. The aim of this study was to determine the occurrence of human astrovirus infection in children with acute gastroenteritis.

METHODS

Stool specimens were collected from 506 children under 5 years of age hospitalized with acute diarrhoea (289 male and 208 female), and human astrovirus was investigated by RT-PCR. Associations of socio-demographic, clinical, and behavioural conditions with infection were analysed.

RESULTS

The overall prevalence of human astrovirus was found to be 10.3%. The mean age of positive cases was 12.41 ± 6.21 months and this was associated with infection (p = 0.013). Children >18 months of age were at three times the risk of infection when compared to those aged 0-6 months (odds ratio (OR) 3.19, 95% confidence interval (CI) 1.15-8.88; p = 0.026). Children living in houses with more than one room (OR 0.60, 95% CI 0.28-0.96; p = 0.036) and mothers using treated water (OR 0.47, 95% CI 0.25-0.86; p = 0.015) were associated with reduced infection.

CONCLUSIONS

In this study, infection with astrovirus was common in acute gastroenteritis cases among children younger than 5 years of age. Drinking treated water and living in non-crowded environments protected the children from infection.

An experimental test of the role of male mating history on paternal effects in the livebearer fish Gambusia holbrooki

Studies often show that paternal age affects offspring fitness. However, such effects could be due either to age, or to a male's previous mating effort (which is necessarily confounded with age). We experimentally tested whether differences in the mating history of old males affect offspring performance in the mosquitofish Gambusia holbrooki. Upon maturation, males were housed for a duration of the natural field-breeding season (23 weeks) either with mating access to females (lifetime-mating), or with visual but no physical access to females (no-mating). We then paired these males with a female to test whether male mating history had a significant effect on their mate's breeding success or offspring performance. The daughters, but not the sons, of 'no-mating' treatment males matured significantly sooner, and at a significantly smaller size, than those of 'lifetime-mating' treatment males. There was, however, no effect of male mating history on their daughters' initial fecundity, or on proxy measures of their sons' reproductive success. These results, when combined with earlier studies showing effects of male mating history on sperm quality, growth and immunity, suggest that variation in paternal effects currently attributed to male age could partly arise because older males have usually mated more often than younger males.

The deteriorating soma and the indispensable germline: gamete senescence and offspring fitness

The idea that there is an impenetrable barrier that separates the germline and soma has shaped much thinking in evolutionary biology and in many other disciplines. However, recent research has revealed that the so-called 'Weismann Barrier' is leaky, and that information is transferred from soma to germline. Moreover, the germline itself is now known to age, and to be influenced by an age-related deterioration of the soma that houses and protects it. This could reduce the likelihood of successful reproduction by old individuals, but also lead to long-term deleterious consequences for any offspring that they do produce (including a shortened lifespan). Here, we review the evidence from a diverse and multidisciplinary literature for senescence in the germline and its consequences; we also examine the underlying mechanisms responsible, emphasizing changes in mutation rate, telomere loss, and impaired mitochondrial function in gametes. We consider the effect on life-history evolution, particularly reproductive scheduling and mate choice. Throughout, we draw attention to unresolved issues, new questions to consider, and areas where more research is needed. We also highlight the need for a more comparative approach that would reveal the diversity of processes that organisms have evolved to slow or halt age-related germline deterioration.

Is it time to establish age restrictions in ART?

Providers specializing in reproductive medicine are treating increasing numbers of women pursuing parenthood in their 40s, 50s, and beyond. The rise in later-life parenting can be linked to factors ranging from the advent of assisted reproductive technologies and donor oocytes to the highly publicized pregnancies of older celebrities. We explore the medical and psychosocial implications of this trend for both older parents and their children. We also discuss ethical arguments regarding older parents' access to fertility care, existing professional guidelines, and both public and provider opinions about setting age limits for fertility treatment. Finally, we share preliminary considerations of whether age policies should be established, applied to men as well as women, and standardized or considered on a case-by-case basis.

Parental breeding age effects on descendants' longevity interact over 2 generations in matrilines and patrilines

Individuals within populations vary enormously in mortality risk and longevity, but the causes of this variation remain poorly understood. A potentially important and phylogenetically widespread source of such variation is maternal age at breeding, which typically has negative effects on offspring longevity. Here, we show that paternal age can affect offspring longevity as strongly as maternal age does and that breeding age effects can interact over 2 generations in both matrilines and patrilines. We manipulated maternal and paternal ages at breeding over 2 generations in the neriid fly Telostylinus angusticollis. To determine whether breeding age effects can be modulated by the environment, we also manipulated larval diet and male competitive environment in the first generation. We found separate and interactive effects of parental and grand-parental ages at breeding on descendants' mortality rate and life span in both matrilines and patrilines. These breeding age effects were not modulated by grand-parental larval diet quality or competitive environment. Our findings suggest that variation in maternal and paternal ages at breeding could contribute substantially to intrapopulation variation in mortality and longevity.

Intergenerational effects on offspring telomere length: interactions among maternal age, stress exposure and offspring sex

Offspring produced by older parents often have reduced longevity, termed the Lansing effect. Because adults usually have similar-aged mates, it is difficult to separate effects of maternal and paternal age, and environmental circumstances are also likely to influence offspring outcomes. The mechanisms underlying the Lansing effect are poorly understood. Variation in telomere length and loss, particularly in early life, is linked to longevity in many vertebrates, and therefore changes in offspring telomere dynamics could be very important in this context. We examined the effect of maternal age and environment on offspring telomere length in zebra finches. We kept mothers under either control (ad libitum food) or more challenging (unpredictable food) circumstances and experimentally minimized paternal age and mate choice effects. Irrespective of the maternal environment, there was a substantial negative effect of maternal age on offspring telomere length, evident in longitudinal and cross-sectional comparisons (average of 39% shorter). Furthermore, in young mothers, sons reared by challenged mothers had significantly shorter telomere lengths than sons reared by control mothers. This effect disappeared when the mothers were old, and was absent in daughters. These findings highlight the importance of telomere dynamics as inter-generational mediators of the evolutionary processes determining optimal age-specific reproductive effort and sex allocation.

Social behavior and aging: A fly model

The field of behavioral genetics has recently begun to explore the effect of age on social behaviors. Such studies are particularly important, as certain neuropsychiatric disorders with abnormal social interactions, like autism and schizophrenia, have been linked to older parents. Appropriate social interaction can also have a positive impact on longevity, and is associated with successful aging in humans. Currently, there are few genetic models for understanding the effect of aging on social behavior and its potential transgenerational inheritance. The fly is emerging as a powerful model for identifying the basic molecular mechanisms underlying neurological and neuropsychiatric disorders. In this review, we discuss these recent advancements, with a focus on how studies in Drosophila melanogaster have provided insight into the effect of aging on aspects of social behavior, including across generations.

A birth-death model of ageing: from individual-based dynamics to evolutive differential inclusions

Ageing's sensitivity to natural selection has long been discussed because of its apparent negative effect on an individual's fitness. Thanks to the recently described (Smurf) 2-phase model of ageing (Tricoire and Rera in PLoS ONE 10(11):e0141920, 2015) we propose a fresh angle for modeling the evolution of ageing. Indeed, by coupling a dramatic loss of fertility with a high-risk of impending death-amongst other multiple so-called hallmarks of ageing-the Smurf phenotype allowed us to consider ageing as a couple of sharp transitions. The birth-death model (later called bd-model) we describe here is a simple life-history trait model where each asexual and haploid individual is described by its fertility period [Formula: see text] and survival period [Formula: see text]. We show that, thanks to the Lansing effect, the effect through which the "progeny of old parents do not live as long as those of young parents", [Formula: see text] and [Formula: see text] converge during evolution to configurations [Formula: see text] in finite time. To do so, we built an individual-based stochastic model which describes the age and trait distribution dynamics of such a finite population. Then we rigorously derive the adaptive dynamics models, which describe the trait dynamics at the evolutionary time-scale. We extend the Trait Substitution Sequence with age structure to take into account the Lansing effect. Finally, we study the limiting behaviour of this jump process when mutations are small. We show that the limiting behaviour is described by a differential inclusion whose solutions [Formula: see text] reach the diagonal [Formula: see text] in finite time and then remain on it. This differential inclusion is a natural way to extend the canonical equation of adaptive dynamics in order to take into account the lack of regularity of the invasion fitness function on the diagonal [Formula: see text].

Mature sperm small-RNA profile in the sparrow: implications for transgenerational effects of age on fitness

Mammalian sperm RNA has recently received a lot of interest due to its involvement in epigenetic germline inheritance. Studies of epigenetic germline inheritance have shown that environmental exposures can induce effects in the offspring without altering the DNA sequence of germ cells. Most mechanistic studies were conducted in laboratory rodents and C.elegans while observational studies confirm the phenotypic phenomenon in wild populations of humans and other species including birds. Prominently, paternal age in house sparrows affects offspring fitness, yet the mechanism is unknown. This study provides a first reference of house sparrow sperm small RNA as an attempt to uncover their role in the transmission of the effects of paternal age on the offspring. In this small-scale pilot, we found no statistically significant differences between miRNA and tRNA fragments in aged and prime sparrow sperm. These results indicate a role of other epigenetic information carriers, such as distinct RNA classes, RNA modifications, DNA methylation and retained histones, and a clear necessity of future studies in wild populations.

Maternal age alters offspring lifespan, fitness, and lifespan extension under caloric restriction

Maternal age has a negative effect on offspring lifespan in a range of taxa and is hypothesized to influence the evolution of aging. However, the mechanisms of maternal age effects are unknown, and it remains unclear if maternal age alters offspring response to therapeutic interventions to aging. Here, we evaluate maternal age effects on offspring lifespan, reproduction, and the response to caloric restriction, and investigate maternal investment as a source of maternal age effects using the rotifer, Brachionus manjavacas, an aquatic invertebrate. We found that offspring lifespan and fecundity decline with increasing maternal age. Caloric restriction increases lifespan in all offspring, but the magnitude of lifespan extension is greater in the offspring from older mothers. The trade-off between reproduction and lifespan extension under low food conditions expected by life history theory is observed in young-mother offspring, but not in old-mother offspring. Age-related changes in maternal resource allocation to reproduction do not drive changes in offspring fitness or plasticity under caloric restriction in B. manjavacas. Our results suggest that the declines in reproduction in old-mother offspring negate the evolutionary fitness benefits of lifespan extension under caloric restriction.

Epigenetic inheritance of telomere length in wild birds

Telomere length (TL) predicts health and survival across taxa. Variation in TL between individuals is thought to be largely of genetic origin, but telomere inheritance is unusual, because zygotes already express a TL phenotype, the TL of the parental gametes. Offspring TL changes with paternal age in many species including humans, presumably through age-related TL changes in sperm, suggesting an epigenetic inheritance mechanism. However, present evidence is based on cross-sectional analyses, and age at reproduction is confounded with between-father variation in TL. Furthermore, the quantitative importance of epigenetic TL inheritance is unknown. Using longitudinal data of free-living jackdaws Corvus monedula, we show that erythrocyte TL of subsequent offspring decreases with parental age within individual fathers, but not mothers. By cross-fostering eggs, we confirmed the paternal age effect to be independent of paternal age dependent care. Epigenetic inheritance accounted for a minimum of 34% of the variance in offspring TL that was explained by paternal TL. This is a minimum estimate, because it ignores the epigenetic component in paternal TL variation and sperm TL heterogeneity within ejaculates. Our results indicate an important epigenetic component in the heritability of TL with potential consequences for offspring fitness prospects.

Epigenetic inheritance of telomere length in wild birds

Telomere length (TL) predicts health and survival across taxa. Variation in TL between individuals is thought to be largely of genetic origin, but telomere inheritance is unusual, because zygotes already express a TL phenotype, the TL of the parental gametes. Offspring TL changes with paternal age in many species including humans, presumably through age-related TL changes in sperm, suggesting an epigenetic inheritance mechanism. However, present evidence is based on cross-sectional analyses, and age at reproduction is confounded with between-father variation in TL. Furthermore, the quantitative importance of epigenetic TL inheritance is unknown. Using longitudinal data of free-living jackdaws Corvus monedula, we show that erythrocyte TL of subsequent offspring decreases with parental age within individual fathers, but not mothers. By cross-fostering eggs, we confirmed the paternal age effect to be independent of paternal age dependent care. Epigenetic inheritance accounted for a minimum of 34% of the variance in offspring TL that was explained by paternal TL. This is a minimum estimate, because it ignores the epigenetic component in paternal TL variation and sperm TL heterogeneity within ejaculates. Our results indicate an important epigenetic component in the heritability of TL with potential consequences for offspring fitness prospects.

Mutations of mitochondrial DNA are not major contributors to aging of fruit flies

Mutations of mtDNA accumulate in aging humans and other mammals to cause mitochondrial dysfunction in a subset of cells in various tissues. Furthermore, experimental induction of mtDNA mutations causes a premature aging syndrome in the mouse. To study if mitochondrial dysfunction is universally involved in shortening life span in metazoans, we generated a series of fruit fly lines with varying levels of mtDNA mutations. Unexpectedly, we report that fruit flies are remarkably tolerant to mtDNA mutations, as exemplified by their lack of effect on physiology and lifespan. Only an artificially induced, very drastic increase of the mtDNA mutation load will lead to reduced lifespan, showing that mtDNA mutations are unlikely to limit lifespan in natural fruit fly populations.

Mammals develop age-associated clonal expansion of somatic mtDNA mutations resulting in severe respiratory chain deficiency in a subset of cells in a variety of tissues. Both mathematical modeling based on descriptive data from humans and experimental data from mtDNA mutator mice suggest that the somatic mutations are formed early in life and then undergo mitotic segregation during adult life to reach very high levels in certain cells. To address whether mtDNA mutations have a universal effect on aging metazoans, we investigated their role in physiology and aging of fruit flies. To this end, we utilized genetically engineered flies expressing mutant versions of the catalytic subunit of mitochondrial DNA polymerase (DmPOLγA) as a means to introduce mtDNA mutations. We report here that lifespan and health in fruit flies are remarkably tolerant to mtDNA mutations. Our results show that the short lifespan and wide genetic bottleneck of fruit flies are limiting the extent of clonal expansion of mtDNA mutations both in individuals and between generations. However, an increase of mtDNA mutations to very high levels caused sensitivity to mechanical and starvation stress, intestinal stem cell dysfunction, and reduced lifespan under standard conditions. In addition, the effects of dietary restriction, widely considered beneficial for organismal health, were attenuated in flies with very high levels of mtDNA mutations.

Maternal reproductive senescence shapes the fitness consequences of the parental age difference in ruffed lemurs

In humans, pronounced age differences between parents have deleterious fitness consequences. In particular, the number of children is lower when mothers are much older than fathers. However, previous analyses failed to disentangle the influence of differential parental age per se from a direct age effect of each parent. In this study, we analyse the fitness consequences of both parental age and parental age differences on litter size and offspring survival in two closely related species of lemurs living in captivity. As captive lemurs do not choose their reproductive partner, we were able to measure litter size and offspring survival across breeding pairs showing a wide range of parental age differences. However, we demonstrated that the effect of the parental age difference on litter size was fully accounted for by female reproductive senescence because females mating with much younger males were old females. On the other hand, both parental age difference and female reproductive senescence influenced offspring survival. Our results emphasize the importance of teasing apart the effect of parental reproductive senescence when investigating the health and fitness consequences of parental age differences and also provide new insights for conservation programmes of endangered species.

Disentangling Pre- and Postnatal Maternal Age Effects on Offspring Performance in an Insect with Elaborate Maternal Care

Maternal effect senescence has attracted much recent scientific interest. However, the age-related effects of pre- and postnatal maternal age are often conflated, as these naturally originate from the same individual. Additionally, many maternal effect senescence studies fail to account for potential biases associated with selective disappearance. Here we use a cross-fostered laboratory population of a burying beetle, Nicrophorus vespilloides, to examine both the effects of female pre- and postnatal maternal age on offspring life-history traits and the postcare outcomes of mothers while accounting for selective disappearance of postnatal caregivers. Neither pre- nor postnatal maternal age affected offspring longevity or larval weight at hatching, and postnatal age had no effect on postcare maternal outcomes except to confirm the presence of actuarial senescence. There was weak evidence for concave relationships between two larval traits (dispersal weight and survival) and the age of egg producers. Selective disappearance of caregivers had no clear effect on any of the measured offspring traits. Contrary to predictions from evolutionary theory, maternal effect senescence and reproductive effort increases do not always manifest, and current theory may be insufficient to account for the true diversity of aging patterns relating to maternal care.