Sophie M Dupont

Christophe Barbraud

Olivier Chastel

Karine Delord

Marie Pallud

Charline Parenteau

Henri Weimerskirch

Frédéric Angelier

How does maternal age influence reproductive performance and offspring phenotype in the snow petrel (Pagodroma nivea)?

Keywords: Procellariforms, Maternal effect, Guarding period, Body size, Corticosterone levels, Survival probability

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

In vertebrates, age has a strong influence on individual reproductive performance [START_REF] Th | Reproductive success: studies of individual variation in contrasting breeding systems[END_REF][START_REF] Forslund | Age and reproduction in birds-hypotheses and tests[END_REF]. Breeding success usually increases with advancing age up to a point before senescence occurs [START_REF] Nussey | Senescence in natural populations of animals: widespread evidence and its implications for bio-gerontology[END_REF]). Multiple hypotheses have been proposed to explain the age-related improvement of reproductive performance (such as the selection, restraint and constraint hypotheses, [START_REF] Williams | Natural selection, the costs of reproduction, and a refinement of Lack's principle[END_REF][START_REF] Curio | Why de young birds reproduce less well[END_REF][START_REF] Forslund | Age and reproduction in birds-hypotheses and tests[END_REF]. In birds, an extensive body of literature has focused on laying date, clutch size, hatching success, and fledging success to investigate this age-related improvement of reproductive performance [START_REF] Pugesek | The relationship between parental age and reproductive effort in the California gull (Larus californicus)[END_REF][START_REF] Cameron | Aging and improving reproductive success in horses: declining residual reproductive value or just older and wiser?[END_REF][START_REF] Mauck | Age-specific reproductive success: evidence for the selection hypothesis[END_REF][START_REF] Beamonte-Barrientos | Senescence of maternal effects: aging influences egg quality and rearing capacities of a long-lived bird[END_REF][START_REF] Fay | From early life to senescence: individual heterogeneity in a long-lived seabird[END_REF][START_REF] Ivimey-Cook | The diversity of maternal-age effects upon pre-adult survival across animal species[END_REF][START_REF] Saraux | Age-related breeding success in little penguins: a result of selection and ontogenetic changes in foraging and phenology[END_REF]. However, most of these studies have failed to measure the condition of the offspring before fledging, mostly due to the constraints associated with the study systems. However, offspring quality could be a robust and relevant additional proxy of parental reproductive performance [START_REF] Barks | Parental age effects and the evolution of senescence[END_REF][START_REF] Barreaux | Incorporating effects of age on energy dynamics predicts nonlinear maternal allocation patterns in iteroparous animals[END_REF] but see, for instance, [START_REF] Bouwhuis | Sex-specific pathways of parental age effects on offspring lifetime reproductive success in a long-lived seabird[END_REF][START_REF] Schroeder | Reduced fitness in progeny from old parents in a natural population[END_REF], especially because it correlates with the probably of postfledging survival. Indeed, there is now increasing evidence that only a small percentage of fledglings will subsequently survive and significantly contribute to future generations through the production of offspring [START_REF] Mccleery | Agespecific reproduction in a long-lived species: the combined effects of senescence and individual quality[END_REF][START_REF] Wilson | What is individual quality? An evolutionary perspective[END_REF][START_REF] Cam | Looking for a needle in a haystack: inference about individual fitness components in a heterogeneous population[END_REF][START_REF] Fay | Paternal but not maternal age influences early-life performance of offspring in a long-lived seabird[END_REF][START_REF] Fay | From early life to senescence: individual heterogeneity in a long-lived seabird[END_REF][START_REF] Vedder | Heterogeneity in individual quality in birds: overall patterns and insights from a study on common terns[END_REF].

Juveniles are inexperienced, less able to acquire food [START_REF] Desrochers | Age and foraging success in European blackbirds: variation between and with individuals[END_REF]) and to sustain detrimental conditions (e.g., low food availability, [START_REF] Wiens | Post-fledging survival of northern goshawks: the importance of prey abundance, weather, and dispersal[END_REF]. Consequently, many often disappear from the population before any breeding attempt (e.g., [START_REF] Alderman | Post-fledging survival and dispersal of shy albatross from three breeding colonies in Tasmania[END_REF][START_REF] Fay | Population density and climate shape early-life survival and recruitment in a long-lived pelagic seabird[END_REF][START_REF] Naef-Daenzer | Post-fledging survival of altricial birds: ecological determinants and adaptation[END_REF]. In addition, among juveniles that survive until adulthood, their phenotype may constrain them and reduce their probability to successfully breed later in life (e.g., [START_REF] Van De Pol | A silver spoon for a golden future: long-term effects of natal origin on fitness prospects of oystercatchers (Haematopus ostralegus)[END_REF]. This high individual heterogeneity in performance among individuals is often related to organismal systems (e.g., morphology, behaviour, and physiology), which are at least partly determined during their development [START_REF] Lindström | Early development and fitness in birds and mammals[END_REF][START_REF] Monaghan | Early growth conditions, phenotypic development and environmental change[END_REF][START_REF]Early development, recruitment and life history trajectory in long-lived birds[END_REF][START_REF] Maness | Predictors of juvenile survival in birds[END_REF][START_REF] Hamel | Introduction to: individual heterogeneity-the causes and consequences of a fundamental biological process[END_REF]. In that context, assessing not only reproductive success but also the quality of the offspring appears crucial to better evaluate the influence of age on reproductive performance.

When investigating the influence of age on reproductive performance in birds, several components need therefore to be evaluated. Firstly, phenology, parental effort and fledging success are needed to obtain robust estimates of the ability of parents to successfully breed and rear their chick [START_REF] Th | Reproductive success: studies of individual variation in contrasting breeding systems[END_REF][START_REF] Newton | Lifetime reproduction in birds[END_REF][START_REF] Forslund | Age and reproduction in birds-hypotheses and tests[END_REF][START_REF] Zhang | Age-dependent trait variation: the relative contribution of within-individual change, selective appearance and disappearance in a long-lived seabird[END_REF]. Specifically, high parental skills and investment are often related to early breeding, and consequently, high fledging success, especially in seabird species [START_REF] Bogdanova | Age of the incubating parents affects nestling survival: an experimental study of the herring gull Larus argentatus[END_REF]Angelier et al. 2007b;[START_REF] Rebke | Reproductive improvement and senescence in a long-lived bird[END_REF][START_REF] Sauser | Sea ice and local weather affect reproductive phenology of a polar seabird with breeding consequences[END_REF]. Secondly, several proxies of developmental conditions can be used to assess the quality of the offspring, and therefore, their probability to survive and to recruit into the population [START_REF]Early development, recruitment and life history trajectory in long-lived birds[END_REF][START_REF] Mumme | Natal territory size, group size, and body mass affect lifetime fitness in the cooperatively breeding Florida Scrub-Jay[END_REF]. Notably, several "key" morphological, physiological, and behavioural systems are important during the developmental period to assess offspring quality [START_REF] Schoech | Short-and long-term effects of developmental corticosterone exposure on avian physiology, behavioral phenotype, cognition, and fitness: a review[END_REF]) and to study the relationship between parental age, developmental constraints and offspring quality.

Slower growth, smaller body size, and lower body condition are usually associated with higher developmental constraints, and with lower subsequent performance (e.g., postfledging survival probability; [START_REF] Morrison | Wing length and mass at fledging predict local juvenile survival and age at first return in Tufted Puffins[END_REF][START_REF] Jones | Variation in nestling body condition and wing development predict cause-specific mortality in fledgling dickcissels[END_REF][START_REF] Vernasco | Environmental predictors of nestling condition, postfledging movement, and postfledging survival in a migratory songbird, the Wood Thrush (Hylocichla mustelina)[END_REF][START_REF] Sauser | Increased sea ice concentration worsens fledging condition and juvenile survival in a pagophilic seabird, the Snow Petrel[END_REF][START_REF] Evans | Individual condition, but not fledging phenology, carries over to affect post-fledging survival in a Neotropical migratory songbird[END_REF]. Additionally, organismal-related stress systems are set up during the developmental period, and they are known to determine, at least partly, the ability of individuals to breed and survive when environmental stressors occur [START_REF] Angelier | Importance of the glucocorticoid stress response in a changing world: theory, hypotheses and perspectives[END_REF].

Physiological proxies of stress levels are considered as robust tools to assess not only the constraint that may occur during the developmental period, but also the probability of fledglings to subsequently survive and recruit into the population. When facing a threatening event, corticosterone secretion increases to mobilize energy (e.g., protein catabolism, [START_REF] Sapolsky | How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions[END_REF][START_REF] Romero | Physiological stress in ecology: lessons from biomedical research[END_REF]) and to promote an emergency response that aims to restore homeostasis and helps the chick surviving the acute stressor [START_REF] Angelier | Importance of the glucocorticoid stress response in a changing world: theory, hypotheses and perspectives[END_REF][START_REF] Wingfield | Ecological processes and the ecology of stress: the impacts of abiotic environmental factors[END_REF]. In chicks, developmental conditions are associated with short-and long-term modifications of physiological stress sensitivity [START_REF] Rensel | Repeatability of baseline and stressinduced corticosterone levels across early life stages in the Florida scrub-jay (Aphelocoma coerulescens)[END_REF][START_REF] Zimmer | Developmental programming: cumulative effects of increased pre-hatching corticosterone levels and post-hatching unpredictable food availability on physiology and behavior in adulthood[END_REF][START_REF] Grace | Delayed effect of early-life corticosterone treatment on adult anti-predator behavior in a common passerine[END_REF][START_REF] Grace | Post-natal corticosterone exposure downregulates the HPA axis through adulthood in a common passerine[END_REF][START_REF] Kraft | Developmental stress reduces body condition across avian life-history stages: a comparison of quantitative magnetic resonance data and condition indices[END_REF]. This stress sensitivity can in turn be related to post-hatching survival and even post-fledging performances (e.g., [START_REF] Harvey | A comparison of plucked feathers versus blood samples as DNA sources for molecular sexing[END_REF][START_REF] Blas | Stress response during development predicts fitness in a wild, long lived vertebrate[END_REF][START_REF] Breuner | In search of relationships between the acute adrenocortical response and fitness[END_REF][START_REF] Love | Feather corticosterone predicts offspring performance in a context-dependent manner[END_REF].

Finally, short telomere length has been proposed as a relevant proxy of constraining early-life environmental 1 3 conditions and of poor fledgling quality. Telomeres are terminal chromosomal complexes composed of highly repeated DNA sequences and proteins. Their length is reduced during each cell division due to the incomplete end-replication [START_REF] Blackburn | Telomeres and telomerase: their mechanisms of action and the effects of altering their functions[END_REF]. Interestingly, the occurrence of environmental or nutritional constraints at the early stage seems to accelerate this telomere attrition [START_REF] Monaghan | Organismal stress, telomeres and life histories[END_REF][START_REF] Angelier | Do glucocorticoids mediate the link between environmental conditions and telomere dynamics in wild vertebrates? A review[END_REF][START_REF] Noguera | Reduced telomere length in embryos exposed to predator cues[END_REF][START_REF] Stier | Pace and stability of embryonic development affect telomere dynamics: an experimental study in a precocial bird model[END_REF], and parental age could translate into short telomeres if associated with low quality parental cares (e.g., [START_REF] Dupont | Young parents produce offspring with short telomeres: a study in a long-lived bird, the Black-browed Albatross (Thalassarche melanophrys)[END_REF]. This developmental telomere attrition has been already convincingly associated with reduced longevity and fitness in captive and wild animals [START_REF] Heidinger | Telomere length in early life predicts lifespan[END_REF][START_REF] Asghar | Maternal and genetic factors determine early life telomere length[END_REF][START_REF] Wilbourn | The relationship between telomere length and mortality risk in non-model vertebrate systems: a meta-analysis[END_REF][START_REF] Eastwood | Earlylife telomere length predicts lifespan and lifetime reproductive success in a wild bird[END_REF][START_REF] Heidinger | Longer telomeres during early life predict higher lifetime reproductive success in females but not males[END_REF]) and seems to have potential long-lasting fitness consequences [START_REF] Marasco | How does early-life adversity shape telomere dynamics during adulthood?[END_REF].

In this study, we investigated the influence of maternal age on reproductive performance and offspring quality in the snow petrel (Pagodroma nivea), a long-lived seabird species (average lifespan: ~ 50 years old, [START_REF] Chastel | High annual variability in reproductive success and survival of an Antarctic seabird, the Snow Petrel Pagodroma nivea[END_REF]. In this species, increasing parental age is associated with better breeding performance and reproductive senescence does not occur before very old ages (Angelier et al. 2007a;[START_REF] Berman | Contrasted patterns of age-specific reproduction in long-lived seabirds[END_REF]).We specifically focused on maternal age because known-aged females were more abundant in our study site and because females may have a greater impact on offspring quality than males in this seabird species [START_REF] Barbraud | Early body condition and hatching success in the Snow Petrel Pagodroma nivea[END_REF]Barbraud et al. 1999). Breeding pairs produce at most a single chick per breeding season, making this species a perfect model to study the influence of age on breeding success and offspring phenotype independently of sibling competition. We followed 56 knownaged females (from 8 to 34 years old, which correspond to young and middle-age classes for this species, Angelier et al. 2007a;[START_REF] Berman | Contrasted patterns of age-specific reproduction in long-lived seabirds[END_REF] and their chicks and we specifically monitored their reproductive phenology (hatching date), the duration of the guarding period (a component of parental care), and offspring survival at the nest. We also assessed the influence of maternal age on the quality of developmental conditions through morphological (growth, body size and body condition), physiological (corticosterone), and molecular (telomere length) variables. Because no senescent females were monitored, we expected a linear rather than a quadratic relationship between maternal age and measured reproductive outputs. Specifically, we predict that reproductive performance will improve with advancing maternal age. More precisely, we predict that younger snow petrels should lay later as later breeding is usually related to poor reproductive performance (prediction 1). Because the guarding period is supposed to be longer when the chicks grow slowly, we also predict that younger petrels will guard their chick longer if they are less able to feed their chick and sustain its growth (prediction 2). We also predict that the chicks from younger snow petrels should have a lower probability to survive at the nest (prediction 3). In addition, offspring developmental conditions should also improve with advancing maternal age and younger snow petrels should produce chicks presenting a smaller body size (wing size and tarsus length), with a slower growth and/or a lower body condition (prediction 4). We also predict that offspring physiology will be affected by maternal age. Specifically, developmental energetic constraints are expected to increase the offspring sensitivity to stress. Because younger mothers are expected to be less able to fulfil the energetic needs of their offspring, we then predict that their chicks will present higher basal and stress-induced corticosterone levels (prediction 5). Finally, because telomere attrition is accelerated by increasing developmental constraints, we also predict that younger females should produce chicks with shorter telomeres (prediction 6).

Material and methods

Study species

Our study focused on the snow petrel, a long-lived seabird species with a high survival probability and a low fecundity (only one egg is laid per couple and per year with no replacement clutch in case of breeding failure, [START_REF] Warham | The petrels: their ecology and breeding systems[END_REF][START_REF] Chastel | High annual variability in reproductive success and survival of an Antarctic seabird, the Snow Petrel Pagodroma nivea[END_REF]. This species provides bi-parental care both during the incubation and the chick-rearing periods [START_REF] Warham | The petrels: their ecology and breeding systems[END_REF]. At 10 days old on average, the chick becomes thermally independent and is left unattended at the nest [START_REF] Goutte | Experimentally delayed hatching triggers a magnified stress response in a long-lived bird[END_REF]. Both parents forage at sea to feed their chick and to restore their own body reserves [START_REF] Chastel | High annual variability in reproductive success and survival of an Antarctic seabird, the Snow Petrel Pagodroma nivea[END_REF]). The chick fledges approximatively at 47 days old [START_REF] Brown | Breeding biology of the Snow Petrel, Pagodroma nivea (Forster)[END_REF]Barbraud et al. 1999).

A 56-years-old ongoing mark-recapture program (see [START_REF] Barbraud | Early body condition and hatching success in the Snow Petrel Pagodroma nivea[END_REF] for details on the monitoring protocol) has been conducted at Ile des Pétrels, Pointe Géologie, Terre Adélie, Antarctica (66° 40′ S, 140° 01′ E). At this site, all chicks are banded every year since the beginning of the monitoring program. After fledging, juveniles stay at sea for almost a decade until sexual maturity [START_REF] Chastel | High annual variability in reproductive success and survival of an Antarctic seabird, the Snow Petrel Pagodroma nivea[END_REF][START_REF] Jenouvrier | Long-term contrasted responses to climate of two Antarctic seabirds species[END_REF]. During that period, the juvenile survival probability varies between 10-25% [START_REF] Chastel | High annual variability in reproductive success and survival of an Antarctic seabird, the Snow Petrel Pagodroma nivea[END_REF][START_REF] Sauser | Increased sea ice concentration worsens fledging condition and juvenile survival in a pagophilic seabird, the Snow Petrel[END_REF]. Then, they return to their hatching colony to breed with a high site fidelity (89.8%, [START_REF] Jouventin | Site and mate choice in seabirds: an evolutionary approach[END_REF].Thanks to this high philopatry and this long-term banding effort, around a hundred of known-aged reproductive birds could be found at Iles des Pétrels during our study. The sex of individuals was determined through relative size of both pair members (females are 20% smaller than males) and acoustic signals [START_REF] Barbraud | Body size and determinants of laying date variation in the Snow Petrel Pagodroma nivea[END_REF] or 1 3 thanks to previous studies, during which molecular sexing was conducted.

Determination of maternal age and reproductive monitoring

During the incubation period of austral summer 2017/2018, we checked the bands of all breeding pairs and this allowed us to know the age of the parents that were banded at the colony as chicks. Because we found more breeding knownaged females than known-aged males, we decided to focus our study on known-aged female snow petrels. This decision also resulted from ecological reasons: female adult snow petrels are smaller than males and they seem to be more energetically constrained during reproduction, and therefore, to have a higher impact on reproductive performance (Barbraud and Chastel 1999; Barbraud et al. 1999; but see [START_REF] Fay | Paternal but not maternal age influences early-life performance of offspring in a long-lived seabird[END_REF][START_REF] Bouwhuis | Reduced telomere length in offspring of old fathers in a long-lived seabird[END_REF] in other seabird species). During the incubation period, 56 nests occupied by a knownaged female were identified (range 8-34 years old, which correspond to young and middle-age classes for this species, maximum lifespan: ~ 50 years old) for this study. All these nests were located in crevices and provided good visibility of the content of the nest from a distance. They were left undisturbed until the hatching period. At that time (early January), these nests were daily checked in order to determine the exact hatching date which is an accurate proxy of the laying date in this species [START_REF] Goutte | Age and the timing of breeding in a long-lived bird: a role for stress hormones?[END_REF]). Among the 56 monitored pairs, 45 produced a hatchling (Table 1). After hatching, each of these 45 nests with a chick was observed daily from a distance in order to monitor the age when the chick was left alone by its parents (i.e., age of emancipation), and therefore, to determine the duration of the parental guarding stage (i.e., number of days from hatching until the chick is left unattended at the nest by both parents, N = 42 because 3 chicks died before emancipation, Table 1). Each nest was then visited when the chick was 13 days old (i.e., after the end of the guarding period, N = 41 because 4 of the 45 chicks died before reaching 13 days old, Table 1) and 23 days old (i.e., N = 35 because 6 chicks died between 13 and 23 days old, Table 1), respectively. When visiting the nest, the presence of a parent in the nest was also monitored (i.e., parents regularly come at the nest to provide food to the chick during the chick-rearing period; 1: present vs 0: absent) because parental presence can affect corticosterone levels and body condition [START_REF] Dupont | Home alone!" influence of nest parental attendance on offspring behavioral and hormonal stress responses in an Antarctic seabird, the snow petrel (Pagodroma nivea)[END_REF]. Although one parent was sometimes seen at the nest when the chicks were 13 days old, all the chicks were alone at 23 days old and this variable was therefore not considered when analysing the phenotype of 23-days-old chicks.

Morphometric measurements, body condition and growth

At 13 and 23 days old, each surviving chick was captured by hand at its nest (see Table 1 for sample sizes). Tarsus length and wing length were measured with a calliper (± 0.1 mm) and a ruler (± 1 mm), respectively. All birds were weighed with a spring balance (± 5 g). Body condition was calculated using the scaled mass index (SMI) following [START_REF] Peig | New perspectives for estimating body condition from mass/length data: the scaled mass index as an alternative method[END_REF]. Tarsus length was highly correlated with body mass (tarsus: r = 0.869; P < 0.001) and was therefore used to calculate the SMI of growing snow petrels by following this formula:

SMI i = M i × ( L 0 L i ) b
. The terms M i and L i respectively correspond to the body mass and the tarsus length of the individual i. The term L 0 is the arithmetic mean value of tarsus length for the whole study population (L 0 = 32.8 mm). The exponent b corresponds to the slope estimate of a standardized major axis regression of log-transformed body mass on log-transformed tarsus length (b = 2.15). (13) Telomere, corticosterone Age, parental presence, body condition, body size 1 3

We then determined the change in body size (wing and tarsus growth) and body condition (SMI) from 13 to 23 days after hatching for the chicks that survived until this age (N = 35, Table 1). This has been calculated as the difference between body size variables (i.e., wing size and tarsus length) or condition (SMI) measured at day 23 to the data recorded at day 13. To note, if we expressed the change in body size or body condition in terms of percentage, results remain similar. Body mass and body condition were strongly correlated at both ages (F 1,39 = 149.6, P < 0.001; F 1,33 = 52.4, P < 0.001, respectively for 13-and 23-days-old chicks) and analyses of body mass and body condition gave similar results (see Supplementary File, Annex 1). Similarly, results using tarsus length and wing length gave very similar results. Therefore, we only present the results focusing on body condition and tarsus length (as a proxy of body size) in the rest of the manuscript.

Physiological measurements

When chicks were 13 days old, their corticosterone (hereafter CORT) stress response was measured from blood samples by using a well-established protocol [START_REF] Wingfield | Seasonal changes of the adrenocortical responses to stress in redpolls, Acanthis flammea, in Alaska[END_REF]. This procedure was conducted on a sub-sample of chicks only, for practical reasons (i.e., bad weather and distance to the station; N = 23, Table 1). Immediately after capture (i.e., within 3 min, Romero and Reed 2005), an initial blood sample (~ 150 µL) was collected from the alar vein with a 25-gauge needle and heparinized microcapillary tubes. This sample was used to measure baseline CORT levels. A second blood sample (~ 150 µL) was collected 30 min after capture and was used to measure the CORT stress response, i.e., the amount of CORT that is released in the bloodstream following a standardized stress protocol (hereafter "stress-induced CORT levels"). Birds were hold in a cloth bag during this 30 min restraint. These blood samples were also used to measure the telomere length of all sampled chicks (N = 23, Table 1). The corticosterone stress response was not measured when the chicks were 23 days old.

Corticosterone assay, molecular sexing, and telomere length

At the end of each nest visit, blood samples were immediately centrifuged in order to separate plasma and blood red cells. Then, all samples were stored at -20 °C until subsequent analyses at the Centre d'Etudes Biologiques de Chizé. Plasma CORT concentrations were determined by radioimmunoassay as described previously in [START_REF] Lormée | Sex-specific patterns in baseline corticosterone and body condition changes in breeding red-footed boobies Sula sula[END_REF].

The corticosterone was extracted with diethyl-ether in 50 µL of plasma and was then assayed in duplicate with RIA method using H3-corticosterone (Perkin Elmer, US) and rabbit antiserum against corticosterone (Sigma Aldrich, US). RIA corticosterone assay was validated on snow petrel plasma. One extract was serially diluted in the appropriate assay buffer, its displacement curve was parallel to the standard curve. Inter-assay and intra-assay precisions were respectively 13.78% and 6.91%. Corticosterone lowest detectable concentration was 0.28 ng/mL.

DNA was extracted from blood red cells of the first blood sample collected as part of the stress response by using the DNeasy blood and tissue kit (Qiagen). The sex of each blood sampled chick (N = 23) was determined by molecular sexing, based on polymerase chain reaction (PCR) amplification of the CHD gene, as detailed by [START_REF] Fridolfsson | A simple and universal method for molecular sexing of non-ratite birds[END_REF]. This sub-sample of chicks allowed us to check for potential sex-dependent effects of maternal age on our variables of interest.

Telomere length was determined, from the first blood sample collected as part of the stress response, at the Centre d'Etudes Biologiques de Chizé. To do so, the TeloTAGGG Telomere Length Assay (Roche, Mannheim, Germany) has been used as previously described [START_REF] Dupont | Young parents produce offspring with short telomeres: a study in a long-lived bird, the Black-browed Albatross (Thalassarche melanophrys)[END_REF][START_REF] Angelier | Is telomere length a molecular marker of individual quality? Insights from a long-lived bird[END_REF], with minor modifications. DNA quality was checked by optical density spectrophotometry. Briefly, 4 μg of DNA was digested with restriction enzymes for 16 h at 37 °C. Digested DNA samples were then separated with a pulse-field gel electrophoresis (Bio-Rad). Then, all samples were run in a single gel at 3.0 V/cm with an initial switch time of 0.5 s to a final switch time of 7 s for 14 h. After this step, the gel was hybridized with a digoxigenin-labelled probe specific for telomeric sequences, and was visualized with a Chemidoc (Bio Rad). Telomere length was determined using ImageJ by analysing telomere smear densities.

Statistical analyses

All statistical analyses were performed with SAS Studio. Model selections were performed using a secondorder Akaike's Information Criterion (AICc) to select the most parsimonious model [START_REF] Burnham | AIC model selection and multimodel inference in behavioral ecology: some background, observations, and comparisons[END_REF]. AICc were used to compare all possible models and ΔAICC and AICc weight were used to select the most parsimonious model [START_REF] Burnham | AIC model selection and multimodel inference in behavioral ecology: some background, observations, and comparisons[END_REF]. Values for difference in AICc values (ΔAICc) were computed by subtracting the minimum AICc from all candidate model AICc. Differences between AICc values for different models can be used to determine which provides the most adequate description of the data based on the fewest model parameters. ΔAICc values > 2 are a good indicator that the model with the lowest AICc is preferable, whereas ΔAICc values < 2 indicate that models are fairly similar in their ability to describe the data. In that latter case, the model with the fewest number of parameters can be selected and AICc weights provide the likelihood of each competitive 1 3 models [START_REF] Burnham | AIC model selection and multimodel inference in behavioral ecology: some background, observations, and comparisons[END_REF]. We used Generalized Linear Models (GLM) with a normal (identity link function) or a binomial distribution (logit link function) depending on the dependent variables of interest. The parameter estimates (Mean ± SE, and 95% Confidence Intervals) and effect sizes (β) of the best selected models were reported.

Several model selections were conducted to test our biological hypotheses and different sets of models had to be run because of different sample sizes (Table 1) and different data distribution (see Annex 2 for histograms of all response variables). Firstly, we tested whether maternal age was related to hatching date and the length of the guarding period. Secondly, we tested the effect of maternal age, hatching date, and the length of the guarding period on the probability to survive from 13 to 23 days old. We also tested the influence of offspring body size (tarsus length) and body condition on this survival probability. We then tested the relationships between CORT levels (baseline and stress-induced), telomere length and this survival probability. Finally, we tested the influence of maternal age on body size (tarsus length), body condition and the growth of the chicks. We also tested the influence of maternal age, body condition, and body size on corticosterone levels and telomere length. Parental presence was included when relevant (13-days-old chicks) as a previous study found that this variable can affect body condition and corticosterone levels of young chicks [START_REF] Dupont | Home alone!" influence of nest parental attendance on offspring behavioral and hormonal stress responses in an Antarctic seabird, the snow petrel (Pagodroma nivea)[END_REF]. Note that the sex of the chicks was not included as an explanatory factor in these analyses because it was available for a limited number of chicks only (N = 23). We ran additional models including the sex factor with this limited sample size and they gave similar results to our main analyses, suggesting that the sex of the offspring does not affect our results.

Results

Influence of maternal age on hatching date and duration of the guarding period

Hatching date was negatively associated with maternal age (GLM, ΔAICc = 4.33; estimate (mean 95% CI): -0.153 [-0.269; -0.037], β = -0.368; Fig. 1a). More precisely, the chicks from older females hatched earlier than those from younger females. In addition, the duration of the guarding period was also negatively associated with maternal age (GLM, ΔAICc = 1.78; estimate (mean 95% CI): -0.115 [-0.228; -0.003], β = -0.305; Fig. 1b): the chicks from older females were left alone earlier than those from younger females.

Influence of maternal age and offspring phenotype on survival rate

Survival rate from 13 to 23 days after hatching was significantly associated with maternal age but not with the hatching date or the duration of the guarding period (Table 2a, Fig. 2). Specifically, the chicks from older females had a higher survival rate at the nest (estimate (mean, 95% CI): -0.233 [-0.440; -0.026], β = 0.242). In addition, this survival probability was not related to offspring body size (tarsus length) and body condition (Table 2b). Regarding physiology, the survival rate was significantly and positively related to offspring telomere length measured at 13 days old (Table 2). More precisely, chicks with longer telomeres had a higher survival probability (estimate (mean, 95% CI): -7.607 [-15.054; -0.159], β = 0.001). However, survival rate was not linked with CORT levels (baseline or stress-induced, Table 2c).

Influence of maternal age on growth and morphometric measurements in chicks

In 13-days-old chicks, body size was not affected by maternal age or parental presence at the nest (Table 3a, Fig. 3). Although body condition was not affected by maternal age, chicks with a parent in the nests were in better condition than those that were alone in the nest at the time of capture (Table 3b). Tarsus growth was significantly and positively correlated with maternal age (GLM, ΔAICc = 3.57; estimate (mean 95% CI): 0.125 [0.025; -0.225], β = 0.763; Fig. 4). However, the change in body condition from 13 to 23 days old was not related with maternal age as the most parsimonious model was the null model (ΔAICc = -2.20). In 23-days-old chicks, tarsus length was significantly and positively correlated with maternal age (GLM, ΔAICc = 5.11; estimate (mean 95% CI): 0.139 [0.042; -0.237], β = 0.849; Fig. 3B) but body condition was not significantly associated with maternal age as the most parsimonious model was the null model (ΔAICc = -2.26).

Influence of maternal age on physiological measurements in 13-days-old chicks

In 13-days-old chicks, baseline CORT levels were not affected by maternal age or by the presence of a parent in the nests (Table 4a). However, baseline CORT levels were significantly and negatively correlated with body condition (estimate (mean 95% CI): -0.022 [-0.034; -0.010], β = -0.677; Table 4) and slightly but not significantly with body size (tarsus length, estimate (mean 95% CI): -0.567 [-1.206; 0.072], β = -0.318; Table 4a). The selected model for stress-induced CORT levels only included body condition, but a more complex model including parental presence and maternal age had a lower AICc (ΔAICc = 1.174) and a higher AICc weight (AICc weight = 0.274 vs. 0153, Table 4b). These two competitive models were therefore considered. In the simplest model, stress-induced CORT levels were negatively correlated with body condition (estimate (mean 95% CI): -0.108 [-0.171; -0.045). In the more complex model, stress-induced CORT levels were positively associated with maternal age (estimate (mean 95% CI): 0.535 [0.017; 1.052], β = 0.295; Table 4b, Fig. 5), and negatively with body condition (estimate (mean 95% CI): -0.074 [-0.139; -0.009], β = -0.400; Table 4). Stress-induced CORT levels were also lower when a parent was present in the nest (estimate (mean 95% CI): -9.874 [-18.888; -0.859], β = 0.894; Table 4b, Fig. 5). However, stress-induced CORT levels were not linked with body size (Table 4b). Telomere length was not significantly associated with maternal age or body condition (Table 4c). However, telomere length was negatively correlated with tarsus length (estimate (mean 95% CI): -0.357 [-0.693; -0.020], β = -0.404; Table 4c).

Discussion

In this study, we showed that maternal age had an important and significant influence on reproductive behaviour and offspring performance. Specifically, older females bred and left their chick alone earlier. Importantly, we also showed that maternal age had an impact on offspring morphology and physiology, and ultimately, on chick survival. Importantly, these morphological effects were not found in young chicks (13 days old), and the influence of maternal age on growth seems to become apparent after that age only as the chicks grow and require an increasing amount of food/ energy. After 13 days, chicks from older females were larger, heavier, grew faster, and had a higher survival probability at the nest. Moreover, 13-days-old chicks had a higher sensitivity to stress, as shown by moderately higher stress-induced corticosterone levels. Altogether, these results demonstrate not only that younger mothers have lower reproductive performances, but also that maternal age affects the offspring phenotype with potential long-term consequences. Importantly, our parental sample size was only composed of young and middle-aged females (< 35 years old). Therefore, it was not possible to detect sign of senescence on reproductive output in this study [START_REF] Berman | Contrasted patterns of age-specific reproduction in long-lived seabirds[END_REF]. In addition, we specifically focused on adult females in this study and we did not consider the potential importance of paternal age. This decision resulted from practical reasons because we found more known-aged females than known-aged males in our study colony, but also from ecological reasons because female snow petrels are smaller than males. As such, they seem to be more constrained in their ability to deliver food to the offspring and they have a higher impact on reproductive performance than male snow petrels [START_REF] Barbraud | Early body condition and hatching success in the Snow Petrel Pagodroma nivea[END_REF]Barbraud et al. 1999).

Reproductive phenology, duration of the guarding period and offspring survival

Consistent with our prediction 1, we found that younger female snow petrels reproduced later. Accordingly, numerous studies have also reported that laying date or hatching date are negatively affected by parental age [START_REF] Perrins | The timing of birds' breeding seasons[END_REF][START_REF] Curio | Why de young birds reproduce less well[END_REF][START_REF] De Forest | The effect of age on timing of breeding and reproductive success in the Thick-billed murre[END_REF][START_REF] Cam | Apparent inferiority of first-time breeders in the Kittiwake: the role of heterogeneity among age classes[END_REF][START_REF] Verhulst | The timing of birds' breeding seasons: a review of experiments that manipulated timing of breeding[END_REF][START_REF] Blas | Age-related improvement in reproductive performance in a long-lived raptor: a cross-sectional and longitudinal study[END_REF][START_REF] Bauer | Chronological and biological age predict seasonal reproductive timing: an investigation of clutch initiation and telomeres in birds of known age[END_REF][START_REF] Reséndiz-Infante | Temporal changes in reproductive success and optimal breeding decisions in a long-distance migratory bird[END_REF]. In birds, and more specifically snow petrels, laying date and reproductive phenology are influenced by environmental conditions [START_REF] Barbraud | Early body condition and hatching success in the Snow Petrel Pagodroma nivea[END_REF][START_REF] Barbraud | Antarctic birds breed later in response to climate change[END_REF][START_REF] Dickey | Climatic effects on the breeding phenology and reproductive success of an arctic-nesting goose species[END_REF][START_REF] Verhulst | The timing of birds' breeding seasons: a review of experiments that manipulated timing of breeding[END_REF][START_REF] Moe | Climate change and phenological responses of two seabird species breeding in the high-Arctic[END_REF][START_REF] Descamps | Individual optimization of reproduction in a long-lived migratory bird: a test of the condition-dependent model of laying date and clutch size[END_REF][START_REF] Sauser | Sea ice and local weather affect reproductive phenology of a polar seabird with breeding consequences[END_REF]) and internal state (body condition: [START_REF] Bêty | Body condition, migration, and timing of reproduction in Snow Geese: a test of the conditiondependent model of optimal clutch size[END_REF][START_REF] Descamps | Individual optimization of reproduction in a long-lived migratory bird: a test of the condition-dependent model of laying date and clutch size[END_REF]stress physiology: Goutte et al. 2010).

In the snow petrel, [START_REF] Barbraud | Body size and determinants of laying date variation in the Snow Petrel Pagodroma nivea[END_REF] found that laying date was tightly connected to the duration of the pre-laying exodus, during which females forage at sea to improve their body condition. This suggests that younger females may be less able to acquire food and to build as quickly as older females the body reserves, which are required for egg laying.

In addition, we also reported that younger females guarded their chick for a longer period (prediction 2). To our knowledge, our study is the first to demonstrate that maternal age affects the duration of the guarding period in an altricial species. In petrels, the duration of the guarding phase is related to the environmental condition and to the quality of the parents [START_REF] Amundsen | Egg size and early nestling growth in the Snow Petrel[END_REF][START_REF] Tveraa | Body condition and parental decisions in the Snow Petrel (Pagodroma nivea)[END_REF][START_REF] Varpe | State-dependent parental care in the Antarctic petrel: responses to manipulated chick age during early chick rearing[END_REF]), but also to the chick's needs in terms of food provisioning and protection [START_REF] Varpe | State-dependent parental care in the Antarctic petrel: responses to manipulated chick age during early chick rearing[END_REF]; but see [START_REF] Goutte | Experimentally delayed hatching triggers a magnified stress response in a long-lived bird[END_REF]. Leaving a chick unattended can be beneficial because both parents can forage simultaneously at sea, increasing therefore chick provisioning (quantity and frequency, [START_REF] Catry | Factors affecting the solution of a parental dilemma in albatrosses: at what age should chicks be left unattended?[END_REF]). However, this may also entail some costs because the chick is left unguarded and is therefore more susceptible to inclement weather and/or predation [START_REF] Weathers | Thermoregulation in Antarctic fulmarine petrels[END_REF][START_REF] Catry | Factors affecting the solution of a parental dilemma in albatrosses: at what age should chicks be left unattended?[END_REF]. Older females may be better at provisioning their chick during the first days after hatching and their chicks may therefore reach earlier a body condition/size that allow them to thermoregulate. This could explain why older females guarded their chick for shorter periods. Unfortunately, our data did not allow us to test this hypothesis as the first morphometric measurements were recorded at day 13 (i.e., maximum length of the guarding period) for all the chicks and not at the end of the guarding period. This hypothesis is however not supported by the available data because we did not find any difference in body size and body condition at day 13. Instead, older females may be more experienced and better at estimating when the chick can be left alone without any major risk for its survival. Alternatively, older females may be in poorer condition, and as a consequence, they may have to leave the nest unguarded at an earlier age to replenish their body reserves [START_REF] Tveraa | Body mass and parental decisions in the Antarctic petrel Thalassoica antarctica: how long should the parents guard the chick?[END_REF]). However, this explanation is quite unlikely because previous studies have not found a relationship between age and body condition in this species (Angelier et al. 2007a[START_REF] Angelier | When do older birds better resist stress? A study of the corticosterone stress response in snow petrels[END_REF][START_REF] Goutte | Age and the timing of breeding in a long-lived bird: a role for stress hormones?[END_REF].

In line with our prediction 3, we found a strong positive correlation between offspring survival at the nest and maternal age, as previously reported in multiple bird species including the snow petrel (Angelier et al. 2007a;[START_REF] Sergio | Sequential settlement and site dependence in a migratory raptor[END_REF]). Although our sample size was too small to detect a link between phenology and offspring survival, our study confirms that offspring survival is linked to parental age, probably through the timing of reproduction, as previously found in numerous altricial species [START_REF] Blas | Age-related improvement in reproductive performance in a long-lived raptor: a cross-sectional and longitudinal study[END_REF][START_REF] Culina | Familiarity breeds success: pairs that meet earlier experience increased breeding performance in a wild bird population[END_REF] including the snow petrel [START_REF] Sauser | Sea ice and local weather affect reproductive phenology of a polar seabird with breeding consequences[END_REF].

Offspring growth, body size, and body condition

According to our fourth prediction, we found that younger mothers had smaller chicks (i.e., at 23 days old) compared to older ones, highlighting therefore that maternal age has an important impact on their offspring developmental conditions. Specifically, we found that the chicks from younger females grew slower and reached a lower body size 23 days after hatching (wing and tarsus length). Importantly, this impact of maternal age on body size was not apparent 13 days after hatching. This suggests that young females can sustain their offspring needs at the beginning of the developmental period, when the chick is small and cannot ingest large meals. However, the provisioning effort of young females may not be sufficient later as the chick becomes larger and requires increasing amounts of food, explaining the influence of maternal age on growth and body size when offspring reaches 23 days old. In other words, small differences in provisioning effort that are not apparent on day 13 may accumulate through the chick-rearing period, and become significant at a later stage only (i.e., day 23).

In our study, the condition of snow petrel chicks was not related to maternal age, suggesting that chicks from young females did not suffer from nutritional stress. Interestingly, we however found that the chicks from younger females grew slower and were smaller at 23 days old. This suggests that snow petrel chicks may maintain their body condition (a major determinant of post-fledging survival, [START_REF] Sauser | Increased sea ice concentration worsens fledging condition and juvenile survival in a pagophilic seabird, the Snow Petrel[END_REF] at the expense of their body size, which is at least partly developmentally determined (Barbraud et al. 1999). This contrasts with other studies, which have suggested that developing seabirds may prioritize growth at the expense of their condition and their survival (e.g., [START_REF] Harris | Breeding biology of the Manx Shearwater Puflnus pujinus[END_REF]. Interestingly, body size is closely associated with adult performance in this species: smaller snow petrels feed their chick less often and seem to be less efficient foragers (Barbraud et al. 1999[START_REF] Barbraud | Sexual segregation in a highly pagophilic and sexually dimorphic marine predator[END_REF]. Therefore, chicks from younger females may have lower post-fledging survival probabilities and reproductive performance later in life, although these hypotheses need to be explicitly tested in the future.

Offspring sensitivity to stress

As previously reported in this species [START_REF] Dupont | Home alone!" influence of nest parental attendance on offspring behavioral and hormonal stress responses in an Antarctic seabird, the snow petrel (Pagodroma nivea)[END_REF], we reported that the presence of a parent in the nest may mitigate the stress sensitivity of its chick. Specifically, snow petrel chicks had lower stress-induced CORT when a parent was present in the nest at the time of capture, 13 days after hatching (see [START_REF] Dupont | Home alone!" influence of nest parental attendance on offspring behavioral and hormonal stress responses in an Antarctic seabird, the snow petrel (Pagodroma nivea)[END_REF] for further details).

In addition, we found that stress-induced CORT levels seem to be affected by maternal age in our study although the effect size could be considered as moderate (β = 0.295). Specifically, chicks from older females have higher stressinduced CORT levels, suggesting that they have a higher adrenocortical stress sensitivity (prediction 5). Elevated stress-induced CORT levels are classically associated with a poor body condition and with nutritional stress in chicks [START_REF] Kitaysky | Corticosterone facilitates begging and affects resource allocation in the Black-legged kittiwake[END_REF][START_REF] Pravosudov | Effects of nutritional restrictions during post-hatching development on adrenocortical function in western scrub-jays (Aphelocoma californica)[END_REF][START_REF] Love | Plasticity in the adrenocortical response of a free-living vertebrate: the role of pre-and post-natal developmental stress[END_REF][START_REF] Angelier | Ontogeny and individual heterogeneity of the corticosterone stress response in a wild altricial seabird, the snow petrel (Pagodroma nivea)[END_REF]. Our result on stress-induced CORT levels is therefore surprising because we did not find any relationship between maternal age and offspring body condition. Interestingly, this pattern is not equivocal since other studies report no or opposite effects of nutritional stress or poor body condition on stress-induced CORT levels [START_REF] Wada | Ontogeny and individual variation in the adrenocortical response of zebra finch (Taeniopygia guttata) nestlings. 1 3[END_REF]. For example, in the tufted puffin (Fratercula cirrhata), chicks are known to suppress Hypothalamic-Pituitary-Adrenal (HPA) axis activity and to have therefore lower stress-induced CORT levels when facing nutritional stress [START_REF] Kitaysky | The adrenocortical response of tufted puffin chicks to nutritional deficits[END_REF]. Then, the observed reduced CORT stress sensitivity in 13-days-old 1 3 snow petrels produced by young females may be interpreted as a way to protect the chick against the detrimental effect of elevated circulating CORT levels (reviewed in [START_REF] Sapolsky | How do glucocorticoids influence stress responses? Integrating permissive, suppressive, stimulatory, and preparative actions[END_REF]. However, it remains unclear why older females produce chicks with higher stress-induced CORT levels. In laboratory bird species, the corticosterone stress response increases with age as the chicks develop [START_REF] Wada | Development of stress reactivity in white-crowned sparrow nestlings: total corticosterone response increases with age, while free corticosterone response remains low[END_REF][START_REF] Wada | Ontogeny and individual variation in the adrenocortical response of zebra finch (Taeniopygia guttata) nestlings. 1 3[END_REF] and higher stress-induced corticosterone levels could therefore reflect a more developed HPA axis, and therefore a more advanced developmental state, in the chicks from older mothers. Finally, and importantly, CORT levels were unrelated to offspring survival, questioning therefore the relevance of this physiological marker of fitness in snow petrel chicks. Further studies are definitely needed to better understand how stress-induced CORT levels relate to developmental constraints and offspring survival.

Importantly, there is increasing evidence that the adrenocortical stress response is repeatable among life-history stages [START_REF] Wada | Adrenocortical responses in zebra finches (Taeniopygia guttata): individual variation, repeatability, and relationship to phenotypic quality[END_REF][START_REF] Grace | Corticosterone stress response shows long-term repeatability and links to personality in free-living Nazca boobies[END_REF][START_REF] Vitousek | Stress and success: individual differences in the glucocorticoid stress response predict behavior and reproductive success under high predation risk[END_REF][START_REF] Small | Sex differences in the long-term repeatability of the acute stress response in long-lived, free-living Florida scrub-jays (Aphelocoma coerulescens)[END_REF][START_REF] Jimeno | Effects of developmental conditions on glucocorticoid concentrations in adulthood depend on sex and foraging conditions[END_REF], meaning that snow petrel chicks from older females may also have higher stress-induced CORT levels later in life. Although the potential benefits of mounting a strong stress response remains debated [START_REF] Breuner | In search of relationships between the acute adrenocortical response and fitness[END_REF][START_REF] Angelier | Importance of the glucocorticoid stress response in a changing world: theory, hypotheses and perspectives[END_REF][START_REF] Vitousek | Hormones and fitness: evidence for trade-offs in glucocorticoid regulation across contexts[END_REF], having elevated stress-induced CORT levels may promote survival under some situations [START_REF] Angelier | What factors drive prolactin and corticosterone responses to stress in a long-lived bird species (Snow Petrel, Pagodroma nivea)?[END_REF]). Our study shows for the first time that maternal age can affect offspring CORT stress sensitivity and future studies are now needed to fully understand the fitness consequences of such phenotypic plasticity.

Offspring telomere length

Contrary to our sixth prediction and to other studies (e.g., [START_REF] Asghar | Maternal and genetic factors determine early life telomere length[END_REF][START_REF] Dupont | Young parents produce offspring with short telomeres: a study in a long-lived bird, the Black-browed Albatross (Thalassarche melanophrys)[END_REF][START_REF] Eisenberg | Paternal age at conception effects on offspring telomere length across species-what explains the variability?[END_REF], we did not find any relationship between maternal age and offspring telomere length. Other studies also failed to find such an effect of parental age on offspring telomere in vertebrates (e.g., [START_REF] Noguera | Experimental demonstration that offspring fathered by old males have shorter telomeres and reduced lifespans[END_REF][START_REF] Belmaker | The environmental and genetic determinants of chick telomere length in Tree Swallows (Tachycineta bicolor)[END_REF][START_REF] Van Lieshout | Estimation of environmental, genetic and parental age at conception effects on telomere length in a wild mammal[END_REF], suggesting that the influence of parental age on the telomere length of the progeny varies between species and depends if we consider maternal age or paternal age. Indeed, previous studies in humans have suggested that paternal age could have a stronger impact on telomere length than maternal age [START_REF] Eisenberg | Paternal and grandpaternal ages at conception and descendant telomere lengths in chimpanzees and humans[END_REF]. Therefore, maternal age might only be related to offspring telomere length if paternal and maternal age are strongly correlated although this hypothesis has never been explicitly tested in wild vertebrates to our knowledge. In our study, we also did not find any strong relationship between body condition and telomere length in 13-days-old chicks. We however found a negative association between telomere length and tarsus length at this age, suggesting that growth may affect telomere attrition and telomere length in snow petrel chicks. Indeed, developmental constraints experienced by the chicks have been shown to affect the allocation of resources to both growth and telomere maintenance [START_REF] Boonekamp | Nestling telomere shortening, but not telomere length, reflects developmental stress and predicts survival in wild birds[END_REF][START_REF] Vedder | Telomere attrition and growth: a life-history framework and case study in common terns[END_REF][START_REF] Monaghan | Somatic growth and telomere dynamics in vertebrates: relationships, mechanisms and consequences[END_REF]. However, in our study, most of the effects of maternal age on body size were not apparent when the chicks were 13 days old and they appeared at an older age (e.g., 23 days old). This could explain why we did not find any strong relationship between telomere length and maternal age in our study. In future studies, it would be relevant to measure telomere length several times during the development to test whether the influence of maternal and paternal age on telomere length exacerbates as the chick grows. Actually, we aimed to sample the chicks 32 days after hatching in our study, but the colony was no longer accessible later in the season because of successive heavy snowstorms.

Finally, we found that telomere length was a reliable predictor of survival in snow petrel chicks: 13-days-old chicks with shorter telomere had a lower survival probability until 23 days old. This link between telomere length and survival at early stage has already been found in an increasing number of studies [START_REF] Quque | Contrasting associations between nestling telomere length and pre and postnatal helpers' presence in a cooperatively breeding bird[END_REF], and our result supports the idea that telomere length is a relevant proxy of individual quality both at juvenile and adult stages [START_REF] Angelier | Is telomere length a molecular marker of individual quality? Insights from a long-lived bird[END_REF][START_REF] Bichet | Telomere length is repeatable, shortens with age and reproductive success, and predicts remaining lifespan in a longlived seabird[END_REF].

Conclusion

Our study shows that maternal age had an important influence on reproductive performance and offspring morphology and physiology in an Antarctic long-lived bird species. Further studies should now aim to examine the influence of both maternal and paternal ages on offspring physiology to better understand how they contribute to offspring quality. Such studies should also investigate the consequence of such physiological modifications on the lifelong performance of the offspring (recruitment and reproduction).

3

Funding Fieldwork was financially and logistically supported by the Institut Paul-Emile Victor (IPEV Project 109) and the Terres Australes et Antarctiques Françaises. S.M. Dupont was supported by a grant from the Conseil Général des Deux-Sèvres and the Région Nouvelle-Aquitaine.

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Fig. 1

 1 Fig. 1 Influence of maternal age on a hatching date and b the duration of the guarding period in snow petrels. The solid lines represent the predicted relationships between maternal age and these two variables. The dotted lines represent the 95% confidence intervals for these relationships

Fig. 2

 2 Fig. 2 Influence of maternal age on offspring survival probability from 13 to 23 days after hatching in snow petrel chicks. Box-andwhisker plots represent the data: the top and bottom of the boxes represent the first and last quartiles, respectively; the line across the box represents the median. The whiskers represent the 5th and 95th percentiles, and the circles represent outliers. Significant difference is indicated by an asterisk (*P < 0.05)

Fig. 3 Fig. 4

 34 Fig. 3 Influence of maternal age effect on offspring body size in 13-days-old (fill circles) and 23-days-old (fill triangles) snow petrel chicks. The solid line represents the positive/significant relationship between maternal age and offspring tarsus length in 23-days-old chicks

Fig. 5

 5 Fig. 5 Influence of maternal age effect on offspring stress-induced CORT levels in 13-days-old snow petrel chicks. Filled and open symbols represent alone chicks and attended chicks, respectively. The solid and the broken lines represent the relationships between maternal age and offspring stress-induced CORT levels for alone and attended chicks, respectively

Table 1

 1 Biological assumptions of the study and associated model selections Sample sizes differ because of chick mortality through the study period and because a sub-sample of 13-days-old chicks were monitored for physiological parameters

	Biological assumption	Dependent variables	Independent variables	n
	Effect of maternal age on hatching date	Hatching date	Age	45
	Effect of maternal age on the guarding period	Guarding period	Age	42
	Effect of maternal age on survival	Survival	Age, hatching date, guarding period	41
	Effect of the phenotype of the chick on survival	Survival	Body size, body condition	41
	Effect of the physiology of the chick on survival	Survival	Telomere, corticosterone	23
	Effect of maternal age on the phenotype of the chick (13)	Body size, body condition	Age, parental presence	41
	Effect of maternal age on the phenotype of the chick (23)	Body size, body condition	Age	35
	Effect of maternal age on the growth of the chick	Growth, change in body condition	Age	35
	Effect of maternal age on the physiology of the chick

Table 2 Influence

 2 The three best models and the null model are represented. Values for difference in AICc values (ΔAICc) were computed by subtracting the minimum AICc from all candidate model AICc. K and weight refer to the number of parameters and to AICc weight, respectively

	of (a) maternal age, hatching date,		Dependent variable	Independent variables	K	AICc	ΔAICc	Weight
	and the duration of the guarding period; (b) body condition and body size of 13-days-old chicks; (c) physiological variables	a	Survival of the chick	Age Age, hatching date Age, guarding duration	2 3 3	31.58 33.70 33.91	0.000 2.12 2.32	0.529 0.184 0.166
	(corticosterone (CORT) levels			Null	1	36.24	4.66	0.052
	and telomere length; on the survival of the chick (from 13 to 23 days old)	b	Survival of the chick	Null Body condition Body size, body condition	1 2 2	36.24 36.53 36.76	0.000 0.290 0.522	0.300 0.260 0.231
				Body size	3	36.96	0.721	0.209
		c	Survival of the chick	Telomere	2	15.31	0.000	0.396
				Telomere, baseline CORT	3	15.80	0.491	0.310
				Telomere, stress-induced CORT	3	17.86	2.55	0.110
				Null	1	36.24	20.93	< 0.001

Table 3

 3 Influence of maternal age and parental presence in the nest on (a) body size and (b) body condition in 13-days-old snow petrel chicks The three best models and the null model are represented. Values for difference in AICc values (ΔAICc) were computed by subtracting the minimum AICc from all candidate model AICc. K and weight refer to the number of parameters and to AICc weight, respectively

		Dependent variable	Independent variables	K	AICc	ΔAICc	Weight
	a	Body size (13 days old)	Null	1	117.46	0.000	0.552
		(tarsus length)	Parental presence	3	119.43	1.98	0.205
			Age	2	119.70	2.25	0.179
			Age, parental presence	4	121.78	4.33	0.063
	b	Body condition (13 days old)	Parental presence	2	111.19	0.000	0.725
			Age, parental presence	3	113.47	2.28	0.232
			Null	1	117.46	6.27	0.032
			Age	2	119.41	8.22	0.012

Table 4

 4 Influence of maternal age, body size, body condition, and parental presence in the nest (for corticosterone levels only) on (a) baseline and (b) stress-induced corticosterone levels and (c) telomere length in 13-days-old snow petrel chicks The three best models and the null model are represented. Values for difference in AICc values (ΔAICc) were computed by subtracting the minimum AICc from all candidate model AICc. K and weight refer to the number of parameters and to AICc weight, respectively

		Dependent variable	Independent variables	K AICc ΔAICc Weight
	a	Baseline corticosterone	Body condition, body size	3 90.92 0.000 0.334
			Body condition	2 91.38 0.453 0.267
			Parental presence, body condition	3 93.58 2.66	0.089
			Null	1 97.61 6.68	0.012
	b	Stress-induced corticosterone Age, parental presence, body condition 4 168.38 0.000 0.274
			Body condition	2 169.55 1.17	0.153
			Parental presence, body condition	3 169.73 1.35	0.139
			Null	1 176.94 8.56	0.004
	c	Telomere	Body size	2 63.42 0.000 0.357
			Body condition, body size	3 65.02 1.60	0.160
			Age, body size	3 65.21 1.80	0.145
			Null	1 65.23 1.81	0.144

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Acknowledgements

We are indebted to A. Baduel and C. Sauser for their assistance in the field. We thank C. Ribout for her expertise and technical help in molecular sexing. We thank the two reviewers and the Handling editor who helped us improving this manuscript.

Data availability

All data produced from this study will be provided as a supplementary file.

Code availability Not applicable.

Declarations

Supplementary Information

The online version contains supplementary material available at https:// doi. org/ 10. 1007/ s00442-023-05451-5.

Author contribution statement SMD, CB, OC, HW and FA originally formulated the idea, MP and CP generated molecular analyses, KD and CP achieved data curation, SMD and FA performed statistical analyses, SMD and FA wrote the manuscript; other authors provided editorial advice.

Conflict of interest

Authors have no conflicts of interest to declare.

Ethics approval

Consent to participate Not applicable.

Consent for publication Not applicable.

Authors and Affiliations

Sophie M. Dupont


T Sim

R Alami

Planning sensor-based motions for mobile robot navigation

Motion planning and control are two important aspects for mobile robot navigation. They are often considered as two separate phases, leading to a lack of robustness when experimented in real world settings. The objective of the presented approach is to bridge the gap between motion planning and motion control. Motion planning is performed in terms of closed-loop sensor-based primitives rather than in terms of a geometric path whose execution is more sensitive to perception and motion uncertainties. Experiments performed with the Hilare2 mobile robot show the e ectiveness of the algorithms for achieving robust navigation in a priori known indoors environments.

Introduction

Motion planning and control are two important aspects required for mobile robot autonomous navigation. However, they are frequently considered as two separate phases. Many motion planning techniques have been proposed to produce a collision-free and feasible path avoiding the obstacles of the workspace (see 6] for a survey). Motion control then consists in making the robot follow this path, possibly using a potential-eld based method [START_REF] Hait | Robust motion planning for rough terrain navigation[END_REF][START_REF] Khatib | Real-time obstacle avoidance for manipulators and mobile robots[END_REF] for reacting to unexpected obstacles sensed during the execution. Such decoupled approach su ers from a lack of robustness when experimented in real world settings since the execution of the planned trajectory is conditioned by several sources of uncertainties.

Control and sensing errors are particularly signicant in the context of mobile robot navigation. Indeed, mobile robots are not generally equipped with an absolute positioning system and are subject to cumulative dead-reckoning errors. Such inaccuracies in localizing the robot with respect to its environment may lead to execution failures. To overcome the uncertainty accumulated during the motions, the robot can be equipped with environment sensors that provide additional information by identifying appropriate features of the workspace. Localization techniques (e.g. 2, 8]) can be applied to reduce the uncertainty of the esti-Figure 1: Motion plans using odometry based commands (a), landmark localizations (b) and wall-following commands (c) mated con guration. One may also use sensor-based motion commands which are more tolerant to errors than classical position-controlled commands. Sensorbased control generally considers the development of speci c primitives (e.g., wall-following using ultrasonic sensors 10] or vision 13]), without connection with a planning component. In situations where much is known in advance on the environment, it may be preferable to combine such sensor-based commands with a planning component reasonning onto the uncertainty possibly accumulated during the motions and onto the capacities of the available sensing functions. Such component may allow to use the available knowledge to produce robust motions plans that will reliably guide the robot towards its goal.

The paper illustrates this approach with the algorithms that have been developped and integrated onto the Hilare2 mobile robot for achieving robust navigation in an a priori known o ce-like environment 11]. The robustness comes from the link between a planning component 1] reasoning onto uncertainties and sensor-based motion control 10].

Motion primitives

We rst introduce the several types of motion primitives that are considered both at planning and execution level:

Free space motions: the move primitives correspond to classical position-controlled commands using odometry. The position error is de ned as a function of the distance covered by the robot.

The move landmark primitive is controlled by the measure provided by an external sensor (eg. camera) which allows to maintain the position error to the sensor accuracy.

Guarded motions: move to contact executes a straight line motion stopped when an obstacle is detected. This allows to reset the position error along the direction orthogonal to the edge. A parallelize primitive can then be used to align the robot with a wall.

Sensor-based motions: wall follow is a com- posed sensor-based command for following a succession of walls. Several events (corner detection, traveled distance...) are checked during its execution. This primitive only accumulates error in the direction of the followed wall because of the use of the odometric sensor to determine the covered distance. However, this error can be reduced when corners are detected during the wall following.

Robust motion strategies

Given a model of the uncertainty accumulated by the motion primitives de ned above, we consider the problem of computing a motion strategy composed by a sequence of such primitives. A robust motion strategy should guarantee that the robot, starting from an uncertain initial position, can reliably reach its goal with an error lower than a pre-speci ed value, despite the errors accumulated by the motion commands. It should also contain the corrective sensor-based motions needed to reduce the error (e.g. by entering in landmark regions or by detecting some walls or corners in the environment). Figure 2 shows the uncertainty evolution for di erent motion strategies that may be used to solve the same planning problem. Free space motions (strategy 1) would not allow in this example to connect the \Init" and \Goal" positions since the accumulated error would be too important to safely pass the doorway. Strategy 2 solves the problem by traversing a landmark region (within which the uncertainty remains bounded) whereas strategy 3 illustrates the evolution of uncertainty using wall-following motions.

We proposed several algorithms for solving di erent instances of such problem (related problems were also adressed in several other works -e.g. [START_REF] Sim Eon | Planning robust motion strategies for a mobile robot in a polygonal world[END_REF][START_REF] Latombe | Robot Motion Planning[END_REF][START_REF] Leonard | Mobile robot localization by tracking geometric beacons[END_REF]12]). The algorithm 14] produces a sequence of follow-wall commands, based onto an analytic computation of reachability regions in the parameter space of these commands. The landmark-based planner 3] developped in the context of outdoors navigation takes into account possible error reduction by introducing movelandmark commands inside the motion plan. The planning algorithm 1] described below and that was integrated onto our Hilare2 robot o ers more powerfull capabilities: it is able , whenever possible to navigate without localizing the robot when the task does not impose it (free-space motions may be faster than following a wall), and also allows to combine wallfollow and move-landmark commands for error reduction.

Planning algorithm

The planner 1] considers a polygonal description of the obstacles and also a set of landmark regions where the robot can be relocalized in the environment. The algorithm is based on the propagation of a numerical potential modeling the uncertainty evolution and on a geometric analysis of the reachability of environments features (walls or landmark regions). During the propagation of the potential, collisions are checked between the obstacles and the robot shape grown by the current uncertainty. The robot is approximated by its enclosing disk during the free-space motions. The exact shape is only considered during the wall-following commands for which the robot has to be aligned with the wall. This allows to solve constrained problems (eg. crossing of narrow doorways) where the circular approximation would be too conservative, while only considering a two-dimensional conguration space. When the propagation reaches a position which may collide with a given edge because of a too large uncertainty, a geometric visibility test is performed to check if a guarded motion is guaranteed to end onto this edge (Fig. 4). When this test succeeds, the algorithm starts from this position a propagation adapted to the uncertainty model of the wall follow commands (Fig. 3-a). Similarly, a propagation adapted to the move landmark command is started at positions where the robot grown by its current uncertainty is included in a landmark region (Fig. 3-b). Finally, once the goal position is reached with an admissible uncertainty, the motion plan is deduced by backchaining con gurations from the goal to the initial position. The strategies returned by the planner either minimize the distance crossed by the robot (see Fig. 5-left, ignoring in this case relocalizations when the task does not impose it) or the nal uncertainty (Fig. 5-right).

1 B not visible 1 B 2 B B 1 B 1 B visible 1 A d A A

Experimentations

This section illustrates some of the experiments that have been performed in our laboratory to demonstrate the robustness of the approach. The Hilare2 mobile robot is equipped with a belt of 32 sonars and a laser range nder. Sonar data are used for the wall-follow, move to contact and parallelize actions. The laser is used for edge detection and corner matching during a wall-following.

The sensor-based motion primitives are de ned at the execution level by speci c functions called Task-Potential functions [START_REF] Valle | Evaluating motion strategies under non deterministic or probabilistic uncertainties in sensing and control[END_REF][START_REF] Khatib | An extended potentiel eld approach for mobile robot sensor-based motions[END_REF]. The task potential is a non convex potential function that allows to express a sensor-based action in a space parametrized in terms of the sensor output variables. The execution of the task corresponds to a gradient descent of a global potential composed linearly from several elementary potential functions. The experiment of gure 7 corresponds to a case where the wall cannot be reliably reached with openloop actions, because of their uncertainty evolution.

The motion plan rst reduces the position error by using the landmark zone before seeking the contact with the wall. Finally, a more signi cant task is shown in Figure 8. Starting with a rough estimate of its initial position (A) inside the laboratory, the robot has to cross a constrained doorway and then to move in a long corridor in order to reach the goal (B), and nally to go back. to the initial position (A). The robot executed this 60 meters roundtrip from the motion plan computed by the planning component, and shown in Figure 8. One can note that this navigation task would have been hardly feasible with open-loop motions because of the important traveled distance in a rather constrainted environement. This task, performed with our sensorbased planning and control algorithms, was successful almost at every execution.

Figure 2 :

 2 Figure 2: Example of motion strategies

Figure 3 :

 3 Figure 3: Numerical potential with possible error reduction by following a wall (a) or entering in landmark regions ( b)

Figure 4 :

 4 Figure 4: Visibility test for guarded motions

Figure 5 :

 5 Figure 5: Examples of computed strategies

Figure 6 Figure 7 :

 67 Figure 6: Experiment 1 Figure 6 shows the trace of the motion plan executed by Hilare2 during one of the experiments. Given the rough estimate of the initial position, the goal is not reachable using a direct open-loop free-space motion. The planner strategy was to generate several sensorbased actions (move to contact, follow wall until vertex) to reduce the uncertainty, then the goal could be reached with open-loop actions. © Oper