Genetic adaptation of earthworms to copper pollution: is adaptation associated with fitness costs in Dendrobaena octaedra?

Chronic metal contamination shapes the size structure of Gammarus fossarum populations in French headwater rivers

Assessing the effects of multigenerational exposure of aquatic animal populations to chemical contamination is essential for ecological risk assessment. However, beyond rare examples reporting the sporadic emergence of a toxicological tolerance within populations that persist in contaminated environments, conclusive results are even more limited from field studies when it comes to the alteration of life-history traits. Here, we investigated whether long-term exposure to cadmium (Cd) influences size-related life-history traits (i.e., size at puberty, median adult size, maximum size) in Gammarus fossarum, a keystone species of European stream ecosystems. We studied 13 field populations of G. fossarum (cryptic lineage B) living in headwater rivers located in natural areas scattered at a large geographical scale and exposed to contrasted bioavailable Cd contamination levels due to different local geochemical backgrounds. We achieved a detailed description of the physical and physicochemical conditions of the river reaches investigated. Land-use parameters, hydrological characteristics (flow, slope, river width, flow structure, mosaic of substrates), and physicochemical conditions (temperature, conductivity, dissolved oxygen) were measured. Metallic bioavailable contamination was assessed using a standardized active biomonitoring procedure (Gammarus caging). Based on the field demographic census of the 13 populations, our results demonstrated that chronic Cd contamination significantly influences life-history in the G. fossarum species, with a significant reduction in all size traits of populations (size at puberty, median adult size, maximum size). In addition, we confirmed Cd-tolerance in contaminated populations during exposure tests in the laboratory. Various hypotheses can be then put forward to explain the modification of size-related life-history traits: a direct toxic effect of Cd, a cost of Cd-tolerance, or an adaptive evolution of life-history exposed to toxic pressure.

Insights into the molecular mechanisms of pesticide tolerance in the Aporrectodea caliginosa earthworm

Diffuse pollution of the environment by pesticides has become a major soil threat to non-target organisms, such as earthworms for which declines have been reported. However some endogeic species are still abundant and persist in intensively cultivated fields, suggesting they become tolerant to long-term anthropogenic pressure. We thus considered the working hypothesis that populations of Aporrectodea caliginosa earthworms from conventionally managed fields developed a tolerance to pesticides compared with those from organically managed fields. To investigate this hypothesis, we studied earthworm populations of the same genetic lineage from soils that were either lowly or highly contaminated by pesticides to detect any constitutive expression of differentially expressed molecular pathways between these populations. Earthworm populations were then experimentally exposed to a fungicide-epoxiconazole-in the laboratory to identify different molecular responses when newly exposed to a pesticide. State-of-the-art omics technology (RNA sequencing) and bioinformatics were used to characterize molecular mechanisms of tolerance in a non-targeted way. Additional physiological traits (respirometry, growth, bioaccumulation) were monitored to assess tolerance at higher levels of biological organization. In the present study, we generated the de novo assembly transcriptome of A. caliginosa consisting of 64,556 contigs with N50 = 2862 pb. In total, 43,569 Gene Ontology terms were identified for 21,593 annotated sequences under the three main ontologies (biological processes, cellular components and molecular functions). Overall, we revealed that two same lineage populations of A. caliginosa earthworms, inhabiting similar pedo-climatic environment, have distinct gene expression pathways after they long-lived in differently managed agricultural soils with a contrasted pesticide exposure history for more than 22 years. The main difference was observed regarding metabolism, with upregulated pathways linked to proteolytic activities and the mitochondrial respiratory chain in the highly exposed population. This study improves our understanding of the long-term impact of chronic exposure of soil engineers to pesticide residues.

Influence of biochar remediation on Eisenia fetida in Pb-contaminated soils

In this study, the remediation influence of maize straw biochar on earthworms (Eisenia fetida) in contaminated soils (with Pb at 0, 300, 700, and 1000 mg kg^-1) amended with different amounts of biochar (0%, 1%, 3%, and 5%) was investigated. The results showed that applying biochar to metal-polluted soils effectively reduced the mobility of Pb, promoting the transformation of Pb from exchangeable (EXC) and bound-to-carbonate (Carb) fractions to Fe/Mn oxide (FeMnOx), organic bound (ORG) and residual (RES) fractions. Consequently, a reduction in the mortality and weight loss of earthworms was also achieved by biochar. The accumulation amount of Pb in earthworms steadily increased with exposure time, and with the increasing dosage of biochar, the accumulated Pb decreased by 50.8-78.0% (300 mg kg^-1), 30.9-67.3% (700 mg kg^-1), and 17.4-55.1% (1000 mg kg^-1), which was significantly positively correlated with the mortality of earthworms. Simultaneously, the application of biochar increased the soil pH (0.05-0.23 units), cation exchange capacity (CEC) (0.26-4.54 cmol kg^-1), and content of organic matter (0.54-11.66%). There were higher soil enzyme activities (including sucrase activity, urease activity, and alkaline phosphatase activity) in the treatments with a biochar addition of 3%. Through remediation, Proteobacteria (50.82%), Actinobacteriota (32.37%), Firmicutes (4.83%) and Bacteroidota (1.88%) were the most important phyla in the microbiota communities. Furthermore, soil pH value and leaching toxicity concentration showed the most striking effects on earthworms. Therefore, the influence of earthworms must be taken into account in the remediation of Pb-contaminated soil with biochar.

Toxicity of binary mixtures of Cu, Cr and As to the earthworm Eisenia andrei

Chromated copper arsenate (CCA) mixtures were used in the past for wood preservation, leading to large scale soil contamination. This study aimed at contributing to the risk assessment of CCA-contaminated soils by assessing the toxicity of binary mixtures of copper, chromium and arsenic to the earthworm Eisenia andrei in OECD artificial soil. Mixture effects were related to reference models of Concentration Addition (CA) and Independent Action (IA) using the MIXTOX model, with effects being related to total and available (H₂O and 0.01 M CaCl₂ extractable) concentrations in the soil. Since only in mixtures with arsenic dose-related mortality occurred (LC₅₀ 92.5 mg/kg dry soil), it was not possible to analyze the mixture effects on earthworm survival with the MIXTOX model. EC₅₀s for effects of Cu, Cr and As on earthworm reproduction, based on total soil concentrations, were 154, 449 and 9.1 mg/kg dry soil, respectively. Effects of mixtures were mainly antagonistic when related to the CA model but additive related to the IA model. This was the case when mixture effects were based on total and H₂O-extractable concentrations; when based on CaCl₂-extractable concentrations effects mainly were additive related to the CA model except for the Cr-As mixture which acted antagonistically. These results suggest that the CCA components do interact leading to a reduced toxicity when present in a mixture.

Genetic analysis in earthworm population from area contaminated with radionuclides and heavy metals

This study assessed the effects of environmental contamination by naturally occurring radionuclides and heavy metals on the genetic structure of a population of the earthworm Aporrectodea caliginosa. A. caliginosa were collected from four sites and characterized by amplified fragment length polymorphism (AFLP) analyses. No differences in genetic structure and diversity were found between sites that differed greatly in soil contamination levels of radionuclides and metals. However, when the genetic structure of the A. caliginosa population was analyzed without considering information about the sampling site, a complex intraspecific genetic structure was identified. At least three highly divergent lineages were found, in unequal proportions, of each genetically isolated group from each study site. No associations were found between the distribution of the detected genetic clusters and the geographical origin of the samples. Thus, no noticeable adaptive changes or signs of directional selection were detected, despite the long history of genotoxic waste disposal at the sampling site. These results suggest a combined effect of three factors on the genetic structure and diversity of A. caliginosa in soils: the complexity of the contaminant composition, the heterogeneous spatial distribution of the pollutants, and the complexity of the intraspecific genetic structures of A. caliginosa.

Mixed evidence for adaptation to environmental pollution

Adaptation to pollution has been studied since the first observations of heavy metal tolerance in plants decades ago. To document micro-evolutionary responses to pollution, researchers have used phenotypic, molecular genetics, and demographic approaches. We reviewed 258 articles and evaluated the evidence for adaptive responses following exposure to a wide range of pollutants, across multiple taxonomic groups. We also conducted a meta-analysis to calculate the magnitude of phenotypic change in invertebrates in response to metal pollution. The majority of studies that reported differences in responses to pollution were focused on phenotypic responses at the individual level. Most of the studies that used demographic assays in their investigations found that negative effects induced by pollution often worsened over multiple generations. Our meta-analysis did not reveal a significant relationship between metal pollution intensity and changes in the traits studied, and this was probably due to differences in coping responses among different species, the broad array of abiotic and biotic factors, and the weak statistical power of the analysis. We found it difficult to make broad statements about how likely or how common adaptation is in the presence of environmental contamination. Ecological and evolutionary responses to contamination are complex, and difficult to interpret in the context of taxonomic, and methodological biases, and the inconsistent set of approaches that have been used to study adaptation to pollution in the laboratory and in the field. This review emphasizes the need for: (a) long-term monitoring programs on exposed populations that link demography to phenotypic, genetic, and selection assays; (b) the use of standardized protocols across studies especially for similar taxa. Approaches that combine field and laboratory studies offer the greatest opportunity to reveal the complex eco-evolutionary feedback that can occur under selection imposed by pollution.

An uptake and elimination kinetics approach to assess the bioavailability of chromium, copper, and arsenic to earthworms (Eisenia andrei) in contaminated field soils

The aim of this study was to determine the bioavailability of metals in field soils contaminated with chromated copper arsenate (CCA) mixtures. The uptake and elimination kinetics of chromium, copper, and arsenic were assessed in the earthworm Eisenia andrei exposed to soils from a gradient of CCA wood preservative contamination near Hartola, Finland. In soils contaminated with 1480-1590 mg Cr/kg dry soil, 642-791 mg Cu/kg dry soil, and 850-2810 mg Ag/kg dry soil, uptake and elimination kinetics patterns were similar for Cr and Cu. Both metals were rapidly taken up and rapidly excreted by Eisenia andrei with equilibrium reached within 1 day. The metalloid As, however, showed very slow uptake and elimination in the earthworms and body concentrations did not reach equilibrium within 21 days. Bioaccumulation factors (BAF) were low for Cu and Cr (< 0.1), but high for As at 0.54-1.8. The potential risk of CCA exposure for the terrestrial ecosystem therefore is mainly due to As.

Impact of heavy metal bioaccumulation on antioxidant activities and DNA profile in two earthworm species and freshwater prawn from Ogun River

The use of freshwater invertebrates as bioindicator of heavy metal pollution is an important tool for environmental biomonitoring. This study investigated antioxidant activities and DNA profile in two limicolous earthworms (Alma millsoni and Libyodrilus violaceus) and freshwater prawns (Macrobrachium vollenhovenii) at selected points of Ogun River, Abeokuta. Heavy metal concentrations and DNA profile in the earthworms and prawn tissues were measured using standard procedures. Zn concentration was higher than other heavy metals in A. millsoni (685.83±114.42mg/kg), L. violaceus (1913.3±1098.7mg/kg) and M. vollenhovenii (134.7±13.61mg/kg). Superoxide dismutase activity ranged from 62.44±7.16-79.82±11.18U/g tissues, 60.26±11.18-71.07±7.54U/g tissues and 74.07±16.69-87.79±8.50U/g tissues in A. millsoni, L. violaceus and M. vollenhovenii respectively. RAPD-PCR revealed varying DNA profile among the earthworms samples; the UPGMA dendrogram formed two distinct clusters at genetic similarity coefficient of 0.15-0.2 with one cluster consisting of Alma millsoni and Libyodrilus violaceus from Sokori, Enugada and Iberekodo sampling points and the second cluster forming two distinct sub-clusters comprising Arakanga and Ago-ika's L. violaceus in one and A. millsoni in the other. High genetic variability was recorded among the earthworm species while the freshwater prawn showed no variability. Antioxidant activities and genetic variability in earthworms could serve as biomarkers of heavy metal pollution in freshwater environment.

Turning natural adaptations to oncogenic factors into an ally in the war against cancer

Both field and experimental evolution studies have demonstrated that organisms naturally or artificially exposed to environmental oncogenic factors can, sometimes rapidly, evolve specific adaptations to cope with pollutants and their adverse effects on fitness. Although numerous pollutants are mutagenic and carcinogenic, little attention has been given to exploring the extent to which adaptations displayed by organisms living in oncogenic environments could inspire novel cancer treatments, through mimicking the processes allowing these organisms to prevent or limit malignant progression. Building on a substantial knowledge base from the literature, we here present and discuss this progressive and promising research direction, advocating closer collaboration between the fields of medicine, ecology, and evolution in the war against cancer.

Speciation of heavy metals and bacteria in cow dung after vermicomposting by the earthworm, Eisenia fetida

This work was conducted to evaluate the total concentration and speciation of heavy metals (Cd, Pb and Cr) in vermicompost product (EFCD) by Eisenia fetida (EF) with cow dung (FCD). Meanwhile, the bacterial community and diversity of the three were compared by high-throughput sequencing. Results showed that heavy metal concentrations were declined significantly in EFCD. Sequential extraction indicated that the exchangeable fraction of Cd and Pb decreased markedly and the residual fractions increased in EFCD. Though the exchangeable fraction of Cr increased, the total concentration reduced greatly. Furthermore, the speciation of Cd, Pb and Cr bioaccumulated in EF were different. Besides, the bacterial diversity was highest in EFCD, and twelve genera with species having heavy metal resistance/tolerance were found from the genus of different abundance of the three. Vermicomposting effectively reduced the total concentration and toxicity for heavy metals, and the bacterial composition and diversity were changed greatly during vermicomposting.

Variation in gene expression within clones of the earthworm Dendrobaena octaedra

Gene expression is highly plastic, which can help organisms to both acclimate and adapt to changing environments. Possible variation in gene expression among individuals with the same genotype (among clones) is not widely considered, even though it could impact the results of studies that focus on gene expression phenotypes, for example studies using clonal lines. We examined the extent of within and between clone variation in gene expression in the earthworm Dendrobaena octaedra, which reproduces through apomictic parthenogenesis. Five microsatellite markers were developed and used to confirm that offspring are genetic clones of their parent. After that, expression of 12 genes was measured from five individuals each from six clonal lines after exposure to copper contaminated soil. Variation in gene expression was higher over all genotypes than within genotypes, as initially assumed. A subset of the genes was also examined in the offspring of exposed individuals in two of the clonal lines. In this case, variation in gene expression within genotypes was as high as that observed over all genotypes. One gene in particular (chymotrypsin inhibitor) also showed significant differences in the expression levels among genetically identical individuals. Gene expression can vary considerably, and the extent of variation may depend on the genotypes and genes studied. Ensuring a large sample, with many different genotypes, is critical in studies comparing gene expression phenotypes. Researchers should be especially cautious inferring gene expression phenotypes when using only a single clonal or inbred line, since the results might be specific to only certain genotypes.

Effects of an aged copper contamination on distribution of earthworms, reproduction and cocoon hatchability

Contaminated soil is a problem throughout the industrialized world, and a significant proportion of these sites are polluted with heavy metals such as copper. Ecological risk assessment of contaminated sites requires ecotoxicological studies with spiked soils as well as in-situ ecological observations. Here, we report laboratory and field assessment of copper toxicity for earthworms at a Danish site (Hygum) exclusively contaminated with an increasing gradient in copper from background to highly toxic levels (>1000mgkg^-1 dry soil). More specifically, we report effects on field populations, body contents of copper, hatching of earthworm cocoons and reproduction of the common species Aporrectodea tuberculata. Abundance of earthworms and cocoons decreased significantly from about 400-150m^-2 along the gradient as the soil copper concentration increased from ca. 50 to ca. 1000mgkg^-1. At lower concentrations, the population was dominated by endogeic species, whereas at high concentrations the population was dominated by epigeic species. At high copper contents the internal concentration of copper was in the range 100-160mgkg^-1 dry tissue. Despite the high internal copper contents, hatchability of field collected cocoons was not impaired in any species. The EC50 reproduction value of A. tuberculata was about 220mg copper kg^-1 dry soil in the first two exposure periods, but nearly doubled in the third period suggesting that an acclimation response had occurred. Also in the laboratory reproduction test, cocoon hatchability was not reduced, but rather slightly stimulated by copper. Based on these results we discuss the possibility that acute exposure in laboratory experiments is more detrimental than exposure in a field situation, perhaps because increased tolerance may be acquired through natural selection and genetic adaptation through increased use of defense mechanisms such as metallothioneins. Further, we discuss that the rather high tissue copper level of earthworms from the Hygum site may have smaller effects in these free-ranging worms than it would have in acute-exposure laboratory tests because the copper is more efficiently sequestered and detoxified in the field situation where populations have been exposed for many generations.

Preliminary evidence of differences in cadmium tolerance in metal-free stocks of the standard earthworm test species Eisenia andrei (Oligochaeta)

To test whether metal-tolerant and metal-sensitive earthworm specimens could be an inherent part of metal-free earthworm populations, (i) we used DNA barcoding to identify and categorize earthworms from 8 populations of the standard test species Eisenia andrei, and (ii) the earthworms carrying three of the identified COI haplotypes (named Hap1, hap3 and Hap3) were paired up and exposed to Cd in order to assess the difference in Cd sensitivity between the breeding pairs. A total of six breeding pairs were exposed to 0, 25, 50 and 100 mg Cd/kg for 4 weeks at 20 °C. The survival of the breeding pairs, their change in biomass and cocoon production were assessed. For all of the endpoints assessed, the results indicated that couple 6 (Hap3 × Hap3) was the most sensitive breeding pair whereas couple 4 (Hap1 × Hap3) was the least sensitive one. The analysis of Cd tissue contents revealed that with increasing Cd concentration, Cp6 (Hap3 × Hap3) could accumulate significantly more Cd than any other breeding pair (p ≤ 0.01). Our findings indicate that E. andrei may harbour intrinsically Cd-tolerant and Cd-sensitive individuals and that this may be due to individual differences in Cd accumulation kinetics. In the context of ecotoxicological testing, our results underline the importance of using genetically diverse populations in laboratory testing to prevent generating flawed data from genetically homogeneous laboratory stocks. Although we do not regard the present mitochondrial haplotypes as proxy for possibly nuclear encoded traits, we discuss the necessity of a standardised earthworm barcoding protocol that could help not only to confirm the taxonomy of laboratory earthworm stocks but also to select genetically diverse stocks suitable for laboratory testing.

Assessment of metal toxicity and bioavailability in metallophyte leaf litters and metalliferous soils using Eisenia fetida in a microcosm study

The leaf litters of tree species, Acacia pycnantha (Ap) and Eucalyptus camaldulensis (Ec), predominantly growing at an abandoned copper (Cu) mine and mine soils including controls, were assessed for determining the metal toxicity and bioavailability using earthworm species Eisenia fetida, in a microcosm. Significant reduction in body weight as well as mortality were observed when the worms were introduced into mine soil or its combination with mine Ap litter. Virtually, there were no juveniles when the worms were fed on substratum that contained mine soil or mine leaf litter. The extent of bioaccumulation was dependent on water-soluble fraction of a metal in soil. The accumulation of cadmium, lead and copper in worm tissue was significantly more in treatments that received mine soil with or without mine leaf litter. However, the tissue concentration of zinc did not differ much in earthworms irrespective of its exposure to control or contaminated samples. Mine leaf litter from Ec, a known Cu hyperaccumulator, was more hospitable to earthworm survival and juvenile than that of Ap litter. Validation of the data on bioaccumulation of metals indicated that the mine leaf litter significantly contributed to metal bioavailability. However, it was primarily the metal concentration in mine soil that was responsible for earthworm toxicity and bioavailability. Our data also indicate that detrivores like earthworm is greatly responsible for heavy metal transfer from mines into the ecosystem.

Freezing of body fluids induces metallothionein gene expression in earthworms (Dendrobaena octaedra)

The molecular mechanisms activated by environmental contaminants and natural stressors such as freezing need to be investigated in order to better understand the mechanisms of interaction and potential effects that combined stressors may have on organisms. Using the freeze-tolerant earthworm Dendrobaena octaedra as model species, we exposed worms to freezing and exposure to sublethal copper in a factorial design and investigated the transcription of candidate genes for metal and cold stress. We hypothesised that both freezing and copper would induce transcription of genes coding for heat shock proteins (hsp10 and hsp70), metallothioneins (mt1 and mt2), and glutathione-S-transferase (gst), and that the combined effects of these two stressors would be additive. The gene transcripts hsp10, hsp70, and gst were significantly upregulated by freezing, but only hsp10 was upregulated by copper. We found that copper at the time of sampling had no effect on transcription of two metallothionein genes whereas transcription was strongly upregulated by freezing. Moreover, there was a significant interaction causing more than additive transcription rates of mt1 in the copper/freezing treatment suggesting that freeze-induced cellular dehydration increases the concentration of free copper ions in the cytosol. This metallothionein response to freezing is likely adaptive and possibly provides protection against freeze-induced elevated metal concentrations in the cytosol and excess ROS levels due to hypoxia during freezing.

Microevolution due to pollution in amphibians: A review on the genetic erosion hypothesis

The loss of genetic diversity, due to exposure to chemical contamination (genetic erosion), is a major threat to population viability. Genetic erosion is the loss of genetic variation: the loss of alleles determining the value of a specific trait or set of traits. Almost a third of the known amphibian species is considered to be endangered and a decrease of genetic variability can push them to the verge of extinction. This review indicates that loss of genetic variation due to chemical contamination has effects on: 1) fitness, 2) environmental plasticity, 3) co-tolerance mechanisms, 4) trade-off mechanisms, and 5) tolerance to pathogens in amphibian populations.

Drosophila subobscura flies adapted to low lead concentration carry no fitness cost

As a response to the long-term presence of heavy metals in the environment, populations can evolve resistance. Its maintenance may have detrimental effect on population's fitness, causing a fitness cost. Lead is one of the widely distributed elements in the environment exhibiting high toxicity on organisms. By analyzing developmental stages viability and developmental time, we evaluated fitness cost in Drosophila subobscura flies adapted to low lead concentration and control flies derived from the same wild population, as well as their hybrids. Significant changes in specific developmental stages viability were detected in both lines, as well as their hybrids, suggesting complex response to low lead concentration. The results show that a long-term exposure to low lead concentration may have a significant impact on a population's survival, especially in a changing environment conditions.

Population growth rate and genetic variability of small and large populations of Red flour beetle (Tribolium castaneum) following multigenerational exposure to copper

We reared large (1000 individuals) and small (20 individuals) populations of Tribolium castaneum on diet contaminated with copper in order to determine if the size of a population affects its ability to adapt to adverse environmental conditions. After 10 generations, we used microsatellite markers to estimate and subsequently compare the genetic variability of the copper-treated populations with that of the control populations, which were reared on uncontaminated medium. Additionally, we conducted a full cross-factorial experiment which evaluated the effects of 10 generations of "pre-exposure" to copper on a population's fitness in control and copper-contaminated environments. In order to distinguish results potentially arising from genetic adaptation from those due to non-genetic effects associated to parental exposure to copper, we subjected also F11 generation, originating from parents not exposed to copper, to the same cross-factorial experiment. The effects of long-term exposure to copper depended on population size: the growth rates of small populations that were pre-exposed to copper were inhibited compared to those of small populations reared in uncontaminated environments. Large Cu-exposed populations had a higher growth rate in the F10 generation compared to the control groups, while the growth rate of the F11 generation was unaffected by copper exposure history. The only factor that had a significant effect on genetic variability was population size, but this was to be expected given the large difference in the number of individuals between large and small populations. Neither copper contamination nor its interaction with population size affected the number of microsatellite alleles retained in the F10 generation.

Metallothionein gene expression differs in earthworm populations with different exposure history

Metals are persistent pollutants in soils that can harm soil organisms and decrease species diversity. Animals can cope with metal contamination with the help of metallothioneins, small metal-binding proteins involved in homeostasis and detoxification of metals. We studied the expression of metallothionein with qPCR in a small, epigeic earthworm, Dendrobaena octaedra. We compared expression patterns and metal body content in earthworms collected from two sites with different metal contamination histories: Harjavalta, contaminated by a Cu-Ni smelter operational for over 50 years, and Jyväskylä, an uncontaminated site. Earthworms from both sites were also experimentally exposed to different concentrations of Cu (control, 50, 100 or 200 mg/kg) or Zn (control, 75, 150 or 300 mg/kg) for 7, 14 or 28 days to determine if there is a time related dose-response in gene expression. Population comparison showed that metallothionein expression was higher in earthworms from the contaminated site. In the exposure experiment, exposure time affected expression, but only in the earthworms from the uncontaminated site, suggesting that there is a delay in the metallothionein response of earthworms in this population. In contrast, earthworms from the contaminated site showed higher and constant levels of metallothionein expression at all exposure concentrations and durations. The constant metallothionein expression in earthworms from the contaminated site suggests that inducibility of metallothionein response could be lost in earthworms with metal exposure history. Adaptation of D. octaedra to metal exposure could explain the differences between the populations and explain the persistence of this species in contaminated forest soils.

Earthworm tolerance to residual agricultural pesticide contamination: field and experimental assessment of detoxification capabilities

This study investigates if acclimatization to residual pesticide contamination in agricultural soils is reflected in detoxification, antioxidant enzyme activities and energy budget of earthworms. Five fields within a joint agricultural area exhibited different chemical and farming histories from conventional cultivation to organic pasture. Soil multiresidual pesticide analysis revealed up to 9 molecules including atrazine up to 2.4 ng g(-1) dry soil. Exposure history of endogeic Aporrectodea caliginosa and Allolobophora chlorotica modified their responses to pesticides. In the field, activities of soluble glutathione-S-transferases (sGST) and catalase increased with soil pesticide contamination in A. caliginosa. Pesticide stress was reflected in depletion of energy reserves in A. chlorotica. Acute exposure of pre-adapted and naïve A. caliginosa to pesticides (fungicide Opus(®), 0.1 μg active ingredient epoxiconazole g(-1) dry soil, RoundUp Flash(®), 2.5 μg active ingredient glyphosate g(-1) dry soil, and their mixture), revealed that environmental pre-exposure accelerated activation of the detoxification enzyme sGST towards epoxiconazole.

Response of Tribolium castaneum to elevated copper concentrations is influenced by history of metal exposure, sex-specific defences, and infection by the parasite Steinernema feltiae

We studied how copper toxicity in the red flour beetle, Tribolium castaneum changed as a result of infection by the entomopathogenic nematode Steinernema feltiae. Measured traits were: respiration, growth and survival, as well as the concentrations of copper within beetle tissues and in its diet. By comparing F1 and F5 generation we were able to answer how long-term metal exposure changed the responses to both copper and the parasite. The beetles did accumulate copper; however, the results indicated that copper concentrations in beetle tissues were affected by nematode infection, the sex of the experimental animals, and the number of generations of exposure. Five generations of exposure to copper resulted in the highest dry body mass of infected beetles of both sexes; additionally, this group also had the lowest copper concentrations in their tissues. The only factor that had a significant effect on respiration was infection by nematodes: infected beetles of both sexes in both generational groups had significantly decreased respiration rates. Survival was lowest in nematode-infected animals of both sexes from both generations, regardless of exposure to copper. Our results confirm that an organism's response to metal pollution is dependent on its health status and sex. We also found that the history of exposure to metal was equally important-we found enhanced resistance to copper intoxication after only five generations of exposure.

Familial differences in the effects of mercury on reproduction in zebra finches

Ecotoxicologists often implicitly assume that populations are homogenous entities in which all individuals have similar responses to a contaminant. However, genetically variable responses occur within populations. This variation can be visualized using dose-response curves of genetically related groups, similar to the way that evolutionary biologists construct reaction norms. We assessed the variation in reproductive success of full-sibling families of captive zebra finches (Taeniopygia guttata) experimentally exposed to methylmercury. We found significant variation among families in the effects of methylmercury on several reproductive parameters. This variation suggests that there may be strong responses to selection for resistant genotypes in contaminated areas. This has important implications for the evolution of tolerance as well as risk assessment and wildlife conservation efforts on sites with legacy contamination.

Subacute toxicity of copper and glyphosate and their interaction to earthworm (Eisenia fetida)

Glyphosate (GPS) and copper (Cu) are common pollutants in soils, and commonly co-exist. Due to the chemical structure of GPS, it can form complexes of heavy metals and interface their bioavailability in soil environment. In order to explore the interactions between GPS and Cu, subacute toxicity tests of Cu and GPS on soil invertebrate earthworms (Eisenia fetida) were conducted. The relative weight loss and whole-worm metal burdens increased significantly with the increasing exposure concentration of Cu, while the toxicity of GPS was insignificant. The joint toxicity data showed that the relative weight loss and the uptake of Cu, as well as the superoxide dismutase, catalase and malondialdehyde activities, were significantly alleviated in the present of GPS, which indicated that GPS could reduce the toxicity and bioavailability of Cu in the soil because of its strong chelating effects.

Using biomarkers in an evolutionary context: lessons from the analysis of biological responses of oligochaete annelids to metal exposure

Anthropogenic activities may lead to the accumulation of inorganic and organic compounds in topsoils. Biota living in close contact with contaminated soils may experience stress at different levels of biological organization throughout the continuum from molecular to community level. Biological responses observed at the individual or infra-individual level of biological organization led to the development of biomarkers. The development of biomarkers consists often in evidencing biological modifications following a contaminant stress in laboratory conditions, using naïve organisms and it is sometime proposed to use the biological state of individuals from sentinel species collected in the field to evaluate the level of environmental exposure. However, considering the possibility of local adaptation following long-term exposure, organisms response sampled in the field may substantially differ from laboratory specimens. In this review, we discuss this point focusing on the definition and validity of molecular biomarkers of metal pollution using earthworms of the Lumbricidae family.

Contaminant driven genetic erosion and associated hypotheses on alleles loss, reduced population growth rate and increased susceptibility to future stressors: an essay

Microevolution due to pollution can occur mainly through genetic drift bottlenecks, especially of small sized populations facing intense lethal pulses of contaminants, through mutations, increasing allelic diversity, and through natural selection, with the disappearance of the most sensitive genotypes. This loss of genotypes can lead to serious effects if coupled to specific hypothetical scenarios. These may be categorized as leading, first, to the loss of alleles-the recessive tolerance inheritance hypothesis. Second, leading to a reduction of the population growth rate-the mutational load and fitness costs hypotheses. Third, leading to an increased susceptibility of further genetic erosion both at future inputs of the same contaminant-differential physiological recovery, endpoints (dis)association, and differential phenotypic plasticity hypotheses-and at sequential or simultaneous inputs of other contaminants-the multiple stressors differential tolerance hypothesis. Species in narrowly fluctuating environments (tropics and deep sea) may have a particularly high susceptibility to genetic erosion-the Plus ça change (plus c'est la meme chose) hypothesis. A discussion on the consequences of these hypotheses is what this essay aimed at.

Disturbances, organisms and ecosystems: a global change perspective

The present text exposes a theory of the role of disturbances in the assemblage and evolution of species within ecosystems, based principally, but not exclusively, on terrestrial ecosystems. Two groups of organisms, doted of contrasted strategies when faced with environmental disturbances, are presented, based on the classical r-K dichotomy, but enriched with more modern concepts from community and evolutionary ecology. Both groups participate in the assembly of known animal, plant, and microbial communities, but with different requirements about environmental fluctuations. The so-called "civilized" organisms are doted with efficient anticipatory mechanisms, allowing them to optimize from an energetic point of view their performances in a predictable environment (stable or fluctuating cyclically at the scale of life expectancy), and they developed advanced specializations in the course of evolutionary time. On the opposite side, the so-called "barbarians" are weakly efficient in a stable environment because they waste energy for foraging, growth, and reproduction, but they are well adapted to unpredictably changing conditions, in particular during major ecological crises. Both groups of organisms succeed or alternate each other in the course of spontaneous or geared successional processes, as well as in the course of evolution. The balance of "barbarians" against "civilized" strategies within communities is predicted to shift in favor of the first type under present-day anthropic pressure, exemplified among others by climate warming, land use change, pollution, and biological invasions.

Variation in metallothionein gene expression is associated with adaptation to copper in the earthworm Dendrobaena octaedra

Evolution of resistance to heavy metals has been reported for several populations of soil living organisms occurring at metal contaminated sites. Such genetically based and heritable resistance contribute to the persistence of populations in contaminated areas. Here we report on molecular responses to experimental copper in populations of the earthworm, Dendrobaena octaedra, originating from copper contaminated soil near Gusum (Sweden) where heavy metal pollution has been present for several decades. We studied gene expression of six genes potentially involved in resistance to copper toxicity using F2-generations of D. octaedra populations, originating from reference sites and contaminated (High, Medium and Low) sites around Gusum. The main result was different expression patterns of genes encoding for two different isoforms (mt1 and mt2) of metallothionein proteins during experimental exposure to copper contaminated soil. Expression of mt1 showed a fast and significant upregulation in the High population and a slower, albeit significant, upregulation in Medium and Low populations. However, in the three reference populations no upregulation were seen. In comparison, a fast upregulation was also seen for the High population in the isoform mt2, whereas, gene expression of all other populations, including reference populations, showed slower upregulation in response to experimental copper. The results indicate that copper resistance in D. octaedra from contaminated areas is related to an increased expression of metallothioneins.

Assessment of ecological risks at former landfill site using TRIAD procedure and multicriteria analysis

Old industrial landfills are important sources of environmental contamination in Europe, including Finland. In this study, we demonstrated the combination of TRIAD procedure, multicriteria decision analysis (MCDA), and statistical Monte Carlo analysis for assessing the risks to terrestrial biota in a former landfill site contaminated by petroleum hydrocarbons (PHCs) and metals. First, we generated hazard quotients by dividing the concentrations of metals and PHCs in soil by the corresponding risk-based ecological benchmarks. Then we conducted ecotoxicity tests using five plant species, earthworms, and potworms, and determined the abundance and diversity of soil invertebrates from additional samples. We aggregated the results in accordance to the methods used in the TRIAD procedure, conducted rating of the assessment methods based on their performance in terms of specific criteria, and weighted the criteria using two alternative weighting techniques to produce performance scores for each method. We faced problems in using the TRIAD procedure, for example, the results from the animal counts had to be excluded from the calculation of integrated risk estimates (IREs) because our reference soil sample showed the lowest biodiversity and abundance of soil animals. In addition, hormesis hampered the use of the results from the ecotoxicity tests. The final probabilistic IREs imply significant risks at all sampling locations. Although linking MCDA with TRIAD provided a useful means to study and consider the performance of the alternative methods in predicting ecological risks, some uncertainties involved still remained outside the quantitative analysis.

Does glyphosate impact on Cu uptake by, and toxicity to, the earthworm Eisenia fetida?

Glyphosate (GPS) is a wildly-used pesticide throughout the world. It affects metal behaviors in soil-water system as its functional groups such as amine, carboxylate and phosphonate can react with metal ions to form metal complexes. The reaction will result in the decreasing of heavy metal bioavailability. A laboratory experiment was conducted to investigate the interactions between GPS and copper (Cu) on the acute toxicity of soil invertebrate earthworm (Eisenia fetida), which was exposed to aqueous solutions for 48 h with different mixing concentrations of Cu and GPS (technical-grade Gly acid). The mortality rates, Cu uptake by earthworm, and some biomarkers such as superoxide dismutase (SOD) activity, glutathione (GSH) content, and acetylcholinesterase (AchE) activity were measured. The mortality rates and whole-worm metal burdens increased significantly with the increasing Cu concentration in solution. However, toxicity of GPS to earthworms was not observed in this study. Furthermore, the presence of GPS could significantly reduce the acute toxicity of Cu to earthworms. The mortality rates decreased sharply and the uptake of Cu was nearly halted in the presence of GPS. In addition, the SOD activity, GSH content, and AchE activity almost declined to the levels of the control. These results demonstrate that GPS could control the toxicity as well as the bioavailability of heavy metals in soil solutions where both GPS and heavy metals often coexist.

No costs on freeze tolerance in genetically copper adapted earthworm populations (Dendrobaena octaedra)

For nearly three centuries the area around Gusum, in south-east Sweden, has been highly polluted with copper. An earlier study in this area showed that populations of the freeze-tolerant earthworm Dendrobaena octaedra were genetically adapted to copper. Apparently, no life-history costs to reproduction or growth were imposed by this adaptation. In the present paper we therefore investigated how laboratory raised F1-generations of these populations coped when exposed to increased copper concentrations in the soil and to sub-zero temperatures. We found that D. octaedra from polluted sites accumulated the same amount of copper as reference worms. Furthermore, earthworms from polluted sites survived equally to reference worms when exposed to freezing temperatures (-8 or -12°C). However, when simultaneously exposed to the lowest temperature and copper, the worms from polluted sites survived significantly better than reference worms. The overall conclusion of this study is that worms from polluted sites seem to be better at handling copper and accrue no costs in terms of reduced cold tolerance in connection to genetic adaptation in these populations.