ETUDE DE LA PLASTICITE DES REPONSES ADAPTATIVES PAR UNE APPROCHE DE MODELISATION MULTICRITERE CHEZ LA TRUITE ARC-ENCIEL

The ability of an organism to respond to an environmental perturbation is a growing scientific concern in animal ecology and animal production sciences. Depending on animal vulnerability, these environmental perturbations can affect health, welfare, or fitness of the animal. Robustness, defined as the ability to resist to environmental change, are therefore important components of production sustainability or biodiversity. Our work aimed at better estimating and characterizing the robustness in rainbow trout by describing the degree of perturbation when facing an acute perturbation. Adaptive responses to environmental perturbations are diversified and numerous, but they can be described by temporal patterns giving indications on the resistance, the recovery ability or the environmental sensitivity of the animal. The integration of these features provides an estimation of the degree of perturbation of the animal facing the environmental change. Physiological and behavioral responses of two isogenic lines (within each line, all individuals have the same genome) of rainbow trout were followed before, during and after an acute challenge. The effects of a confinement or a hypercapnia challenge were investigated. Temporal patterns were analyzed in order to characterize within and between line variabilies in reactivity to the challenge and recovery capacities.All measures were impacted by the challenges, indicating that both lines triggered adaptive responses. The cortisol release rate was the only measure showing significant mean differences between the two lines in both studies. Multivariate analyses highlighted two independent coping strategies consisting in either favoring behavior or physiology modification. The results showed also a strong and unexpected within line variability, suggesting the importance of life history on the degree of perturbation. At last, the between-study comparison showed an inversion in physiological reactivity between the two lines, suggesting that robustness is challenge-specific or robustness implies challenge-specific reactivities.This study sets also the basis for a model able to precisely and explicitly characterize the degree of perturbation of a perturbed system. The model was validated on the data analyzed in this project but should be sufficiently generic to cope with data from other species.La capacité des animaux à faire face à des perturbations environnementales est une préoccupation croissante en écologie et en production. En fonction de la vulnérabilité des animaux, les modifications environnementales peuvent impacter leur santé, leur bien-être ou leur capacité de reproduction. La robustesse, définie comme la capacité à conserver ses fonctions malgré les perturbations environnementales est donc une composante importante de la durabilité d’une production ou de la biodiversité. Le travail présenté ici vise à apporter des éléments de réponses quant à la robustesse chez la truite arc-en-ciel, en décrivant le degré de perturbation face à une perturbation aiguë. Le degré de perturbation de l’animal est décrit en intégrant les différentes réponses adaptatives de l’animal face à une perturbation donnée. Des réponses adaptatives physiologiques et comportementales ont été suivies chez deux lignées isogéniques (au sein de chaque lignée tous les individus présentent le même génome) de truite arc-en-ciel avant, pendant et après une perturbation aiguë. Les effets de challenges aigus de confinement ou d’hypercapnie ont été étudiés. Les cinétiques de réponses ont été analysées afin de faire ressortir la variabilité intra- et inter-lignée de réactivité au challenge et de capacité à récupérer du challenge. Chez les deux lignées, toutes les mesures effectuées montrent un effet de la perturbation indiquant la mise en place de mécanismes adaptatifs. La mesure de cortisol dans l’eau s’est avérée être la seule mesure montrant des différences moyennes inter-lignées de réponses face au challenge. Parallèlement, les analyses multivariées ont souligné la présence de deux stratégies d’adaptation indépendantes, consistant à modifier son comportement ou sa physiologie. Nous avons également observé une forte et inattendue variabilité intra-lignée, illustrant l’importance de l’histoire de vie sur le degré de perturbation de la truite arc-en-ciel. Finalement, la comparaison entre les deux expériences montre une inversion de réactivité physiologique entre les deux lignées isogéniques suggérant que la robustesse est challengespécifique ou que la robustesse nécessite des réactivités challenge-specifiques. Ce travail pose également les bases d’un modèle capable de caractériser de façon précise et explicite les degrés de perturbation à partir de cinétiques de réponses adaptativesface à une perturbation aiguë. Le modèle a été validé sur des données de truite arc-en-ciel mais devrait être suffisamment générique pour s’adapter aux réponses d’autres espèces

Nature-based tourism elicits a phenotypic shift in the coping abilities of fish

Nature-based tourism is gaining extensive popularity, increasing the intensity and frequency of human-wildlife contacts. As a consequence, behavioral and physiological alterations were observed in most exposed animals. However, while the majority of these studies investigated the effects of punctual exposure to tourists, the consequences of constant exposition to humans in the wild remains overlooked. This is an important gap considering the exponential interest for recreational outdoor activities. To infer long-term effects of intensive tourism, we capitalized on Odontostilbe pequira, a short-lived sedentary Tetra fish who spends its life close to humans, on which it feeds on dead skin. Hence, those fish are constantly exposed to tourists throughout their lifecycle. Here we provide an integrated picture of the whole phenomenon by investigating, for the first time, the expression of genes involved in stress response and neurogenesis, as well as behavioral and hormonal responses of animals consistently exposed to tourists. Gene expression of the mineralocorticoid (and cortisol) receptor (mr) and the neurogenic differentiation factor (NeuroD) were significantly higher in fish sampled in the touristic zone compared to those sampled in the control zone. Additionally, after a simulated stress in artificial and controlled conditions, those fish previously exposed to visitors produced more cortisol and presented increased behavioral signs of stress compared to their non-exposed conspecifics. Overall, nature-based tourism appeared to shift selection pressures, favoring a sensitive phenotype that does not thrive under natural conditions. The ecological implications of this change in coping style remain, nevertheless, an open question

Temperature increase and its effects on fish stress physiology in the context of global warming

The capacity of fishes to cope with environmental variation is considered to be a main determinant of their fitness and is partly determined by their stress physiology. By 2100, global ocean temperature is expected to rise by 1–4°C, with potential consequences for stress physiology. Global warming is affecting animal populations worldwide, through chronic temperature increases and an increase in the frequency of extreme heatwave events. As ectotherms, fishes are expected to be particularly vulnerable to global warming. Although little information is available about the effects of global warming on stress physiology in nature, multiple studies describe the consequences of temperature increases on stress physiology in controlled laboratory conditions, providing insight into what can be expected in the wild. Chronic temperature increase constitutes a physiological load than can alter the ability of fishes to cope with additional stressors, which might compromise their fitness. Besides, rapid temperature increases are known to induce acute stress responses in fishes and might be of ecological relevance in particular situations. This review summarizes knowledge about effects of temperature increases on the stress physiology of fishes, and discusses these in a context of global warming

On the use of a simple physical system analogy to study robustness features in animal sciences

Environmental perturbations can affect the health, welfare, and fitness of animals. Being able to characterize and phenotype adaptive capacity is therefore of growing scientific concern in animal ecology and in animal production sciences. Terms borrowed from physics are commonly used to describe adaptive responses of animals facing an environmental perturbation, but no quantitative characterization of these responses has been made. Modeling the dynamic responses to an acute challenge was used in this study to facilitate the characterization of adaptive capacity and therefore robustness. A simple model based on a spring and damper was developed to simulate the dynamic responses of animals facing an acute challenge. The parameters characterizing the spring and the damper can be interpreted in terms of stiffness and resistance to the change of the system. The model was tested on physiological and behavioral responses of rainbow trout facing an acute confinement challenge. The model has proven to properly fit the different responses measured in this study and to quantitatively describe the different temporal patterns for each statistical individual in the study. It provides therefore a new way to explicitly describe, analyze and compare responses of individuals facing an acute perturbation. This study suggests that such physical models may be usefully applied to characterize robustness in many other biological systems

Group size, temperature and body size modulate the effects of social hierarchy on basal cortisol levels in fishes

Social rank in a structured society has been linked to basal levels of glucocorticoids in various species, with dominant individuals generally presenting lower levels than subordinates. The biotic and abiotic factors influencing glucocorticoids levels across social ranks are still, however, unclear in fishes. We investigated the influences of group size, fish size, sex, age, and reproduction type, plus water salinity and temperature, on the basal levels of cortisol, the major stress hormone in fishes. A phylogenetically controlled meta-analysis was performed on data from 72 studies over 22 species of fishes. As expected, dominants generally exhibited lower levels of cortisol than subordinates. More importantly, the strength of the correlation between cortisol and rank was modulated by three main factors, group size, environmental temperature, and fish size. Differences in basal cortisol between dominants and subordinates were significantly greater in small groups (dyadic contexts) when compared to larger groups. Differences between dominants and subordinates were also greater in temperate regions when compared to the tropics, and in species with larger body size. These results provide valuable insights into the links among hierarchy, stress and metabolism in fishes

Multiple working hypotheses for hyperallometric reproduction in fishes under metabolic theory

WOS:000564687300002Hyperallometric reproduction, whereby large females contribute relatively more to the renewal of the population than small females, is purported to be widespread in wild populations, especially in fish species. Bioenergetic models derived from a sufficiently general metabolic theory should be able to capture such a relationship but it was recently stated that no existing models adequately capture hyperallometric reproduction. If this were true it would seriously challenge our capacity to develop robust predictions of the life history and population dynamics in changing environments for many species. Here, using the European sea bass (Dicentrarchus labrax) as a test case, we demonstrate multiple ways that hyperallometric reproduction in a population may emerge from the Dynamic Energy Budget (DEB) theory, some inherently related to the metabolism and life history and others related to plastic or genetically based intraspecific variation. In addition, we demonstrate an empirical and modelled hypoallometric scaling of reproduction in this species when environment is controlled. This work shows how complex metabolic responses may underlie apparently simple relationships between weight and reproduction in the wild and provides new and testable hypotheses regarding the factors driving reproductive scaling relationships found in the wild

Human protection drives the emergence of a new coping style in animals

Wild animals face novel environmental threats from human activities that may occur along a gradient of interactions with humans. Recent work has shown that merely living close to humans has major implications for a variety of antipredator traits and physiological responses. Here, we hypothesize that when human presence protects prey from their genuine predators (as sometimes seen in urban areas and at some tourist sites), this predator shield, followed by a process of habituation to humans, decouples commonly associated traits related to coping styles, which results in a new range of phenotypes. Such individuals are characterized by low aggressiveness and physiological stress responses, but have enhanced behavioral plasticity, boldness, and cognitive abilities. We refer to these individuals as “preactive,” because their physiological and behavioral coping style falls outside the classical proactive/reactive coping styles. While there is some support for this new coping style, formal multivariate studies are required to investigate behavioral and physiological responses to anthropogenic activities

Spatial distribution and activity patterns as welfare indicators in response to water quality changes in European sea bass, Dicentrarchus labrax

International audienceIn aquaculture,fish are exposed to unavoidable stressors that can be detrimental for their health and welfare.However, welfare in farmedfish can be difficult to assess, and, so far, no standardized test has been universallyaccepted as a welfare indicator. This work contributes to the establishment of behavioural welfare indicators in amarine teleost in response to different water quality acute stressors. Groups of tenfish were exposed to highTotal Ammonia Nitrogen concentration (High TAN, 18 mg.L-1), Hyperoxia (200 % O2saturation), Hypoxia (20 %O2saturation), or control water quality (100% O2saturation and TAN < 2.5 mg.L-1) over 1 hour. Fish were thentransferred in a novel environment for a group behaviour test under the same water quality conditions over 2hours. Videos were recorded to assess thigmotaxis, activity and group cohesion. After this challenge, plasmacortisol concentration was measured in a subsample, while individual behavioural response was measured in theotherfish using novel tank diving test. Prior to this study, the novel tank diving test was validated as a beha-vioural challenge indicative of anxiety state, by using nicotine as anxiolytic drug. Overall, all stress conditionsinduced a decrease in activity and thigmotaxis and changes in group cohesion while onlyfish exposed toHypoxia and High TAN conditions displayed elevated plasma cortisol concentrations. Inpost-stress condition,activity was still affected but normal behaviour was recovered within the 25 minutes of the test duration. Ourwork suggests that the activity, thigmotaxis and group cohesion are good behavioural indicators of exposure todegraded water quality, and could be used as standardized measures to assessfish welfare