The slow-fast continuum is a commonly used framework to describe variation in life-history strategies across species. Individual life histories have also been assumed to follow a similar pattern, ...especially in the pace-of-life syndrome literature. However, whether a slow-fast continuum commonly explains life-history variation among individuals within a population remains unclear. Here, we formally tested for the presence of a slow-fast continuum of life histories both within populations and across species using detailed long-term individual-based demographic data for 17 bird and mammal species with markedly different life histories. We estimated adult lifespan, age at first reproduction, annual breeding frequency, and annual fecundity, and identified the main axes of life-history variation using principal component analyses. Across species, we retrieved the slow-fast continuum as the main axis of life-history variation. However, within populations, the patterns of individual life-history variation did not align with a slow-fast continuum in any species. Thus, a continuum ranking individuals from slow to fast living is unlikely to shape individual differences in life histories within populations. Rather, individual life-history variation is likely idiosyncratic across species, potentially because of processes such as stochasticity, density dependence, and individual differences in resource acquisition that affect species differently and generate non-generalizable patterns across species.
To maximize long-term average reproductive success, individuals can diversify the phenotypes of offspring produced within a reproductive event by displaying the ‘coin-flipping’ tactic. Wild boar (Sus ...scrofa scrofa) females have been reported to adopt this tactic. However, whether the magnitude of developmental plasticity within a litter depends on stochasticity in food resources has not been yet investigated. From long-term monitoring, we found that juvenile females produced similar-sized fetuses within a litter independent of food availability. By contrast, adult females adjusted their relative allocation to littermates to the amount of food resources, by providing a similar allocation to all littermates in years of poor food resources but producing highly diversified offspring phenotypes within a litter in years of abundant food resources. By minimizing sibling rivalry, such a plastic reproductive tactic allows adult wild boar females to maximize the number of littermates for a given breeding event.
An increasing number of empirical studies aim to quantify individual variation in demographic parameters because these patterns are key for evolutionary and ecological processes. Advanced approaches ...to estimate individual heterogeneity are now using a multivariate normal distribution with correlated individual random effects to account for the latent correlations among different demographic parameters occurring within individuals. Despite the frequent use of multivariate mixed models, we lack an assessment of their reliability when applied to Bernoulli variables.
Using simulations, we estimated the reliability of multivariate mixed effect models for estimating correlated fixed individual heterogeneity in demographic parameters modelled with a Bernoulli distribution. We evaluated both bias and precision of the estimates across a range of scenarios that investigate the effects of life‐history strategy, levels of individual heterogeneity and presence of temporal variation and state dependence. We also compared estimates across different sampling designs to assess the importance of study duration, number of individuals monitored and detection probability.
In many simulated scenarios, the estimates for the correlated random effects were biased and imprecise, which highlight the challenge in estimating correlated random effects for Bernoulli variables. The amount of fixed among‐individual heterogeneity was frequently overestimated, and the absolute value of the correlation between random effects was almost always underestimated. Simulations also showed contrasting performances of mixed models depending on the scenario considered. Generally, estimation bias decreases and precision increases with slower pace of life, large fixed individual heterogeneity and large sample size.
We provide guidelines for the empirical investigation of individual heterogeneity using correlated random effects according to the life‐history strategy of the species, as well as, the volume and structure of the data available to the researcher. Caution is warranted when interpreting results regarding correlated individual random effects in demographic parameters modelled with a Bernoulli distribution. Because bias varies with sampling design and life history, comparisons of individual heterogeneity among species is challenging. The issue addressed here is not specific to demography, making this warning relevant for all research areas, including behavioural and evolutionary studies.
Summary
The founding evolutionary theories of ageing indicate that the force of mortality imposed by environmental factors should influence the strength of natural selection against actuarial ...senescence and its evolution. To rigorously test this idea, field biologists need methods that yield estimates of age‐specific mortality according to cause of death.
Here, we present existing methods commonly applied in studies of human health that could be used to accomplish these goals in studies of wild species for which fate can be determined with certainty. We further present a new application of hidden Markov models for capture‐reencounter studies of wild animals that can be used to estimate age‐specific trajectories of cause‐specific mortality when detection is imperfect.
By applying our new hidden Markov model with the e‐surge and mark softwares to capture‐reencounter data sets for long‐lived species, we demonstrate that senescence can be severe for natural causes of mortality in the wild, while being largely non‐existent for anthropogenic causes.
Moreover, we show that conflation of mortality causes in commonly used survival analyses can induce an underestimation of the intensity of senescence and overestimation of mortality for pre‐senescent adults. These biases have important implications for both age‐structured population modelling used to guide conservation and comparative analyses of senescence across species. Similar to frailty, individual differences in causes of death can generate individual heterogeneity that needs to be accounted for when estimating age‐specific mortality patterns.
The proposed hidden Markov method and other competing risk estimators can nevertheless be used to formally account for these confounding effects, and we additionally discuss how our new method can be used to gain insight into the mechanisms that drive variation in ageing across the tree of life.
1. An increasing number of empirical studies aim to quantify individual variation in demographic parameters because these patterns are key for evolutionary and ecological processes. Advanced ...approaches to estimate individual heterogeneity are now using a multivariate normal distribution with correlated individual random effects to account for the latent correlations among different demographic parameters occurring within individuals. Despite the frequent use of multivariate mixed models, we lack an assessment of their reliability when applied to Bernoulli variables.
2. Using simulations, we estimated the reliability of multivariate mixed effect models for estimating correlated fixed individual heterogeneity in demographic parameters modelled with a Bernoulli distribution. We evaluated both bias and precision of the estimates across a range of scenarios that investigate the effects of life-history strategy, levels of individual heterogeneity and presence of temporal variation and state dependence. We also compared estimates across different sampling designs to assess the importance of study duration, number of individuals monitored and detection probability.
3. In many simulated scenarios, the estimates for the correlated random effects were biased and imprecise, which highlight the challenge in estimating correlated random effects for Bernoulli variables. The amount of fixed among-individual heterogeneity was frequently overestimated, and the absolute value of the correlation between random effects was almost always underestimated. Simulations also showed contrasting performances of mixed models depending on the scenario considered. Generally, estimation bias decreases and precision increases with slower pace of life, large fixed individual heterogeneity and large sample size.
4. We provide guidelines for the empirical investigation of individual heterogeneity using correlated random effects according to the life-history strategy of the species, as well as, the volume and structure of the data available to the researcher. Caution is warranted when interpreting results regarding correlated individual random effects in demographic parameters modelled with a Bernoulli distribution. Because bias varies with sampling design and life history, comparisons of individual heterogeneity among species is challenging. The issue addressed here is not specific to demography, making this warning relevant for all research areas, including behavioural and evolutionary studies.
Témoignages Métraux, Daniel; Schulmann, Fernande; Lévi-Strauss, Monique ...
Journal de la Société des américanistes,
01/2017
Journal Article
Recenzirano
Odprti dostop
La série de colloques organisés pour honorer la mémoire d’Alfred Métraux a démarré, en décembre 2013, année du cinquantenaire de sa disparition, par une succession de témoignages de parents, de ...collègues et d’amis qui avaient été ses proches. Empêché d’assister en personne, Daniel Métraux, Professor of Asian Studies au Mary Baldwin College (Staunton VA), a cependant tenu à envoyer le courrier reproduit ci-dessous. En son absence, Philippe Erikson en a donné lecture dans la salle de cinéma du ...
Évaluer prospectivement la toxicité chronique gastro-intestinale chez les patientes atteintes de cancer du col utérin traité par irradiation classique ou avec modulation d’intensité (RCMI).
Entre ...juin 2005 et septembre 2013, 109 patientes ont bénéficié d’une radiothérapie externe suivie d’une curiethérapie pour un cancer du col utérin à l’institut de cancérologie de Lorraine. Chaque patiente prise en charge par RCMI a été appariée à une patiente traitée par irradiation classique sur les critères suivants : chimiothérapie concomitante, complément de dose ganglionnaire, traitement de l’aire ganglionnaire lombo-aortique, âge. Le recueil de toxicité était prospectif selon la classification du Radiation Therapy Oncology Group. L’objectif principal était de comparer l’incidence de la toxicité digestive chronique entre les deux groupes. L’influence des paramètres dosimétriques sur la toxicité digestive chronique a été étudiée dans un second temps. La comparaison de la toxicité aiguë, la toxicité chronique génito-urinaire, la survie globale et la survie sans récidive constituaient des objectifs secondaires.
Soixante-six patientes ont pu être appariées. La probabilité de survie globale à 36 mois était de 71 % après irradiation classique contre 73 % après RCMI (p=0,54). Il n’existait significativement pas de différence entre les deux groupes, en termes de toxicité chronique digestive (p=0,17), ni de toxicité aiguë digestive (p=0,6445) et génito-urinaire (p=0,5724). La RCMI épargnait significativement dès 30Gy l’intestin grêle (p==0,0006) et le rectum (p=0,0046), et la vessie à 45Gy (p<0,001). L’incidence de la toxicité génito-urinaire était significativement différente entre les deux groupes (p=0,03), en faveur de la radiothérapie classique.
Notre étude ne semble pas mettre en évidence de différence significative concernant la survenue de toxicité chronique digestive entre les deux groupes. L’efficacité clinique paraît comparable. Des études avec un effectif plus important et une durée de suivi plus longue doivent être menées.
To evaluate prospectively chronic gastrointestinal toxicity in patients with cervical cancer treated with conventional irradiation or with intensity-modulated irradiation (IMRT).
Between June 2005 and September 2013, 109 patients underwent external radiotherapy followed by brachytherapy for cervical cancer at the “Institut de Cancérologie de Lorraine”. Each patient receiving IMRT was paired with a patient receiving conventional radiotherapy on the following criteria: concomitant chemotherapy, additional nodal dose, treatment of para-aortic lymph node area, age. The toxicity collection was prospective using the RTOG scale. The main objective was to compare the incidence of gastrointestinal toxicity chronic between the two groups. In a second time, the influence of dosimetric parameters on chronic GI toxicity was investigated. Comparisons of acute toxicity, chronic genitourinary toxicities, overall survival, disease-free survival were secondary objectives.
Sixty-six patients were able to be matched. Overall survival at 36 months was 71% in the conventional radiotherapy group against 73% in the IMRT group (P=0.54). There was no significant difference between the two groups in terms of digestive chronic toxicity (P=0.17), nor in terms acute gastrointestinal toxicities (P=0.6445) and genitourinary (P=0.5724). IMRT spared significantly small bowel (P=0.0006) and rectum (P=0.0046) from 30Gy dose, and bladder from 45Gy (P<0.001). The incidence of genitourinary toxicity was significantly different between the two groups (P=0.03) in favor of conventional radiotherapy.
Our study does not seem to show significant difference in the occurrence of chronic gastrointestinal toxicities between the two groups. Clinical efficacy seems comparable. Larger studies with longer follow-up period should be conducted.
Évaluer prospectivement la toxicité chronique gastro-intestinale après une radiothérapie classique ou avec modulation d’intensité (RCMI) du cancer du col utérin.
Entre novembre 2009 et septembre ...2013, 33 patientes ont bénéficié, à l’institut de cancérologie de Lorraine, d’une RCMI puis d’une curiethérapie pour un cancer du col utérin. Ces patientes ont été appariées à un groupe témoin traité par irradiation classique selon quatre critères : chimiothérapie, complément de dose ganglionnaire, traitement de la chaîne lomboaortique, âge (±5 ans). Le recueil de toxicité était prospectif selon la classification du Radiation Therapy Oncology Group (RTOG). L’objectif principal était l’évaluation de la toxicité digestive chronique. Les objectifs secondaires concernaient la toxicité aiguë génito-urinaire et digestive, la toxicité chronique génito-urinaire, la réponse histologique, la survie globale et la survie sans récidive.
Au total, 66 patientes ont pu être appariées. La durée de suivi médiane était de 30,1 mois. La probabilité de survie globale à 36 mois était de 71 % après radiothérapie classique et 73 % après RCMI (p=0,54). À 12 mois, 90 % des patientes ayant reçu une radiothérapie classique ne souffraient pas de toxicité digestive chronique, contre 83 % de celles ayant reçu une RCMI. À 24 mois et à 36 mois, elles étaient alors respectivement 70 % et 59 % à ne souffrir d’aucune toxicité digestive (p=0,17).
La chimioradiothérapie concomitante avec modulation d’intensité est bien tolérée. L’efficacité semble comparable à celle de la radiothérapie classique. Une étude avec plus de patientes et un suivi plus long serait nécessaire pour compléter notre analyse.
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