Birds with high lifetime reproductive success experience increased telomere loss

Telomere- and oxidative stress dynamics in Psittacidae species with different longevity trajectories

Telomeres, conserved DNA sequences at chromosome ends, naturally shorten with age, exacerbated by external factors like environmental challenges and reproduction. Birds, particularly psittacine, are gaining prominence as new aging models over the years because of their unique characteristics. This study explores erythrocyte telomere length (TL) and oxidative stress markers in plasma of long- and short-lived captive birds of the order Psittaciformes over four years. Long-lived birds consistently exhibited longer TL than short-lived ones (p = 0.012) but experienced a more pronounced TL shortening rate (p < 0.001) than short-lived ones. Breeding individuals experienced increased TL shortening compared to non-reproductive counterparts in long-lived birds (p = 0.008). Interestingly, long-lived birds showed a higher total antioxidant capacity than short-lived ones (p < 0.001), which was also increased during breeding (p = 0.026). A significant correlation was found between the telomere length shortening rate within the 4 years of study and the accumulated oxidative stress (r = 0.426, p = 0.069) in short-lived birds. These findings shed light on TL and oxidative stress dynamics over time, revealing distinct patterns influenced by life-traits among longevity groups.

Overcoming the pitfalls of categorizing continuous variables in ecology, evolution and behaviour

Many variables in biological research-from body size to life-history timing to environmental characteristics-are measured continuously (e.g. body mass in kilograms) but analysed as categories (e.g. large versus small), which can lower statistical power and change interpretation. We conducted a mini-review of 72 recent publications in six popular ecology, evolution and behaviour journals to quantify the prevalence of categorization. We then summarized commonly categorized metrics and simulated a dataset to demonstrate the drawbacks of categorization using common variables and realistic examples. We show that categorizing continuous variables is common (31% of publications reviewed). We also underscore that predictor variables can and should be collected and analysed continuously. Finally, we provide recommendations on how to keep variables continuous throughout the entire scientific process. Together, these pieces comprise an actionable guide to increasing statistical power and facilitating large synthesis studies by simply leaving continuous variables alone. Overcoming the pitfalls of categorizing continuous variables will allow ecologists, ethologists and evolutionary biologists to continue making trustworthy conclusions about natural processes, along with predictions about their responses to climate change and other environmental contexts.

Increased Reproductive Output and Telomere Shortening Following Calcium Supplementation in a Wild Songbird

Life history theory predicts increased parental investment comes with fitness costs, often expressed as negative effects on survival and future reproduction. To better understand the costs of reproduction and life history trade-offs, we evaluated calcium supplementation at a high-elevation site in Colorado as a novel approach to experimentally alter reproductive investment in nesting female Tachycineta bicolor (tree swallow). Calcium is a nutrient critical to avian reproduction as the intake of natural calcium is essential for egg production, embryo development, and nestling growth. Altering calcium availability exclusively during the breeding season allowed examination of individual biological responses to experimental modification of reproduction, as well as the reproductive costs associated with egg production and laying an entire clutch. As a functional endpoint and proxy for fitness and longevity, telomere length was measured at the beginning and end of each breeding season. Telomeres-protective "caps" at the ends of chromosomes-have been shown to shorten with aging and a variety of stressors, including higher reproductive output. Results demonstrate that tree swallow mothers supplemented with calcium during the breeding season experience higher reproductive output and produce offspring with longer telomeres, which came at the cost of relatively shorter telomeres during the reproductive season. These findings provide additional support for reproductive trade-offs, and also challenge previous calcium supplementation studies that suggest excess calcium reduces the cost of reproduction.

Effects of persistent organic pollutants on telomere dynamics are sex and age-specific in a wild long-lived bird

Chemical pollution is a major man-made environmental threat to ecosystems and natural animal populations. Of concern are persistent organic pollutants (POPs), which can persist in the environment for many years. While bioaccumulating throughout the lives of wild animals, POPs can affect their health, reproduction, and survival. However, measuring long-term effects of POPs in wild populations is challenging, and therefore appropriate biomarkers are required in wildlife ecotoxicology. One potential target is telomere length, since telomere preservation has been associated to survival and longevity, and stressors as chemical pollution can disrupt its maintenance. Here, we investigated the effects of different classes of POPs on relative telomere length (RTL) and its rate of change (TROC) in wild long-lived Alpine swifts (Tachymarptis melba). As both RTL and TROC are often reported to differ between sexes and with chronological age, we tested for sex- and age-specific (pre-senescent vs. senescent, ≥ 9 age of years, individuals) effects of POPs. Our results showed that senescent females presented longer RTL and elongated telomeres over time compared to pre-senescent females and males. These sex- and age-related differences in RTL and TROC were influenced by POPs, but differently depending on whether they were organochlorine pesticides (OCPs) or industrial polychlorinated biphenyls (PCBs). OCPs (particularly drins) were negatively associated with RTL, with the strongest negative effects being found in senescent females. Conversely, PCBs led to slower rates of telomere shortening, especially in females. Our study indicates diametrically opposed effects of OCPs on RTL and PCBs on TROC, and these effects were more pronounced in females and senescent individuals. The mechanisms behind these effects (e.g., increased oxidative stress by OCPs; upregulation of telomerase activity by PCBs) remain unknown. Our results highlight the importance in wildlife ecotoxicology to account for sex- and age-related effects when investigating the health effects of pollutants on biomarkers such as telomeres.

Genetic and telomeric variability: Insights from a tropical avian hybrid zone

Telomere lengths and telomere dynamics can correlate with lifespan, behaviour and individual quality. Such relationships have spurred interest in understanding variation in telomere lengths and their dynamics within and between populations. Many studies have identified how environmental processes can influence telomere dynamics, but the role of genetic variation is much less well characterized. To provide a novel perspective on how telomeric variation relates to genetic variability, we longitudinally sampled individuals across a narrow hybrid zone (n = 127 samples), wherein two Manacus species characterized by contrasting genome-wide heterozygosity interbreed. We measured individual (n = 66) and population (n = 3) differences in genome-wide heterozygosity and, among hybrids, amount of genetic admixture using RADseq-generated SNPs. We tested for population differences in telomere lengths and telomere dynamics. We then examined how telomere lengths and telomere dynamics covaried with genome-wide heterozygosity within populations. Hybrid individuals exhibited longer telomeres, on average, than individuals sampled in the adjacent parental populations. No population differences in telomere dynamics were observed. Within the parental population characterized by relatively low heterozygosity, higher genome-wide heterozygosity was associated with shorter telomeres and higher rates of telomere shortening-a pattern that was less apparent in the other populations. All of these relationships were independent of sex, despite the contrasting life histories of male and female manakins. Our study highlights how population comparisons can reveal interrelationships between genetic variation and telomeres, and how naturally occurring hybridization and genome-wide heterozygosity can relate to telomere lengths and telomere dynamics.

Adult telomere length is positively correlated with survival and lifetime reproductive success in a wild passerine

Explaining variation in individual fitness is a key goal in evolutionary biology. Recently, telomeres, repeating DNA sequences capping chromosome ends, have gained attention as a biomarker for body state, physiological costs, and senescence. Existing research has provided mixed evidence for whether telomere length correlates with fitness, including survival and reproductive output. Moreover, few studies have examined how the rate of change in telomere length correlates with fitness in wild populations. Here, we intensively monitored an insular population of house sparrows, and collected longitudinal telomere and life history data (16 years, 1225 individuals). We tested whether telomere length and its rate of change predict fitness measures, namely survival, lifespan and annual and lifetime reproductive effort and success. Telomere length positively predicted short-term survival, independent of age, but did not predict lifespan, suggesting either a diminishing telomere length-survival correlation with age or other extrinsic factors of mortality. The positive association of telomere length with survival translated into reproductive benefits, as birds with longer telomeres produced more genetic recruits, hatchlings and reared more fledglings over their lifetime. In contrast, there was no association between telomere dynamics and annual reproductive output, suggesting telomere dynamics might not reflect the costs of reproduction in this population, potentially masked by variation in individual quality. The rate of change of telomere length did not correlate with neither lifespan nor lifetime reproductive success. Our results provide further evidence that telomere length correlates with fitness, and contribute to our understanding of the selection on, and evolution of, telomere dynamics.

Pleiotropic effects of melanin pigmentation: haemoparasite infection intensity but not telomere length is associated with plumage morph in black sparrowhawks

There is increasing recognition of the potential pleiotropic effects of melanin pigmentation, particularly on immunity, with reports of variation in haemoparasite infection intensity and immune responses between the morphs of colour-polymorphic bird species. In a population of the black sparrowhawk (Accipiter melanoleucus) in western South Africa, light morphs have a higher haemoparasite infection intensity, but no physiological effects of this are apparent. Here, we investigate the possible effects of haemoparasite infection on telomere length in this species and explore whether relative telomere length is associated with either plumage morph or sex. Using quantitative polymerase chain reaction analysis, we confirmed that dark morphs had a lower haemoparasite infection intensity than light morphs. However, we found no differences in telomere length associated with either the haemoparasite infection status or morph in adults, although males have longer telomeres than females. While differences in haemoparasite intensity between morphs are consistent with pleiotropic effects of melanin pigmentation in the black sparrowhawk, we found no evidence that telomere length was associated with haemoparasite infection. Further work is needed to investigate the implications of possible pleiotropic effects of plumage morph and their potential role in the maintenance of colour polymorphism in this species.

Early-life telomere length predicts life-history strategy and reproductive senescence in a threatened wild songbird

Telomeres are well known for their associations with lifespan and ageing across diverse taxa. Early-life telomere length can be influenced by developmental conditions and has been shown positively affect lifetime reproductive success in a limited number of studies. Whether these effects are caused by a change in lifespan, reproductive rate or perhaps most importantly reproductive senescence is unclear. Using long-term data on female breeding success from a threatened songbird (the hihi, Notiomystis cincta), we show that the early-life telomere length of individuals predicts the presence and rate of future senescence of key reproductive traits: clutch size and hatching success. In contrast, senescence of fledging success is not associated with early-life telomere length, which may be due to the added influence of biparental care at this stage. Early-life telomere length does not predict lifespan or lifetime reproductive success in this species. Females may therefore change their reproductive allocation strategy depending on their early developmental conditions, which we hypothesise are reflected in their early-life telomere length. Our results offer new insights on the role that telomeres play in reproductive senescence and individual fitness and suggest telomere length can be used as a predictor for future life history in threatened species.

Taking flight: An ecological, evolutionary and genomic perspective on bat telomeres

Over 20% of all living mammals are bats (order Chiroptera). Bats possess extraordinary adaptations including powered flight, laryngeal echolocation and a unique immune system that enables them to tolerate a diversity of viral infections without presenting clinical disease symptoms. They occupy multiple trophic niches and environments globally. Significant physiological and ecological diversity occurs across the order. Bats also exhibit extreme longevity given their body size with many species showing few signs of ageing. The molecular basis of this extended longevity has recently attracted attention. Telomere maintenance potentially underpins bats' extended healthspan, although functional studies are still required to validate the causative mechanisms. In this review, we detail the current knowledge on bat telomeres, telomerase expression, and how these relate to ecology, longevity and life-history strategies. Patterns of telomere shortening and telomerase expression vary across species, and comparative genomic analyses suggest that alternative telomere maintenance mechanisms evolved in the longest-lived bats. We discuss the unique challenges faced when working with populations of wild bats and highlight ways to advance the field including expanding long-term monitoring across species that display contrasting life-histories and occupy different environmental niches. We further review how new high quality, chromosome-level genome assemblies can enable us to uncover the molecular mechanisms governing telomere dynamics and how phylogenomic analyses can reveal the adaptive significance of telomere maintenance and variation in bats.

Telomeres, the loop tying cancer to organismal life-histories

Recent developments in telomere and cancer evolutionary ecology demonstrate a very complex relationship between the need of tissue repair and controlling the emergence of abnormally proliferating cells. The trade-off is balanced by natural and sexual selection and mediated via both intrinsic and environmental factors. Here, we explore the effects of telomere-cancer dynamics on life history traits and strategies as well as on the cumulative effects of genetic and environmental factors. We show that telomere-cancer dynamics constitute an incredibly complex and multifaceted process. From research to date, it appears that the relationship between telomere length and cancer risk is likely nonlinear with good evidence that both (too) long and (too) short telomeres can be associated with increased cancer risk. The ability and propensity of organisms to respond to the interplay of telomere dynamics and oncogenic processes, depends on the combination of its tissue environments, life history strategies, environmental challenges (i.e., extreme climatic conditions), pressure by predators and pollution, as well as its evolutionary history. Consequently, precise interpretation of telomere-cancer dynamics requires integrative and multidisciplinary approaches. Finally, incorporating information on telomere dynamics and the expression of tumour suppressor genes and oncogenes could potentially provide the synergistic overview that could lay the foundations to study telomere-cancer dynamics at ecosystem levels.

Causes and consequences of telomere lengthening in a wild vertebrate population

Telomeres have been advocated to be important markers of biological age in evolutionary and ecological studies. Telomeres usually shorten with age and shortening is frequently associated with environmental stressors and increased subsequent mortality. Telomere lengthening - an apparent increase in telomere length between repeated samples from the same individual - also occurs. However, the exact circumstances, and consequences, of telomere lengthening are poorly understood. Using longitudinal data from the Seychelles warbler (Acrocephalus sechellensis), we tested whether telomere lengthening - which occurs in adults of this species - is associated with specific stressors (reproductive effort, food availability, malarial infection and cooperative breeding) and predicts subsequent survival. In females, telomere shortening was observed under greater stress (i.e., low food availability, malaria infection), while telomere lengthening was observed in females experiencing lower stress (i.e., high food availability, assisted by helpers, without malaria). The telomere dynamics of males were not associated with the key stressors tested. These results indicate that, at least for females, telomere lengthening occurs in circumstances more conducive to self-maintenance. Importantly, both females and males with lengthened telomeres had improved subsequent survival relative to individuals that displayed unchanged, or shortened, telomeres - indicating that telomere lengthening is associated with individual fitness. These results demonstrate that telomere dynamics are bidirectionally responsive to the level of stress that an individual faces, but may poorly reflect the accumulation of stress over an individuals lifetime.

Experimentally elevated testosterone shortens telomeres across years in a free-living songbird

Reproductive investment often comes at a cost to longevity, but the mechanisms that underlie these long-term effects are not well understood. In male vertebrates, elevated testosterone has been shown to increase reproductive success, but simultaneously to decrease survival. One factor that may contribute to or serve as a biomarker of these long-term effects of testosterone on longevity is telomeres, which are often positively related to lifespan and have been shown to shorten in response to reproduction. In this longitudinal study, we measured the effects of experimentally elevated testosterone on telomere shortening in free-living, male dark-eyed juncos (Junco hyemalis carolinensis), a system in which the experimental elevation of testosterone has previously been shown to increase reproductive success and reduce survival. We found a small, significant effect of testosterone treatment on telomeres, with testosterone-treated males exhibiting significantly greater telomere shortening with age than controls. These results are consistent with the hypothesis that increased telomere shortening may be a long-term cost of elevated testosterone exposure. As both testosterone and telomeres are conserved physiological mechanisms, our results suggest that their interaction may apply broadly to the long-term costs of reproduction in male vertebrates.

Population differences in the length and early-life dynamics of telomeres among European pied flycatchers

Telomere length and shortening rate are increasingly being used as biomarkers for long-term costs in ecological and evolutionary studies because of their relationships with survival and fitness. Both early-life conditions and growth, and later-life stressors can create variation in telomere shortening rate. Studies on between-population telomere length and dynamics are scarce, despite the expectation that populations exposed to varying environmental constraints would present divergent telomere length patterns. The pied flycatcher (Ficedula hypoleuca) is a passerine bird breeding across Eurasia (from Spain to western Siberia) and migrating through the Iberian Peninsula to spend the nonbreeding period in sub-Saharan Africa. Thus, different populations show marked differences in migration distance. We studied the large-scale variation of telomere length and early-life dynamics in the pied flycatcher by comparing six European populations across a north-south gradient (Finland, Estonia, England and Spain) predicting a negative effect of migration distance on adult telomere length, and of nestling growth on nestling telomere dynamics. There were clear population differences in telomere length, with English birds from midlatitudes having the longest telomeres. Telomere length did not thus show consistent latitudinal variation and was not linearly linked to differences in migration distance. Early-life telomere shortening rate tended to vary between populations. Fast growth was associated with shorter telomeres in the early life, but faster nestling growth affected telomeres more negatively in northern than southern populations. While the sources of between-population differences in telomere-related biology remain to be more intensively studied, our study illustrates the need to expand telomere studies at the between-population level.

Effects of long-term ethanol storage of blood samples on the estimation of telomere length

Telomeres, DNA structures located at the end of eukaryotic chromosomes, shorten with each cellular cycle. The shortening rate is affected by factors associated with stress, and, thus telomere length has been used as a biomarker of ageing, disease, and different life history trade-offs. Telomere research has received much attention in the last decades, however there is still a wide variety of factors that may affect telomere measurements and to date no study has thoroughly evaluated the possible long-term effect of a storage medium on telomere measurements. In this study we evaluated the long-term effects of ethanol on relative telomere length (RTL) measured by qPCR, using blood samples of magpies collected over twelve years and stored in absolute ethanol at room temperature. We firstly tested whether storage time had an effect on RTL and secondly we modelled the effect of time of storage (from 1 to 12 years) in differences in RTL from DNA extracted twice in consecutive years from the same blood sample. We also tested whether individual amplification efficiencies were influenced by storage time, and whether this could affect our results. Our study provides evidence of an effect of storage time on telomere length measurements. Importantly, this effect shows a pattern of decreasing loss of telomere sequence with storage time that stops after approximate 4 years of storage, which suggests that telomeres may degrade in blood samples stored in ethanol. Our method to quantify the effect of storage time could be used to evaluate other storage buffers and methods. Our results highlight the need to evaluate the long-term effects of storage on telomere measurements, particularly in long-term studies.

Combined effects of cold snaps and agriculture on the growth rates of Tree Swallows (Tachycineta bicolor)

The decline of avian aerial insectivores has been greater than any other foraging guild and both climate change and agricultural intensification are leading hypotheses explaining this decline. Spring cold snaps are predicted to increase in frequency due to climate change, and factors associated with agricultural intensification (e.g., toxicological agents, simplification of agricultural landscapes, and reductions of insect prey) potentially exacerbates the negative effects of cold snaps on aerial insectivore nestling growth and body condition. We evaluated this hypothesis using repeated measures of Tree Swallow (Tachycineta bicolor (Vieillot, 1808)) nestling body mass and 9th primary length across an expansive gradient of agricultural intensification. Growth rate, asymptotic body mass, and near fledging 9th primary length were lower for nestlings in landscapes consisting of more agro-intensive monocultures. This 14-year data set of body measures occurring at 2, 6, 12 and 16 days of age showed that the negative impact of cold snaps on the growth of these two traits was stronger for nestlings reared in more agro-intensive landscapes. Our findings provide further evidence that two of the primary hypothesized drivers for the decline of many aerial insectivores may interact and aggravate their decline by reducing fledging survival.

Telomere dynamics in female Columbian ground squirrels: recovery after emergence and loss after reproduction

Telomeres are specialized non-coding DNA sequences located at the end of chromosomes and that protect genetic information. Telomere loss over lifespan is generally viewed as a phenomenon associated with aging in animals. Recently, telomere elongation after hibernation has been described in several mammals. Whether this pattern is an adaptation to repair DNA damage caused during rewarming from torpor or if it coevolved as a mechanism to promote somatic maintenance in preparation for the upcoming reproductive effort remains unclear. In a longitudinal study measuring telomere length using buccal swabs, we tested if telomere elongation was related to reproductive success in wild adult female Columbian ground squirrels (Urocitellus columbianus) that were monitored from emergence from hibernation to the end of the reproductive season. We found three key results. First, female telomere length increased at the start of the breeding season, both in breeding and non-breeding individuals. Second, post-emergence telomere lengthening was unrelated to female future reproductive output. Third, telomere length decreased in breeding females during lactation, but remained stable in non-breeding females over a similar period. Within breeders, telomeres shortened more in females producing larger and heavier litters. We concluded that telomere lengthening after hibernation did not constrain immediate female reproductive capacities. It was more likely to be part of the body recovery process that takes place after hibernation. Telomere erosion that occurs after birth may constitute a physiological cost of female reproduction.

Inbreeding is associated with shorter early-life telomere length in a wild passerine

Inbreeding can have negative effects on survival and reproduction, which may be of conservation concern in small and isolated populations. However, the physiological mechanisms underlying inbreeding depression are not well-known. The length of telomeres, the DNA sequences protecting chromosome ends, has been associated with health or fitness in several species. We investigated effects of inbreeding on early-life telomere length in two small island populations of wild house sparrows (Passer domesticus) known to be affected by inbreeding depression. Using genomic measures of inbreeding we found that inbred nestling house sparrows (n = 371) have significantly shorter telomeres. Using pedigree-based estimates of inbreeding we found a tendency for inbred nestling house sparrows to have shorter telomeres (n = 1195). This negative effect of inbreeding on telomere length may have been complemented by a heterosis effect resulting in longer telomeres in individuals that were less inbred than the population average. Furthermore, we found some evidence of stronger effects of inbreeding on telomere length in males than females. Thus, telomere length may reveal subtle costs of inbreeding in the wild and demonstrate a route by which inbreeding negatively impacts the physiological state of an organism already at early life-history stages.

Telomere length declines with age, but relates to immune function independent of age in a wild passerine

Telomere length (TL) shortens with age but telomere dynamics can relate to fitness components independent of age. Immune function often relates to such fitness components and can also interact with telomeres. Studying the link between TL and immune function may therefore help us understand telomere-fitness associations. We assessed the relationships between erythrocyte TL and four immune indices (haptoglobin, natural antibodies (NAbs), complement activity (CA) and heterophil-lymphocyte (HL) ratio; n = 477-589), from known-aged individuals of a wild passerine (Malurus coronatus). As expected, we find that TL significantly declined with age. To verify whether associations between TL and immune function were independent of parallel age-related changes (e.g. immunosenescence), we statistically controlled for sampling age and used within-subject centring of TL to separate relationships within or between individuals. We found that TL positively predicted CA at the between-individual level (individuals with longer average TL had higher CA), but no other immune indices. By contrast, age predicted the levels of NAbs and HL ratio, allowing inference that respective associations between TL and age with immune indices are independent. Any links existing between TL and fitness are therefore unlikely to be strongly mediated by innate immune function, while TL and immune indices appear independent expressions of individual heterogeneity.

Longer telomeres during early life predict higher lifetime reproductive success in females but not males

The mechanisms that contribute to variation in lifetime reproductive success are not well understood. One possibility is that telomeres, conserved DNA sequences at chromosome ends that often shorten with age and stress exposures, may reflect differences in vital processes or influence fitness. Telomere length often predicts longevity, but longevity is only one component of fitness and little is known about how lifetime reproductive success is related to telomere dynamics in wild populations. We examined the relationships between telomere length beginning in early life, telomere loss into adulthood and lifetime reproductive success in free-living house sparrows (Passer domesticus). We found that females, but not males, with longer telomeres during early life had higher lifetime reproductive success, owing to associations with longevity and not reproduction per year or attempt. Telomeres decreased with age in both sexes, but telomere loss was not associated with lifetime reproductive success. In this species, telomeres may reflect differences in quality or condition rather than the pace of life, but only in females. Sexually discordant selection on telomeres is expected to influence the stability and maintenance of within population variation in telomere dynamics and suggests that any role telomeres play in mediating life-history trade-offs may be sex specific.

Telomere lengths correlate with fitness but assortative mating by telomeres confers no benefit to fledgling recruitment

Assortative mating by telomere lengths has been observed in several bird species, and in some cases may increase fitness of individuals. Here we examined the relationship between telomere lengths of Blue-footed Booby (Sula nebouxii) mates, long-lived colonial seabirds with high annual divorce rates. We tested the hypothesis that interactions between maternal and paternal telomere lengths affect offspring and parental survival. We found that relative telomere lengths (RTL) were strongly positively correlated between members of a breeding pair. In addition, RTL of both parents interacted to predict fledgling recruitment, although fledglings with two very long-RTL parents performed only averagely. Telomere lengths also predicted adult survival: birds with long telomeres were more likely to survive, but birds whose mate had long telomeres were less likely to survive. Thus, having long telomeres benefits survival, while choosing a mate with long telomeres benefits reproductive output while penalizing survival. These patterns demonstrate that while a breeder's RTL predicts offspring quality, assortative mating by RTL does not enhance fitness, and a trade-off between different components of fitness may govern patterns of assortative mating by telomere length. They also illustrate how testing the adaptive value of only one parent’s telomere length on either survival or reproductive success alone may provide equivocal results.

Telomere dynamics from hatching to sexual maturity and maternal effects in the 'multivariate egg'

Avian eggs contain a large number of molecules deposited by the mother that provide the embryo with energy but also potentially influence its development via the effects of maternally derived hormones and antibodies: the avian egg is thus 'multivariate'. Multivariate effects on offspring phenotype were evaluated in a study on captive zebra finches, by simultaneously manipulating maternally derived antibodies (MAb) by lipopolysaccharide (LPS) treatment of mothers and injection of testosterone into the egg yolk. LPS treatment had a positive effect on body mass growth at 30 days after hatching and immune response at sexual maturity, while egg testosterone treatment positively influenced immune response at fledging and courtship behaviour in sexually mature male offspring. Maternal effects are known to modulate offspring telomere length (TL). However, the multivariate effects of egg-derived maternal components on offspring telomere dynamics from hatching to sexual maturity are undefined. Here, we tested: (1) the effects of LPS and testosterone treatments on TL from hatching to sexual maturity (day 82); (2) how LPS treatment modulated TL over reproduction in adult females; and (3) the relationship between maternal and offspring TL. We predicted that TL would be shorter in LPS fledglings (as a cost of faster growth) and that TL would be longer in sexually mature adults after yolk testosterone treatment (as a proxy of individual quality). In adult females, there was an overall negative relationship between laying and rearing investments and TL, this relationship was weaker in LPS-treated females. In chicks, there was an overall negative effect of LPS treatment on TL measured at fledging and sexual maturity (day 25-82). In addition, at fledging, there was a Sex×LPS×Testosterone interaction, suggesting the existence of antagonistic effects of our treatments. Our data partially support the hypothesis that telomeres are proxies of individual quality and that individual differences in TL are established very early in life.

Telomere attrition with age in a wild amphibian population

Telomere shortening with age has been documented in many organisms, but few studies have reported telomere length measurements in amphibians, and no information is available for growth after metamorphosis, nor in wild populations. We provide both cross-sectional and longitudinal evidence of net telomere attrition with age in a wild amphibian population of natterjack toads (Epidalea calamita). Based on age-estimation by skeletochronology and qPCR telomere length measurements in the framework of an individual-based monitoring programme, we confirmed telomere attrition in recaptured males. Our results support that toads experience telomere attrition throughout their ontogeny, and that most attrition occurs during the first 1-2 years. We did not find associations between telomere length and inbreeding or body condition. Our results on telomere length dynamics under natural conditions confirm telomere shortening with age in amphibians and provide quantification of wide telomere length variation within and among age-classes in a wild breeding population.

Sex-specific telomere length and dynamics in relation to age and reproductive success in Cory's shearwaters

Individuals in free‐living animal populations generally differ substantially in reproductive success, lifespan and other fitness‐related traits, but the molecular mechanisms underlying this variation are poorly understood. Telomere length and dynamics are candidate traits explaining this variation, as long telomeres predict a higher survival probability and telomere loss has been shown to reflect experienced “life stress.” However, telomere dynamics among very long‐lived species are unresolved. Additionally, it is generally not well understood how telomeres relate to reproductive success or sex. We measured telomere length and dynamics in erythrocytes to assess their relationship to age, sex and reproduction in Cory's shearwaters (Calonectris borealis), a long‐lived seabird, in the context of a long‐term study. Adult males had on average 231 bp longer telomeres than females, independent of age. In females, telomere length changed relatively little with age, whereas male telomere length declined significantly. Telomere shortening within males from one year to the next was three times higher than the interannual shortening rate based on cross‐sectional data of males. Past long‐term reproductive success was sex‐specifically reflected in age‐corrected telomere length: males with on average high fledgling production were characterized by shorter telomeres, whereas successful females had longer telomeres, and we discuss hypotheses that may explain this contrast. In conclusion, telomere length and dynamics in relation to age and reproduction are sex‐dependent in Cory's shearwaters and these findings contribute to our understanding of what characterises individual variation in fitness.