Intergenerational Transfer of Ageing: Parental Age and Offspring Lifespan

Maternal effect senescence and caloric restriction interact to affect fitness through changes in life history timing

Environmental factors and individual attributes, and their interactions, impact survival, growth and reproduction of an individual throughout its life. In the clonal rotifer Brachionus, low food conditions delay reproduction and extend lifespan. This species also exhibits maternal effect senescence; the offspring of older mothers have lower survival and reproductive output. In this paper, we explored the population consequences of the individual-level interaction of maternal age and low food availability. We built matrix population models for both ad libitum and low food treatments, in which individuals are classified both by their age and maternal age. Low food conditions reduced population growth rate (Δ λ = - 0.0574 ) and shifted the population structure to older maternal ages, but did not detectably impact individual lifetime reproductive output. We analysed hypothetical scenarios in which reduced fertility or survival led to approximately stationary populations that maintained the shape of the difference in demographic rates between the ad libitum and low food treatments. When fertility was reduced, the populations were more evenly distributed across ages and maternal ages, while the lower-survival models showed an increased concentration of individuals in the youngest ages and maternal ages. Using life table response experiment analyses, we compared populations grown under ad libitum and low food conditions in scenarios representing laboratory conditions, reduced fertility and reduced survival. In the laboratory scenario, the reduction in population growth rate under low food conditions is primarily due to decreased fertility in early life. In the lower-fertility scenario, contributions from differences in fertility and survival are more similar, and show trade-offs across both ages and maternal ages. In the lower-survival scenario, the contributions from decreased fertility in early life again dominate the difference inλ . These results demonstrate that processes that potentially benefit individuals (e.g. lifespan extension) may actually reduce fitness and population growth because of links with other demographic changes (e.g. delayed reproduction). Because the interactions of maternal age and low food availability depend on the population structure, the fitness consequences of an environmental change can only be fully understood through analysis that takes into account the entire life cycle.

Genetic variation in age-dependent attractiveness in a fish with a mixed mating system

Reproductive senescence is common across taxa and females often show a predictable decline in fecundity after maturity. Attending to these age-dependent cues could help males make optimal mate choice decisions. Here, we examined reproductive senescence and male mate choice in the androdioecious mangrove rivulus (Kryptolebias marmoratus), where self-fertilizing hermaphrodites exist with rare males. Hermaphrodites showed a strong decline in fecundity as they aged and genetic lineages varied in their fecundity at both young and old ages. Surprisingly, when given a simultaneous choice between genetically identical old and young hermaphrodites, males did not simply prefer younger hermaphrodites. Instead, male preference for younger versus older partners depended on the genetic lineage of the partners, resulting in a strong genotype × age interaction. For some genetic lineages, hermaphrodites were more attractive to males when younger, but for other genetic lineages, hermaphrodites were more attractive when older. Our results suggest that the genetic identity of the partner is key to how males weigh age-dependent changes in fecundity and that males are able to assess genetic variation in attractiveness over a partner's reproductive lifespan. Exploring how gamete viability and outcrossing are affected by age across genetic lineages could help us further understand these male preferences.

Older mothers produce smaller eggs without compromising offspring quality: a study of a thelytokous mite predator (Acari: Phytoseiidae)

Negative relationships between the parental age and offspring life history traits have been widely observed across diverse animal taxa. However, there is a lack of studies examining the influence of parental age on offspring performance using mites, particularly phytoseiid predators as subjects. This study explored the influence of maternal age on offspring life history traits in Amblyseius herbicolus (Chant) (Acari: Mesostigmata), a phytoseiid predatory mite reproducing through thelytokous parthenogenesis. We hypothesised that increased maternal age negatively impacts offspring traits, including developmental duration, body size, fecundity and lifespan. Amblyseius herbicolus was reared under controlled laboratory conditions, and the life history traits of offspring from mothers of varying ages were analysed using linear mixed-effect models. Our results showed that the increase in maternal age significantly reduced individual egg volume, but did not significantly affect offspring developmental duration, body size, fecundity or lifespan. These findings indicate that while older A. herbicolus females produced smaller eggs, the subsequent performance (i.e. body size, fecundity and lifespan) of offspring remained largely unaffected, suggesting possible compensatory mechanisms in the offspring or alternative maternal provisioning strategies. The results of this study offer useful insights into the reproductive strategies of phytoseiid predators and asexually reproducing species, enhancing our understanding of how maternal age affects offspring fitness. Further studies can examine how offspring of A. herbicolus from mothers of different ages perform under adverse environmental conditions.

A scenario for an evolutionary selection of ageing

Signs of ageing become apparent only late in life, after organismal development is finalized. Ageing, most notably, decreases an individual's fitness. As such, it is most commonly perceived as a non-adaptive force of evolution and considered a by-product of natural selection. Building upon the evolutionarily conserved age-related Smurf phenotype, we propose a simple mathematical life-history trait model in which an organism is characterized by two core abilities: reproduction and homeostasis. Through the simulation of this model, we observe (1) the convergence of fertility's end with the onset of senescence, (2) the relative success of ageing populations, as compared to non-ageing populations, and (3) the enhanced evolvability (i.e. the generation of genetic variability) of ageing populations. In addition, we formally demonstrate the mathematical convergence observed in (1). We thus theorize that mechanisms that link the timing of fertility and ageing have been selected and fixed over evolutionary history, which, in turn, explains why ageing populations are more evolvable and therefore more successful. Broadly speaking, our work suggests that ageing is an adaptive force of evolution.

Wolbachia affect female mate preference and offspring fitness in a parasitoid wasp

BACKGROUND

Wolbachia are widespread intracellular bacteria in insects that often have high rates of spread due to their impact on insect reproduction. These bacteria may also affect the mating behavior of their host with impacts on the fitness of host progeny. In this study, we investigated the impact of Wolbachia on a preference for mating with young or old males in the parasitoid wasp Habrobracon hebetor.

RESULTS

Our results showed that uninfected females from a tetracycline-treated line preferred to mate with young males, whereas Wolbachia-infected females had no preference. Time to mating was relatively shorter in the infected lines. Regardless of Wolbachia infection status, progeny resulting from matings with young males showed higher fitness than those from crosses with old males, and infected females crossed with infected young males showed the highest performance.

CONCLUSION

These results suggest an impact of Wolbachia on female mate preference and offspring fitness although it is unclear how this phenomenon increases Wolbachia transmission of infected wasps. © 2024 Society of Chemical Industry.

Reproductive aging weakens offspring survival and constrains the telomerase response to herpesvirus in Pacific oysters

Telomere length (TL) is increasingly recognized as a molecular marker that reflects how reproductive aging affects intergenerational transmissions. Here, we investigated the effects of parental age on offspring survival and the regulation of TL by examining the telomere-elongating activity of telomerase in the Pacific oyster. We assessed the classical hallmarks of aging in parents at three age classes (young, middle-aged, and old) and crossbred them using a split-brood design to examine the consequences of the nine maternal-by-paternal age combinations on their offspring. Reproductive aging leads to increased larval mortality and accelerated telomere shortening in spats, rendering them more susceptible to infection by the Ostreid herpesvirus. Viral exposure stimulates telomerase activity, a response that we identified as adaptive, but weakened by parental aging. While telomerase lengthens a spat's telomere, paradoxically, longer individual TL predicts higher mortality in adults. The telomerase-telomere complex appeared as a conservative biomarker for distinguishing survivors and losers upon exposure to polymicrobial diseases.

What does not kill you makes you stronger? Effects of paternal age at conception on fathers and sons

Advancing male age is often hypothesized to reduce both male fertility and offspring quality due to reproductive senescence. However, the effects of advancing male age on reproductive output and offspring quality are not always deleterious. For example, older fathers might buffer the effects of reproductive senescence by terminally investing in reproduction. Similarly, males that survive to reproduce at an old age might carry alleles that confer high viability (viability selection), which are then inherited by offspring, or might have high reproductive potential (selective disappearance). Differentiating these mechanisms requires an integrated experimental study of paternal survival and reproductive performance, as well as offspring quality, which is currently lacking. Using a cross-sectional study in Drosophila melanogaster, we test the effects of paternal age at conception (PAC) on paternal survival and reproductive success, and on the lifespans of sons. We discover that mating at an old age is linked with decreased future male survival, suggesting that mating-induced mortality is possibly due to old fathers being frail. We find no evidence for terminal investment and show that reproductive senescence in fathers does not onset until their late-adult life. Additionally, we find that as a father's lifespan increases, his probability of siring offspring increases for older PAC treatments only. Lastly, we show that sons born to older fathers live longer than those born to younger fathers due to viability selection. Collectively, our results suggest that advancing paternal age is not necessarily associated with deleterious effects for offspring and may even lead to older fathers producing longer-lived offspring.

Consolidating multiple evolutionary theories of ageing suggests a need for new approaches to study genetic contributions to ageing decline

Understanding mechanisms of ageing remains a complex challenge for biogerontologists, but recent adaptations of evolutionary ageing theories offer a compelling lens in which to view both age-related molecular and physiological deterioration. Ageing is commonly associated with progressive declines in biochemical and molecular processes resulting from damage accumulation, yet the role of continued developmental gene activation is less appreciated. Natural selection pressures are at their highest in youthful periods to modify gene expression towards maximising reproductive capacity. After sexual maturation, selective pressure diminishes, subjecting individuals to maladaptive pleiotropic gene functions that were once beneficial for developmental growth but become pathogenic later in life. Due to this selective 'shadowing' in ageing, mechanisms to counter such hyper/hypofunctional genes are unlikely to evolve. Interventions aimed at targeting gene hyper/hypofunction during ageing might, therefore, represent an attractive therapeutic strategy. The nematode Caenorhabditis elegans offers a strong model for post-reproductive mechanistic and therapeutic investigations, yet studies examining the mechanisms of, and countermeasures against, ageing decline largely intervene from larval stages onwards. Importantly, however, lifespan extending conditions frequently impair early-life fitness and fail to correspondingly increase healthspan. Here, we consolidate multiple evolutionary theories of ageing and discuss data supporting hyper/hypofunctional changes at a global molecular and functional level in C. elegans, and how classical lifespan-extension mutations alter these dynamics. The relevance of such mutant models for exploring mechanisms of ageing are discussed, highlighting that post-reproductive gene optimisation represents a more translatable approach for C. elegans research that is not constrained by evolutionary trade-offs. Where some genetic mutations in C. elegans that promote late-life health map accordingly with healthy ageing in humans, other widely used genetic mutations that extend worm lifespan are associated with life-limiting pathologies in people. Lifespan has also become the gold standard for quantifying 'ageing', but we argue that gerospan compression (i.e., 'healthier' ageing) is an appropriate goal for anti-ageing research, the mechanisms of which appear distinct from those regulating lifespan alone. There is, therefore, an evident need to re-evaluate experimental approaches to study the role of hyper/hypofunctional genes in ageing in C. elegans.

Effects of maternal age and environmental enrichment on learning ability and brain size

It is well known that maternal age at reproduction affects offspring lifespan and some other fitness-related traits, but it remains understudied whether maternal senescence affects how offspring respond to their environments. Early environment often plays a significant role in the development of an animal's behavioral phenotype. For example, complex environments can promote changes in cognitive ability and brain morphology in young animals. Here, we study whether and how maternal effect senescence influences offspring plasticity in cognition, group behavior, and brain morphology in response to environmental complexity. For this, juvenile 3-spined sticklebacks from young and old mothers (i.e. 1-yr and 2-yr-old) were exposed to different levels of environmental enrichment and complexity (i.e. none, simple, and complex), and their behavior, cognitive ability, and brain size were measured. Exposing fish to enriched conditions improved individual learning ability assessed by a repeated detour-reaching task, increased the size of the whole brain, and decreased aggressive interactions in the shoal. Maternal age did not influence the inhibitory control, learning ability, and group behavioral responses of offspring to the experimental environmental change. However, maternal age affected how some brain regions of offspring changed in response to environmental complexity. In offspring from old mothers, those exposed to the complex environment had larger telencephalons and cerebellums than those who experienced simpler environments. Our results suggest that maternal effect senescence may influence how offspring invest in brain functions related to cognition in response to environmental complexity.

The effect of parental age on the quantity and quality of offspring in Syngnathus typhle, a species with male pregnancy

Parental age impacts offspring quantity and quality. Most prior research focused on maternal age. Since in most organisms the mother produces the costly eggs plus provides all or most parental care, it is difficult to distinguish maternal effects mediated via the egg from later maternal care. Here, we addressed the effects of parental age on offspring in Syngnathus typhle, a pipefish with male pregnancy. The divide between one parent producing the eggs and the second parent being the exclusive provider of parental care facilitates a distinction between the effects of parental age on egg quality versus parental age on early development. We fully reciprocally crossed young and old mothers and young and old fathers and assessed impact of parental age combination on offspring number, offspring size, and offspring gene expression patterns. Neither parental combination significantly influenced offspring size or male gestation duration; however, they influenced the number of offspring. Paternal, but not maternal, age strongly affected the offspring gene expression. Offspring from old fathers exhibited substantial changes in the expression of genes related to cell cycle regulation, protein synthesis, DNA repair, and neurogenesis. Our findings thus highlight the importance of gestation, as opposed to gamete production, in shaping the parental contribution to offspring development.

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.

Linking telomere dynamics to evolution, life history and environmental change: perspectives, predictions and problems

This perspectives paper considers the value of studying telomere biology outside of a biomedical context. I provide illustrative examples of the kinds of questions that evolutionary ecologists have addressed in studies of telomere dynamics in non-model species, primarily metazoan animals, and what this can contribute to our understanding of their evolution, life histories and health. I also discuss why the predicted relationships between telomere dynamics and life history traits, based on the detailed cellular studies in humans and model organisms, are not always found in studies in other species.

Born with an advantage: early life and maternal effects on fitness in female ground squirrels

Lifetime fitness and its determinants are an important topic in the study of behavioral ecology and life-history evolution. Early life conditions comprise some of these determinants, warranting further investigation into their impact. In some mammals, babies born lighter tend to have lower life expectancy than those born heavier, and some of these life-history traits are passed on to offspring, with lighter-born females giving birth to lighter offspring. We investigated how weight at weaning, the relative timing of birth in the season, maternal weight, and maternal age affected the longevity and lifetime reproductive success (LRS) of female Columbian ground squirrels (Urocitellus columbianus). We hypothesized that early life conditions such as offspring weight would not only have lifetime fitness consequences but also intergenerational effects. We found that weight at weaning had a significant impact on longevity, with heavier individuals living longer. The relative timing of an individual's birth did not have a significant association with either longevity or LRS. Individuals born to heavier mothers were found to have significantly higher LRS than those born to lighter mothers. Finally, maternal age was found to be significantly associated with their offspring's LRS, with older mothers having less successful offspring. Our results provide evidence that early life conditions do have lifelong fitness and sometimes intergenerational consequences for Columbian ground squirrels.

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.

Maternal aging increases offspring adult body size via transmission of donut-shaped mitochondria

Maternal age at childbearing has continued to increase in recent decades. However, whether and how it influences offspring adult traits are largely unknown. Here, using adult body size as the primary readout, we reveal that maternal rather than paternal age has an evolutionarily conserved effect on offspring adult traits in humans, Drosophila, and Caenorhabditis elegans. Elucidating the mechanisms of such effects in humans and other long-lived animals remains challenging due to their long life course and difficulties in conducting in vivo studies. We thus employ the short-lived and genetically tractable nematode C. elegans to explore the mechanisms underlying the regulation of offspring adult trait by maternal aging. By microscopic analysis, we find that old worms transmit aged mitochondria with a donut-like shape to offspring. These mitochondria are rejuvenated in the offspring's early life, with their morphology fully restored before adulthood in an AMPK-dependent manner. Mechanistically, we demonstrate that early-life mitochondrial dysfunction activates AMPK, which in turn not only alleviates mitochondrial abnormalities but also activates TGFβ signaling to increase offspring adult size. Together, our findings provide mechanistic insight into the ancient role of maternal aging in shaping the traits of adult offspring.

Virulence and transgenerational effects of Metarhizium anisopliae on Oxycarenus hyalinipennis

BACKGROUND

Insect pests cause major yield losses to Gossypium hirsutum, often requiring the use of chemical insecticides. To avoid human health, environmental and resistance problems, entomopathogenic fungi (EPF) can be used to control insect pests. In our study, the pathogenicity of Metarhizium anisopliae to Oxycarenus hyalinipennis was determined by the immersion method. Furthermore, the sublethal and lethal effects of M. anisopliae on the biological parameters of O. hyalinipennis were investigated by age-stage, two-sex life table software.

RESULTS

M. anisopliae infection was lethal to the fourth instar of O. hyalinipennis with LC50 values of 8.84 × 104 spores mL-1 . The sublethal and lethal concentrations of M. anisopliae not only affected the parental generation (F0 ) but also the demographic parameters of the offspring of the filial generation (F1 ). Transgenerational results of F1 infected with M. anisopliae showed decreased net reproductive rate (R0 ), intrinsic rate of increase (r) and mean generation time (T) compared to those of the control group. The larval developmental duration significantly decreased to 15.52 and 19.02 days in the LC50 and LC20 groups, respectively, compared to 21.08 days in the control group. There was a noteworthy decline in mean fecundity in the LC50 and LC20 groups, i.e., 16.0 and 20.96 eggs, compared to 33.26 eggs in the control group. Adult longevity was likewise considerably reduced in the LC50 and LC20 treated groups.

CONCLUSION

The study showed that M. anisopliae can have an enduring impact on the biological parameters of O. hyalinipennis, which may enhance its use in eco-friendly management programs. © 2023 Society of Chemical Industry.

Life history and deleterious mutation rate coevolution

The cost of germline maintenance gives rise to a trade-off between lowering the deleterious mutation rate and investing in life history functions. Therefore, life history and the mutation rate coevolve, but this coevolution is not well understood. We develop a mathematical model to analyse the evolution of resource allocation traits, which simultaneously affect life history and the deleterious mutation rate. First, we show that the invasion fitness of such resource allocation traits can be approximated by the basic reproductive number of the least-loaded class; the expected lifetime production of offspring without deleterious mutations born to individuals without deleterious mutations. Second, we apply the model to investigate (i) the coevolution of reproductive effort and germline maintenance and (ii) the coevolution of age-at-maturity and germline maintenance. This analysis provides two resource allocation predictions when exposure to environmental mutagens is higher. First, selection favours higher allocation to germline maintenance, even if it comes at the expense of life history functions, and leads to a shift in allocation towards reproduction rather than survival. Second, life histories tend to be faster, characterised by individuals with shorter lifespans and smaller body sizes at maturity. Our results suggest that mutation accumulation via the cost of germline maintenance can be a major force shaping life-history traits.

Maternal effect senescence via reduced DNA repair ability in the three-spined stickleback

Maternal effect senescence, a decline in offspring viability with maternal age, has been documented across diverse animals, but its mechanisms remain largely unknown. Here, we test maternal effect senescence and explore its possible molecular mechanisms in a fish. We compared the levels of maternal mRNA transcripts of DNA repair genes and mtDNA copies in eggs and the levels of DNA damage in somatic and germline tissues between young and old female sticklebacks. We also tested, in an in vitro fertilization experiment, whether maternal age and sperm DNA damage level interactively influence the expression of DNA repair genes in early embryos. Old females transferred less mRNA transcripts of DNA repair genes into their eggs than did young females, but maternal age did not influence egg mtDNA density. Despite a higher level of oxidative DNA damage in the skeletal muscle, old females had a similar level of damage in the gonad to young females, suggesting the prioritization for germline maintenance during ageing. The embryos of both old and young mothers increased the expression of DNA repair genes in response to an increased level of oxidative DNA damage in sperm used for their fertilization. The offspring of old mothers showed higher rates of hatching, morphological deformity and post-hatching mortality and had smaller body size at maturity. These results suggest that maternal effect senescence may be mediated by reduced capacity of eggs to detect and repair DNA damages, especially prior to the embryonic genomic activation.

An evolutionary perspective of lifespan and epigenetic inheritance

In the last decade epigenetics has come to the fore as a discipline which is central to biogerontology. Age associated epigenetic changes are routinely linked with pathologies, including cardiovascular disease, cancer, and Alzheimer's disease; moreover, epigenetic clocks are capable of correlating biological age with chronological age in many species including humans. Recent intriguing empirical observations also suggest that inherited epigenetic effects could influence lifespan/longevity in a variety of organisms. If this is the case, an imperative exists to reconcile lifespan/longevity associated inherited epigenetic processes with the evolution of ageing. This review will critically evaluate inherited epigenetic effects from an evolutionary perspective. The overarching aim is to integrate the evidence which suggests epigenetic inheritance modulates lifespan/longevity with the main evolutionary theories of ageing.

Investigating the unaccounted ones: insights on age-dependent reproductive loss in a viviparous fly

Most empirical and theoretical studies on reproductive senescence focus on observable attributes of offspring produced, such as size or postnatal survival. While harder to study, an important outcome of reproduction for a breeding individual is whether a viable offspring is produced at all. While prenatal mortality can sometimes be directly observed, this can also be indicated through an increase in the interval between offspring production. Both direct reproductive loss and presumed losses have been found to increase in older females across several species. Here, we study such reproductive loss (or "abortion") in tsetse, a viviparous and relatively long-lived fly with high maternal allocation. We consider how age-dependent patterns of abortion depend on the developmental stage of offspring and find that, as per previous laboratory studies, older females have higher rates of abortion at the late-larval stage, while egg-stage abortions are high both for very young and older females. We track the reproductive output of individual females and find little evidence that experiencing an abortion is an adaptive strategy to improve future reproductive outcomes. After an abortion, females do not generally take less time to produce their next offspring, these offspring are not larger, and there is no sex bias towards females, the sex with presumed higher fitness returns (being slightly larger and longer-lived than males, and with high insemination rates). Abortion rates are higher for breeding females experiencing stress, measured as nutritional deprivation, which echoes previous work in tsetse and other viviparous species, i.e., humans and baboons. We discuss our results in the context of studies on reproductive loss across taxa and argue that this is an important yet often overlooked reproductive trait which can vary with maternal age and can also depend on environmental stressors.

Sex-specific paternal age effects on offspring quality in Drosophila melanogaster

Advanced paternal age has been repeatedly shown to modulate offspring quality via male- and/or female-driven processes, and there are theoretical reasons to expect that some of these effects can be sex-specific. For example, sex allocation theory predicts that, when mated with low-condition males, mothers should invest more in their daughters compared to their sons. This is because male fitness is generally more condition-dependent and more variable than female fitness, which makes it less risky to invest in female offspring. Here, we explore whether paternal age can affect the quality and quantity of offspring in a sex-specific way using Drosophila melanogaster as a model organism. In order to understand the contribution of male-driven processes on paternal age effects, we also measured the seminal vesicle size of young and older males and explored its relationship with reproductive success and offspring quality. Older males had lower competitive reproductive success, as expected, but there was no difference between the offspring sex ratio of young and older males. However, we found that paternal age caused an increase in offspring quality (i.e., offspring weight), and that this increase was more marked in daughters than sons. We discuss different male- and female-driven processes that may explain such sex-specific paternal age effects.

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 whether such maternal age effects vary among genotypes for a given species, however. We compared maternal age effects among four strains of rotifers in the Brachionus plicatilis species complex. For each strain, we measured lifespan, reproductive schedule, and lifetime reproductive output of offspring produced by young, middle-aged, and old mothers. We found unexpected 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 the other strains. Across strains, advanced maternal age had positive effects, negative effects, or no effect on lifetime reproductive output. For all but one strain, older mothers produced offspring that had higher maximum daily reproduction early in life. Maternal age effects appear to be genetically determined traits, not features of life history strategy or due to accumulation of age-related damage in the germline. Investigating intraspecific variability is critical for understanding the ubiquity of maternal age effects and their role in the evolution of life history and aging.

The effect of advanced paternal age on the lifespan of male offspring in an ancient Chinese genealogical data set

BACKGROUND

Advanced paternal age has been reported to be associated with a variety of short-term outcomes in offspring, but long-term effects are rarely examined. The present study evaluated the impact of advanced paternal age on offspring's longevity.

METHODS

We studied the effect of paternal reproductive age on the lifespan of male offspring using a Chinese genealogy data set that spans 226 years of the Qing Dynasty (1683-1909). Multivariable-adjusted Cox regression analyses of 1274 men with survival data were used to calculate hazard ratios (HRs) of advanced parental age at reproduction. We also evaluated whether the lifespan of brothers differed when they were born to the same parents at different ages.

RESULTS

In models adjusted for maternal age, advanced paternal age was negatively associated with the lifespan of male offspring. Individuals born to fathers aged >40 years had a 32 % higher HR of a lifespan shorter than those born to fathers aged 25-29 years (adjusted HR 1.320, 95 % CI: 1.066-1.634). The adjusted HR for offspring born to fathers aged 35-39 years was 1.232 (95 % CI: 1.013-1.500). Older brothers born to fathers aged 20-34 years had a significantly lower risk of a reduced lifespan compared with their younger brothers with fathers aged ≥35 years at reproduction (P < 0.01).

CONCLUSION

Advanced paternal age at reproduction is a negative factor for male offspring's life expectancy. With the sustained increase in paternal age over the past generation, further investigation is warranted into the impact on birth outcomes and public health.

Parental age at conception on mouse lemur's offspring longevity: Sex-specific maternal effects

Parental age at conception often influences offspring's longevity, a phenomenon referred as the "Lansing effect" described in large variety of organisms. But, the majority of the results refer to the survival of juveniles, mainly explained by an inadequate parental care by the elderly parents, mostly the mothers. Studies on the effect of parental age on offspring's longevity in adulthood remain few, except in humans for whom effects of parental age vary according to statistical models or socioeconomic environments. In a small primate in which the longevity reaches up to 13 years, we investigated the effects of parental age at conception on the longevity of offspring (N = 278) issued from parents with known longevity. None of the postnatal parameters (body mass at 30 and 60 days after birth, size and composition of the litter) influenced offspring's longevity. Mothers' age at conception negatively affected offspring's longevity in males but not in females. By contrast, fathers' age at conception did not influence offspring's longevity. Finally, the longevity of female offspring was significantly positively related to the longevity of both parents. Compared with current studies, the surprisingly minor effect of fathers 'age was related to the high seasonal reproduction and the particular telomere biology of mouse lemurs.

Inbreeding effects on telomeres in hatchling sand lizards (Lacerta agilis): An optimal family affair?

Telomeres are nucleotide-protein caps, predominantly at the ends of Metazoan linear chromosomes, showing complex dynamics with regard to their lengthening and shortening through life. Their complexity has entertained the idea that net telomere length and attrition could be valuable biomarkers of phenotypic and genetic quality of their bearer. Intuitively, those individuals could be more heterozygous and, hence, less inbred. However, some inbred taxa have longer, not shorter, telomeres. To understand the role of inbreeding in this complex scenario we need large samples across a range of genotypes with known maternity and paternity in telomere-screened organisms under natural conditions. We assessed the effects of parental and hatchling inbreeding on telomere length in >1300 offspring from >500 sires and dams in a population of sand lizards (Lacerta agilis). Maternal and paternal ID and their interactions predict hatchling telomere length at substantial effect sizes (R²  > .50). Deviation from mean maternal heterozygosity statistically predicts shorter offspring telomeres but this only when sibship is controlled for by paternal ID, and then is still limited (R²  = .06). Raw maternal heterozygosity scores, ignoring absolute deviation from the mean, explained 0.07% of the variance in hatchling telomere length. In conclusion, inbreeding is not a driver of telomere dynamics in the sand lizard (Lacerta agilis) study system.

Telomere heritability and parental age at conception effects in a wild avian population

Individual variation in telomere length is predictive of health and mortality risk across a range of species. However, the relative influence of environmental and genetic variation on individual telomere length in wild populations remains poorly understood. Heritability of telomere length has primarily been calculated using parent-offspring regression which can be confounded by shared environments. To control for confounding variables, quantitative genetic "animal models" can be used, but few studies have applied animal models in wild populations. Furthermore, parental age at conception may also influence offspring telomere length, but most studies have been cross-sectional. We investigated within- and between-parental age at conception effects and heritability of telomere length in the Seychelles warbler using measures from birds caught over 20 years and a multigenerational pedigree. We found a weak negative within-paternal age at conception effect (as fathers aged, their offspring had shorter telomeres) and a weak positive between-maternal age at conception effect (females that survived to older ages had offspring with longer telomeres). Animal models provided evidence that heritability and evolvability of telomere length were low in this population, and that variation in telomere length was not driven by early-life effects of hatch period or parental identities. Quantitative polymerase chain reaction plate had a large influence on telomere length variation and not accounting for it in the models would have underestimated heritability. Our study illustrates the need to include and account for technical variation in order to accurately estimate heritability, as well as other environmental effects, on telomere length in natural populations.

Sex-dependent effects of parental age on offspring fitness in a cooperatively breeding bird

Parental age can have considerable effects on offspring phenotypes and health. However, intergenerational effects may also have longer term effects on offspring fitness. Few studies have investigated parental age effects on offspring fitness in natural populations while also testing for sex- and environment-specific effects. Further, longitudinal parental age effects may be masked by population-level processes such as the selective disappearance of poor-quality individuals. Here, we used multigenerational data collected on individually marked Seychelles warblers (Acrocephalus sechellensis) to investigate the impact of maternal and paternal age on offspring life span and lifetime reproductive success. We found negative effects of maternal age on female offspring life span and lifetime reproductive success, which were driven by within-mother effects. There was no difference in annual reproductive output of females born to older versus younger mothers, suggesting that the differences in offspring lifetime reproductive success were driven by effects on offspring life span. In contrast, there was no association between paternal age and female offspring life span or either maternal or paternal age and male offspring life span. Lifetime reproductive success, but not annual reproductive success, of male offspring increased with maternal age, but this was driven by between-mother effects. No paternal age effects were found on female offspring lifetime reproductive success but there was a positive between-father effect on male offspring lifetime reproductive success. We did not find strong evidence for environment-dependent parental age effects. Our study provides evidence for parental age effects on the lifetime fitness of offspring and shows that such effects can be sex dependent. These results add to the growing literature indicating the importance of intergenerational effects on long-term offspring performance and highlight that these effects can be an important driver of variation in longevity and fitness in the wild.

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.

Inverse Lansing Effect: Maternal Age and Provisioning Affecting Daughters' Longevity and Male Offspring Production

AbstractMaternal age effects on offspring life history are known in a variety of organisms, with offspring of older mothers typically having lower life expectancy (the Lansing effect). However, there is no consensus on the generality and mechanisms of this pattern. We tested predictions of the Lansing effect in several Daphnia magna clones and observed clone-specific magnitude and direction of the maternal age effect on offspring longevity. We also report ambidirectional, genotype-specific effects of maternal age on the propensity of daughters to produce male offspring. Focusing on two clones with contrasting life histories, we demonstrate that maternal age effects can be explained by lipid provisioning of embryos by mothers of different ages. Individuals from a single-generation maternal age reversal treatment showed intermediate life span and intermediate lipid content at birth. In the clone characterized by the "inverse Lansing effect," neonates produced by older mothers showed higher mitochondrial membrane potential in neural tissues than their counterparts born to younger mothers. We conclude that an inverse Lansing effect is possible and hypothesize that it may be caused by age-specific maternal lipid provisioning creating a calorically restricted environment during embryonic development, which in turn reduces fecundity and increases life span in offspring.

Inferring the age of breeders from easily measurable variables

Age drives differences in fitness components typically due to lower performances of younger and senescent individuals, and changes in breeding age structure influence population dynamics and persistence. However, determining age and age structure is challenging in most species, where distinctive age features are lacking and available methods require substantial efforts or invasive procedures. Here we explore the potential to assess the age of breeders, or at least to identify young and senescent individuals, by measuring some breeding parameters partially driven by age (e.g. egg volume in birds). Taking advantage of a long-term population monitored seabird, we first assessed whether age influenced egg volume, and identified other factors driving this trait by using general linear models. Secondly, we developed and evaluated a machine learning algorithm to assess the age of breeders using measurable variables. We confirmed that both younger and older individuals performed worse (less and smaller eggs) than middle-aged individuals. Our ensemble training algorithm was only able to distinguish young individuals, but not senescent breeders. We propose to test the combined use of field monitoring, classic regression analysis and machine learning methods in other wild populations were measurable breeding parameters are partially driven by age, as a possible tool for assessing age structure in the wild.

The combination of DNA methylome and transcriptome revealed the intergenerational inheritance on the influence of advanced maternal age

BACKGROUND

The number of women delivering at advanced maternal age (AMA; > = 35) continuously increases in developed and high-income countries. Large cohort studies have associated AMA with increased risks of various pregnancy complications and adverse pregnancy outcomes, which raises great concerns about the adverse effect of AMA on the long-term health of offspring. Specific acquired characteristics of parents can be passed on to descendants through certain molecular mechanisms, yet the underlying connection between AMA-related alterations in parents and that in offspring remains largely uncharted.

METHODS

We profiled the DNA methylomes of paired parental peripheral bloods and cord bloods from 20 nuclear families, including 10 AMA and 10 Young, and additional transcriptomes of 10 paired maternal peripheral bloods and cord bloods.

RESULTS

We revealed that AMA induced aging-like changes in DNA methylome and gene expression in both parents and offspring. The expression changes in several genes, such as SLC28A3, were highly relevant to the disorder in DNA methylation. In addition, AMA-related differentially methylated regions (DMRs) identified in mother and offspring groups showed remarkable similarities in both genomic locations and biological functions, mainly involving neuron differentiation, metabolism, and histone modification pathways. AMA-related differentially expressed genes (DEGs) shared by mother and offspring groups were highly enriched in the processes of immune cell activation and mitotic nuclear division. We further uncovered developmental-dependent dynamics for the DNA methylation of intergenerationally correlated DMRs during pre-implantation embryonic development, as well as diverse gene expression patterns during gametogenesis and early embryonic development for those common AMA-related DEGs presenting intergenerational correlation, such as CD24. Moreover, some intergenerational DEGs, typified by HTRA3, also showed the same significant alterations in AMA MII oocyte or blastocyst.

CONCLUSIONS

Our results reveal potential intergenerational inheritance of both AMA-related DNA methylome and transcriptome and provide new insights to understand health problems in AMA offspring.

Parental ecological history can differentially modulate parental age effects on offspring physiological traits in Drosophila

Parents adjust their reproductive investment over their lifespan based on their condition, age, and social environment, creating the potential for inter-generational effects to differentially affect offspring physiology. To date, however, little is known about how social environments experienced by parents throughout development and adulthood influence the effect of parental age on the expression of life-history traits in the offspring. Here, I collected data on Drosophila melanogaster offspring traits (i.e., body weight, water content, and lipid reserves) from populations where either mothers, fathers both, or neither parents experienced different social environments during development (larval crowding) and adulthood. Parental treatment modulated parental age effects on offspring lipid reserves but did not influence parental age effects on offspring water content. Importantly, parents in social environments where all individuals were raised in uncrowded larval densities produced daughters and sons lighter than parental treatments which produced the heaviest offspring. The peak in offspring body weight was delayed relative to the peak in parental reproductive success, but more strongly so for daughters from parental treatments where some or all males in the parental social environments were raised in crowded larval densities (irrespective of their social context), suggesting a potential father-to-daughter effect. Overall, the findings of this study reveal that parental ecological history (here, developmental and adult social environments) can modulate the effects of parental age at reproduction on the expression of offspring traits.

Global warming leads to larger bats with a faster life history pace in the long-lived Bechstein's bat (Myotis bechsteinii)

Whether species can cope with environmental change depends considerably on their life history. Bats have long lifespans and low reproductive rates which make them vulnerable to environmental changes. Global warming causes Bechstein’s bats (Myotis bechsteinii) to produce larger females that face a higher mortality risk. Here, we test whether these larger females are able to offset their elevated mortality risk by adopting a faster life history. We analysed an individual-based 25-year dataset from 331 RFID-tagged wild bats and combine genetic pedigrees with data on survival, reproduction and body size. We find that size-dependent fecundity and age at first reproduction drive the observed increase in mortality. Because larger females have an earlier onset of reproduction and shorter generation times, lifetime reproductive success remains remarkably stable across individuals with different body sizes. Our study demonstrates a rapid shift to a faster pace of life in a mammal with a slow life history.

Warming summers across a 25-year study are linked to larger body sizes in female bats, leading to a switch from a slow-reproducing, long-lived species to a faster pace of life.

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.

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.

Cancer Susceptibility as a Cost of Reproduction and Contributor to Life History Evolution

Reproduction is one of the most energetically demanding life-history stages. As a result, breeding individuals often experience trade-offs, where energy is diverted away from maintenance (cell repair, immune function) toward reproduction. While it is increasingly acknowledged that oncogenic processes are omnipresent, evolving and opportunistic entities in the bodies of metazoans, the associations among reproductive activities, energy expenditure, and the dynamics of malignant cells have rarely been studied. Here, we review the diverse ways in which age-specific reproductive performance (e.g., reproductive aging patterns) and cancer risks throughout the life course may be linked via trade-offs or other mechanisms, as well as discuss situations where trade-offs may not exist. We argue that the interactions between host–oncogenic processes should play a significant role in life-history theory, and suggest some avenues for future research.

When Older Males Sire More Offspring—Increased Attractiveness or Higher Fertility?

Abstract

In birds with extrapair mating, older males usually have higher fertilization success than younger males. Two hypotheses can potentially explain this pattern: 1) females prefer older, and often more ornamented males, or 2) older males invest more in reproduction and fertility than younger males. Here we studied factors associated with age-related male fertilization success in a population of barn swallows Hirundo rustica in Canada. We document that male fertilization success increased gradually up to a minimum age of four-year old. The age effect was especially strong for the number of extrapair offspring obtained and the occurrence of a second brood. The higher fertilization success of older males was also associated with an early start of breeding in spring. The length of the elongated outermost tail feathers, a postulated male ornament preferred by females, also increased with age (in both sexes), but it was not a significant predictor of male fertilization success within age classes. Male fertility traits, especially testis size, but also sperm motility and sperm velocity, increased significantly across age groups. Our results suggest that the higher fertilization success by older males is due to their higher reproductive investments and that their longer tails are an adaptation to early arrival on the breeding grounds.

Significance statement

The barn swallow is a socially monogamous passerine with extensive extrapair mating. We found that males become more successful in siring both withinpair and extrapair offspring as they become older. Their increased fertilization success was associated with a higher reproductive effort as indicated by larger testes, more motile sperm, and an earlier start of breeding in spring. The length of the outer tail feathers increased with age in both sexes, but long tails did not enhance male fertilization success among males of the same age. Long tails are probably an adaptation to rapid migration and earlier arrival on the breeding grounds. Our findings suggest that the commonly observed age-related increase in male fertilization success in passerine birds is better explained by life history theory than by sexual selection theory.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00265-022-03170-0.

Incorporating effects of age on energy dynamics predicts nonlinear maternal allocation patterns in iteroparous animals

Iteroparous parents face a trade-off between allocating current resources to reproduction versus maximizing survival to produce further offspring. Parental allocation varies across age and follows a hump-shaped pattern across diverse taxa, including mammals, birds and invertebrates. This nonlinear allocation pattern lacks a general theoretical explanation, potentially because most studies focus on offspring number rather than quality and do not incorporate uncertainty or age-dependence in energy intake or costs. Here, we develop a life-history model of maternal allocation in iteroparous animals. We identify the optimal allocation strategy in response to stochasticity when energetic costs, feeding success, energy intake and environmentally driven mortality risk are age-dependent. As a case study, we use tsetse, a viviparous insect that produces one offspring per reproductive attempt and relies on an uncertain food supply of vertebrate blood. Diverse scenarios generate a hump-shaped allocation when energetic costs and energy intake increase with age and also when energy intake decreases and energetic costs increase or decrease. Feeding success and environmentally driven mortality risk have little influence on age-dependence in allocation. We conclude that ubiquitous evidence for age-dependence in these influential traits can explain the prevalence of nonlinear maternal allocation across diverse taxonomic groups.

Maternal age and maternal environment affect egg composition, yolk testosterone, offspring growth and behaviour in laying hens

Maternal effects have been reported to alter offspring phenotype in laying hens. In this study, we investigated the effects of maternal environment and maternal age on egg traits and offspring development and behaviour. For this, we ran two experiments. First (E1), commercial hybrid hens were reared either in aviary or barren brooding cages, then housed in aviary, conventional cages or furnished (enriched) cages, thus forming different maternal housing treatments. Hens from each treatment were inseminated at three ages, and measures of egg composition, yolk testosterone concentration and offspring’s development, anxiety and fearfulness were assessed. In experiment 2 (E2), maternal age effects on offspring's growth and behaviour were further investigated using fertile eggs from commercial breeder flocks at three different ages. Results from E1 showed that Old hens laid heavier eggs with less yolk testosterone and produced offspring with fewer indicators of anxiety and fearfulness. Maternal rearing and housing affected egg traits, offspring weight and behaviour, but not in a consistent way. Effects of maternal age were not replicated in E2, possibly due to differences in management or higher tolerance to maternal effects in commercial breeders. Overall, our research confirms that maternal age and maternal environment affects egg composition, with maternal age specifically affecting yolk testosterone concentration, which may mediate physical and behavioural effects in offspring.

Mitochondrial DNA content in eggs as a maternal effect

The transmission of detrimental mutations in animal mitochondrial DNA (mtDNA) to the next generation is avoided by a high level of mtDNA content in mature oocytes. Thus, this maternal genetic material has the potential to mediate adaptive maternal effects if mothers change mtDNA level in oocytes in response to their environment or body condition. Here, we show that increased mtDNA abundance in mature oocytes was associated with fast somatic growth during early development but at the cost of increased mortality in three-spined sticklebacks. We also examined whether oocyte mtDNA and sperm DNA damage levels have interacting effects because they can determine the integrity of mitochondrial and nuclear genes in offspring. The level of oxidative DNA damage in sperm negatively affected fertility, but there was no interacting effect of oocyte mtDNA abundance and sperm DNA damage. Oocyte mtDNA level increased towards the end of the breeding season, and the females exposed to warmer temperatures during winter produced eggs with increased mtDNA copies. Our results suggest that oocyte mtDNA level can vary according to the expected energy demands for offspring during embryogenesis and early growth. Thus, mothers can affect offspring development and viability through the context-dependent effects of oocyte mtDNA abundance.

An age-related decline in the expression of a red carotenoid-based ornament in wild birds

The past decades have provided valuable information on how animals age in the wild. However, examples of male reproductive senescence are scarce. In particular, few studies have described an age-related decline in the expression of conspicuous traits influencing mating success. Red ornaments could be good candidates to detect this decline because their expression may depend on the availability of pigments (carotenoids) related to oxidative stress, the latter frequently linked to senescence. Furthermore, it has been argued that efficient mitochondrial metabolism is key to express red carotenoid-based ornaments, and mitochondrial dysfunction is usually associated with senescence. We studied the age-linked expression of a red carotenoid-based trait: the yellow-to-red plumage coloration of male common crossbills (Loxia curvirostra). This coloration has recently been experimentally related to mitochondrial function. Here, we analyzed longitudinal plumage coloration data obtained throughout 28 years in free-living birds. We detected an initial increase in redness during the first 2 years of life and a subsequent decline. The relationship between color and age was unrelated to within-individual body mass variability. As far as we know, this is the first demonstration of an age-related ketocarotenoid-based color decrease detected by simultaneously testing within- and between-individual variability in wild animals.

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.

Effects of maternal age and stress on offspring quality in a viviparous fly

Many organisms show signs of deterioration with age in terms of survival and reproduction. We tested whether intraspecific variation in such senescence patterns can be driven by resource availability or reproductive history. We did this by manipulating nutritional stress and age at first reproduction and measuring age-dependent reproductive output in tsetse (Glossina morsitans morsitans), a viviparous fly with high maternal allocation. Across all treatments, offspring weight followed a bell-shaped curve with maternal age. Nutritionally stressed females had a higher probability of abortion and produced offspring with lower starvation tolerance. There was no evidence of an increased rate of reproductive senescence in nutritionally stressed females, or a reduced rate due to delayed mating, as measured by patterns of abortion, offspring weight or offspring starvation tolerance. Therefore, although we found evidence of reproductive senescence in tsetse, our results did not indicate that resource allocation trade-offs or costs of reproduction increase the rate of senescence.

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.