Criscuolo Particle

François Suffix

Claire Suffix

Rita Suffix

Martin Quque

Matthieu Paquet

Sandrine Zahn

Frank Théron

Bruno Faivre

• Cédric Sueur

François Criscuolo

Claire Doutrelant

Rita Covas

Kevin D Matson

Contrasting associations between nestling telomere length and pre and postnatal helpers' presence in a cooperatively breeding bird

Keywords: separated by '-') Sociable weaver -Cross-fostering -Offspring -Early environment -Survival Sociable weaver, Cross-fostering, Ofspring, Early environment, Survival

Studies on cooperative breeders have addressed the effects of non-breeding 'helpers' on reproduction and parental care, but the consequences for offspring physiology and long-term survival are less understood. Helpers are expected to benefit offspring, but their presence can also lead to decreased pre-or post-natal parental reproductive effort. To examine whether prenatal and postnatal helpers influence offspring condition, we conducted a whole-clutch cross-fostering experiment in sociable weavers (Philetairus socius) that altered the nestlings' social environment (presence/absence of helpers). We tested whether relative telomere length (rTL), an indicator of somatic maintenance, was influenced by prenatal and/or postnatal presence of helpers 9 and 17 days after hatching, and whether rTL predicted long-term survival. Nine days after hatching, we found an overall positive effect of postnatal helpers on rTL: for nestlings with prenatal helpers, a reduction in the number of helpers post-hatch was associated with shorter telomeres, while nestlings swapped from nests without helpers to nests with helpers had a larger rTL. However, when prenatal helpers were present, an increased number of helpers after hatching led to shorter telomeres. Nineday old chicks with longer rTL tended to be more likely to survive over the 5 years following hatching. However, close to fledging, there was no detectable effect of the experiment on rTL and no link between rTL and survival. This experimental study of a wild cooperative breeder, therefore, presents partial support for the importance of the presence of helpers for offspring rTL and the link between early-life telomere length and long-term survival.

U N C O R R E C T E D P R O O F

Introduction

In iteroparous species, individuals are expected to maximize their lifetime reproductive success through trade-ofs between the investments in current reproduction vs. survival and future reproduction [START_REF] Stearns | The evolution of life history traits: a critique of the theory and a review of the data[END_REF]. For egg-laying species, females may vary the allocation of nutrients, antibodies, or other substances to eggs, thereby inluencing the environment in which their ofspring will develop. This allocation is in turn inluenced by the mother's breeding environment, which is expected to be an indication of the environment in which the ofspring will develop. In agreement, studies have shown that when females can anticipate the conditions experienced during reproduction they can inluence traits such as egg size (e.g. [START_REF] Fox | Egg size plasticity in a seed beetle: an adaptive maternal efect[END_REF][START_REF] Taborsky | Mothers determine ofspring size in response to own juvenile growth conditions[END_REF][START_REF] Vijendravarma | Efects of parental larval diet on egg size and ofspring traits in Drosophila[END_REF], and hormonal investment [START_REF] Groothuis | Revisiting mechanisms and functions of prenatal hormone-mediated maternal efects using avian species as a model[END_REF], and these traits can correlate with ofspring survival or behavior (e.g. [START_REF] Krist | Egg size and ofspring quality: a meta-analysis in birds[END_REF]Paquet et al. 2015a).

Among the environmental efects experienced by females and their developing ofspring, sociality has been receiving increasing attention (e.g. [START_REF] Russell | Reduced egg investment can conceal helper efects in cooperatively breeding birds[END_REF][START_REF] Russell | Maternal investment tactics in superb fairy-wrens[END_REF][START_REF] Dixit | The relationship between egg size and helper number in cooperative breeders: a meta-analysis across species[END_REF]. In cooperatively breeding species, sexually mature non-breeding individuals-called 'helpers'-assist in raising the ofspring of others by bringing additional food to the nest and performing other tasks such as territory defense [START_REF] Cockburn | Evolution of helping behavior in cooperatively breeding birds[END_REF]. The presence of these helpers is therefore thought to improve the breeding conditions experienced by females and/or ofspring, and studies on several species have generally shown that helper presence is associated with improved juvenile condition and survival (e.g. [START_REF] Ridley | Factors afecting ofspring survival and development in a cooperative bird: social, maternal and environmental efects[END_REF][START_REF] Kingma | Multiple beneits of cooperative breeding in purple-crowned fairy-wrens: a consequence of idelity?[END_REF][START_REF] Brouwer | Helpers at the nest improve late-life ofspring performance: evidence from a longterm study and a cross-foster experiment[END_REF][START_REF] Preston | Adult helpers increase the recruitment of closely related ofspring in the cooperatively breeding rileman[END_REF][START_REF] Tanaka | Helpers increase the reproductive success of breeders in the cooperatively breeding cichlid Neolamprologus obscurus[END_REF]. Breeding females may respond to this improvement in reproductive conditions by either maintaining their investment in eggs or food provisioning [START_REF] Clutton-Brock | Efects of helpers on juvenile development and survival in meerkats[END_REF][START_REF] Doerr | Positive efects of helpers on reproductive success in the brown treecreeper and the general importance of future beneits[END_REF][START_REF] Lejeune | Male and female helper efects on maternal investment and adult survival in redwinged fairy-wrens[END_REF], or decreasing it [START_REF] Crick | Load-lightening in cooperatively breeding birds and the cost of reproduction[END_REF][START_REF] Santos | Load lightening in southern lapwings: group-living mothers lay smaller eggs than pair-living mothers[END_REF][START_REF] Dixit | The relationship between egg size and helper number in cooperative breeders: a meta-analysis across species[END_REF], thereby reducing their cost of reproduction and increasing their survival and future reproduction. Reduction in maternal investment should then be compensated by the additional food brought by helpers [START_REF] Russell | Maternal efects in cooperative breeders: from hymenopterans to humans[END_REF]. The direction and magnitude of the response are expected to be inluenced by the species' life-history strategy and especially by the efects of maternal investment on mother's survival prospects and chances of breeding successfully in the future [START_REF] Russell | Maternal efects in cooperative breeders: from hymenopterans to humans[END_REF]. In birds, cooperatively breeding species tend to be long-lived [START_REF] Arnold | Cooperative breeding in birds: a comparative test of the life history hypothesis[END_REF][START_REF] Downing | Sex, long life and the evolutionary transition to cooperative breeding in birds[END_REF], and for long-lived species, maximization of lifetime reproductive success was suggested to be more eiciently achieved through increasing the number of breeding events in life than through increased investment in each breeding event [START_REF] Ghalambor | Fecundity-survival trade-ofs and parental risk-taking in birds[END_REF][START_REF] Drent | The prudent parent: energetic adjustments in avian breeding[END_REF][START_REF] Reid | Age-speciic reproductive performance in red-billed choughs Pyrrhocorax pyrrhocorax: patterns and processes in a natural population[END_REF], In agreement, a recent meta-analysis on 10 cooperatively breeding birds highlighted a tendency for mothers to reduce egg size in larger groups in most species studied [START_REF] Dixit | The relationship between egg size and helper number in cooperative breeders: a meta-analysis across species[END_REF]but see Fortuna et al. 2021).

It is less clear whether such diferential maternal investments translate into diferences in the condition and survival of ofspring and what is the relative inluence of the pre-and post-natal environment. For example, in birds, there are indications that larger eggs are positively associated with nestling's body size, growth and survival [START_REF] Krist | Egg size and ofspring quality: a meta-analysis in birds[END_REF]). However, these associations could arise from genetic and hormonal efects of parents [START_REF] Morrison | Cross-fostering reveals sources of variation in innate immunity and hematocrit in nestling tree swallows Tachycineta bicolor[END_REF][START_REF] Voillemot | Efects of brood size manipulation and common origin on phenotype and telomere length in nestling collared lycatchers[END_REF][START_REF] Weber | Pre-and postnatal efects of experimentally manipulated maternal corticosterone on growth, stress reactivity and survival of nestling house wrens[END_REF], and/ or from rearing conditions independently from parental phenotype [START_REF] Bize | Covariation between egg size and rearing condition determines ofspring quality: an experiment with the alpine swift[END_REF][START_REF] Velando | Male coloration and chick condition in blue-footed booby: a cross-fostering experiment[END_REF]. From the ofspring's perspective, the presence of helpers can be associated with weaker prenatal maternal egg investment [START_REF] Russell | Reduced egg investment can conceal helper efects in cooperatively breeding birds[END_REF][START_REF] Paquet | Maternal efects in relation to helper presence in the cooperatively breeding sociable weaver[END_REF]Paquet et al. , 2015a;;[START_REF] Langmore | Egg size investment in superb fairy-wrens: helper efects are modulated by climate[END_REF]) but identical or higher total feeding rate, as more carers are present [START_REF] Sappington | Breeding biology of house sparrows in North Mississippi[END_REF][START_REF] Wilkinson | Efect of helpers on the feeding rates of nestlings in the chestnut-bellied starling Spreo pulcher[END_REF][START_REF] Clarke | Cooperative breeding by the Australian bell miner Manorina melanophrys Latham: a test of kin selection theory[END_REF][START_REF] Hunter | Cooperative breeding in purple gallinules: the role of helpers in feeding chicks[END_REF]. Higher levels of care can lead to increased growth rate and potentially better condition or higher body mass at ledging, and thus increased likelihood to survive the irst few months after ledging [START_REF] Russell | Reduced egg investment can conceal helper efects in cooperatively breeding birds[END_REF][START_REF] Canestrari | Helpers at the nest compensate for reduced maternal investment in egg size in carrion crows[END_REF][START_REF] De Loock | Cooperative breeding shapes post-ledging survival in an Afrotropical forest bird[END_REF]. The prenatal and postnatal efects of helpers' presence can thus exert opposite inluences on nestling itness. Studies of maternal efects concerning the social environment, therefore, need to investigate the inluence of these two distinct environments. This requires (i) identifying meaningful proxies of ofspring itness and (ii) conducting experiments to separate the inluence of the pre-and post-natal environments.

Meaningful proxies of ofspring condition should strongly correlate with ofspring survival. Telomeres are repeated sequences at the ends of eukaryotic chromosomes. Replication leads to the shortening of the telomeric DNA sequence at each cell division, and beyond a certain number of cell division, telomeres become too short, triggering cell replicative senescence, which participates in the senescence of the whole organism [START_REF] Tchkonia | Cellular senescence and the senescent secretory phenotype: therapeutic opportunities[END_REF]. Consequently, telomeres became increasingly used as predictors of agerelated survival. Telomere length (TL) and/or telomere shortening rate have been shown to predict adult survival in numerous studies involving bird species [START_REF] Pauliny | Age-independent telomere length predicts itness in two bird Species[END_REF][START_REF] Bize | Telomere dynamics rather than age predict life expectancy in the wild[END_REF][START_REF] Salomons | Telomere shortening and survival in free-living corvids[END_REF][START_REF] Heidinger | Telomere length in early life predicts lifespan[END_REF][START_REF] Barrett | Telomere length and dynamics predict mortality in a wild longitudinal study[END_REF][START_REF] Boonekamp | Nestling telomere shortening, but not telomere length, relects developmental stress and predicts survival in wild birds[END_REF]). Both ecological [START_REF] Geiger | Catching-up but telomere loss: half-opening the black box of growth and ageing trade-of in wild king penguin chicks[END_REF][START_REF] Stier | Starting with a handicap: phenotypic diferences between early-and late-born king penguin chicks and their survival correlates (D Costa, Ed)[END_REF][START_REF] Salmón | Urban environment shortens telomere length in nestling great tits Parus major[END_REF][START_REF] Spurgin | Spatio-temporal variation in lifelong telomere dynamics in a long-term ecological study[END_REF]) and social [START_REF] Hall | Telomere loss in relation to age and early environment in long-lived birds[END_REF][START_REF] Nettle | An experimental demonstration that early-life competitive disadvantage accelerates telomere loss[END_REF][START_REF] Hammers | Breeders that receive help age more slowly in a cooperatively breeding bird[END_REF]) environments may increase or decrease TL (see [START_REF] Dugdale | Heritability of telomere variation: it is all about the environment![END_REF] for a review of the environment inluence on vertebrate telomere length). This inluence of ecological and social environment on TL may be efective very early in an individual's life, even before birth. For example, in birds, unstable incubation temperature [START_REF] Stier | Pace and stability of embryonic development afect telomere dynamics: an experimental study in a precocial bird model[END_REF], predator cues during embryonic development [START_REF] Noguera | Reduced telomere length in embryos exposed to predator cues[END_REF], increased clutch size [START_REF] Noguera | Gull chicks grow faster but lose telomeres when prenatal cues mismatch the real presence of sibling competitors[END_REF], or embryonic exposure to corticosterone [START_REF] Haussmann | Embryonic exposure to corticosterone modiies the juvenile stress response, oxidative stress and telomere length[END_REF]) are all factors associated with shorter telomeres in nestlings. Although not all studies have established a clear link between telomere length and longevity or survival (e.g. [START_REF] Beaulieu | Oxidative status and telomere length in a long-lived bird facing a costly reproductive event[END_REF][START_REF] Caprioli | Nestling telomere length does not predict longevity, but covaries with adult body size in wild barn swallows[END_REF][START_REF] Reichert | Increased brood size leads to persistent eroded telomeres[END_REF], the general trend in birds, mammals and reptiles is towards a consistent positive association between long telomeres and survival [START_REF] Wilbourn | The relationship between telomere length and mortality risk in non-model vertebrate systems: a meta-analysis[END_REF]. Taken together these studies support the use of telomeres as reliable indicators of longevity and/or individual quality, sensitive to early ecological and social stress, especially when measured during early life in birds [START_REF] Eastwood | Early-life telomere length predicts lifespan and lifetime reproductive success in a wild bird[END_REF]. In this study, we conducted a cross-fostering experiment to investigate how the pre-and post-natal social environments inluence ofspring condition, measured by relative telomere length (rTL). In addition, we controlled for a potential trade-of suggested in the literature (e.g. reviewed in [START_REF] Monaghan | Somatic growth and telomere dynamics in vertebrates: relationships, mechanisms and consequences[END_REF] between telomere length (related to self-maintenance) and mass or body condition (related to growth). We further assessed the relationship between rTL and survival by testing whether rTL predicts juvenile apparent survival as estimated with capture-markrecapture models.

Our study model was the sociable weaver (Philetairus socius), a colonial cooperatively breeding passerine endemic to the semi-arid Kalahari savannahs of southern Africa. These weavers are long-lived among passerines (up to 16 years, Covas 2012) and nest predation by snakes leads to an extremely low reproductive success [START_REF] Covas | Helpers in colonial cooperatively breeding sociable weavers Philetairus socius contribute to bufer the efects of adverse breeding conditions[END_REF]. In sociable weavers, egg nutritional and hormonal content were negatively associated with the number of helpers at the nest [START_REF] Paquet | Maternal efects in relation to helper presence in the cooperatively breeding sociable weaver[END_REF]. On the other hand, the overall food load provided to nestlings increases when the number of helpers increases [START_REF] Covas | Helpers in colonial cooperatively breeding sociable weavers Philetairus socius contribute to bufer the efects of adverse breeding conditions[END_REF]). In our cross-fostering experiment, we transferred whole clutches to a foster nest (see cross-fostering design in Table 1). The nestlings might thus have been conceived in the presence of helpers but raised in their absence (or vice-versa) and thus their prenatal social environment may difer from the post-natal social environment. Based on the previous knowledge of this species' life-history, and a previous result showing that females with helpers lay smaller eggs with lower levels of steroid hormones than females without helpers [START_REF] Paquet | Maternal efects in relation to helper presence in the cooperatively breeding sociable weaver[END_REF]), we predict: (i) a negative efect of the prenatal presence of helpers on chick rTL; (ii) a positive efect of the postnatal presence of helpers on chick rTL. In addition, we expect an interaction between pre-and post-natal helper presence, and we predict (iii) longer rTL of chicks that beneit from both higher maternal investment in eggs (absence of pre-hatching helpers) and additional care provided by an increased postnatal helper presence; (iv) a stronger negative impact on chick rTL when the postnatal social environment is unfavorable (decreased presence of postnatal helpers), while prenatal conditions were unfavorable too (presence of prenatal helpers). Finally, we expect that telomere length will be positively associated with survival after ledging.

Material and methods

Species and study area

The study was conducted at Benfontein Game Farm in the Northern Cape Province, South Africa (approx. 28° 53′ S, 24° 89′ E). The study area covers 15 km 2 and contains approximately 30 sociable weaver colonies. The vegetation is Kalahari sandveld, consisting of open savannah dominated by Stipagrostis grasses and the camelthorn tree Acacia erioloba. The area is semi-arid, experiencing low and unpredictable rainfall (average 431 ± 127 mm/year, C.V. = 35.4; Weather Bureau, Pretoria). Most of the precipitation in the study area falls during the summer months, from September to April, when breeding usually takes place.

Sociable weavers are small (ca. 27 g) sexually monomorphic passerine birds endemic to southern Namib and Kalahari regions of Southern Africa. They build a large communal nest made of numerous independent chambers, wherein the birds roost throughout the year and breeding takes place (Maclean 1973a). These weavers are facultative cooperative breeders, with up to eight helpers assisting a breeding pair in raising the chicks, notably by feeding them [START_REF] Covas | Helpers in colonial cooperatively breeding sociable weavers Philetairus socius contribute to bufer the efects of adverse breeding conditions[END_REF]. This lighter parental workload may increase the survival of young female breeders (Paquet et al. 2015b) but has no detectable association with clutch size [START_REF] Covas | Helpers in colonial cooperatively breeding sociable weavers Philetairus socius contribute to bufer the efects of adverse breeding conditions[END_REF]Fortuna et al. 2021). Helpers are most often the ofspring of one or both breeders [START_REF] Covas | Kin associations and direct vs indirect itness beneits in colonial cooperatively breeding sociable weavers Philetairus socius[END_REF]. Younger Immediately after hatching, the whole clutch was transferred from its original nest with or without helpers to a foster nest with or without helpers, resulting in chicks with a similar or diferent pre-and post-hatching social environment. Chicks were swapped within the same colonies. 50 chicks were involved in this procedure, the sample sizes for nestlings and nests where they come from can be read within the brackets in bold font. In bold are also indicated the corresponding experimental groups (EG; + 1: increased number of helpers, 0: no change, -1: decreased number of helpers) helpers are both males and females while, when older than one year, helpers are usually males [START_REF] Doutrelant | Unexpected sex ratio adjustment in a colonial cooperative bird: pairs with helpers produce more of the helping sex whereas pairs without helpers do not[END_REF]).

There is no extra-pair paternity in this species [START_REF] Covas | Kin associations and direct vs indirect itness beneits in colonial cooperatively breeding sociable weavers Philetairus socius[END_REF]Paquet et al. 2015b). Sociable weavers feed mostly on insects, but also seeds and other plant products (Maclean 1973b).

Data collection

Data were collected between September 2013 and February 2014 (for the variables related to breeding, growth, and telomeres) and until 2019 for chick survival. Unique numbered aluminum ring and color combination are attributed to each adult during the annual captures in winter and to each nestling before ledging, allowing individual identiication of each bird. During the breeding season, all chambers in the study colonies are checked every three days, allowing us to identify new clutches and estimate clutch size (in this study, clutch size: mean = 3.5 and SD = 0.57 eggs; brood size before ledging: mean = 2.25 and SD = 0.84 birds). All chambers are visited daily at the end of the incubation period (approximately 15 days), to identify the hatching date. The nestling period usually lasts 21-24 days (Maclean 1973a). Two sets of measurements were performed nine days (D9) and seventeen days (D17) after the irst chick hatched in each nest. Hence, chicks were captured only twice, limiting stress. D9 is the earliest moment where all chicks can be ringed and sampled for blood and D17 was chosen to have a measure as late as possible before ledging (as nestlings will ledge prematurely if handled from day 18 onwards). At these two dates, we measured brood size (number of chicks) and nestling mass, and we took blood samples from the brachial vein for sex determination and telomere analysis. This procedure was conducted on a total of 132 nestlings distributed among 15 colonies (containing approximately 400 chambers). In our study, we observed that approximately 39% of the individual nests (chambers) lacked helpers, whereas 61% had helpers. Individual nests harbored from 0 to 4 helpers and the average group size (parents + potential helpers) was 3.2 birds (median = 3, SD = 1.2). Blood samples at D9 were stored in 95% ethanol. In contrast, because of use in other experiments, blood samples at D17 were centrifuged immediately upon collection and red blood cells were stored frozen. Because diferent storage conditions may afect rTL measured via quantitative polymerase chain reaction (qPCR, [START_REF] Reichert | Telomere length measurement by qPCR in birds is afected by storage method of blood samples[END_REF], we restricted our analysis to the same nestling age comparisons, storage conditions within samples from the same nestling age being strictly identical and could not afect the outcomes.

Tarsus length at D17 was also recorded and used as a proxy for body size. The body condition of a chick was calculated as the residual value from the regression between tarsus length and mass at D17 (regression plot and statistics available in Electronic Supplementary Material, ESM 1). Tarsus length was not measured at D9. The 15 colonies from where the 132 chicks in this study originated are monitored annually, allowing us to analyze the relationship between the early rTL and survival from birth to the present (6 years).

Cross-fostering procedure

The detailed methods can be found in Paquet et al. (2015a), with the diference that here we focused on the reproduction period from September 2013 to February 2014. In brief, when two clutches from the same colony and of the same size were laid synchronously (or within a 1-day interval), both whole clutches were swapped on the day after the last egg was laid. Group sizes after hatching (i.e. parents + number of postnatal helpers) were established by counting the number of birds seen feeding the chicks. Observations and counting took place from under a hide placed at 3-5 m from the colony. The group size within a nest usually remains stable during the breeding cycle (from nest building to ofspring ledging; [START_REF] Paquet | Communal roosting, thermoregulatory beneits and breeding group size predictability in cooperatively breeding sociable weavers[END_REF], allowing us to infer the number of helpers before cross-fostering retrospectively. Within the 132 nestlings sampled during this study, 72 were involved in the cross-fostering protocol, among them, the presence (or absence) of helpers was known for 50 of them (18 broods). The pre-and post-natal social environments for these 50 chicks are detailed in Table 1.

Telomere length measurements

To assess the prenatal and postnatal efect of helpers on chick rTL, we measured early relative telomere length at D9 and just before ledging at D17 in chicks using the qPCR procedure. This protocol was irst developed by Cawthon [START_REF] Cawthon | Telomere measurement by quantitative PCR[END_REF] and thereafter popularized in birds' studies [START_REF] Criscuolo | Real-time quantitative PCR assay for measurement of avian telomeres[END_REF][START_REF] Herborn | Stress exposure in early post-natal life reduces telomere length: an experimental demonstration in a long-lived seabird[END_REF][START_REF] Nettle | An experimental demonstration that early-life competitive disadvantage accelerates telomere loss[END_REF][START_REF] Meillère | Traic noise exposure afects telomere length in nestling house sparrows[END_REF][START_REF] Costanzo | Brood size, telomere length, and parent-ofspring color signaling in barn swallows[END_REF]. The qPCR provides a non-absolute measure of an individual's TL, a relative telomere length as it is expressed relatively to one speciic sample that is given arbitrarily the value of 1 (see [START_REF] Nussey | Measuring telomere length and telomere dynamics in evolutionary biology and ecology[END_REF][START_REF] Lai | Comparison of telomere length measurement methods[END_REF]) for a comparison between TL measurement methods). Shortly, after genomic DNA extraction from red blood cells (nucleated in birds) using silicamembrane columns (Nucleospin Blood QuickPure, Macherey-Nagel, Düren, Germany), DNA quantity and quality were assessed based on spectrophotometer absorbance (Nanodrop 1000 Thermo Scientiic, ratios A260/280 and A260/230) and gel-migration (on a sub-sample randomly chosen of 30 samples, see ESM 2). Dilutions of extracted DNA (at 2.5 ng/uL) were prepared using sterile distilled water and were ampliied using telomere and control gene primers with the BRYT Green luorescent dye (GoTaq qPCR Master Mix, Promega Charbonnières-les-Bains, France). We used recombination activating gene RAG1 as our control gene for weavers, designed to be non-variable among the individuals of our population (as advised by [START_REF] Smith | Chasing telomeres, not red herrings, in evolutionary ecology[END_REF]; see ESM 2). The forward and reverse primers for the control gene were: SOWEA-F: 5′-TGC AAA GAG ATT TCG ATA TGATG-3′, SOWEA-R: 5′-TCA CTG ACA TCT CCC ATT CC-3′. Tel1b: 5′-CGG TTT GTT TGG GTT TGG GTT TGG GTT TGG GTT TGG GTT-3′, Tel2b: 5′-GGC TTG CCT TAC CCT TAC CCT TAC CCT TAC CCT TAC CCT-3′ for the telomere ampliication. An automated thermocycler (CFX 384 Biorad Hercules, USA) was used, with reaction conditions set at 95 °C for 2 min, followed by 40 cycles of data collection at 95 °C for 1 min and a 60 °C annealing-extension step for 1 min for RAG1. For the telomeric sequence, the conditions were set at 95 °C for 2 min followed by 30 cycles of data collection for 15 s at 95 °C, 30 s at 56 °C, and 1 min at 72 °C. The 132 weaver samples used in the present study were part of 504 samples that were measured in duplicates on 5 diferent runs. Each run includes 1 plate of telomere sequence ampliication and 1 plate of control gene sequence ampliication, due to the diferences in qPCR temperature conditions. On each plate, we ran a dilution curve (20-0.313 ng) to check that the eiciency of ampliication did not vary among plates, and a melting curve to check for ampliication artifacts (like primer-dimer signal, see ESM 2). The mean qPCR amplifying eiciencies were 99.8% (99.4-99.9) for telomere and 99.9% (99.7-100.1) for the control gene (100% relect a doubling of the DNA sequence at each ampliication step). Samples were randomly distributed over the plates, and 40 were repeated to assess interplate variation. As advised by [START_REF] Eisenberg | Telomere length measurement validity: the coeicient of variation is invalid and cannot be used to compare quantitative polymerase chain reaction and Southern blot telomere length measurement techniques[END_REF], rather than coeicients of variation, we reported the interplate and intraplate intra-class correlation coeicients for T/S ratio, respectively, 0.895 and 0.767. The rTL is then calculated from the T/S ratio, where 'T' is the copy number of the telomeric sequence and 'S' is the copy number of the control sequence. We took into account the slight variation of efficiency between telomere and RAG1 ampliications by calculating the T/S ratio accordingly to Pfal's recommendation [START_REF] Pfal | A new mathematical model for relative quantiication in real-time RT-PCR[END_REF]):

where 'E' is the ampliication eiciency and 'ΔCq' the difference in time required to reach the fluorescence detectability threshold between control and sample (Cqcontrol -Cqsample).

Statistical analysis

Categorical variables were tested through ANOVA (package 'stats' v.3.6, R Core Team 2019). Post-hoc comparisons

1 + E (telomere) ∧ ΔCq (telomere) ∕ 1 + E (RAG1) ∧ ΔCq (RAG1)
were done using the multcomp R package with Tukey contrasts corrections [START_REF] Hothorn | Simultaneous inference in general parametric models[END_REF]. Quantitative variables including the T/S ratio were irst z-scored and then tested directly through the t statistics provided by default by the function 'lmer'. Statistical tests were performed by the R software (R Core Team 2019) at the signiicance threshold α = 5%.

Efects of helpers on chick telomere length: deinition of variables

In our analysis, we considered the efects of (i) the natural presence of helper in the nest of origin (hereafter referred to as 'prenatal presence') and (ii) the postnatal change in helper presence induced by the cross-fostering (hereafter referred to as 'postnatal helper change'). The prenatal presence of helpers was coded 0 (no helpers) and 1 (presence of helpers) while the postnatal helper change was coded 0 (no change), -1 (reduced number of helpers) and + 1 (presence or increased number of helpers).

We tested if the prenatal presence of helpers and the postnatal helper change, as well as their interaction had an impact on early telomere length (i) nine days after hatching and (ii) later, just before ledging, at seventeen days after hatching. Telomere length and dynamics are known to be afected by individual characteristics, such as sex [START_REF] Barrett | Sex diferences in telomeres and lifespan[END_REF][START_REF] Young | Age, sex, and telomere dynamics in a long-lived seabird with male-biased parental care[END_REF] or growth rate [START_REF] Ringsby | On being the right size: increased body size is associated with reduced telomere length under natural conditions[END_REF][START_REF] Monaghan | Somatic growth and telomere dynamics in vertebrates: relationships, mechanisms and consequences[END_REF][START_REF] Vedder | Embryonic growth rate afects telomere attrition: an experiment in a wild bird[END_REF], as well as by the social environment [START_REF] Hall | Telomere loss in relation to age and early environment in long-lived birds[END_REF][START_REF] Nettle | An experimental demonstration that early-life competitive disadvantage accelerates telomere loss[END_REF][START_REF] Dugdale | Heritability of telomere variation: it is all about the environment![END_REF][START_REF] Hammers | Breeders that receive help age more slowly in a cooperatively breeding bird[END_REF]. Hence, in addition to the prenatal presence and the postnatal helper change, we tested the inluence of the following explanatory variables: sex, breeding period (diferent climatic conditions), brood size (intra-nest social competition), and body condition (an indicator of chick growth). The breeding period had two levels: the irst between October and November 2013 (sparse rains) and the second between December 2013 and January 2014 (abundant rains). The prenatal presence of helpers and the postnatal helper change were not correlated: (χ 2 = 0.040, P = 0.842), which validates the randomness of the crossfostering procedure. Moreover, there was no evidence for collinearity between all other variables (Variance Inlation Factors were less than three: VIF max = 1.49).

Efects of helpers on chick telomere length: model itting and selection

For the tests conducted either on day 9 or day 17, we built separated mixed linear models (LMM) with 'nest' as a random factor nested in 'colony' to control for non-independence of chicks in a nest. Due to the relatively low sample size (n = 50), we decided not to include more than ive explanatory variables to avoid over itting [START_REF] Harrison | A brief introduction to mixed efects modelling and multi-model inference in ecology[END_REF]. We applied a model selection procedure with the 'MuMIn package on R, based on the lowest Aikake's information criterion corrected for small sample sizes (AIC; v. 1.43 [START_REF] Bartoń | MuMIn: multi-model inference[END_REF]. The procedure was adjusted to provide models containing no more than ive variables, including the two main efects we wanted to test, i.e., prenatal presence and postnatal variation in the number of helpers. We chose models as complete as possible with a maximum ∆AIC of 2. Then, depending on the selection procedure, the interaction term 'prenatal presence x postnatal helper change' may not be included in the lowest AIC model. All proposed and selected models involving telomere length are available in the electronic supplementary material (ESM 3, Table S1).

We graphically ensured that model residuals did not signiicantly difer from a Gaussian distribution and related Anderson-Darling's tests had P value > 0.05 for rTL both 9 and 17 days after hatching, respectively, A = 0.25, P = 0.72 and A = 0.33, P = 0.51, indicating that the model residuals itted a normal distribution. A Pearsons' correlation test was conducted to test for correlation of intra-individual values of chick telomere lengths repeatedly measured at day 9 and day 17 post-hatch.

Chick body condition and body mass growth vs. telomere length

Chick body condition was calculated as the residuals of the regression of body mass vs. tarsus length both measured at D17. Using the same statistical procedure as for telomere length, we tested whether the efect of helpers could be relected in the body condition of chicks through mixed linear models with mass at D9 and body condition at D17 as dependent variables. Full models used in the model selection procedure included brood sizes at D9 or D17, chick sex and season, as well as nest/colony as random factors. Furthermore, we used the same statistical approach to examine the link between body condition at D17, body mass at D17 or body mass gain between D9 and D17 and chick telomere length at D17.

Telomere length and apparent survival

To estimate whether rTL predicted apparent survival we itted Cormack-Joly-Seber (CJS) models [START_REF] Gimenez | State-space modelling of data on marked individuals[END_REF]) on six years of capture-mark-recapture history of 132 ledglings (59 females and 73 males from cross-fostered as well as non-cross-fostered nests). We measured apparent survival, which does not allow us to diferentiate dead individuals from those that permanently dispersed beyond the area studied. However, both sexes are philopatric [START_REF] Van Dijk | Fine-scale genetic structure relects sex-speciic dispersal strategies in a population of sociable weavers (Philetairus socius)[END_REF], and the 15-20 colonies in the study area are captured yearly, allowing us to re-capture birds dispersing between colonies (usually less than 10%; Covas 2011). Furthermore, by considering detectability values lower than one, CMR models ofer a reliable and explicit way to perform survival analysis in the wild [START_REF] Gimenez | The risk of lawed inference in evolutionary studies when detectability is less than one[END_REF]). The CJS model is composed of apparent survival probability ϕ (deined as the probability to survive and not permanently emigrate the next year) and recapture probability p (deined as the probability of an individual apparently alive in a year to be recaptured with mist nets that year). We set ϕ to vary linearly with rTL (scaled) on the logit scale. We also allowed both ϕ and p to vary with the sex of the individuals as we expected them to be lower for females [START_REF] Van Dijk | Fine-scale genetic structure relects sex-speciic dispersal strategies in a population of sociable weavers (Philetairus socius)[END_REF]Paquet et al. 2015b) and to make sure that any relationship between rTL and apparent survival was not solely due to sex diferences. We found an average recapture probability of 0.722 (min = 0.568, max = 0.854) for females and of 0.826 for males (min = 0.738, max = 0.900).

We speciied both capture-recapture models using JAGS, version 4.2.0 (Plummer 2015) run using the rjags package [START_REF] Plummer | rjags: Bayesian graphical models using MCMC[END_REF] in Program R, version 3.4.3 (see ESM 4 for JAGS code). We estimated parameters using vague priors (see ESM 4 for priors and initial values). We used 3000 posterior samples from three Markov Chain Monte Carlo (MCMC) chains based on 3000 iterations after an adaptation period of 5000, a burn-in of 10,000 and thinning interval of 3. We assessed model convergence both visually and by using the "R hat" Gelman-Rubin statistic [START_REF] Gelman | Inference from iterative simulation using multiple sequences[END_REF]) and found the 95% upper limits of potential scale reduction factors to equal 1 for all estimated parameters, indicating that convergence was achieved. We assessed the it of our two models to the data (i.e. posterior predictive checks) by simulating capture recaptures histories from our two models at each iteration and comparing the number of simulated recaptures for the 3000 posterior samples with the number of observed recaptures. Simulated values systematically lower or higher than observed values would indicate a lack of it [i.e. p (simulated < observed) close to 0 or 1]. We obtained p (simulated < observed) = 0.47 and 0.49 for models looking at rTL at D9 and D17, respectively, indicating a good it to the data.

Ethical statement

All experiments were conducted with permission from the Northern Cape Department of Tourism Environment and Conservation (permit FAUNA 942/2012) and the approval of the Ethics Committee of the University of Cape Town (2009/V12/RCREN). Our procedures involved the capture, coninement, handling, and blood sampling of the birds in the ield, with the time elapsed between extracting the birds from the nets until the last bird was released ranging from 2 to 3 h. While queuing to be processed, birds rested in individual bird bags and were placed in a quiet, ventilated and shaded area. The sampling volume (ca. 75 µl) remained well below the prescribed limits for the percentage of the total blood volume of this passerine. After handling, the adult birds could recover for a few minutes before being released in small groups. Any birds that showed signs of fatigue or injury were taken to an indoor aviary to recover and were subsequently released. This happened for less than 1% of the birds handled. To decrease handling times, captures were conducted with a team of 8-12 experienced ringers that were allocated speciic tasks to streamline the procedures conducted.

Results

We present for each result below the estimate ± standard error in brackets. In Table 2 (telomere-related models) and Table 3 (body mass-related models), we present in addition 95% confidence interval (CI95%), test statistics and P values. After the model selection procedure (detailed in ESM 3, Table S1), all models contained the following independent variables: prenatal presence, postnatal helper change and the random effect of the nest nested in the colony. The interaction between pre-and post-natal helpers (prenatal presence × postnatal helper change), as well as chick sex and brood size were kept only for the presence of helpers at D9. Only the breeding season was kept as an additional fixed factor for the model testing individual variability in rTL at D17. The original data sets regarding both the effect of helpers on chick rTL and the effect of rTL on survival are available online as distinct tables in ESM5. Chicks rTL measured at D9 and D17 were found to be significantly correlated-even if the correlation is not high (r = 0.27, t = 2.64, P = 0.009, n = 93, Pearson's correlation).

Efect of the prenatal and postnatal presence of helpers on chick rTL

The detailed statistics are given in Table 2 and related plots are Fig. 1a for D9 and 1B for D17. Nine days after hatching, we found a signiicant interaction between the prenatal helpers' presence and the postnatal helpers' presence (-1.76 ± 0.54). The Tukey contrasts post-hoc comparisons showed that for the chicks from nests without helpers during the prenatal stage, obtaining postnatal helpers was associated with larger rTL nine days after hatching (Fig. 1a, 0/1 vs 0/0, post-hoc: 1.54 ± 0.49, z = 3.13, P = 0.01). For chicks that had prenatal helpers, a decrease in the number of helpers was associated with a shorter rTL (1/ -1 vs 1/0, post-hoc: -1.21 ± 0.44, z = -2.75, P = 0.042). However, the rTL of chicks swapped from nests with helpers to nests with more helpers was not afected by the increase in helper number after hatching (1/ + 1 vs 1/0 and 1/ -1, post-hoc: respectively, -1.23 ± 1.20, z = -1.03, P = 0.83 and 1.20 ± 0.51, z = 2.35, P = 0.12). Among the chicks experiencing additional helpers, those with prenatal helpers had shorter telomeres on average (0/ + 1 vs 1/ + 1, post-hoc: -1.18 ± 0.44, z = -2.73, P = 0.043). The efect of chick sex and brood size were not signiicant (respectively, -0.43 ± 0.25 and 0.09 ± 0.17). When measured at D17 post-hatch, neither the prenatal presence or the postnatal helper change nor their interaction term were found to be signiicantly related to ofspring's rTL (Fig. 1b, Table 2b).

The breeding season, while kept in the selected model, had no signiicant efect (0.12 ± 0.18).

Efects of helpers on chick body mass and body condition

Neither the prenatal or the postnatal presence of helpers were associated with a change in chick body mass at D9, or chick body condition at D17 (Table 3). Only brood sizes (D9 and D17) negatively afected body mass at D9 and body condition at D17, respectively. Testing body mass at D17 or the gain in body mass between D9 and D17 did not shown any signiicant relationships (data not shown). There was no relationship between body mass gain (D17-D9) and chick rTL at D17 (ESM 6, Table S2).

Chick telomere length and apparent survival rate

We found that sociable weaver chicks with longer rTL at D9 tended to have a higher apparent survival rate the following ive years although the 95% credible interval overlapped zero [estimate (95% credible interval) = 0.21 (-0.072, 0.52),

Fig. 1 Relative telomere length (rTL, T/S ratio) 9 days (a) and 17 days (b) after hatching in relation to helpers' presence in sociable weavers. We compared the rTL of 50 cross-fostered individuals according to (i) the presence of helpers before the cross-fostering and (ii) after the cross-fostering. This latter experimental factor is categorised as increased number of helpers (+ 1, blue); no change in helpers' presence (0, green) and decreased number of helpers (-1, red). a Post-hoc signiicant diferences (Tukey contrasts) concerned: longer rTL in chicks that started with no helpers but get experimental helpers' presence (P = 0.010); decreased rTL in chicks that started with helper presence but thereafter experienced no helpers (P = 0.042); shorter rTL in chicks that started with helpers and experienced increased helpers presence after hatching compared to chicks that had helpers only after hatching (P = 0. p (estimate > 0) = 0.928, Fig. 2]. We found no clear association between rTL at D17 and apparent survival [estimate = -0.013 (-0.24, 0.22), p (estimate > 0) = 0.458].

Discussion

We investigated the inluence of the prenatal and postnatal presence of helpers on rTL and the link between rTL and survival in nestlings of the sociable weaver, a cooperatively breeding bird. Early-life rTL (i.e. measured nine days after hatching) was overall positively associated with the presence of post-natal helpers but was also inluenced by an interaction of the presence of pre-and post-natal helpers. Speciically, we found that for chicks coming from nests without prenatal helpers, rTL was longer when postnatal helpers were added after hatching. For the chicks coming from nests that already had prenatal helpers, telomere length was shorter when the number of helpers decreased after hatching. For those chicks, however, an increase in the number of postnatal helpers had no signiicant efect on ofspring rTL. The interaction between the prenatal presence and postnatal helper change showed that the increase in postnatal helpers was associated with a greater ofspring rTL only when no prenatal helper was present. The efects observed nine days after hatching (D9) were not observed at the end of the nestling period (D17; but see below). Finally, the CMR analysis conducted to assess the link between early rTL and post-ledgling survival showed a tendency for rTL at D9 to be positively related to survival up to ive years after hatching, but this relationship was no longer present at D17.

Contrasting efects of pre-and post-natal helpers on ofspring's telomeres

Nestlings from original nests without helpers had greater rTL at D9 when raised with postnatal helpers than without. On the other hand, reducing the number of postnatal helpers (i.e. concerned nests with prenatal helpers) was associated with shorter chicks' rTL. These two indings support a beneicial efect of post-hatching helpers on ofspring rTL in sociable weaver. Such positive postnatal inluence is thought to be mediated by the enhancement of developmental conditions that nestlings experience through the additional care provided [START_REF] Covas | Helpers in colonial cooperatively breeding sociable weavers Philetairus socius contribute to bufer the efects of adverse breeding conditions[END_REF][START_REF] Bebbington | Joint care can outweigh costs of nonkin competition in communal breeders[END_REF]. This additional care may also contribute to decreasing sibling competition in larger broods, which has been shown as a modulating mechanism of rTL in chicks from diferent species [START_REF] Voillemot | Efects of brood size manipulation and common origin on phenotype and telomere length in nestling collared lycatchers[END_REF][START_REF] Boonekamp | Nestling telomere shortening, but not telomere length, relects developmental stress and predicts survival in wild birds[END_REF][START_REF] Nettle | An experimental demonstration that early-life competitive disadvantage accelerates telomere loss[END_REF][START_REF] Young | Efects of developmental conditions on growth, stress and telomeres in black-legged kittiwake chicks[END_REF]. A negative efect of sibling competition on ofspring development was also suggested here through a negative efect of brood size on body mass. Nevertheless, this beneicial efect appears to be limited, since the addition of postnatal helpers in nests already harboring prenatal helpers had no signiicant efect. We found in addition an interaction between the prenatal presence and postnatal helper change indicating that the positive efect of postnatal helpers on chick rTL is dependent on the presence of prenatal helpers. Indeed, adding helpers after hatching was negatively associated with chick's rTL if those chicks had experienced prenatal helpers (i.e. they had on average shorter rTL than those without prenatal helpers); the efect persisted even when removing the two extreme values for the 0/1 condition (Fig. 1a). This outcome is expected if there is a prevalent negative prenatal efect resulting from a reduced maternal investment during egg production in presence of prenatal helpers, compared to the beneits of being raised with post-natal helpers. In fact, previous studies have shown that the conditions experienced during embryonic life may alter telomere length at birth [START_REF] Entringer | Stress exposure in intrauterine life is associated with shorter telomere length in young adulthood[END_REF][START_REF] Haussmann | Embryonic exposure to corticosterone modiies the juvenile stress response, oxidative stress and telomere length[END_REF][START_REF] Vedder | Embryonic growth rate afects telomere attrition: an experiment in a wild bird[END_REF]Noguera andVelando 2019, 2020;[START_REF] Stier | Pace and stability of embryonic development afect telomere dynamics: an experimental study in a precocial bird model[END_REF]. Sociable weavers females were found to lay smaller eggs with lower steroid hormone content [START_REF] Paquet | Maternal efects in relation to helper presence in the cooperatively breeding sociable weaver[END_REF]. Telomere shortening may thus arise from this weaker maternal investment in the presence of pre-hatching helpers. Our results suggest that such initial telomere handicap may not be reversed by the beneicial efects of post-natal helpers. Still, our sample size does not allow us to draw deinitive conclusions, and the pre/ post-natal helpers interaction efects deserve further study.

A non-exclusive explanation for the lack of a positive efect of an increased number of postnatal helpers for nestlings with prenatal helpers might be that, above an optimal threshold, adding more helpers would have no beneits, or could even become detrimental for ofspring rTL. A previous study in the same species has actually shown that larger group sizes may result in a weaker ofspring survival likelihood [START_REF] Covas | The efect of helpers on the postledging period in a cooperatively breeding bird, the sociable weaver[END_REF], but see Wood 2017 chap. 3). When analyzing only the efect of group size before and after hatching, we found that the number of helpers had no efect on telomere length at either D9 or D17 (ESM 7). This conirms the results presented here and supports the interpretation that, in our case, a larger number of helpers does not provide greater beneits for the ofspring, whatever their age. In addition, a previous study on this population found that the positive efect of helpers on chicks after hatching is mostly detected under adverse environmental conditions [START_REF] Covas | Helpers in colonial cooperatively breeding sociable weavers Philetairus socius contribute to bufer the efects of adverse breeding conditions[END_REF]. If fewer helpers provide suicient help under usual climatic conditions, this may explain why we found no signiicant efect of an increased number of helpers post-hatch when prenatal helpers were already present (1/ + 1 vs 1/0 and 1/ -1). Given the association between helpers' presence and rTL at day 9, it may be surprising to ind no association at day 17. However, in addition to the presence of helpers, several environmental factors such as climate [START_REF] Mizutani | Environmental perturbations inluence telomere dynamics in long-lived birds in their natural habitat[END_REF], sibling rivalry (Nettle et al. 2015; [START_REF] Mizutani | How do growth and sibling competition afect telomere dynamics in the irst month of life of long-lived seabird? (JM Avilés[END_REF] or food availability [START_REF] Spurgin | Spatio-temporal variation in lifelong telomere dynamics in a long-term ecological study[END_REF]) might have blurred possible helper efects at D17. For example, in black-tailed gull chicks (Larus crassirostris), the efect of sibling competition on telomeres was weak on the irst day after hatching and became stronger 30 days after hatching, potentially concealing the efect of other factors [START_REF] Mizutani | How do growth and sibling competition afect telomere dynamics in the irst month of life of long-lived seabird? (JM Avilés[END_REF]. In European starlings (Sturnus vulgaris), the efect of sibling rivalry on telomere attrition was also dependent on nestling age: not detectable at 3 days after hatching (D3), detectable at D12 and faded at D24 [START_REF] Nettle | An experimental demonstration that early-life competitive disadvantage accelerates telomere loss[END_REF]. In the same study, the efect on oxidative status was detectable at D3 but no longer at D12. Those studies and ours seem to indicate that the efect of diferent environmental factors might vary with individual age and species.

Body mass growth, telomeres, and survival

The suggestion that ofspring's early rTL is a proxy of survival rate has been supported in other species [START_REF] Geiger | Catching-up but telomere loss: half-opening the black box of growth and ageing trade-of in wild king penguin chicks[END_REF][START_REF] Heidinger | Telomere length in early life predicts lifespan[END_REF][START_REF] Stier | Starting with a handicap: phenotypic diferences between early-and late-born king penguin chicks and their survival correlates (D Costa, Ed)[END_REF][START_REF] Young | Efects of developmental conditions on growth, stress and telomeres in black-legged kittiwake chicks[END_REF][START_REF] Eastwood | Early-life telomere length predicts lifespan and lifetime reproductive success in a wild bird[END_REF][START_REF] Chatelain | The association between stressors and telomeres in non-human vertebrates: a meta-analysis[END_REF]; but see [START_REF] Boonekamp | Nestling telomere shortening, but not telomere length, relects developmental stress and predicts survival in wild birds[END_REF] or [START_REF] Wood | Telomere attrition predicts reduced survival in a wild social bird, but short telomeres do not[END_REF]) for a critical view on telomere shortening and survival. Although the 95% credible interval slightly overlapped zero, our study tends also to suggests that chick rTL early after hatching might predict post-ledging apparent survival, at least up to 5 years after hatching. In this species, a previous study showed that helpers had a negative efect on ofspring survival but only during the irst year after ledging, after that, this negative efect disappeared [START_REF] Covas | The efect of helpers on the postledging period in a cooperatively breeding bird, the sociable weaver[END_REF]. Even if in the medium term (ive years here) the presence of postnatal helpers seems to be rather positive for ofspring apparent survival, the consequences of helpers could be more complex especially in the very irst years of life. This adds another level of complexity in understanding the evolutionary advantages and disadvantages of social structure involving cooperative breeding. [START_REF] Heidinger | Telomere length in early life predicts lifespan[END_REF] have shown that rTL measured within the irst month in zebra inches predicted lifespan better than subsequent measurements. Our results are in line with this inding, as we did not detect an association between rTL and apparent survival for older chicks (before ledging). However, the exact reasons for why earlier telomere length is a better predictor or survival than later telomere length remain elusive [START_REF] Ingles | Telomeres, species diferences, and unusual telomeres in vertebrates: presenting challenges and opportunities to understanding telomere dynamics[END_REF][START_REF] Van Lieshout | Individual variation in early-life telomere length and survival in a wild mammal[END_REF].

The improved rearing conditions induced by postnatal helpers could have led also to improve body condition. However, and similarly to a previous study in the same species [START_REF] Paquet | Maternal efects in relation to helper presence in the cooperatively breeding sociable weaver[END_REF], both mass at D9 and ledglings' body condition (D17) did not vary with the presence of helpers. These results support previous suggestions on this and other species in showing the ability of helpers to compensate for the diferential maternal investment in eggs so that, on average, ledglings have the same body condition. Since, in our study, chicks varied in their day 9 rTL but not body condition, it seems that for the chicks that do not have helpers, allocation of energy is toward growth at the expense of their telomeres. Such a trade-of between growth and telomere maintenance has been shown in numerous vertebrate species [START_REF] Tarry-Adkins | Poor maternal nutrition followed by accelerated postnatal growth leads to telomere shortening and increased markers of cell senescence in rat islets[END_REF][START_REF] Geiger | Catching-up but telomere loss: half-opening the black box of growth and ageing trade-of in wild king penguin chicks[END_REF][START_REF] Stier | Starting with a handicap: phenotypic diferences between early-and late-born king penguin chicks and their survival correlates (D Costa, Ed)[END_REF][START_REF] Pauliny | Rapid growth accelerates telomere attrition in a transgenic ish[END_REF][START_REF] Ringsby | On being the right size: increased body size is associated with reduced telomere length under natural conditions[END_REF][START_REF] Vedder | Telomere attrition and growth: a life-history framework and case study in common terns[END_REF][START_REF] Vedder | Embryonic growth rate afects telomere attrition: an experiment in a wild bird[END_REF]. A quicker post-hatching growth ensures a higher success rate at ledging [START_REF] Kersten | Growth, ledging success and post-ledging survival of juvenile Oystercatchers Haematopus ostralegus[END_REF][START_REF] Harris | The post-ledging survival of young Guillemots Uria aalge in relation to hatching date and growth[END_REF][START_REF] Canestrari | Helpers at the nest compensate for reduced maternal investment in egg size in carrion crows[END_REF][START_REF] De Loock | Cooperative breeding shapes post-ledging survival in an Afrotropical forest bird[END_REF][START_REF] Hipfner | The relationship between egg size and posthatching development in the thick-billed murre[END_REF] and an earlier ledging date may decrease predation risk in sociable weavers [START_REF] Ferreira | Maternal allocation in relation to weather, predation and social factors in a colonial cooperative bird[END_REF]. As a result, there could be a stronger evolutionary pressure on body growth rather than telomere length; in other words, short-term survival by avoiding predation rather than long-term survival through somatic maintenance. Alternatively, resource-investment trade-ofs may be relected not in body condition or mass, but in tissue maturation rate, which could be relected in shorter telomeres [START_REF] Criscuolo | Oxidative status and telomere length are related to somatic and physiological maturation in chicks of European starlings (Sturnus vulgaris)[END_REF].

Conclusions

Here, we set to investigate the efect of the social environment (presence of helpers) before and after hatching on ofspring rTL. Our results suggest an overall positive efect of postnatal helpers on the ofspring rTL early in life, but our study did not provide evidence that this relationship is conserved until ledging. Furthermore, the positive postnatal efect of helper presence was dependent on prenatal conditions, being stronger in nests that did not have pre-natal helpers. Thus, the presence of helpers may induce opposite efects depending on whether helpers are present before or after hatching and that the interaction between the prenatal and postnatal environment is essential to understand the consequences of the social environment on ofspring. In addition to the social environment, the ecological context (e.g., temperature, food availability) may also afect rTL, both before and after hatching, but this was not investigated here. This calls for data over longer periods spanning diferent climatic conditions, to decipher the interaction between social and ecological environment. According to our results, the chicks with the shortest telomeres in their early life might also be less likely to survive the irst years of life. Although other factors inluence rTL, such as genetics or the quality of care provided, our study suggests that social context, has a potential important role to play in inluencing individual development and survival in cooperatively breeding birds. However, the mechanisms that sustain these pre-and post-natal social efects on rTL remain to be identiied and further studies

  Fig.2Relation between relative telomere length (rTL, T/S ratio) 9 days after hatching and apparent survival. 132 birds were annually captured from 2014 to the present (6 years). Estimate and 95% Credibility Interval = 0.21 (-0.07; 0.52), p (estimate > 0) = 0.928

Table 1

 1 Cross-fostering procedure design

Table 2

 2 Efect

	of the prenatal and postnatal presence of	Predictors	rTL D9
	helpers on chick relative		Estimates	Std. error	CI	Statistic	P
	telomere length (rTL,
	z-transformed)	(a)
		Intercept	-0.08	0.55	-1.17-1.00	-0.15	0.880
		Prenatal presence of helpers	0.29	0.45	-0.58-1.17	0.65	0.513
		Postnatal helper change	1.18	0.50	0.20-2.16	2.36	0.018
		Brood size D9	0.09	0.17	-0.24-0.43	0.54	0.587
		Chick sex	-0.43	0.25	-0.91-0.05	-1.74	0.082
		Prenatal presence × postnatal	-1.76	0.54	-2.81 to -0.70	-3.27	0.001
		helper change
		Random efects
		σ 2	0.46
		τ 00 (nest:colony_id)	0.50
		τ 00 (colony_id)	0.39
		ICC	0.66
		N (nest)	18
		N (colony_id)	3
		Observations	50
		Marginal R 2 /conditional R 2	0.177/0.718
		(b)
		Intercept	1.91	0.17	1.57-2.25	11.04	< 0.001
		Prenatal presence of helpers	-0.13	0.21	-0.53-0.28	-0.61	0.542
		Postnatal helper change	-0.06	0.12	-0.29-0.18	-0.48	0.635
		Breeding season	0.12	0.18	-0.23-0.46	0.66	0.508
		Random Efects
		σ 2	0.39
		τ00 (nest:colony_id)	0.00
		τ00 (colony_id)	0.00
		N nest	18
		N (colony_id)	3
		Observations	50
		Marginal R 2 /conditional R 2	0.017/NA

The following tables list the estimates ('est.'), 95% conidence interval ('CI 95%'), standard error ('SE'), test statistics ('stat.', t or F, respectively, for continuous or categorical variables) and P values ('P') from linear mixed models. We only consider the variables retained after the model selection procedure (ESM 3). Continuous variables have been scaled and transformed into z-scores. Lines in bold indicate a signiicant test with α = 0.05 as a threshold. Results are given for chick telomere length at 9 (a) and 17 (b) days after hatching. In this latter case, random efects did not explain a signiicant part of the variance

Table 3

 3 Efect

	of the prenatal
	and postnatal presence of
	helpers on the chick mass at day
	9 (a) and chick body condition
	at day 17 (b) post-hatch (linear
	mixed models)

Acknowledgements Data collection would have not been possible without the contribution of several people working in the ield, in particular, Max Loubon, Margaux Rat, Lara Broom, and all the students and volunteers that contributed to the annual sociable weaver captures. We thank Sophie Lardy for the helpful discussion regarding the study design and analysis, and two reviewers for relevant and helpful comments. De Beers Consolidated Mines permitted us to work at Benfontein Reserve.

Funding

The sociable weaver project and the present study have been supported by funding from the FitzPatrick Institute of African Ornithology (DST-NRF Centre of Excellence) at the University of Cape Town (South Africa), the European program Marie Curie-IRSES (FP7-PEOPLE-2012-IRSES; 'Cooperation' 318994), FCT (Portugal) through grants IF/01411/2014/CP1256/CT0007 and PTDC/ BIA-EVF/5249/2014 to RC and ANR (France) through Project ANR-15-CE32-0012-02 to CD. This work was conducted under the CNRS-CIBIO Laboratoire International Associé (LIA) and the OSU OREME.

Declarations

Conflict of interest The authors declare that the research was conducted in the absence of any commercial or inancial relationships that could be construed as a potential conlict of interest.

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Kindly check and conirm the updated page number are correct in references [START_REF] Criscuolo | Oxidative status and telomere length are related to somatic and physiological maturation in chicks of European starlings (Sturnus vulgaris)[END_REF][START_REF] Nettle | An experimental demonstration that early-life competitive disadvantage accelerates telomere loss[END_REF][START_REF] Noguera | Reduced telomere length in embryos exposed to predator cues[END_REF][START_REF] Reichert | Increased brood size leads to persistent eroded telomeres[END_REF][START_REF] Vedder | Embryonic growth rate afects telomere attrition: an experiment in a wild bird[END_REF][START_REF] Young | Age, sex, and telomere dynamics in a long-lived seabird with male-biased parental care[END_REF]].

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Kindly check and conirm the updated volume and page number are correct in references [START_REF] Eisenberg | Telomere length measurement validity: the coeicient of variation is invalid and cannot be used to compare quantitative polymerase chain reaction and Southern blot telomere length measurement techniques[END_REF][START_REF] Haussmann | Embryonic exposure to corticosterone modiies the juvenile stress response, oxidative stress and telomere length[END_REF][START_REF] Spurgin | Spatio-temporal variation in lifelong telomere dynamics in a long-term ecological study[END_REF]].

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Élie Aur

Conges

Imt Mines

Albi Peipei

Frederick Benaben
email: frederick.benaben@mines-albi.fr

Col Jacob

Using Virtual Reality to Facilitate Common Operational PicturesŔ epresentation

Keywords: Virtual reality, visualization, common operational picture, cooperation

During crisis, different organizations are involved, each with their jargon and communication devices. Information about the situation is needed by all and it is vital to be able to share the data. To centralize that data, Common Operational Pictures are implemented, but they do not remove the risk of information overload. We propose to use virtual reality to create a virtual environment improving COP representations, thus improving situational awareness and collaborative decision making.

Index Terms: Human-centered computing-Human computer interaction (HCI)-Interaction paradigms-Virtual reality; Humancentered computing-Visualization-Visualization systems and tools-Visualization toolkits

INTRODUCTION

In an emergency situation, shared and accurate awareness of the situation is crucial for the decision-makers to make the best decisions to solve the crisis. Here, by crisis, we refer to military or civilian crises, from battlefields to industries, from floods or fires to terrorist attacks. The emergency response to a crisis situation generally involves several organizations such as a fire department, medical services, the police, or the military. Each of those organizations has a chain of command, and needs information to make the appropriate decision regarding the situation. That information may be relevant to several organizations, but it may not be available to all, depending on their location during the crisis. It is then crucial for all organizations to be able to share the information to effectively respond to a disaster [START_REF] Inoguchi | Visualization methods and associated challenges of disaster data for common operational picture[END_REF]. This information sharing, communication, and coordination between organizations are not easy and often limited [START_REF] Bharosa | Challenges and obstacles in sharing and coordinating information during multi-agency disaster response: Propositions from field exercises[END_REF][START_REF] Netten | Improving Communication in Crisis Management by Evaluating the Relevance of Messages[END_REF]. To overcome those problems, Common Operational Pictures (COP) are implemented during a crisis. A COP is "a single identical display of relevant information shared by more than one command that facilitates collaborative planning and assists all echelons to achieve situational awareness" [START_REF]Military Dictionary[END_REF]. The term "common" means that it is for everyone involved, from the highest decision-maker to the implementer. "Operational" refers to the actual status and development on the crisis site, preferably in real-time, and is opposed to the broader strategic level. And "picture" refers to a unique, visual, and graphical representation of the environment, actors, and actions. They are a display method allowing on-scene and off-scene actors to access and be able to understand and treat the same information about the crisis to achieve situational awareness [START_REF] Wolbers | The Common Operational Picture as Collective Sensemaking[END_REF]. A COP is "established and maintained by the gathering, collating, synthesizing, and disseminating of incident information to all appropriate parties involved" [START_REF]National Incident Management System[END_REF].

In the context of emergency management, where more than one organization is involved, building a common operational picture "is essential for clear communication and coordination of actions among emergency response organizations" [START_REF] Comfort | Crisis Management in Hindsight: Cognition, Communication[END_REF].

COP are often displayed as geographical representations, using Geographic Information Systems (GIS), and emergency management services often use separate GIS interface and communicate only through verbal communication tools [START_REF] Steen-Tveit | Using Audio-Logs for Analyzing the Development of a Common Operational Picture in Multi-agency Emergency Response[END_REF]. Those representations might induce difficulties for the data analysis, particularly in a large scale crisis with a huge amount of gathered data. "The COP needs to be more than a handy geospatial picture. The COP must depict not only what is ongoing currently but also depict those things that facilitate situational awareness over a longer term (readiness, logistics, future availabilities, etc.)" [START_REF] Copeland | Emergency Response: Unity of Effort Through a Common Operational Picture[END_REF]. Besides the geographical data, representing the crisis sites and the actors´positions, a COP needs to show data less easy to represent, such as the available resources, the possible consequences of decisions, or any information that could influence the decision-making process, and all of that data must be always up to date. A challenge arises with this information sharing. During a crisis, a huge quantity of data can be gathered, but not all of it concerns each involved actor. Thus, there is a risk of information overload that must be taken into account: the information must be available to the relevant organization, and must not distract actors that do not need it [START_REF] Fertier | Reducing Information Load to Enhance Collaborative Awareness Thanks to a Pre-selection of Information[END_REF]. This implies the need for a visualization tool that allows the representation of a lot of data, intended for different organizations, in a clear and relevant way.

To sum up, to be as efficient as possible, COP need to overcome the following challenges:

• Display a huge amount of data in a readable and easily understandable way, to decision-makers from different organization

• Display geolocated data, and more abstract data such as resources, consequences or logistics

• Display updated data, in real-time Immersive Analytics is "the use of engaging, embodied analysis tools to support data understanding and decision making" [START_REF] Dwyer | Immersive Analytics: An Introduction[END_REF]. With Virtual Reality (VR), it offers new means of visualization that aims at removing "barriers between people, their data, and the tools they use for analysis by developing more engaging, embodied analysis tools that support data understanding and decision making everywhere and by everyone, either working individually or collaboratively" [START_REF] Dwyer | Immersive Analytics: An Introduction[END_REF]. These technologies allow the users to immerse themselves in the data and viscerally understand them, for instance by extending the range of their stimulated senses. VR is a great learning tool that allows a customized and challenging environment [START_REF] Holopainen | Exploring the Learning Outcomes with Various Technologies -Proposing Design Principles for Virtual Reality Learning Environments[END_REF], and training in VR is increasingly common, whether in the military, medical, or crisis management field [START_REF] Kwok | A Virtual Collaborative Simulation-based Training System[END_REF]. However, it seems that this technology is still confined to the training grounds, and is not yet allowed on the "real" crisis response. As we said, COP mostly consist of paper maps or 2D GIS, which are often heterogeneous and not interoperable. Boards on the walls and pins or post-its complete the set up in crisis cells. These tools are definitely not optimal for sharing and visualizing complex and critical data. We believe that introducing VR to COP could improve that data sharing and visualization, making it smoother, more efficient, and more distributed, which would result in a better situational awareness for crisis managers, thus improving decisionmaking and crisis management. This article presents our proposal for a Common Operational Picture displayed in Virtual Reality. After presenting the background for this proposal, we will describe how VR can improve what is already done, and then how VR can provide new functionalities that will further upgrade crisis management. In the perspectives' part, we link our VR COP with a decision-support software and present our future work.

BACKGROUND

Virtual Reality for data visualization

Virtual reality offers the freedom to intuitively explore and interact with an environment. Users can adopt different points of view, observe objects from different angles, and evolve among them. According to [8], an "immersive environment engage the user to interact with the data", which induces an immersion that "provides valuable intuition of data with complex geometries". The idea is to extend the range of solicited sensory channels and to involve more than just the user's vision. The user is no longer just watching the data from an external point of view: as explained in [START_REF] Mccormack | Multisensory Immersive Analytics[END_REF], with Immersive Analytics and VR, the idea is to be surrounded by data that can be touched, heard, or even smelled. The user can move around the data, approaching it from a variety of points of view, using forces and gestures to interact with it. This would allow more natural interfaces, matching the usual movements of our bodies. Immersive data offer "opportunities to display substantial quantity of data, and use human metaphors such as front and back (where interesting aspects are in front of us, with those items of less interest pushed behind us)" [START_REF] Mccormack | Multisensory Immersive Analytics[END_REF]. Immersion leads to "a demonstrably better perception of datascape geometry, more intuitive data understanding and a better retention of the perceived relationships in the data" [START_REF] Donalek | Immersive and collaborative data visualization using virtual reality platforms[END_REF], and "immersive environments can be exploited to more efficiently extract information from [large amounts of high-dimensional data]" [8]. Collaboration can also be enhanced thanks to VR. Immersive visualization and virtual reality "can provide an easy and natural path to a collaborative data visualization and exploration, where scientists can interact with their data and their colleagues in the same visual space" [START_REF] Donalek | Immersive and collaborative data visualization using virtual reality platforms[END_REF]. One of the advantages of virtual environments is that they could bring together people that are not in the same location, allowing them to work together, surrounded by the shared data. In the context of emergency management and Common Operational Pictures, this could mean that off-site and on-site commanders and decision-makers from several organizations could meet in a virtual environment, sharing a common crisis representation, to decide together how to deal with the situation.

Virtual Reality for Graphical Information System and Common Operational Picture

We couldn't find many examples of VR COP outside of Sci-Fi movies where they are much more common, from "Minority Report" to "Avatar" or "Iron Man 3". However, VR GIS are more common. Among the advantages of using VR to display 3D GIS, one can cite better visualization of the geographical data and an improvement of the associated decision-making, and new ways of interacting with GIS databases. Being able to observe a map in 3D, from several points of view, exo-centered or ego-centered, offers a better understanding of our environment. This, linked with relevant data sharing between several organizations or several levels of command during a crisis, would be very helpful for situational awareness and decision support.

In [START_REF] Hodicky | Decision support system for a commander at the operational level[END_REF], the authors present a project called "Virtual reality devices in ground forces tactical command and control system", accepted by the Defense Department of Czech Republic. The idea is to use 3D visualization of the terrain and virtual reality to increase commander situational awareness, at a tactical and operational level. To do so, they replaced a 2D map representing data from the battlefield with a 3D representation, accessible through head-mounted displays and VR. The result is a better view and a better understanding of the situation, which can now be explored from the inside, in 3D, and support of the decision-making process of the commanders. This 3D visualization and the possibility of exploring the scene from the inside are really interesting, as it offers to the decision-makers an internal but still safe point of view that is not usual in an emergency situation.

Besides the military domain, we found an example of using VR to improve COP in the Cybersecurity domain [START_REF] Kabil | 3D CyberCOP: Collaborative Platform for Cybersecurity Data Analysis and Training[END_REF]. The authors propose a 3D cyber virtual environment for collaborative cybersecurity investigations and reporting practices. In this virtual environment, users have specific roles, and actions are granted according to those roles. Different points of view and filtering systems are offered, which help users understanding the data. The objective is to "merge immersive data visualizations with learning approaches [. . . ]to increase users' cyber situational awareness". From this virtual environment, we want to keep the filtering system and the different roles that can be attributed to users and which define the visible data for each user, depending on what they need to know at a given moment.

Regarding the disaster management field, there does not seem to be VR versions of COP that are actually used in a real crisis. We believe that virtualizing the crisis cell and the COP can offer great advantages and better tools for decision-making and situation awareness. We describe our proposal in the next part.

OUR PROPOSAL: A COP IN VR

Virtual reality can be approached from two angles. First, VR is a great tool to replicate reality. This is great for situational awareness of the crisis: we can imagine having access to a sizable replica of the crisis situation, maintained in real-time with a COP, available to every involved organization and commander. Provided that a 3D model of the crisis place is available, for instance from Google Maps, or Microsoft, or Open Street Map, users could adopt a "God-like" point of view, where they would be able to get a global overview of the situation. With 3D models of buildings, they could also be able to zoom on the model until they can evolve inside of it, in real size, as if they were in the middle of the crisis but without the risks. However, for data visualization, the second angle might be even more interesting. VR can be used to go beyond reality, to break free from the constraints that exist in the real world. As put by [START_REF] Lester | Pathfinder Linden's guide to getting started in Second Life[END_REF], "if you want to teach biology, why build a virtual classroom with desks and a blackboard in Second Life when you could build a whole interactive human cell?". Taken together, these two angles provide great tools for situational awareness and decision making. In this part, we propose a virtual environment dedicated to situation awareness and decision making in a disaster situation, and we present a prototype of this environment. This article presents the prototype in the state it is in at the moment we write, as well as the directions we want to follow. It will evolve in the future, as we find new functionalities to add to it (see Perspectives).

Presentation of the virtual environment

To enhance situational awareness and support decision making, we propose a virtual environment dedicated to the decision-maker in a crisis situation. This environment would be available to every emergency management service involved, as a common place in which they could meet and talk even if they are not physically in the same place. Thus, all of them would be able to use the same interface for the COP. This environment is composed of a 3D map around which users can stand and walk. This map is placed on a table, its size and location are fixed, but users can interact with it through controllers. Thus, it is possible to zoom in and out to show a precise location or the general surroundings of a place. It is also possible to slide the map so that it shows another place, anywhere in the world (which we refer to as panning the map in this article). The map will automatically adapt so that it always fits the size of the block, no matter how zoomed it is, and no matter what location is displayed. The zooming function allows the users to have a "God-like" point of view of the situation, allowing for a good stand back to get a view of the global situation, but also to zoom in the scene until being inside the crisis in real size, experiencing the crisis at the first person, but without taking risks. This would allow the decision-makers to get all the necessary information about the situation, to make the best decision.

The environment also offers the possibility to pin information on the map, such as actors, or sensors. The user can choose from a list the kind of element that he wants to add on the map, and then place it wherever he wants. Those pins can be moved or deleted if needed. The environment can take JSON files as inputs, and produce JSON files as outputs. This means that the environment can exchange data with an external source, like software, or sensors. For instance, sensors could send geolocations for the actors to the virtual environment, which would then be able to show them on the map at their real location, in real-time. The decision-makers would then be able to follow the on-site actors and know their position at each time. Then, if a decision-maker moves an actor's pin, the location would change and would be sent out, via a JSON file, to a decision support system for instance. This could also allow users to communicate with actors on the field: moving an actor's pin on the virtual environment could send a message to the real actor with the new location, showing him where the decision-maker wants him to be. In the same way, adding a new fireman pin on the virtual map could result in a message sent to the on-field commander, telling him to send a fireman to the location where the new pin was placed. We can also imagine to click or select a pin to request information from the corresponding actor, such as the state of the task he has to do, or information about the situation or the resources available on site.

Architecture

The virtual environment was created using Unity© 1 , in the version 2019.3.14.f1. The interaction with the environment is made with 1 https://unity.com/ HTC Vive Pro©2 and controllers. Steam VR©3 was used to deploy the virtual environment and Photon Network© and Photon Voice©4 to implement the multi-player aspect, for its advanced state of connection between users.

The map software development used is Microsoft MapsSDK-Unity 5 . Microsoft officially provides two methods to install Microsoft MapsSDK. One is cloning the sample project offered by Microsoft from Github, another is starting from scratch. In this project, we choose the second option and installed the package directly within Unity® after configuring the Package Manager.

To read and produce JSON files, we used Newtonsoft.Json© 6 . In crisis management, the amount of data can quickly become huge, and the corresponding JSON files can be very complex, with for instance null values and lists of JSON. This explains why we used Newtonsoft.Json© instead of other widely used solutions like LitJ-SON 7 and JsonUtility8 which we tried, but which did not work as well as Newtonsoft.Json© (it generated errors and did not support the complex JSON files that we used).

The workflow of the virtual environment in his current state is shown in Figure 3.

After the user starts running, the map will be initialized. The location and zoom level will be set as the initial value. Then the script will parse the JSON file provided as an input. The initial pins will be put on the map according to the information from the JSON file. Users will then see a 3D map with several pins. They can then start operating on the map, zooming in and out of the map, and panning the map to find the desired location. It is also then possible to add pins with a selected role, to delete or move existing pins, as described in the previous part. The map is updated in real-time as new JSON files are received. This means that the pins on the map will move as the corresponding actor's location on-site is changing, and the information available in the virtual environment can be updated in real-time with data coming from the field. JSON files containing the information displayed on the map are also regularly exported and sent, for instance, to decision support systems. This continuous file exchange allows the COP and connected external systems to always remain up-to-date.

Technical aspects

The main algorithm of this virtual environment is about movement, including panning the map, zooming in or out, and moving the pins. Those functionalities allow an improvement of the crisis visualization, providing the decision-makers with global points of view as well as more precise points of view. Besides, the panning function allows the decision-makers to see the surrounding area without having to use another tool or another map. The core of panning the map is to keep the wanted location at the center of the map. When panning the map, a vector is produced that shows the distance and direction of the map's movement. We needed to calculate the new center point of the map according to the vector. Then the tile supporting the map is updated with the new center point. For moving pins, we need to catch the pin game object first. So we put all pins on separate layers to avoid unnecessary issues. We can use rays to catch the pins on the pins' layer and get the point on the map. Then like for panning the map, we get the movement's vector, calculate the new location, and replace the pin's location. The process of these two operations can be abstracted to the flowchart shown in Figure 4.

PERSPECTIVES 4.1 Improve the existing

The virtual environment that we propose aims to improve situational awareness in a crisis context, in particular by improving COP' representations. As stated in the first parts of that article, COP usually consist of paper maps, boards, and post-it, which are manually maintained according to data exchanged vocally thanks to radio or phone calls. Our environment provides a 3D and interactive map of the crisis location, that is updated automatically and in real-time through JSON exchanges with sensors or decision support systems. The data displayed on this map can also be updated manually if needed.

Let's imagine a crisis cell in our virtual environment. No more paper maps on the wall, they are replaced with a single floating 3D map in the middle of the room. The decision-makers from every emergency management services are standing around the map, enjoying a global vision of the surroundings. They can see each other, communicate with each other, and interact together on the map. At some point, one of them needs to take a closer look. No need to find a more precise map, he can just zoom in on the 3D map. If the 3D model of involved buildings is available, he can even step inside it, to gathered first-hand information on the situation. Information about distance, altitude, or scale is directly available on the map. The available resources are arranged in toolboxes in the room: 4 fire trucks, 20 firemen, 3 police cars, and 15 policemen. . . Those are the actors and resources that can be used on site. They can be placed on the map, either automatically if their geolocation can be informatically sent to the environment, or manually by grabbing them and placing them on the map. As soon as they are on the map, their location is registered in a JSON file, ready to be sent out to on-site actors or decision support systems. Other data can also be registered; such as orders or suggestions for them to do a task or go where their avatar is on the map. Various sensors on the crisis site are connected to the environment: presence, heat, smoke, water level. . . they are sending information that can be displayed on the map as soon as received. This means that a replica of the crisis can be seen in real-time on the 3D map of the virtual crisis cell. In the case of a large scale crisis, a huge amount of data can be gathered, and not all of them are necessary to every decision-maker. In the virtual crisis cell, each decision-maker could have a designated role that would act as a filtering system to only show him the data that is necessary to him. This filter could be activated or deactivated as needed so that he can avoid information overload, but also keep a global vision of the situation. Not all those functionalities are currently available in our environment, so we are going to keep working on it to implement them in the next steps.

A technological crisis management platform (R-IO Suite), described in [START_REF] Benaben | A conceptual framework and a suite of tools to support crisis management[END_REF], has been developed as a decision support system dedicated to improving multi-organizational crisis management. Based on a knowledge database filled with the geographical context of the crisis site and with the available actors (such as firemen, policemen, or medical doctors) and their abilities, this platform can provide a crisis response process aiming to help the different organizations working together most effectively. This platform also allows to track the response to the crisis, and to compare the expected response and the actual situation, to adapt the response process in real-time.

We want to link this platform with our environment, to take advantage of the virtual reality to improve the platform, but also to take advantage of the platform's functionalities to improve our virtual environment. For instance, besides the visualization advantages offered by the virtual environment, we would like to allow the visualization of the knowledge base, using immersive analytics technics. Basically, the idea is to use the virtual environment as a more natural interface to use R-IO Suite. This link will also allow us to provide new functionalities to the crisis management domain, which we described in the next part.

Offer new functionnalities

In a crisis situation, given the necessary data about the context, resources, and objectives, R-IO Suite can provide a BPMN process of how to best solve the crisis, using the resources and availabilities of all emergency management services available most efficiently [START_REF] Benaben | A conceptual framework and a suite of tools to support crisis management[END_REF]. At the moment, this process can only be displayed in 2D on R-IO Suite.

Let's imagine that this process could be available in the virtual crisis cell, as shown in Figure 7. We can imagine having it floating above the map, each task pointing to the concerned actor or location. This would allow decision-makers to know at first glance if actors were unoccupied, or if locations of the crisis site were neglected. For instance, in a fire situation, one of the tasks of the process would be for a fireman to go to a fire and extinguish it. In the crisis cell, when a decision-maker would touch this task, the fireman and the fire would start glowing on the map, to make them easier to notice among the data displayed on the map. We can also imagine that an urgent task would be more visible than a background task and that they would start fading away as they are being completed. If a divergence between the expected state of the crisis and the reality where to be detected, (for instance, a new fire-starting or a fire that should have been extinguished but is not) the environment could solicit multiple sensory channels: we can imagine a sound alarm, vibrations in the handlers, or even a smoky smell appearing in the virtual environment, besides a visual element such as a flashing fire popping on the map. This would reduce the decision-makers' chance of missing new information, and improve their reaction time. Another functionality of R-IO Suite that we would like to implement in this environment is the anticipation. This would allow decision-makers to visualize the planned evolution of the situation on the 3D map. Predicting the state of the crisis in an hour, a day, based on the current situation would be a valuable tool to help make the good decision to manage the crisis. This would also allow commanders to test solutions, or to test new conditions (like weather conditions or the number of involved actors). Visualizing them, and their consequences, in the virtual environment before ordering them in the real crisis site would allow commanders to check the relevance of a solution, and thus applying it with fewer risks of making mistakes. Apart from the functionalities of R-IO Suite, virtual reality could also provide new ways of analyzing the crisis retrospectively. All the data gathered and shared in the virtual environment, as well as the manipulations and actions taken during the crisis, could be registered. This would allow decision-makers to re-watch the management of the crisis to look for what worked or what did not work so well. Thanks to immersive analytics, exploring and analyzing the huge amount of data gathered during the crisis would be easier. Lessons would be easier to retrieve and thus, mistakes would be easier to avoid next time.

Figure 1 :

 1 Figure 1: Inputs and outputs of the environment

Figure 2 :

 2 Figure 2: View of the map in the virtual environment

Figure 3 :

 3 Figure 3: The workflow of the virtual environment

Figure 4 :

 4 Figure 4: Flowchart of the algorithms

Figure 5 :

 5 Figure 5: Picture of the virtual crisis cell

Figure 6 :

 6 Figure 6: Details of the virtual crisis cell

Figure 7 :

 7 Figure 7: The process above the virtual map

Figure 8 :

 8 Figure 8: Anticipation example

https://www.vive.com/fr/product/vive-pro/

https://store.steampowered.com/steamvr?l=french

https://www.photonengine.com/

https://www.microsoft.com/en-us/maps/mixed-reality

https://www.newtonsoft.com/json

https://litjson.net/

https://docs.unity3d.com/ScriptReference/JsonUtility.html