No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Variation in variance means more than mean variations: What does variability tell us about population health status?
... The most striking result of the present study was the statistically significant increase in variation of population response parameters of selected taxa in the treatment mesocosms compared to the controls ( Table 2, Fig. 2). On the one hand, variation in species responses has always been a big issue in ecotoxicology and species tests [51][52][53], as it hinders the statistical evaluation of true effects from background noise with regard to mean values. On the other hand, there is increasing evidence that interreplicate variation of population development parameters as a result of genotype plasticity of individuals, can be an indicative endpoint for chemical pollution [54]. ...
... The observed variation in species response to the 19 times repeated low-dosed PPP application might have been induced by genotype plasticity of respective species. The higher the genotype plasticity of species or communities, the more complex the responses will be in terms of physiological adaptations such as detoxification processes or increased escape responses [53]. In addition, small differences in concentrations of some pesticides (see standard deviation of recovery of AI in streams; Table 1) at the start of the experiment may have further promoted the variation in species responses. ...
... Overall, the increased variation in species response in the treatment mesocosms of the present study should be discussed as a general disturbance measure [53,61], even if it was not possible to link the results to specific pesticide pulses, to genotype plasticity of the species or the differences in exposure between replicates. When assessing population health, e.g. in the risk assessment of pesticides, the parameter "inter-replicate variation" should also be considered. ...
Background
Several large-scale studies revealed impacts and risks for aquatic communities of small rural lakes and streams due to pesticides in agricultural landscapes. It appears that pesticide risk assessment based on single products does not offer sufficient protection for non-target organisms, which are exposed repeatedly to pesticide mixtures in the environment. Therefore, a comprehensive stream mesocosm study was conducted in order to investigate the potential effects of a realistic spraying sequence for conventional orchard farmed apples on a stream community using pesticides at their regulatory acceptable concentrations (RACs). Eight 74-m-long stream mesocosms were established with water, sand, sediment, macrophytes, plankton and benthic macroinvertebrates. In total, nine fungicidal, four herbicidal and four insecticidal pesticides were applied in four of the eight stream mesocosms on 19 spraying event days in the period from April to July while the remaining four stream mesocosms served as controls. The community composition, the abundance of benthos, periphyton and macrophytes, the emergence of insects, physico-chemical water parameters, and drift measurements of aquatic invertebrates were measured.
Results
The pesticide spraying sequence induced significant effects on invertebrates, periphyton, and macrophytes as well as on the water ion composition especially in the second half of the experiment. It was not possible to relate the observed effects on the community to specific pesticides applied at certain time points and their associated toxic pressure using the toxic unit approach. The most striking result was the statistically significant increase in variation of population response parameters of some taxa in the treated mesocosms compared to the controls. This inter-individual variation can be seen as a general disturbance measure for the ecosystem.
Conclusions
The pesticide spraying sequence simulated by using RAC values had notable effects on the aquatic stream community in the conducted mesocosm study. The results indicate that the current risk assessment for pesticides may not ensure a sufficient level of protection to the field communities facing multiple pesticide entries due to spraying sequences and other combined stress. Hence, there is still room for improvement regarding the prospective risk assessment of pesticides to further reduce negative effects on the environment.
... Noticeably, ecotoxicological studies have generally focused on changes in the central value of a biomonitor response, considering variance among individuals as a nuisance ("the tyranny of the golden mean" in Bennett, 1987;Devin et al., 2014). Inter-individual variability has been generally overlooked (but see Lobel et al., 1992;Saavedra et al., 2009 for exceptions), notwithstanding the recognition that it influences the effect of pollutants, the performance of an impacted population, and limits the effectiveness of sampling efforts and protocol design (Forbes and Depledge, 1996;Calow, 1996;Berthet et al., 2011;Devin et al., 2014;Crespo et al., 2015). ...
... Noticeably, ecotoxicological studies have generally focused on changes in the central value of a biomonitor response, considering variance among individuals as a nuisance ("the tyranny of the golden mean" in Bennett, 1987;Devin et al., 2014). Inter-individual variability has been generally overlooked (but see Lobel et al., 1992;Saavedra et al., 2009 for exceptions), notwithstanding the recognition that it influences the effect of pollutants, the performance of an impacted population, and limits the effectiveness of sampling efforts and protocol design (Forbes and Depledge, 1996;Calow, 1996;Berthet et al., 2011;Devin et al., 2014;Crespo et al., 2015). Current approaches focus on standardization, by limiting genetic and phenotypic variability among organisms (Barrick et al., 2016). ...
... Current approaches focus on standardization, by limiting genetic and phenotypic variability among organisms (Barrick et al., 2016). However, this may limit the generality of results, and lead to inadequate conclusions (Devin et al., 2014). Alternatively, correlational and variance partitioning procedures are increasingly used to model the contribution of phenotypic traits to the range of response variation within a population, and provide more ecologicallysound evidence of impacts (among others, McKinley et al., 2012;Drouhot et al., 2014;Chouvelon et al., 2017). ...
In invertebrate biomonitors of chemical pollution, emphasis has been generally given to mean accumulation patterns and how they reflect varying environmental levels of contamination. Intra-population variability, and how it relates with individual phenotypic traits, has received less attention. Here, a set of analytes including trace elements (B, Ba, Cd, Cr, Cu, Fe, Li, Mn, Ni, Pb, Sr, V, and Zn), macroelements (C, Ca, K, Mg, N, Na), and carbon and nitrogen stable isotopes (δ¹³C and δ¹⁵N) was measured in two populations of the crayfish Procambarus clarkii from Lake Trasimeno and Lake Bolsena (Central Italy). The influence of location, sex, body size, and condition factor was assessed; in addition, the analyte correlation profiles of the two populations were compared to verify their congruence. In general, significant inter-lake differences were observed in the concentration of both trace- and macroelements in crayfish tissues, generally mirroring the local chemistry of water and of benthic non-living matrices (sediment and plant detritus). Crayfish CN isotopic signatures excluded the occurrence of inter-lake variations in their omnivorous trophic habits. Correlation profiles varied considerably between the two populations in the nature and strength of bivariate relationships. However, Mantel tests and procrustean analyses indicated a general, significant congruence; C, N, and, to a lesser extent K, Li, Ni, Pb, and δ¹³C showed the highest procrustean residuals, suggesting that their associations with other analytes may be partially influenced by inter-population differences in growing phases. Our study indicates that the local geochemistry of the lacustrine environment influences the elemental fingerprint of Procambarus clarkii; the considerable inter-individual variability in the concentration of analytes, however, does not significantly reflect on their association, thus corroborating its effectiveness as an indicator species.
... In order to characterize the threshold for lethality the lower limit of the BAC was multiplied by two. This threshold was selected in order to be consistent with the concept of ecotoxicological niche that two groups away from the mean is outside the adaptive capability of the population and can lead to localized extinction (Devin et al., 2014). The upper and lower limit of the EAC was then characterized with sublethal effects being defined as between one and two cluster groups away from the mean of the reference site and values two groups away being defined as the threshold for mortality. ...
... This method establishes centroids in a method that maximizes the difference between clusters while minimizing differences within clusters. Groups were classified according to WFD CIS (2005) guidance and the ICES (2010) report with the traffic light scheme adjusted to conform to ecotoxicological theory regarding variation within a population (Devin et al., 2014). This was used to define the upper and lower limit of the BAC. ...
... To adequately introduce biomarkers into environmental monitoring campaigns it is necessary to define quantitative thresholds of natural variation (Burgeot et al., 2010;Devin et al., 2014). Currently it has been identified that more emphasis on statistical analysis and modeling Table 1 Red: lethal effects expected; orange: sublethal effects expected; yellow: range expected in a non-impacted site (BAC); green: above BAC and evidence of good health. ...
... Biological variability proves more challenging to address as there are multiple contributing sources, including seasonal and temporal variation, genetic variation amongst individuals, and choice and life stage of test species (Hrovat et al. 2009;Simmons et al. 2015), differences in physiological status (e.g. size, age, sexual maturity status, etc.), and differential sensitivities of individuals to natural environmental parameters (Devin et al. 2014). Assessing the inter-individual variability of American lobster larvae is crucial for understanding its utility as a model test organism and understanding the risks to the population. ...
... They found there to be rather low levels of genetic variability within the 300 animals surveyed, with the average proportion of heterozygous loci per individual being 3.8%. The small and nearly constant variance in EC50 values observed for lobsters in this study may be indicative of low phenotypic variability, which can be associated with lower genetic variability (Devin et al. 2014), and may be a reflection of the fact that these wild lobsters all had been caught within the same area (Lobster Fishing Area 36) and are of unknown relatedness. The significance of low variability in terms of sensitivity to hydrocarbons observed in this study may speak to a reduced resilience within this population and a reduced pool of survivors to repatriate following an oil spill. ...
Standard model species are commonly used in toxicity tests due to their biological and technical advantages but studying native species increases the specificity and relevance of results generated for the potential risk assessment to an ecosystem. Accounting for intraspecies variability and other factors, such as chemical and physical characterization of test medium, is necessary to develop a reproducible bioassay for toxicity testing with native species. In this study, larval stage I American lobster (Homarus americanus), a commercially important and native species of Atlantic Canada, was used as the test species. Toxicity tests were first conducted by exposing lobster larvae to a reference toxicant of copper sulphate (CuSO4) and then to physically and chemically (using Corexit 9500A) dispersed oil (WAF and CEWAF, respectively). The effect on larval survival was estimated by calculating the 24-h median effect concentration (24-h EC50), and there was no difference between WAF or CEWAF exposure when the results are reported on a total petroleum hydrocarbon (TPH) basis. The 24-h EC50s ranged from 2.54 to 9.73 mg TPH/L when all trials (n = 19) are considered together. The HC5 (hazardous concentration for 5 per cent of the population) value was 2.52 mg TPH/L and similar to the EC50 value when all trials were pooled. To evaluate the reproducibility of the lobster toxicity tests, inter-trial variability was determined, and the resultant coefficients of variation (%CV) were compared to those reported for two standard test species, mysid shrimp (Americamysis bahia) and inland silverside (Menidia beryillina). This comparison showed that the %CV for the lobster toxicity tests were lower than those for the standard species tests indicating that the described larval lobster toxicity bioassay produces reliable and repeatable results.
... These pelagic stages also represent the greatest potential for exposure to hydrocarbons associated with an oil spill and spill response measures (e.g., application of chemical dispersants), which tend to be more concentrated in surface waters. Variability in response may be a result of genetic variability, different sensitivity of individuals to natural environmental parameters, and the physiological status (i.e., effect of size and age of the individuals) on their sensitivity to perturbation (Devin et al. 2014). Assessing the inter-individual sensitivity variability of American lobster larvae is crucial for understanding its utility as a model test organism and understanding the risks to the population. ...
... They found there to be rather low levels of genetic variability within the 300 animals surveyed, with the average proportion of heterozygous loci per individual being 3.8%. The small and nearly constant variance in EC50 values observed for lobsters in this study may be indicative of low phenotypic variability, which can be associated with lower genetic variability (Devin et al. 2014), and may be a re ection of the fact that these wild lobsters all had been caught within the same area (Lobster Fishing Area 36) and are of unknown relatedness. The signi cance of low variability in terms of sensitivity to hydrocarbons observed in this study may speak to a reduced resilience within this population and a reduced pool of survivors to repatriate following an oil spill. ...
Standard model species are commonly used in toxicity tests due to their biological and technical advantages but studying native species increases the specificity and relevance of results generated for the potential risk assessment to an ecosystem. Accounting for intraspecies variability and other factors, such as chemical and physical characterization of test medium, is necessary to develop a reproducible bioassay for toxicity testing with native species. In this study, larval stage I American lobster ( Homarus americanus ) was selected as the test species, which is native to Atlantic Canada. Toxicity tests were first conducted exposing lobster larvae to a reference toxicant of copper sulfate (CuSO 4 ) and then to physically and chemically dispersed oil. The effect on larval survival was estimated by calculating the median effect concentration (EC50) as 2.54-9.73 mg TPH/L when all trials are considered together. The HC5 or PNEC value was 2.52 mg TPH/L and therefore a narrow difference from the EC50 value. The inter-trial variability (coefficient of variability = 17%) was lower than the US Environmental Protection Agency standard test species of mysid shrimp ( Americamysis bahia ) and inland silversides ( Menidia bervillina ). Our results indicate that the described larval lobster bioassay is reliable to produce repeatable results for this commercially important and native species of Atlantic Canada.
... Several authors have reported the relevance of addressing biological variation in ecological and evolutionary studies (Devin et al., 2014;Guscelli et al., 2019;Moran et al., 2016;Salinas et al., 2019). Even if there is no change in a mean response, a change in variance may be seen as an early warning signal and should be interpreted as a population response (Devin et al., 2014). ...
... Several authors have reported the relevance of addressing biological variation in ecological and evolutionary studies (Devin et al., 2014;Guscelli et al., 2019;Moran et al., 2016;Salinas et al., 2019). Even if there is no change in a mean response, a change in variance may be seen as an early warning signal and should be interpreted as a population response (Devin et al., 2014). Previous studies have shown that physiological, metabolic and molecular traits have large intraspecific variation, even under standardized conditions (sex, age, size) (Dong et al., 2017;Guscelli et al., 2019;Norin et al., 2019). ...
Extreme weather events, such as heatwaves, are becoming increasingly frequent, long-lasting and severe as global climate change continues, shaping marine biodiversity patterns worldwide. Increased risk of overheating and mortality across major taxa have been recurrently observed, jeopardizing the sustainability of ecosystem services. Molecular responses of species, which scale up to physiological and population responses, are determinant processes that modulate species sensitivity or tolerance to extreme weather events. Here, by integrating proteomic, fatty acid profiling and physiological approaches, we show that the tolerance of the intertidal ragworm Hediste diversicolor, a keystone species in estuarine ecosystems and an emergent blue bio-resource, to long-lasting heatwaves (24 ºC vs 30 ºC for 30 days) is shaped by calcium homeostasis, immune function and stability of fatty acid profiles. These features potentially enabled H. diversicolor to increase its thermal tolerance limit by 0.81 ºC under the heatwave scenario and maintain survival. No growth trade-offs were detected, as wet weight remained stable across conditions. Biological variation of physiological parameters was lower when compared to molecular measures. Proteins showed an overall elevated coefficient of variation, although decreasing molecular variance under the heatwave scenario was observed for both proteins and fatty acids. This finding is consistent with the phenomenon of physiological canalization in extreme environments and contradicts the theory that novel conditions increase trait variation. Our results show that keystone highly valued marine polychaetes are tolerant to heatwaves, confirming the potential of H. diversicolor as a blue bio-resource and opening new avenues for sustainable marine aquaculture development.
... η 2 is a measure of effect size based on the sums of squares of ANCOVA that estimates the proportion of the total variance in the response variable associated with a certain predictor and that in the case of simple linear regression is identical to the coefficient of determination r 2 . Because it has been suggested that variability could reflect acclimation abilities and should be examined in addition to central tendency (Devin et al. 2014), we also used Breusch-Pagan tests on the regression residuals of ANCOVAs and Fligner-Killeen tests for the factors (group and sex) to test for heteroscedasticity (both from the package performance); (Lüdecke et al. 2021). ...
Captive breeding and stocking are commonly employed strategies for enhancing fisheries and conserving endangered fish species. However, hatchery-raised fish often exhibit reduced performance in the wild, displaying alterations in physiological, morphological, and behavioral traits. We tested for differences in swimming capacity and metabolic traits between wild and hatchery-reared individuals of the Spanish toothcarp (Aphanius iberus) from two different populations. Furthermore, we experimentally tested if these changes translated into fitness differences after their stocking into the wild. There were significant differences in swimming capacity and metabolic traits between wild and hatchery-reared individuals and also between the two populations. Captive-bred individuals displayed consistently lower metabolic rates than wild individuals from the same population (30-76% lower). Critical swimming speed rather differed between the two populations. Sex-specific differences were observed in maximum and standard metabolic rates, with wild individuals and females generally exhibiting higher values but with some exceptions. During a three-month experiment, survival rates did not significantly differ between wild and captive-bred fish. Captive-bred individuals started smaller but exhibited rapid growth during the experiment. Initially, larger captive-bred fish had lower body condition than their wild counterparts, but these differences progressively diminished. In summary, captive-bred individuals of this fish species showed lower metabolic rates, although the differences with wild individuals slightly depended on sex and size.
... The latter are the difference between the measured and predicted values. The residuals, were classified into three groups for each biomarker using the k-means clustering method (Barrick et al., 2016;Devin et al., 2014). To do this, the R software classifies the residuals into three groups and calculates the mean of each group. ...
The characterization of organic and inorganic environmental pollution in coastal ecosystems, such as port areas, is complex and difficult to carry out due to the effect of environmental variables, as well as anthropic activities. For this study, the objective was to define a statistical method, taking into account the confounding factors influence, to define reference values for biomarkers in the black scallop (Mimachlamys varia). Thus, for five biomarkers (SOD (Superoxyde Dismutase), GST (Glutathion-S Transferase), MDA (Malondialdehyde), AChE (Acetylcholinesterase) and LAC (Laccase)), reference data could be described for individuals placed on sites more or less strongly impacted by specific environmental contaminations in port areas for more than two years, which had never been done before. All these results enabled us to calibrate and validate our approach in terms of active biomonitoring for the evaluation of a good ecological status of the environment of a port located on the French Atlantic coast.
... To the best of our knowledge, no such efforts have been produced in the field of terrestrial ecotoxicology and applied to the triad approach. Nonetheless, the integration of natural variability could represent a solution when direct comparison with an appropriate reference is not possible (Devin et al., 2014). ...
Soils can be sinks of pollutant mixtures, whose effects on terrestrial ecosystems are not of obvious interpretation. Risk assessment is rather codified and many approaches can be used. Nevertheless, there are still uncertainties remaining when dealing with diffuse pollution, including chronic inputs of low, sublethal, concentrations of mixtures of micropollutants. In this paper, we reviewed through a comprehensive literature analysis one of the latest promising methodologies, the triad approach, in order to understand its area of application in terrestrial ecosystems, the ways of applicability and the reported actual usage. In the case of diffuse pollution, where all the criteria of the triad approach can differ in their indication, we show that some improvements have to be made in either the chemical, ecological or ecotoxicological approaches to be able to clearly identify the risk and to address the uncertainties linked to the low, sublethal contents of contaminants.
... Besides average physiological responses to temperature, researchers are now recognizing the importance of variation as a population response to changes in the environment (Devin et al., 2014). Here we show that trait variability differs between males and females, with female-biased variability (higher variability in females) for all traits analysed (morphometric traits and thermal limits). ...
As global temperatures continue to rise due to global change, marine heatwaves are also becoming more frequent and intense, impacting marine biodiversity patterns worldwide. Organisms inhabiting shallow water environments, such as the commercially relevant ditch shrimp Palaemon varians, are expected to be the most affected by rising temperatures. Thus, addressing species' thermal ecology and climate extinction-risk is crucial to foster climate-smart conservation strategies for shallow water ecosystems. Here, we estimated sex-specific upper thermal tolerance limits for P. varians via the Critical Thermal Maximum method (CTmax), using loss of equilibrium as endpoint. We further calculated thermal safety margins for males and females and tested for correlations between upper thermal limits and shrimps' body size. To determine sex-biased variation in P. varians’ traits (CTmax, weight and length), we compared trait variation for females and males through the coefficient of variation ratio (lnCVR). Females displayed an average CTmax value 1.8% lower than males (CTmaxfemales = 37.0 °C vs CTmaxmales = 37.7 °C). This finding may be related to the larger body size exhibited by females (156% heavier and 39% larger than males), as both length and weight had a significant effect on CTmax. The high energetic investment of females in offspring may also contribute to the differences recorded in thermal tolerance. Overall, organisms with a smaller body-size displayed a greater tolerance to elevated temperature, thus suggesting that smaller individuals may be positively selected in warmer environments. This selection may result in a reduction of size-at-maturity and shifts in sex ratio, given the sexual dimorphism in body size of shrimps. The thermal safety margin of P. varians was narrow (∼2.2 °C for males and ∼1.5 °C for females), revealing the vulnerability of this species to ocean warming and heatwaves.
... Such thresholds are missed by monotonic (linear) models commonly used in ecological data interpretation and modeling. The assumption of monotonicity and resulting over-simplification of biological complexity has been criticized by many ecologists [6,7]. ...
Ecological association studies often assume monotonicity such as between biodiversity and environmental properties although there is growing evidence that nonmonotonic relations dominate in nature. Here, we apply machine-learning algorithms to reveal the nonmonotonic association between microbial diversity and an anthropogenic-induced large-scale change, the browning of freshwaters, along a longitudinal gradient covering 70 boreal lakes in Scandinavia. Measures of bacterial richness and evenness (alpha-diversity) showed nonmonotonic trends in relation to environmental gradients, peaking at intermediate levels of browning. Depending on the statistical methods, variables indicative for browning could explain 5% of the variance in bacterial community composition (beta-diversity) when applying standard methods assuming monotonic relations and up to 45% with machine-learning methods taking non-monotonicity into account. This non-monotonicity observed at the community level was explained by the complex interchangeable nature of individual taxa responses as shown by a high degree of nonmonotonic responses of individual bacterial sequence variants to browning. Furthermore, the nonmonotonic models provide the position of thresholds and predict alternative bacterial diversity trajectories in boreal freshwater as a result of ongoing climate and land-use changes, which in turn will affect entire ecosystem metabolism and likely greenhouse gas production. ISME Communications (20 21) 1: 3 7 ; https://doi.
... High variability of biological responses, though beneficial for populations in reacting to stress, hinders quantification of adverse effects in ecotoxicological studies (Devin et al., 2014). In this way, it is important to characterize the natural variability of the selected biomarkers to better understand biological impact of contaminants during biomonitoring studies. ...
The relevance of a biomarker for biomonitoring programs was influenced both by the knowledge on biomarker natural inter-individual and site variabilities and by the sensitivity of the biomarker towards environmental perturbations. To minimize data misinterpretation, robustness reference values for biomarkers were important in biomonitoring programs. Specific three-spined stickleback, Gasterosteus aculeatus, immune reference ranges for field studies had been determined based on laboratory data and one reference station (Contentieuse river at Houdancourt). In this study, data obtained in one uncontaminated and three contaminated sites were compared to these reference ranges as a validation step before considering them for larger scale biomonitoring programs. When the field reference range were compared to data from the uncontaminated station (Béronelle), only few deviations were shown. In this way, data coming from uncontaminated station (Béronelle) was integrated in the field reference ranges to improve the evaluation of site variability. The new field reference ranges provided better discrimination of sites and spanned a larger range of fish lengths than the initial reference ranges. Furthermore, the results suggest lysosomal presence during several months and phagocytosis capacity in autumn may be the most relevant immunomarkers towards identifying contaminated sites. In the future, combining this reference value approach with active biomonitoring could facilitate the obtention of data in multiple stream conditions.
... A recurrent debate exists within scientific literature on what is the appropriate level of replication in ecological and ecotoxicological studies (Bastos et al., 2013;Devin et al., 2014;Davies and Gray, 2015). Indeed, pseudoreplication can't be avoided, and a tank effect can have occurred in our experiment. ...
The Kerguelen Islands (49°26’S, 69°50’E) represent a unique environment due to their geographical isolation, which protects them from anthropogenic pollution. The ability of the endemic mussel, part of the Mytilus complex, to cope with moderate heat stress was explored using omic tools. Transcripts involved in six major metabolic functions were selected and the qRT-PCR data indicated mainly changes in aerobic and anaerobic energy metabolism and stress response. Proteomic comparisons revealed a typical stress response pattern with cytoskeleton modifications and elements suggesting increased energy metabolism. Results also suggest conservation of protein homeostasis by the long-lasting presence of HSP while a general decrease in transcription is observed. The overall findings are consistent with an adaptive response to moderate stresses in mussels in good physiological condition, i.e. living in a low-impact site, and with the literature concerning this model species. Therefore, local blue mussels could be advantageously integrated into biomonitoring strategies, especially in the context of Global Change.
... However, variance change was not tested statistically either. Devin et al. (2014) elaborated three possible patterns of the dose-dependent variance alteration of a phenotypic parameter under sublethal toxic exposure, which are: (i) constant variance of the parameter across all concentrations due to low phenotypic and genetic variance, (ii) decreasing parameter variance with increasing toxicant concentration that can result from canalisation of the response, i.e. individuals develop more similar phenotypes in the presence of the toxicant than in a clean environment, (iii) increasing parameter variance with the toxicant can occur if individuals show different biological responses. In case (ii), the background of the higher baseline phenotypic variability can be genetic or environmental (other uncontrolled environmental factors or epigenetic differences) variability and accordingly, genetic or environmental canalisation can happen (Flatt, 2005). ...
The hypothesis that the inter-individual parameter variability is an unexploited area of ecotoxicology was proposed several decades ago. Although some illustrative examples were presented to support this hypothesis in the last decades, it has never been tested on an extensive, coherent database. In this study, variance changes of 105 dose-response curves were analysed. All data originated from the same experiment, where the effects of the insecticide Trebon EC were investigated in a dose-response manner on 15 traits of the collembolan Folsomia candida in four subsequent generations and two types of insecticide treatments. A consistent relationship between inter-individual variance and insecticide application was found in 2 (first clutch size and growth-reproduction trade-off) out of the 15 of the parameters. Contrary to the mean, the variance of the first clutch size showed consistent differences compared to the control. Furthermore, the variance of the growth-reproduction trade-off was consistently different from the control except in one case (F3 generation of the transgenerational treatment). Higher first clutch size variances were found in F1 and a lower one in the F2 and F3 generations than in that of the control. This overall pattern of the variance changes of the first clutch size and the trade-off seems to be a quick response to the insecticide application. In the short term, we have found that variance increased with insecticide treatment (P and F1 generation), because phenotypic variance generally increases due to environmental stress. Disruptive selection could be another mechanism between the more detoxification less reproduction strategy and the more reproduction less detoxification strategy. However, in the later generations (F2-F3) the variance decreases compared to the control, which could be because on short term selection stronger on the viability parameters and in long-term selection on reproduction becomes stronger. According to our results, analysis of the variance changes of some parameters may give information about the effects of the pesticide even when the mean does not predict any impact. Testing variance changes are important in ecotoxicology because variance change can signalise toxicant impact even when the mean does not change in certain cases.
... The first reason is that the threshold value for the concentration of oxidative stress particles for organisms varies significantly between individuals of the same species. This increased variability of the measured biomarkers may indicate an individual's ability to adapt to an environment polluted by microplastics (Devin et al. 2014). ...
In the modern world, plastic has become a major commodity on global scale and is presented in all life aspects. The production of plastics is increasing dramatically throughout the world and is considered to be a serious threat for the aquatic environment. Scientists started to raise questions as to where all the disappeared plastic debris had gone, as the plastic material is a persistent synthetic polymer. The disappearance of plastic suggests that microplastics are generated by fragmentation of larger plastic debris. They also enter the aquatic environment from the cosmetics, clothing, and other industrial manufacturing. Microplastic particles spread in the aquatic, terrestrial, and atmospheric environments due to their small size and ubiquity, showing their high bioavailability. The presence of microplastics has been demonstrated in the digestive tracts of most aquatic organisms at various trophic levels. Evidence of negative effects of microplastics has been found in relation to fertility, mortality, oxidative stress, immune system or metabolic processes.
... There is a lot of niche research on economics (Hommels et al., 2007;Smith et al., 2010;Seol et al., 2012) and management (Baum and Singh, 1994;Hamarat and Kasimoglu, 2003;Hannan et al., 2003), and these studies provide new ideas for economic and managerial decisions of social departments or related organizations. With the continuous development of niche theory, its application scope has become wider and wider, and it has gradually entered the fields of farmland (Niu et al., 2011;Zhao et al., 2019), photovoltaic agriculture (Wang et al., 2019), complex regional ecosystem (Jiang et al., 2018) and ethnic variation (Devin et al., 2014), and has become an important means for scholars to study social systems (Peng and Yan, 2015). Specifically, Raven (2007) assesses two patterns in transition processes for using them as strategies towards a sustainable energy system in European, i.e., niche accumulation and hybridisation. ...
Green technology innovation is the strategy adopted by the manufacturing industry in implementing green innovation. Choosing the right green technology innovation path is crucial to the development of green innovation in manufacturing industry. From the perspective of niche theory, the paper constructs the green technology innovation trend indicators of manufacturing industry, and builds a multi-layer comprehensive evaluation model by using cloud model tools. Taking the green technology of manufacturing industry in Jiangsu Province as an example, the empirical analysis reveals that from 2012 to 2016, Jiangsu Province manufactures. The ecostate value of green technology innovation has been continuously improving, while the ecorole value has fluctuated. The comprehensive niche score has gradually boosted, indicating that the overall development trend of manufacturing green technology innovation capability in Jiangsu Province goes well. When advancing the level of innovation and formulating green technology innovation capability promotion strategies, macro-control and supervision for Jiangsu Province’s manufacturing green technologies should be emphasized, environmental management optimized, stimulation of green innovative talents strengthened, and green technology R&D and service centers intensified. Create a symbiotic environment, increase cooperation between enterprises, and the government, build a green innovation and cultivation mechanism for manufacturing, and facilitate sustainable development with creative approaches in Jiangsu Province.
... 4 gènes précédents (CYP450, COII, 12S et 18S) en Vilaine (milieu peu stressé) vs en Seine (très polluée). Cette variabilité phénotypique dans une population pourrait être considérée comme un proxy de sa variabilité génétique elle pourrait devenir un indicateur de l état de santé d une population en écoto icologie(Devin et al., 2014).Le statut physiologique des poissons pourrait être a priori relativement proche en Vilaine et en Seine (régimes thermiques identiques, forte disponibilité en nourriture à la fin de l automne), or nous observons une différence nette entre ces deux estuaires. Les plus fortes valeurs en Vilaine (vs Seine) concernant l état des réserves et la diversité interindividuelle dans l expression des gènes pourraient refléter une meilleure capacité adaptative de la population de Vilaine vis-à-vis de futurs changements environnementaux.Nous suggérons donc que la population de flets peu stressée de Vilaine présente un risque écologique limité. ...
Le niveau de vulnérabilité de populations naturelles de flet a été abordé dans cette étude, par l’intégration des réponses du poisson aux niveaux moléculaire, individuel et populationnel. Une approche multi-estuaire est développée ; les réponses du flet sont ainsi mesurées dans des conditions contrastées (stress thermique : estuaire du Mondego ; stress chimique : estuaire de Seine ; faibles niveaux de stress : Baie de Douarnenez, estuaires de Vilaine et Canche). Par une approche démo-génétique basée sur la variabilité des marqueurs microsatellites, nous avons mis en évidence une faible taille efficace de la population du Mondego située en limite Sud de l’aire de distribution, et donc caractérisée par un risque écologique élevé. La population de Seine présente une faible variabilité interindividuelle dans l’expression de différents gènes impliqués dans le métabolisme énergétique (COII, 12S), qui pourrait expliquer son faible potentiel à résister au réchauffement climatique. Cette population montre des signatures d’adaptation face au stress chimique (métabolisme énergétique élevé, gestion du stress oxydant, modification des phospholipides membranaires), engendrant probablement un coût physiologique fort (réduction des réserves énergétiques au niveau musculaire). La population de Seine présente donc un risque écologique élevé. Enfin, un encagement de flet a été mené sur un mois en estuaire de Seine; les réponses du poisson analysées par protéomique shot-gun ont mis en évidence un gradient de pollution décroissant amont-aval, soit une estimation de l’état écologique du système à micro-échelle. Cette thèse a identifié différents outils pertinents pour estimer le niveau de vulnérabilité de populations de flet, et pour explorer l’état écologique des écosystèmes estuariens.
... This would account for the high variability observed in some biomarker responses from microplastic-exposed animals (Prendergast-Miller et al., 2019;Rodríguez-Seijo et al., 2018). In fact, increased variability in measured biomarkers is itself a response to pollution, and one that could offer insights into a population's ability to adapt to microplastic-related stresses (Depledge and Lundebye, 1996;Devin et al., 2014). ...
Microplastic ingestion in invertebrates reduces somatic and reproductive growth. This could be caused by energy reserves being detracted from growth processes and redistributed to maintenance processes that preserve life. A potential sink for this diverted energy is the antioxidant system, which minimises oxidative damage and reinstates redox homeostasis following disturbances caused by exposure to pollution. Several microplastic studies have used genetic and molecular redox biomarkers to assess how microplastic ingestion affects the functioning of the antioxidant system. This systematic review synthesises the current understanding of redox biomarker responses in invertebrates that have ingested microplastics. We found that biomarker response information exists for only seven invertebrate taxa, and early life stages have received little scientific attention. The microplastics used by most studies were polystyrene (45% of studies), spherical (51% of studies), and were < 10 μm in diameter (31% of studies). We found multiple examples of microplastic ingestion posing an oxidative challenge to invertebrates, which required upregulation of antioxidant system components. However, the lack of systematic experiments prevented us from clearly identifying which characteristic of microplastics caused these responses. We identify several areas for consideration when investigating biomarker responses to microplastic ingestion and offer research priorities for future studies.
... The variability in biological responses in natural and laboratory populations is a well-known and well-documented phenomenon [36]. We confirmed the validity of our experimental approach by using Cu as a reference toxicant and measured similar variability in the controls for both species when exposed to Fe and Cu. ...
Currently toxicity data for iron (Fe) in seawater is limited; furthermore these data are of poor quality due to the importance of Fe solubility in test solutions being overlooked. This study characterised the solubility and lability of Fe(III) in seawater and then examined the effects of Fe(III) on the fertilisation success and larval survival of the tropical marine scleractinian corals Acropora spathulata and Platygyra daedalea. Here we present the first assessment of the effects of Fe on the early life stages of scleractinian corals. Concentrations of both soluble and labile forms of Fe were very low with dissolved Fe concentrations ≤ 0.195 mg/L in bioassay test solutions and chemical determinations revealing labile Fe concentrations ≤ 1.21 mg/L. For fertilisation experiments the EC50 value for total Fe was 25 mg/L for the most sensitive species P. daedalea, whilst the EC50 values for A. spathulata ranged between 40 to 66 mg/L. The LC50 value for P. daedalea larval survival was 47 mg/L Fe after 72 h exposure. Here we provide Fe toxicity data for tropical marine keystone species that could be used to help generate more reliable guideline values for Fe in marine waters. This article is protected by copyright. All rights reserved.
... The level of inter-individual variation could be a relevant indicator of population health in ecotoxicology. 19 Considering that the physiological status of the sampled fish was probably similar in the two northern estuaries that display a similar thermal regime (immature young of the year, identical feeding status linked to a high abundance of preys in estuaries at the beginning of autumn), we suggest that the higher phenotypic diversity detected in the less stressed environment (Vilaine estuary) could reflect a higher genetic variability and possibly a better adaptive ability of this population. In contrast, the heavily polluted flounder population of the Seine estuary that displays a lower inter-individual variability could be possibly at risk. ...
... Thus, a higher variation was observed among control individuals in comparison to the animals from the other conditions. As described by Devin et al. (2014), sublethal exposure to contaminant can lead to a decrease in interindividual variability and to a canalization of the response to the most efficient one in animals presenting a high phenotypic variability. European eel is indeed a panmictic species that exhibits extreme inter-individual phenotypic variance among teleost fish (Pujolar et al. 2014). ...
Detecting and separating specific effects of contaminants in a multi-stress field context remain a major challenge in ecotoxicology. In this context, the aim of this study was to assess the usefulness of a non-invasive transcriptomic method, by means of a complementary DNA (cDNA) microarray comprising 1000 candidate genes, on caudal fin clips. Fin gene transcription patterns of European eels (Anguilla anguilla) exposed in the laboratory to cadmium (Cd) or a polychloro-biphenyl (PCBs) mixture but also of wild eels from three sampling sites with differing contamination levels were compared to test whether fin clips may be used to detect and discriminate the exposure to these contaminants. Also, transcriptomic profiles from the liver and caudal fin of eels experimentally exposed to Cd were compared to assess the detection sensitivity of the fin transcriptomic response. A similar number of genes were differentially transcribed in the fin and liver in response to Cd exposure, highlighting the detection sensitivity of fin clips. Moreover, distinct fin transcription profiles were observed in response to Cd or PCB exposure. Finally, the transcription profiles of eels from the most contaminated site clustered with those from laboratory-exposed fish. This study thus highlights the applicability and usefulness of performing gene transcription assays on non-invasive tissue sampling in order to detect the in situ exposure to Cd and PCBs in fish.
... Increased COL10 expression was observed in response to experimentally induced notochordal sheath defects in medaka (Renn et al., 2013). The observed high variability (large SEM values) in COL10 expression (Fig. 4) possibility indicates the turning point where homeostasis starts to be disrupted (Devin et al., 2014). In mice, ATF4 is an essential regulator for bone formation by promoting osteoblast activity (Wang et al., 2013). ...
... Consequently, examining the shape of biomarker responses (e.g. mean, variance, maximum values, and coefficient of variations) will provide a more comprehensive picture of stressor effects on populations (Baird et al., 1996;Devin et al., 2014). Statistical analyses such as PCA create linear combinations of measures maximising the variance explained (Ter Braak and Šmilauer, 2014). ...
... But in nature, non-monotonic interactions are commonly seen at the individual, population, community and ecosystem levels. The over-simplification of biological complexity has been criticized by many ecologists (Devin et al., 2014;Steudel et al., 2012). In time series analysis, the Self-Exciting Threshold AutoRegressive (SETAR) models was proposed to allow for higher degree of flexibility in model parameters through a regime switching behavior, depending on the past values of the time series (Chan and Tong, 1986;Tong and Lim, 1980). ...
Coastal areas are important interface environments between marine and terrestrial ecosystems and are also areas of high economic activity related, among others, to trade, fishing and tourism. The port areas of La Rochelle (France) are part of these areas with strong anthropic activities and are therefore subject to potential contamination, particularly with trace metals. Among the various sources of discharges, galvanic (or sacrificial) cathodic protection can be questioned. Indeed, few studies have been carried out on the potential impact of the degradation of sacrificial anodes in ports on the health of bivalves. A study was therefore carried out on the black scallop Mimachlamys varia in the commercial port and the marina of La Rochelle using the caging method. Several biomarkers of the health status of individuals were observed in the laboratory (SOD, GST, MDA, AChE, and LAC). Among the different results obtained over two exposure periods, it appears that the potential effects of sacrificial anodes, whether new or present on site for several years, are masked by meteorological conditions, as well as by harbor activities.
An examination revealed the dominance of the published literature of environmental science by p values. Meanwhile, the use of effect size has been neglected in publications reporting primary data, yet the size of effect is often more informative than p values inference in assessing the effects of pollution on living organisms, comparing susceptibility/resistance among organisms, and ranking pollutants according to their potency, among others. Statistical significance does not necessarily mean biological, practical, or scientific significance, and its use based on (often misinterpreted) p values reflects the average response or effect at average conditions based on an assumed linear model fit to the entire sample. However, pollution impacts and organismal responses are rarely characterized by linear and symmetric features, and dichotomous ‘statistical significance’ based on p values is inadequate to fully describe data and findings. Considering ‘the fallacy of the average’, variance, and differential response of different population percentiles in new studies would provide otherwise wasted biologically, practically, or scientifically significant information. Since p values often inform as to whether some findings warrant further examination, journals should consider mandating the reporting of effect sizes and confidence intervals, together with p values (should they be used), to provide more integrated information regarding pollution impacts. Moreover, replacing ‘statistical significance’ with language of evidence, especially in key components of publications, such as abstracts and conclusions, could help preventing potential misleading of the public and decision and policy makers.
Ecological association studies often assume monotonicity such as between biodiversity and environmental properties although there is growing evidence that non-monotonic relations dominate in nature. Here we apply machine learning algorithms to reveal the non-monotonic association between microbial diversity and an anthropogenic induced large scale change, the browning of freshwaters, along a longitudinal gradient covering 70 boreal lakes in Scandinavia. Measures of bacterial richness and evenness (alpha diversity) showed non-monotonic trends in relation to environmental gradients, peaking at intermediate levels of browning. Depending on the statistical methods, variables indicative for browning could explain 5% of the variance in bacterial community composition (beta diversity) when applying standard methods assuming monotonic relations and up to 45 % with machine learning methods (i.e. extreme gradient boosting and feed-forward neural networks) taking non-monotonicity into account. This non-monotonicity observed at the community level was explained by the complex interchangeable nature of individual taxa responses as shown by a high degree of non-monotonic responses of individual bacterial sequence variants to browning. Furthermore, the non-monotonic models provide the position of thresholds and predict alternative bacterial diversity trajectories in boreal freshwater as a result of ongoing climate and land use changes, which in turn will affect entire ecosystem metabolism and likely greenhouse gas production.
Manganese (Mn) pollution in marine waters is increasing and sensitivities to this metal vary widely among marine species. The aims of this study were to characterise Mn chemistry in seawater, and evaluate the toxic effects of Mn on various life stages of two scleractinian corals – the branching sp. Acropora spathulata and massive sp. Platygyra daedalea, and the anemone Exaiptasia pallida. Analytical and theoretical characterisation experiments showed that 97–100% of Mn (II) additions ≤ 200 mg/L in seawater were soluble over 72 h and largely assumed labile complexes. Concentrations estimated to reduce coral fertilisation success by 50% (5.5-h EC50) were 237 mg/L for A. spathulata and 164 mg/L for P. daedalea. A relatively low 72-h LC50 of 7 mg/L was calculated for A. spathulata larvae. In a pilot test using fragments of adult A. spathulata, intact coral tissue rapidly sloughed away from the underlying skeleton at very low concentrations with a 48-h EC50 of just 0.7 mg/L. For E. pallida, survival, tentacle retraction and reproduction were unaffected by prolonged high exposures (12-d NOEC 54 mg/L). This study provides important data supporting the derivation of separate water quality guidelines for Mn in systems with and without coral – a decision recently considered by Australian and New Zealand authorities. It demonstrates the high sensitivity of coral larvae and adult colonies to Mn and the potential risks associated with relying on other early life stage tests and/or E. pallida as ecotoxicological representatives of critically important scleractinian corals.
En milieu naturel, évaluer l’effet des contaminants sur les organismes aquatiques s’avère difficile dû aux nombreux facteurs (température, oxygénation, prédation, parasitisme, …) agissant sur les organismes. Le but de ces travaux de thèse était alors de tester la possibilité de détecter et hiérarchiser les effets de divers facteurs naturels et anthropiques sur des individus prélevés in situ. Le modèle d’étude utilisé était l’anguille Européenne (Anguilla anguilla) et Américaine (Anguilla rostrata). Pour appréhender les effets in situ des polluants, nous avons tenté d’identifier des gènes pour lesquels le niveau de transcription était spécifiquement corrélé à un polluant ou un facteur naturel mesuré sur le terrain au moyen de deux outils transcriptomiques : le séquençage haut débit et la puce à ADN. Les profils transcriptomiques obtenus à partir des foies d’anguilles directement prélevées sur le terrain ont été comparés dans un deuxième temps, à ceux obtenus à partir d’individus exposés au laboratoire à divers facteurs naturels et anthropiques de façon séparée. La comparaison de ces profils a montré une différence notable des réponses des individus exposés en laboratoire et ceux prélevés in situ, soulevant un effet non négligeable du stress induit par la captivité en mésocosme. La réalisation d’une étude similaire en utilisant la nageoire caudale comme méthode non invasive s’est révélée pertinente dans la capacité de cet organe à discriminer les différentes conditions expérimentales et de terrain. L’utilisation de la puce sur des gonades d’anguilles européennes maturées artificiellement a indiqué que la pollution pourrait affecter les capacités de reproduction des futurs géniteurs et contribuer alors au déclin massif de cette espèce observé depuis les dernières décennies.
The effect of 17β-oestradiol (E2) on the growth of the thymus and its regionalization into cortex and medulla was investigated in juvenile European sea bass Dicentrarchus labrax as they find themselves close to sources of oestrogenic pollution whilst residing in their estuarine nursery areas. While the exposure to 2, 20 and 200 ng l(-1) in 60 days post-hatch (dph) fish tended to cause a non-monotonous dose-response curve with a significant difference of the cortex size between lowest and highest exposures, the exposure to 20 ng l(-1) E2 from 90 dph onwards resulted in a distinct enlargement of the cortex. It is probable that the alteration of the cortex size also affects the T-cell differentiation and proliferation.
© 2015 The Fisheries Society of the British Isles.
Man's impact on his environment often involves a gradient of subsidy and stress effects, which vary along nutrient, climatic, developmental (successional), and other important ecological gradients. Since performance curves that simulate subsidy-stress responses are unimodal, the zone of optimality can be determined on the basis of relatively few experiments where specific input factors are of concern. We have emphasized the importance of assessing the response of the perturbed system at different levels of organization. In practice, at least two levels, the ecosystem and the population (species) level, are necessary for a complete impact evaluation. We have stressed the need for judicious use of terms and the desirability of sticking as closely as possible to basic dictionary definitions if one expects to communicate with large numbers of people. Most of all, we have tried to show how a systems approach, based on simple flow diagram models, can clarify the intended meaning of terms and the cause-and-effect relations, as well as identify the basic processes involved.
The biomarker approach, adopted from medical toxicology, is subject to several theoretical and practical difficulties when used to address environmental problems. The problems are related to the definition that emphasizes measurement but does not specify a requirement to establish cause-effect linkages. An improved definition for a bioindicator is reviewed. The sentinel species approach is judged to be a biomarker rather than a bioindicator, and therefore of limited use for environmental risk assessment. An empirical weight of evidence approach to improve the utility of sentinel species is proposed.
Lineages that are at least superficially morphologically identical but genetically distinct are usually misclassified as a single nominal species and, hence, belong to a cryptic species complex, as for example observed for Gammarus fossarum. Since genetic differentiation between cryptic lineages of the G. fossarum complex is comparable to an interspecific level, deviations in physiological and behavioral characteristics are conceivable. The present study investigates for the first time deviations in the sensitivity between two cryptic G. fossarum lineages - namely lineage A and lineage B. Two size classes of both cryptic lineages were exposed in six independent experiments to different concentrations of the fungicide tebuconazole or the insecticide thiacloprid (each n=20) for seven days. Feeding rate on leaf discs was used as a measure of sensitivity. By combining the outcome of all bioassays in a meta-analysis, cryptic lineage A showed - with an approximate 50% more pronounced decline in feeding - a significantly higher overall sensitivity compared to lineage B (n=17). This was also obvious, when each chemical stressor was considered individually; however, data were not significant for thiacloprid. Although other reasons, like land-use of habitats around sampling sites and physiological characteristics of organisms, could not be excluded as driving factors, the results indicate that affiliation to a cryptic lineage is a potential explanatory variable for the observed deviations in sensitivity. As the present study considered only one population for each cryptic lineage, a final conclusion cannot yet be drawn. Hence, it is recommended to investigate behavioral and physiological deviations between cryptic lineages of the G. fossarum complex in further studies.
Positive relationship between biodiversity and ecosystem functioning has been observed in many studies, but how this relationship is affected by environmental stress is largely unknown. To explore this influence, we measured the biomass of microalgae grown in microcosms along two stress gradients, heat and salinity, and compared our results with 13 published case studies that measured biodiversity-ecosystem functioning relationships under varying environmental conditions. We found that positive effects of biodiversity on ecosystem functioning decreased with increasing stress intensity in absolute terms. However, in relative terms, increasing stress had a stronger negative effect on low-diversity communities. This shows that more diverse biotic communities are functionally less susceptible to environmental stress, emphasises the need to maintain high levels of biodiversity as an insurance against impacts of changing environmental conditions and sets the stage for exploring the mechanisms underlying biodiversity effects in stressed ecosystems.
Despite being recognized as a promoter of diversity and a condition for local coexistence decades ago, the importance of intraspecific variance has been neglected over time in community ecology. Recently, there has been a new emphasis on intraspecific variability. Indeed, recent developments in trait-based community ecology have underlined the need to integrate variation at both the intraspecific as well as interspecific level. We introduce new T-statistics ('T' for trait), based on the comparison of intraspecific and interspecific variances of functional traits across organizational levels, to operationally incorporate intraspecific variability into community ecology theory. We show that a focus on the distribution of traits at local and regional scales combined with original analytical tools can provide unique insights into the primary forces structuring communities.
In situ feeding assays implemented with transplanted crustacean gammarids have been claimed as promising tools for the diagnostic assessment of water quality. Nevertheless the implementation of such methodologies in biomonitoring programs is still limited. This is explained by the necessity to improve the reliability of these bioassays. The present study illustrates how modelling the influence of confounding factors could allow to improve the interpretation of in situ feeding assay with Gammarus fossarum. We proceeded in four steps: (i) we quantified the influence of body size, temperature and conductivity on feeding rate in laboratory conditions; (ii) based on these laboratory findings, we computed a feeding inhibition index, which proved to be robust to environmental conditions and allowed us to define a reference statistical distribution of feeding activity values through the data compilation of 24 in situ assays among diverse reference stations at different seasons; (iii) we tested the sensitivity of the feeding assay using this statistical framework by performing 41 in situ deployments in contaminated stations presenting a large range of contaminant profiles; and (iv) we illustrated in two site-specific studies how the proposed methodology improved the diagnosis of water quality by preventing false-positive and false-negative cases mainly induced by temperature confounding influence. Interestingly, the implementation of the developed protocol could permit to assess water quality without following an upstream/downstream procedure and to compare assays performed at different seasons as part of large-scale biomonitoring programs.
Ecology Letters (2011) 14: 841–851
Ecological specialisation concerns all species and underlies many major ecological and evolutionary patterns. Yet its status as a unifying concept is not always appreciated because of its similarity to concepts of the niche, the many levels of biological phenomena to which it applies, and the complexity of the mechanisms influencing it. The evolution of specialisation requires the coupling of constraints on adaptive evolution with covariation of genotype and environmental performance. This covariation itself depends upon organismal properties such as dispersal behaviour and life history and complexity in the environment stemming from factors such as species interactions and spatio-temporal heterogeneity in resources. Here, we develop a view on specialisation that integrates across the range of biological phenomena with the goal of developing a more predictive conceptual framework that specifically accounts for the importance of biotic complexity and coevolutionary events.
Pseudoreplication occurs when observations are not statistically independent, but treated as if they are. This can occur when there are multiple observations on the same subjects, when samples are nested or hierarchically organised, or when measurements are correlated in time or space. Analysis of such data without taking these dependencies into account can lead to meaningless results, and examples can easily be found in the neuroscience literature.
A single issue of Nature Neuroscience provided a number of examples and is used as a case study to highlight how pseudoreplication arises in neuroscientific studies, why the analyses in these papers are incorrect, and appropriate analytical methods are provided. 12% of papers had pseudoreplication and a further 36% were suspected of having pseudoreplication, but it was not possible to determine for certain because insufficient information was provided.
Pseudoreplication can undermine the conclusions of a statistical analysis, and it would be easier to detect if the sample size, degrees of freedom, the test statistic, and precise p-values are reported. This information should be a requirement for all publications.
The appropriate use of an enzyme activity as a biomarker requires good knowledge of its basal level and its natural variability related to intrinsic biotic and environmental abiotic factors. In view of using whole-body acetylcholinesterase (AChE) activity in Gammarus fossarum as a reliable biomarker of exposure to anti-cholinesterase agents in aquatic ecosystems, (i) the effects of the main biotic (sex, reproductive status, and weight) and abiotic (water temperature) factors on the basal activity level of this enzyme were measured in the laboratory and (ii) the spatio-temporal variability of basal enzyme activity was followed in wild populations over a 1-year period. The results show no direct effect of sex. However, significant differences in AChE activity were observed between females depending on gonadal and embryonic development. A strong negative correlation between the AChE activity levels and organism body weight was observed. Indeed, AChE activity decreases drastically during the early life stages and tends to stabilise in larger individuals. These reports led us to select a standard organism (male; weight range, 15-20mg) to minimise inter-individual variability. No effect of temperature on basal AChE activity was observed in the laboratory for the tested range (6-24 degrees C). Similarly, no spatio-temporal change relative to season or the physico-chemical characteristics of the water (such as conductivity and temperature) was recorded during the field survey. On the basis of field-collected data, we defined the standard organism having a reference activity level with minimal and maximal threshold values. Finally, the value of AChE activity normalisation by protein contents is discussed.
To date, studies on genetic variability in the tolerance of aquatic biota to chemicals have focused on exposure to single chemicals. In the field, metals occur as elemental mixtures, and thus it is essential to study whether the genetic consequences of exposure to such mixtures differs from response to single chemicals. This study determined the feeding responses of three Daphnia magna Straus clones exposed to Cd and Zn, both individually and as mixtures. Tolerance to mixtures of Cd and Zn was expressed as the proportional feeding depression of D. magna to Cd at increasing zinc concentrations. A quantitative genetic analysis revealed that genotype and genotype x environmental factors governed population responses to mixtures of both metals. More specifically, genetic variation in tolerance to sublethal levels of Cd decreased at those Zn concentrations where there were no effects on feeding, and increased again at Zn concentrations that affected feeding. The existence of genotype x environmental interactions indicated that the genetic consequences of exposing D. magna to mixtures of Cd and Zn cannot be predicted from the animals' response to single metals alone. Therefore, current ecological risk assessment methodologies for predicting the effects of chemical mixtures may wish to incorporate the concept of genetic variability. Furthermore, exposure to low and moderate concentrations of Zn increased the sublethal tolerance to Cd. This induction of tolerance to Cd by Zn was also observed for D. magna fed algae pre-loaded with both metals. Furthermore, in only one clone, physiological acclimatization to zinc also induced tolerance to cadmium. These results suggest that the feeding responses of D. magna may be related to gut poisoning induced by the release of metals from algae under low pH conditions. In particular, both induction of metallothionein synthesis by Zn and competition between Zn and Cd ions for uptake at target sites on the gut wall may be involved in determining sublethal responses to mixtures of both metals.
Twenty years ago, Albert Bennett published a paper in the influential book New directions in ecological physiology arguing that individual variation was an 'underutilized resource'. In this paper, I review our state of knowledge of the magnitude, mechanisms and functional significance of phenotypic variation, plasticity and flexibility in endocrine systems, and argue for a renewed focus on inter-individual variability. This will provide challenges to conventional wisdom in endocrinology itself, e.g. re-evaluation of relatively simple, but unresolved questions such as structure-function relationships among hormones, binding globulins and receptors, and the functional significance of absolute versus relative hormone titres. However, there are also abundant opportunities for endocrinologists to contribute solid mechanistic understanding to key questions in evolutionary biology, e.g. how endocrine regulation is involved in evolution of complex suites of traits, or how hormone pleiotropy regulates trade-offs among life-history traits. This will require endocrinologists to embrace the raw material of adaptation (heritable, individual variation and phenotypic plasticity) and to take advantage of conceptual approaches widely used in evolutionary biology (selection studies, reaction norms, concepts of evolutionary design) as well as a more explicit focus on the endocrine basis of life-history traits that are of primary interest to evolutionary biologists (cf. behavioural endocrinology).
Microbial risk assessment is dependent on several biological and environmental factors that affect both the exposure characteristics to the biological agents and the mechanisms of pathogenicity involved in the pathogen-host relationship. Many exposure assessment studies still focus on the location parameters of the probability distribution representing the concentration of the pathogens and/or toxin. However, the mean or median by themselves are insufficient to evaluate the adverse effects that are associated with a given level of exposure. Therefore, the effects on the risk of disease of a number of factors, including the shape parameters characterizing the distribution patterns of the pathogen in their environment, were investigated. The statistical models, which were developed to provide a better understanding of the factors influencing the risk, highlight the role of heterogeneity and its consequences on the commonly used risk assessment paradigm. Indeed, the heterogeneity characterizing the spatial and temporal distribution of the pathogen and/or the toxin contained in the water or food consumed is shown to be a major factor that may influence the magnitude of the risk dramatically. In general, the risk diminishes with higher levels of heterogeneity. This scheme is totally inverted in the presence of a threshold in the dose-response relationship, since heterogeneity will then have a tremendous impact, namely, by magnifying the risk when the mean concentration of pathogens is below the threshold. Moreover, the approach of this article may be useful for risk ranking analysis, regarding different exposure conditions, and may also lead to improved water and food quality guidelines.
The most commonly used threshold in environmental toxicology is the LC50 (or modifications thereof) where 50% of the organisms die or are otherwise affected at a certain concentration of a chemical for a particular time of exposure under specified environmental conditions. Most commonly, this particular threshold is derived from single species laboratory tests low in environmental realism. If the field of ecotoxicology truly examines the effects of chemicals on ecosystems (i.e., complex multivariate systems), serious consideration must be given to thresholds other than those now commonly used in the field of environmental toxicology. Attributes at the community and ecosystem level of organization are not demonstrated at lower levels of biological organization, for example, energy flow and nutrient spiralling. Key issues are whether extrapolation is possible from one threshold to another within a level of biological organization and from one level of biological organization to another for thresholds that do not exist at many levels. Thresholds may be artefacts of testing procedures and may not exist in natural systems. Nevertheless, society must make management decisions about risk with available methods, including those designed to identify some point or threshold below which no deleterious effects are observed. However, these methods and their assumptions deserve more explicit and systematic examination than they have received thus far.
The potential use of biomarkers in ecological risk assessment is explored. The biomarker concept, initially developed to form a basis for studies at the individual/population level, is extended to include community and ecosystem level studies. A strategy is outlined in which biomarkers might be used to assess chemical exposureand the cumulative, adverse effects of toxicants on biotain situ. Protocols for identifying communities, species and populations most at risk are described. The role of biomarkers in the evaluation of the effectiveness of remedial action to alleviate pollution is discussed. It is proposed that, in addition to biomarker measurements on samples obtained from organisms at field sites, biomarker screening tests should be initiated in the laboratory with a range of new chemicals and organisms relevant to the field sites thought to be at risk. This will help to establish links between laboratory-based testing and adverse effectsin situ.
We propose that a niche-based experimental approach at population level could be used to solve some uncertainties in traditional approaches in ecotoxicology. We tested this approach in the context of multiple stressors (i.e. chemical and physical) in a selection of six run-of-river reservoirs with different levels of sediment contamination and associated upstream and downstream river sites. A niche-based approach was tested using three functional traits (habitat, food preferences and body size) and discrepancy between the realized and theoretical niches. We first identified three groups of taxa and then recorded differences along the disturbance gradients, such as an increase in competition, a narrowing of spatial and trophic niche breadth (e.g. of Leuctra major and Gammarus pulex), a widening of spatial niche breadth (e.g. of Ephemerella ignita), a greater proportion of small individuals (e.g. of G. pulex) and a decreasing or an increasing (e.g. L. major) discrepancy between realized and theoretical niches.
Reproductive and life span traits were measured for two obligately parthenogenetic (Artemia parthenogenetica) and three sexual (two A. franciscana and one A. sinica) brine shrimp populations. For each population, clonal lineages or single mating pairs were followed through one life cycle. The relative contributions of environmental and genetic components to total phenotypic variation for 10 life-history traits in response to environmental stress (0, 10, 25 ppb Cu) were estimated. Within treatment variation (CVW) was 39% higher for sexual populations than parthenogenetic populations, with significant (p
Marine ecosystems include a subset in which at least some interrelated geochemical, biochemical, physiological, population and community characteristics are changed by pollutants. Moderate contamination is relatively widespread in coastal and estuarine ecosystems, so the subset of ecosystems with at least some processes affected could be relatively large. Pollutant influences have changed and will probably continue to change on time scales of decades. Biological exposures and dose in such ecosystems are species-specific and determined by how the species is exposed to different environmental media and the geochemistry of individual pollutants within those media. Bioaccumulation models offer significant promise for interpreting such exposures. Biological responses to pollutants need to be more directly linked to exposure and dose. At the level of the individual this might be improved by better understanding relationships between tissue concentrations of pollutants and responses to pollutants. Multi-discipline field and laboratory studies combined with advanced understanding of some basic processes have reduced the ambiguities in interpreting a few physiological/organismic responses to pollutants in nature. Recognition of pollutant-induced patterns in population responses could lead to similar advances. A rational framework for ecotoxicology is developing, but its further advance is dependent upon better integration of ecotoxicology with basic marine ecology and biology.
Considerable research efforts have been made to predict the influences of climate change on species composition in biological communities. However, little is known about how changing environmental conditions and anthropogenic pollution can affect aquatic communities in combination. We investigated the influence of short warming periods on the response of a zooplankton community to the insecticide esfenvalerate at a range of environmentally realistic concentrations (0.03, 0.3 and 3 μg L(-1) ) in 55 outdoor pond microcosms. Warming periods increased the cumulative water temperature, but did not exceed the maximum temperature measured under ambient conditions. Under warming conditions alone the abundance of some zooplankton taxa increased selectively compared to ambient conditions. This resulted in a shift in the community composition that had not recovered by the end of the experiment, 8 weeks after the last warming period. Regarding the pesticide exposure, short-term effects of esfenvalerate on the community structure and the sensitive taxa Daphnia spp. did not differ between the two temperature regimes. In contrast, long-term effects of esfenvalerate on Daphnia spp., a taxon that did not benefit from elevated temperatures, were observed twice as long under warming than under ambient conditions. This resulted in long-term effects on Daphnia spp. until 4 months after contamination at 3 μg L(-1) esfenvalerate. Under both temperature regimes, we identified strength of interspecific competition as the mechanism determining the time until recovery. However, enhanced interspecific competition under warming conditions was prolonged and explained the delayed recovery of Daphnia spp. from esfenvalerate. These results show that, for realistic prediction of the combined effects of changing environmental factors and toxicants on sensitive taxa, the impacts of stressors on the biotic interactions within the community need to be considered.
Disturbance from floods and/or low flows is a pervading force in almost all benthic riverine communities around the world. As such the study of disturbance effects on benthic communities has been a dominant theme of research in benthic river ecology. Many of these studies have been phenomenological or have evaluated hypotheses developed in other areas of ecology. These studies have provided considerable weight to move the common view of ecological communities in general as deterministically structured, to one where stochastic disturbances can be the dominant structuring force in many communities. Benthic river studies investigating the link between disturbance and diversity have generally failed to find support for single variable hypotheses, such as the intermediate disturbance hypothesis, from other areas of ecology, however, river ecologists have been among the first to embrace multivariate models of diversity. The highly mobile, larval life history stage of many riverine invertebrates makes many of the hypotheses generated in general ecology inappropriate for benthic river communities; however, the recently popularized neutral models may prove to be good descriptors of these communities. Food web structure studies indicate riverine webs respond differently to disturbance from the way predicted by ecological theory. The contribution of studies of disturbance in benthic ecology to general ecology has to date been rather limited with some notable exceptions. However, the ubiquity of floods in rivers worldwide offers fertile ground for future contributions that could substantially advance this area of ecology. Benthic river ecologists need to resist the temptation to simply show general ecological models often do not work in streams, and need to develop their own models, which in turn may feed back to wider ecology. Copyright © 2009 John Wiley & Sons, Ltd.
Key points
Variation between measurements may be reduced if sampling is not random
Fixed factors can reduce variation
Replicates are repeated measurements from within an experimental unit
Replication means that samples can no longer be considered random
Comparisons of replicated values require correction, usually by reducing the effect of sample size
Correction requires knowledge of the intra‐class correlation
A vitellogenin (Vg) mass spectrometry-based assay was recently developed to actively biomonitor and assess the exposure of the amphipod Gammarus fossarum to endocrine-disrupting chemicals in freshwater hydrosystems. This paper focuses on the appropriate use of this biomarker, which requires good knowledge of its basal level in males and its natural variability related to intrinsic biotic and environmental abiotic factors. To obtain the lowest biomarker variability, we first studied some of these confounding factors. We observed that the spermatogenesis stage did not have an impact on the Vg level, allowing flexibility in the choice of transplanted gammarids. In the second part of the study, males were transplanted in two clean stations for 21 days, with results indicating a spatial and temporal variability of Vg levels. These Vg changes could not be correlated to environmental factors (e.g., temperature, pH and hardness of waters). Vg induction was then assessed in 21 stations having various levels of contamination. Inductions were observed for only two of the impacted stations studied. Under reference and contaminated conditions, a high interindividual variability of Vg levels was observed in caged organisms, severely limiting the sensitivity of the biomarker and its ability to detect a significant endocrine-disruptor effect. This may be explained by unidentified environmental factors that should later be determined to improved the use of Vg as a biomarker in male G. fossarum. Moreover, as discussed in this paper, recent advancements regarding the pleiotropic functions of the Vg gene in some species may complicate the application of this biomarker in males of invertebrate species.
This paper briefly reviews the utility of physiological measurements as biomarkers of pollutant exposure and biological effect, and then gives a step by step description of methodologies used to measure physiological parameters in mostly fish and invertebrates, but also higher vertebrates where appropriate. The effects of pollutants on respiratory, cardiovascular, osmoregulatory, and neuro-endocrine processes are relatively well described in laboratory experiments and some of these responses (particularly ventilation, heart rate, and also body ion fluxes) have been evaluated as biomonitors or potential biomarkers in the field. Physiological assays are especially useful for monitoring fluctuating or complex exposures, or acting as early warning systems for acute events. Some biomarkers rely on a change in physiological response, and a prerequisite of such assay must be to establish the normal resting response in defined environmental conditions (e.g., temperature, pH, photoperiod, etc.). Biomarkers that rely on variability of response, rather than absolute values, may not require this laboratory calibration. Methods are described for on line cardiovascular monitoring with shore crabs, field applications of closed respirometry and ion flux measurements with fish; and a range of blood parameters for animals including haemoglobin, haematocrit, cell counts, glucose, triglycerides, and protein from blood and organ perfusates. Each method includes a short critic of the approach.
To date, studies on genetic variability in the tolerance of aquatic biota to chemicals have focused on exposure to single chemicals. In the field, metals occur as elemental mixtures, and thus it is essential to study whether the genetic consequences of exposure to such mixtures differs from response to single chemicals. This study determined the feeding responses of three Daphnia magna Straus clones exposed to Cd and Zn, both individually and as mixtures. Tolerance to mixtures of Cd and Zn was expressed as the proportional feeding depression of D. magna to Cd at increasing zinc concentrations. A quantitative genetic analysis revealed that genotype and genotype×environmental factors governed population responses to mixtures of both metals. More specifically, genetic variation in tolerance to sublethal levels of Cd decreased at those Zn concentrations where there were no effects on feeding, and increased again at Zn concentrations that affected feeding. The existence of genotype×environmental interactions indicated that the genetic consequences of exposing D. magna to mixtures of Cd and Zn cannot be predicted from the animals’ response to single metals alone. Therefore, current ecological risk assessment methodologies for predicting the effects of chemical mixtures may wish to incorporate the concept of genetic variability. Furthermore, exposure to low and moderate concentrations of Zn increased the sublethal tolerance to Cd. This induction of tolerance to Cd by Zn was also observed for D. magna fed algae pre-loaded with both metals. Furthermore, in only one clone, physiological acclimatisation to zinc also induced tolerance to cadmium. These results suggest that the feeding responses of D. magna may be related to gut poisoning induced by the release of metals from algae under low pH conditions. In particular, both induction of metallothionein synthesis by Zn and competition between Zn and Cd ions for uptake at target sites on the gut wall may be involved in determining sublethal responses to mixtures of both metals.
Multixenobiotic resistance in aquatic organisms exposed to natural toxins or anthropogenic contaminants is a phenomenon analogous to multidrug resistance in mammalian tumor cell lines tolerant of anti-cancer drugs. Multidrug resistance is commonly due to the elevated expression of transmembrane P-glycoproteins (P-gp) which actively transport a wide variety of structurally and functionally diverse compounds. The purpose of this review is to place aquatic ecotoxicological data in context of the larger multidrug resistance field of study. Information on P-glycoproteins structure, mechanism of transport, and substrate specificity gained through traditional mammalian and cell culture models is examined in conjunction with recent work on aquatic species exposed to xenobiotics both in the field and in the laboratory. The physiological function of P-glycoproteins is explored through studies of gene knockout models and expression patterns in normal tissues and tumors. The effect of xenobiotic exposures on P-gp activity and protein titer is examined in wild and captive populations of aquatic invertebrates and vertebrates. Substrate overlap and evidence of co-expression of phase I detoxification enzymes (e.g. cytochromes P450) and P-gp are presented. The role of P-gp chemosensitizers as environmental pollutants and the ecotoxicological consequences of P-gp inhibition are highlighted. The overwhelming evidence suggests that P-glycoproteins provide aquatic organisms with resistance to a wide range of natural and anthropogenic toxins.
Bioassays can be used in aquatic toxicology to provide individual determinations, however ecotoxicology is now attempting to assess the impact of pollution on populations. The main issue is how to infer the impact on an entire population of the toxic effects observed in individuals. At the individual level, Dynamic Energy Budget in Toxicology (DEBtox) theory provides a set of mechanistic models of survival, reproduction and growth continuously as a function of time and exposure concentration, in which the parameters used have clear biological meanings. These models have been designed for the analysis of data provided by the internationally standardized toxicity tests, and sometimes make it clear which is the mode of action of the contaminant. Matrix population models directly yield the population growth rate, the most robust endpoint in risk assessment at the population level. By combining DEBtox theory and matrix population models, we extrapolate every effects of the toxic compound on the individual (reduced fecundity, growth and survival) to the population level. Both lethal and sublethal effects are integrated into a single parameter, the population growth rate, which is calculated continuously against exposure concentration. We can thus compare the consequences at the population level of choosing one or another assumption about the mode of action of the contaminant at the individual level. We used various complementary matrix population models, in order to perform a complete sensitivity analysis, highlighting critical demographic parameters in the evolution of population growth rate as a function of contaminant concentration. Here, we apply this method to a test organism commonly used in ecotoxicology, Daphnia magna, through a case study of cadmium contamination.
1) Heart rates and midgut gland () ratios of rock crabs (Hemigrapsus edwardsi) were measured in individuals collected along a contaminant gradient in Otago Harbour, New Zealand. 2) Median heart rates decreased by 15–20% while midgut gland ratios increased by 25–30% with increasing contamination of field sites. 3) Intra- and inter-individual variability in heart rate increased markedly at the most severely contaminated sites, as did inter-individual variability in midgut gland ratio. 4) The findings are discussed in the context of the use of the biomarker approach to address ecotoxicological problems.
This article provides an overview how the application of the gene profiling (mainly via microarray technology) can be used in different organisms to address issues of environmental importance. Only recently, environmental sciences, including ecotoxicology, and molecular biology have started to mutually fertilize each other. This conceptual blend has enabled the identification of the interaction between molecular events and whole animal and population responses. Likewise, striking the fine balance between biomonitoring and functional environmental genomics will allow legislative and administrative measures to be based on a more robust platform. The application of DNA microarrays to ecotoxicogenomics links ecotoxicological effects of exposure with expression profiles of several thousand genes. The gene expression profiles are altered during toxicity, as either a direct or indirect result of toxicant exposure and the comparison of numerous specific expression profiles facilitates the differentiation between intoxication and true responses to environmental stressors. Furthermore, the application of microarrays provides the means to identify complex pathways and strategies that an exposed organism applies in response to environmental stressors. This review will present evidence that the widespread phenomenon of hormesis has a genetic basis that goes beyond an adaptive response. Some more practical advantages emerge: the toxicological assessment of complex mixtures, such as effluents or sediments, as well as drugs seems feasible, especially when classical ecotoxicological tests have failed. The review of available information demonstrates the advantages of microarray application to environmental issues spanning from bacteria, over algae and spermatophytes, to invertebrates (nematode Caenorhabditis elegans, crustacea Daphnia spp., earthworms), and various fish species. Microarrays have also highlighted why populations of a given species respond differently to similar contaminations. Furthermore, this review points at inherent limits of microarrays which may not yet have been properly addressed, namely epigenetics, which may explain heritable variation observed in natural population that cannot be explained by differences in the DNA sequence. Finally, the review will address promising future molecular biological developments which may supersede the microarray technique.
The use of gene expression profiling in both clinical and laboratory settings would be enhanced by better characterization of variation due to individual, environmental, and technical factors. Analysis of microarray data from untreated or vehicle-treated animals within the control arm of toxicogenomics studies has yielded useful information on baseline fluctuations in liver gene expression in the rodent. Here, studies which highlight contributions of different factors to gene expression variability in the rodent liver are discussed including a large meta-analysis of rat liver, which identified genes that vary in control animals in the absence of chemical treatment. Genes and their pathways that are the most and least variable were identified in a number of these studies. Life stage, fasting, sex, diet, circadian rhythm and liver lobe source can profoundly influence gene expression in the liver. Recognition of biological and technical factors that contribute to variability of background gene expression can help the investigator in the design of an experiment that maximizes sensitivity and reduces the influence of confounders that may lead to misinterpretation of genomic changes. The factors that contribute to variability in liver gene expression in rodents are likely analogous to those contributing to human interindividual variability in drug response and chemical toxicity. Identification of batteries of genes that are altered in a variety of background conditions could be used to predict responses to drugs and chemicals in appropriate models of the human liver.
New concerns about biodiversity, ecosystem services and human health triggered several new regulations increasing the need for sound ecotoxicological risk assessment. The PEER network aims to share its view on the research issues that this challenges. PEER scientists call for an improved biologically relevant exposure assessment. They promote comprehensive effect assessment at several biological levels. Biological traits should be used for Environmental risk assessment (ERA) as promising tools to better understand relationships between structure and functioning of ecosystems. The use of modern high throughput methods could also enhance the amount of data for a better risk assessment. Improved models coping with multiple stressors or biological levels are necessary to answer for a more scientifically based risk assessment. Those methods must be embedded within life cycle analysis or economical models for efficient regulations. Joint research programmes involving humanities with ecological sciences should be developed for a sound risk management.
There can be considerable variability between species, and within species between genotypes, in responses to toxicants. This needs to be controlled in running ecotoxicity tests and taken into account in carrying out ecological risk assessments. This paper addresses these two aspects of the problem and describes the methodology involved in each.
In the present study we aimed to investigate whether UV-B radiation can exacerbate effects of pesticides fenoxycarb, pirimicarb, and tebufenpyrad on the survival, reproduction, and population growth rate of the standard test species Daphnia magna. We applied sublethal pesticides' concentrations and UV doses and observed no effects on survival. However, we observed synergistic effects of UV and pesticides on both cumulative reproduction and population growth rate (21 days) for fenoxycarb (100 μg/L) and pirimicarb (10 μg/L), but a less-than-additive effect for tebufenpyrad (5-10 μg/L). In the series exposed to UV and fenoxycarb or pirimicarb, the population growth rate dropped down to 0.1, while in the control series it was around 0.3. The results indicate that concentrations of some toxicants that are nontoxic in standard tests can cause harmful population-level effects when combined with UV.
Ecology Letters (2010) 13: 1435–1447
There is increasing evidence that some non-essential substances or environmental stressors can have stimulatory or beneficial effects at low exposure levels while being toxic at higher levels, and that environmental ‘priming’ of certain physiological processes can result in their improved functioning in later life. These kinds of nonlinear dose–response relationships are referred to as hormetic responses and have been described across a wide range of organisms (from bacteria to vertebrates), in response to exposure to at least 1000 different chemical and environmental stressors. Although most work in this area has been in the fields of toxicology and human health, the concept of hormesis also has general applicability in ecology and evolutionary biology as it provides an important conceptual link between environmental conditions and organism function – both at the time of initial exposure to stressors and later in life. In this review, we discuss and clarify the different ways in which the term hormesis is used and provide a framework that we hope will be useful for ecologists interested in the fitness consequences of exposure to stressors. By using ecologically relevant examples from the existing literature, we show that hormesis is connected with both acclimation and phenotypic plasticity, and may play an important role in allowing animals to adjust to changing environments.
The expression of p-glycoprotein (p-gp) in aquatic organisms has been proposed as a biomarker of pollution exposure. Previous research has provided evidence that p-gp is inducible by organic xenobiotics and that p-gp is overexpressed in mussels from degraded areas. However, seasonal changes in expression at polluted sites has not been described previously. The purposes of these studies were to evaluate the expression of p-gp in polluted and unpolluted sites in oysters (Crassostrea virginica) and to determine if there were seasonal differences. P-gp expression and total protein concentrations were measured seasonally in the gills of southeastern oysters, Crassostrea virginica, at degraded and undegraded sites in Charleston Harbor, South Carolina, USA. At all sites, p-gp expression was generally higher during the warmer months and lower in the colder months. Polluted sites tended to show a decrease in p-gp expression in June and September, suggesting that p-gp inhibition may have occurred. P-gp expression was not significantly related to specific classes of sediment contaminants or to overall sediment contaminant loading. Total gill protein concentrations at all sites were lower during the warmer months and higher during the colder months. In general, all sites tended to show decreased total gill protein concentrations when compared to the control site. Total protein concentrations were significantly related to water temperature, specific classes of sediment contaminants and overall sediment contaminant loads, but there was no relationship with salinity.
The application of biochemical measurements that can be used as individual biomarkers of impaired biological function in invertebrates is reviewed to evaluate whether biochemical biomarkers of aquatic invertebrates can predict changes in natural populations. Biomarkers that measure toxic effects at the molecular level (e.g., the inhibition of brain acetylcholinesterase activity by organophosphorus pesticides) have been shown to provide rapid quantitative predictions of a toxic effect upon individuals in laboratory studies. Such biomarkers should not be used as a replacement for conventional aquatic monitoring techniques, but should be applied as supplementary approaches for demonstrating links between sublethal biochemical and adverse effects in natural populations in field studies. The research challenge for using biomarker measurements in aquatic invertebrates is to predict effects at the population level from effects at the individual level measured upon individuals collected in the field.
Despite a wealth of information on biomarkers, they are not routinely used for regulatory purposes, even though the potential benefits of biomarkers to rationalise complex exposure-response relationships are clear. Biomarkers can be inappropriately applied or misinterpreted, because the fundamental assumptions in exposure-response relations have not been considered. Factors causing temporal and spatial variability in biomarker responses are reviewed. These include numerous geochemical and biotic variables. The variation can be minimised by appropriate study site selection, experimental replication, multivariate epidemiological approaches, normalised controls, and temporal calibration of responses; so that the regulatory use of biomarkers for biomonitoring and tracking pollution events, including chronic or multiple exposures to complex mixtures is possible. We propose and define the characteristics of biomarkers of chronic exposure or effect, which must measure changes in pollution/effect against long-term changes in other general stresses (disease, nutrition, environmental quality), relate to cumulative injury, and remain responsive over months or years. Neuroendocrine, immunological, and histological biomarkers are suggested for chronic pollution. We propose a regulatory framework for biomarkers based on a weight of evidence approach that can integrate biomarkers in risk assessment and long-term monitoring programmes.
We contrasted concentrations of macronutrients (C, N and P), essential (As, Cu, Zn and Se) and non-essential metals (Pb, Hg and Cd) in invertebrates across five lakes and June to October in one lake. We predicted that somatic concentrations of tightly regulated elements would be less variable than weakly and unregulated elements. Within each taxon, variation was lowest in macronutrients, intermediate in essential micronutrients, and highest in non-essential metals, which corresponded in rank to homeostatic regulation strength for the same elements calculated from the literature. Hence, homeostatic regulation may strongly influence variation in element concentrations of biota in situ. Of the individual elements, only taxonomic differences in C and N were consistent across lakes and over a season. Nevertheless, canonical discriminant analyses successfully discriminated among taxa based on taxonomic multielement composition. Thus, relative taxonomic differences in multielement composition appear more informative than absolute stoichiometric formulae when considering the role of inherently variable trace elements in ecological investigations.
Risk assessment of metal-contaminated habitats based on responses in the field is complicated by the evolution of local, metal-resistant ecotypes. The unpredictability of occurrence of genetically determined adaptive traits, in terms of site-specific geochemistry, a population's inferred exposure history, and in the physiology of resistance, exacerbates the problem. Micro-evolutionary events warrant the attention of ecotoxicologists because they undermine the application of the bedrock of toxicology, the dose-response curve, to in situ field assessments. Here we survey the evidence for the existence of genetically differentiated, metal-resistant, invertebrate populations; we also describe some of the molecular mechanisms underpinning the adaptations. Quantitative changes in tissue-metal partitioning, and in the molecular and cellular responses (biomarkers)to alterations in internal bioreactive metal pools, are widely accepted as indicators of toxicity and/or exposure in free-living organisms. Both can be modulated by resistance. The understanding that all genomes are intrinsicallyflexible, with subtle sequence changes in promoter regions or epigenetic adjustments conferring significant phenotypic consequences, is deemed highly relevant. Equally relevant is the systems biology insight that genes and proteins are woven into networks. We advocate that biomarker studies should work toward assimilating and exploiting these biological realities through monitoring the activities of suites of genes (transcriptomics) and their expressed products (proteomics), as well as profiling the metabolite signatures of individuals (metabolomics) and by using neutral genetic markers to genotype populations. Ecotoxicology requires robust tools that recognize the imprint of evolution on the constitution of field populations, as well as sufficient mechanistic understanding of the molecular-genetic observations to interpret them in meaningful environmental diagnostic ways.
Distinguishing between effects of natural and anthropogenic environmental factors on ecosystems is a fundamental problem in environmental science. In river systems the longitudinal gradient of environmental factors is one of the most relevant sources of dissimilarity between communities that could be confounded with anthropogenic disturbances. To test the hypothesis that in macroinvertebrate communities the distribution of species' sensitivity to organic toxicants is independent of natural longitudinal factors, but depends on contamination with organic toxicants, we analysed the relationship between community sensitivity SPEAR(organic) (average community sensitivity to organic toxicants) and natural and anthropogenic environmental factors in a large-scale river system, from alpine streams to a lowland river. The results show that SPEAR(organic) is largely independent of natural longitudinal factors, but strongly dependent on contamination with organic toxicants (petrochemicals and synthetic surfactants). Usage of SPEAR(organic) as a stressor-specific longitude-independent measure will facilitate detection of community disturbance by organic toxicants.
- R Coulaud
- O Geffard
- B Xuereb
- E Lacaze
- H Quéau
- J Garric
Coulaud R, Geffard O, Xuereb B, Lacaze E, Quéau H, Garric J, et al. In situ feeding assay with
Gammarus fossarum (Crustacea): modelling the influence of confounding factors to
improve water quality biomonitoring. Water Res 2011;45:6417-29.