Multi-generational effect of an heavy metal pollution on Caenorhabditis elegans

Assessing the evolutionary responses of long-term exposed populations requires multigeneration ecotoxicity tests. However, the analysis of the data from these tests is not straightforward. Mechanistic models allow the in-depth analysis of the variation of physiological traits over many generations, by quantifying the trend of the physiological and toxicological parameters of the model. In this study we assessed the multi-generational effect of a heavy metal, namely uranium, on the life-history traits of an ubiquitous nematode, Caenorhabditis elegans..

Prediction of effects on chemicals on three-spined stickleback populations in mesocosms

To improve environmental risk assessment, mechanistic models predicting the impacts of toxicants on populations such as individual-based models (IBMs) was suggested as relevant tools. Furthermore, IBMs can be coupled with DEB (Dynamic Energy Budget) models which describe physiological processes of an organism. However, the development of DEB-IBMs requires a large number of data on the organism and the population dynamics which make them difficult to build. To this aim, data from mesocosm experiments can be of great interest for developing and calibrating DEB-IBMs. One of the species that can be used in mesocosm experiments is the three-spined stickleback (Gasterosteus aculeatus). Furthermore, the ecology and biology of this teleost fish is relatively well-known and a DEB model for this organism has already been developed. In this study, we used data from several mesocosm experiments to describe stickleback populations under control conditions, and exposed to three concentrations of an endocrine disruptor, the Bisphenol A (BPA, 1, 10 and 100 µg/L). First, using two set of experiments in control conditions, different ways of integrated temperature and food data was tested in order to assess the relevance of the DEB model calibrated with laboratory data for sticklebacks in mesocosms. Then, the DEB-IBM was developed and calibrated and simulated endpoints of the population dynamics in control conditions were compared to the observed enpoints of the population dynamics in control conditions or exposed to BPA. We showed that the DEB model successfully predicted the growth of mature male and female sticklebacks for two set of experiments in control conditions. Furthermore, the calibrated DEB-IBM successfully predicted dynamics of stickleback populations during mesocosm experiments in control conditions. Indeed, the different descriptive variables of the populations (population size, male, female and juvenile frequencies, lengths and coefficient of variations) were well described and were used to compare with the endpoints of mesocosms exposed to BPA. In conclusion, simulated enpoints of stickleback populations can thus be used as a baseline to compare exposed populations to BPA in order to improve environmental risk assessment. In a second step, the DEB-IBM could be adapted in order to introduce the effects of toxicants such as BPA on the individuals and thus extrapolate the effects at the population level

Evaluating effects of a multi-generation pollution on Caenorhabditis elegans' population

The assessment of toxic effects at biologically and ecologically relevant scales is an important challenge in ecosystem protection. Indeed, in most time, stressors impact populations over longterm. The selection pressure exerted by a pollutant is known to amplify the phenomenon of natural selection and could lead to evolutionary changes across generations. It is therefore important to study the evolutionary response of a population submitted to a long term stress. Regarding this background, we assessed the evolution of two populations (control and exposed to 1.1 mM of the heavy radiotoxic metal, uranium) of the ubiquitous nematode Caenorhabditis elegans submitted to a long-term exposure to uranium. The experimentation was conducted over 16 generations and life history traits (growth, reproduction and survival) as well as dose-response evolution were assessed. These parameters were followed daily on individuals extracted from the populations and exposed to a range of concentration (from 0 to 1.2 mM U). Our experiment showed an increase of adverse effects as a function of uranium concentration. Indeed the NOEC for reproduction and growth traits were respectively of 0.5 mM U and 0.9 mM U. Moreover, reproduction and growth were respectively reduced by over 60% and 20% for individual exposed at 1.1 mM U. This reduction remained constant throughout the generations. We also pointed out the appearance of genetics differentiations on reproduction traits throughout the generations. This differentiation, observed from generation 3, showed us that the total egg-laying of the uranium population was significantly decreased compared with the control population. In contrast, no differentiations were highlighted on growth traits. Our results confirm the importance of studying environmental risks related to pollutant through multi-generational studies in order to capture effects that may appear after several generation of exposition

Effects of chronic gamma irradiation : a multigenerational study using Caenorhabditis elegans

The effects of chronic exposure to 137Cs gamma radiation (dose rate ranging from 6.6 to 42.7 mGy h-1) on growth and reproductive ability were carried out over three generations of Caenorhabditis elegans (F0, F1, and F2). Exposure began at the egg stage for the first generation and was stopped at the end of laying of third-generation eggs (F2). At the same time, the two subsequent generations from parental exposure were returned to the control conditions (F1’ and F2’). There was no radiation-induced significant effect on growth, hatchability, and cumulative number of larvae within generations. Moreover, no significant differences were found in growth parameters (hatching length, maximal length, and a constant related to growth rate) among the generations. However, a decrease in the cumulative number of larvae across exposed generations was observed between F0 and F2 at the highest dose rate (238.8 ± 15.4 and 171.2 ± 13.1 number of larvae per individual, respectively). Besides, the F1' generation was found to lay significantly fewer eggs than the F1 generation for tested dose rates 6.6, 8.1, 19.4, and 28.1 mGy h-1. Our results confirmed that reproduction (here, cumulative number of larvae) is the most sensitive endpoint affected by chronic exposure to ionizing radiation. The results obtained revealed transgenerational effects from parental exposure in the second generation, and the second non-exposed generation was indeed more affected than the second exposed generation

Compréhension et prédiction des effets de substances chimiques sur la dynamique de population de l'épinoche à trois épines en mésocosme

En écotoxicologie, le développement de modèles mécanistiques prédisant les impacts des contaminants sur la viabilité des populations permettrait d’obtenir des outils pertinents pour une meilleure évaluation des risques environnementaux. En effet, des modèles individu-centré (IBM) couplés à des modèles bioénergétiques comme le modèle DEB (Dynamic Energy Budget) sont utilisés pour extrapoler les effets des substances chimiques sur l’organisme aux effets sur les populations. Néanmoins, les modèles DEB, permettant de décrire les processus physiologiques d’un individu (croissance, reproduction, maintenance), sont généralement calibrés avec des données de laboratoire en condition standard. En outre, la pertinence de ces modèles pour des organismes en conditions naturelles a jusqu’ici été peu étudiée alors que les facteurs environnementaux pourraient affecter leurs processus énergétiques. L’objectif de cette étude est donc d’évaluer la pertinence d’un modèle DEB calibré en laboratoire pour prédire les processus physiologiques d’un poisson, l’épinoche à trois épines (Gasterosteus aculeatus), en absence de contaminant et soumis à des variations naturelles de facteurs écologiques (température et nourriture). Pour cela, des données de l’INERIS provenant de cinq expériences de sept mois en mésocosmes sont disponibles. La température de l’eau a été mesurée toutes les 10 minutes et les macro-invertébrés et le zooplancton ont été échantillonnés toutes les quatre semaines afin d’estimer la quantité de proies disponibles pour l’épinoche au cours du temps. L’implémentation des données de température et nourriture dans le modèle DEB a nécessité une connaissance précise de la biologie et de l’écologie de l’épinoche à trois épines. La capacité prédictive du modèle DEB lors de variations simultanées de la température et nourriture a été évaluée sur les données individuelles de tailles des poissons introduits en début d’expérience. La variabilité interindividuelle des épinoches a été prise en compte. La comparaison des distributions de tailles prédites par le modèle DEB et observées en fin d’expérience a permis de valider ce modèle pour prédire les processus physiologiques de l’épinoche à trois épines en conditions semi-naturelles et en absence de stress chimique. Cette étude est une première étape de validation d’un modèle DEB-IBM permettant de prédire la dynamique de population de l’épinoche à trois épines en condition témoin. Celui-ci pourra être ensuite adapter pour intégrer les effets toxiques de substances chimiques. Le modèle obtenu sera ainsi pertinent d'un point de vue écologique et permettra de mettre en évidence les effets significatifs des substances chimiques sur la population des épinoches à trois épines

Compréhension et prédiction des effets de substances chimiques sur la dynamique de population de l'épinoche à trois épines en mésocosme

En écotoxicologie, le développement de modèles mécanistiques prédisant les impacts des contaminants sur la viabilité des populations permettrait d’obtenir des outils pertinents pour une meilleure évaluation des risques environnementaux. En effet, des modèles individu-centré (IBM) couplés à des modèles bioénergétiques comme le modèle DEB (Dynamic Energy Budget) sont utilisés pour extrapoler les effets des substances chimiques sur l’organisme aux effets sur les populations. Néanmoins, les modèles DEB, permettant de décrire les processus physiologiques d’un individu (croissance, reproduction, maintenance), sont généralement calibrés avec des données de laboratoire en condition standard. En outre, la pertinence de ces modèles pour des organismes en conditions naturelles a jusqu’ici été peu étudiée alors que les facteurs environnementaux pourraient affecter leurs processus énergétiques. L’objectif de cette étude est donc d’évaluer la pertinence d’un modèle DEB calibré en laboratoire pour prédire les processus physiologiques d’un poisson, l’épinoche à trois épines (Gasterosteus aculeatus), en absence de contaminant et soumis à des variations naturelles de facteurs écologiques (température et nourriture). Pour cela, des données de l’INERIS provenant de cinq expériences de sept mois en mésocosmes sont disponibles. La température de l’eau a été mesurée toutes les 10 minutes et les macro-invertébrés et le zooplancton ont été échantillonnés toutes les quatre semaines afin d’estimer la quantité de proies disponibles pour l’épinoche au cours du temps. L’implémentation des données de température et nourriture dans le modèle DEB a nécessité une connaissance précise de la biologie et de l’écologie de l’épinoche à trois épines. La capacité prédictive du modèle DEB lors de variations simultanées de la température et nourriture a été évaluée sur les données individuelles de tailles des poissons introduits en début d’expérience. La variabilité interindividuelle des épinoches a été prise en compte. La comparaison des distributions de tailles prédites par le modèle DEB et observées en fin d’expérience a permis de valider ce modèle pour prédire les processus physiologiques de l’épinoche à trois épines en conditions semi-naturelles et en absence de stress chimique. Cette étude est une première étape de validation d’un modèle DEB-IBM permettant de prédire la dynamique de population de l’épinoche à trois épines en condition témoin. Celui-ci pourra être ensuite adapter pour intégrer les effets toxiques de substances chimiques. Le modèle obtenu sera ainsi pertinent d'un point de vue écologique et permettra de mettre en évidence les effets significatifs des substances chimiques sur la population des épinoches à trois épines

Evaluating effects of pollution on Caenorhabditis elegans' population dynamic through a bio-energetic approach

The assessment of toxic effects at biologically and ecologically relevant scales is an important issue in ecosystem protection. Mathematical models exist to predict effects of pollutant on population dynamics from individually data. Nevertheless there are only a few datasets and models that account for adaptive phenomena which may appear in a stressed population. The selection pressure exerted by a pollutant is known to amplify the phenomenon of natural selection. It is thus essential to understand and quantify the adaptive dynamics governing populations under stress in order to assess ecological risk. Regarding this background, we adapted a bioenergetic model to study adaptive phenomena in Caenorhabditis elegans population dynamic exposed to a heavy radiotoxic metal (uranium). The Dynamic Energy Budget (DEB) (Kooijman, 2010) bioenergetic approach highlights the distribution of energy fluxes between processes such as growth, reproduction, maturation and maintenance. It is a relevant basis to understand and model the links between assimilation disruptions, growth and reproduction fluctuations in organisms exposed to anthropogenic stress (e.g. pollutant, global change) and to assess potential consequences on population over many generations. We therefore studied the responses of C. elegans exposed to six experimental concentration of uranium over several generations. The individual traits followed were growth curve, egg laying curve, survival until end of egg laying. We showed that uranium impacted C. elegans growth curve and egg laying over several generations, with, consequently, adverse effects on the population dynamic and variations on DEB parameters. Nevertheless, results also tend to show an evolutionary response throughout the generations

Rapid evolutionary responses of life history traits to different experimentally-induced pollutions in Caenorhabditis elegans

International audienceBackground: Anthropogenic disturbances can lead to intense selection pressures on traits and very rapid evolutionary changes. Evolutionary responses to environmental changes, in turn, reflect changes in the genetic structure of the traits, accompanied by a reduction of evolutionary potential of the populations under selection. Assessing the effects of pollutants on the evolutionary responses and on the genetic structure of populations is thus important to understanding the mechanisms that entail specialization to novel environmental conditions or resistance to novel stressors. Results: Using an experimental evolution approach we exposed Caenorhabditis elegans populations to uranium, salt and alternating uranium-salt environments over 22 generations. We analyzed the changes in the average values of life history traits and the consequences at the demographic level in these populations. We also estimated the phenotypic and genetic (co)variance structure of these traits at different generations. Compared to populations in salt, populations in uranium showed a reduction of the stability of their trait structure and a higher capacity to respond by acclimation. However, the evolutionary responses of traits were generally lower for uranium compared to salt treatment; and the evolutionary responses to the alternating uranium–salt environment were between those of constant environments. Consequently, at the end of the experiment, the population rate of increase was higher in uranium than in salt and intermediate in the alternating environment.Conclusions: Our multigenerational experiment confirmed that rapid adaptation to different polluted environments may involve different evolutionary responses resulting in demographic consequences. These changes are partly explained by the effects of the pollutants on the genetic (co)variance structure of traits and the capacity of acclimation to novel conditions. Finally, our results in the alternating environment may confirm the selection of a generalist type in this environment