Exposure to sediments from polluted rivers has limited phenotypic effects on larvae and adults of Chironomus riparius

Mining tailings alter insects: revealing fluctuating asymmetry in the caddisfly Smicridea coronata

The Samarco/Vale/BHP mine tailing dam breach that took place in Minas Gerais, southeastern Brazil, in 2015, deposited high concentrations of metals and metalloids in the Rio Doce basin, severely impacting freshwater and riverine forest ecosystems. To assess developmental instability of caddisflies in response to the environmental impacts of the dam breach, we investigated the fluctuating asymmetry (FA) in the species Smicridea (Rhyacophylax) coronata (Trichoptera: Hydropsychidae). FA was assessed at individual and populational scales using geometric morphometric methods in the cephalic capsule and mandibles of larvae and also on the forewings of adults, both collected under the impacted condition, and under the least disturbed condition. The levels of FA increased in response to stressors on the forewings at the populational scale, and on the mandibles, at individual scale. These morphological variations in the larval and adult stages may lead to detrimental effects and result in high mortality rates as well as lower adult fitness. Trichoptera forewings are revealed as suitable traits for assessing FA, holding potential for applications in biomonitoring programs. Directional asymmetry levels were higher than FA levels for all traits, and this correlation could be explained by a transition from fluctuating to directional asymmetry in the presence of heightened disturbance. Our results validate the relationship between the impacts from the dam breach and increased developmental instability in this species with likely cascade effects on the insect community.

A systematic review of the toxic effects of a nanopesticide on non-target organisms: Estimation of protective concentrations using a species sensitivity distribution (SSD) approach - The case of atrazine

Nanopesticides, such as nanoencapsulated atrazine (nATZ), have been studied and developed as eco-friendly alternatives to control weeds in fields, requiring lower doses. This review contains a historical and systematic literature review about the toxicity of nATZ to non-target species. In addition, the study establishes protective concentrations for non-target organisms through a species sensitivity distribution (SSD) approach. Through the systematic search, we identified 3197 publications. Of these, 14 studies addressed "(nano)atrazine's toxicity to non-target organisms". Chronological and geographic data on the publication of articles, characterization of nATZ (type of nanocarrier, size, polydispersity index, zeta potential), experimental design (test species, exposure time, measurements, methodology, tested concentrations), and toxic effects are summarized and discussed. The data indicate that cell and algal models do not show sensitivity to nATZ, while many terrestrial and aquatic invertebrates, aquatic vertebrates, microorganisms, and plants have high sensitivity to nAZT. The SSD results indicated that D. similis is the most sensitive species to nATZ, followed by C. elegans, E. crypticus, and P. subcapitata. However, the limitations in terms of the number of species and endpoints available to elaborate the SSD reflect gaps in knowledge of the effects of nATZ on different ecosystems.

Chironomus columbiensis (Diptera: Chironomidae) as test organism for aquatic bioassays: Mass rearing and biological traits

Chironomidae are aquatic insects that have become a model in laboratory tests to evaluate toxic effect of different pollutants. The use of chironomids as test organisms depends on standard protocols for the rearing under laboratory conditions and expanding knowledge on its biology. We standardize a culture of C. columbiensis and analyze its life cycle under laboratory conditions. The experiments were carried out with different treatments for water, temperature, and food. As a result, a protocol was proposed for the rearing of C. columbiensis under the following conditions: semi-soft and reconstituted water, shredded paper towels as a substrate, soft aeration, temperature of 22 ± 2°C, fed with 0.3 g TetraMin® twice a week and weekly renewal of 50% of the water. Under these conditions, the duration of the life cycle was 17-31 days, with a continuous growth of 1.16 to 14.05 mm in the larval stage and an average of 530 eggs per oviposition. In comparison with other species in the family, this study indicated that C. columbiensis is a species with a short life cycle, sensible to changing conditions (e.g., temperature and food), wide distribution, so is a good organism for being used in aquatic bioassays.

Bio-based versus synthetic: comparative study of plasticizers mediated stress on Chironomus circumdatus (Diptera-Chironomidae)

Phthalates are used as plasticizers in products made of polyvinyl chloride to increase the flexibility of polymers. Unfortunately, these are known to cause adverse effects on living organisms, and also, fast depletion of petroleum resources calls for the exploration of alternatives as replacements. Recent developments in bio-based plasticizers have led to their use as additives for various applications. As they have received much attention in the past decade, it is crucial to study the effects of these plasticizers on living organisms. Hence, we tried to compare the effects of synthetic plasticizer dioctyl phthalate and bio-based plasticizer ethanolamine on Chironomus circumdatus larvae. Mortality was achieved at a lethal concentration (LC₅₀) value of 0.385 mg/L for ethanolamine and dioctyl phthalate at 0.125 mg/L. Disruption in the level of metabolites along with lipid peroxidation was observed in the larvae exposed to plasticizer mediated stress. To overcome these changes, an increase in the levels of antioxidant enzymes such as Superoxide Dismutase, Catalase, Glutathione Peroxidase and Glutathione Reductase, as well as in the levels of detoxifying enzymes like Glutathione-S-Transferase, Esterases and Mixed Function Oxidase during post-exposure recovery conditions was seen. Alterations in the expression levels of heat shock protein 70 and ecdysone receptor genes were also observed. From the comparative study, it could be concluded that Chironomus circumdatus larvae, to a certain extent, have developed tolerance to both ethanolamine and dioctyl phthalate mediated stress. However, dioctyl phthalate has led to more stress as compared to ethanolamine in these larvae.

Use of nontarget organism Chironomus sancticaroli to study the toxic effects of nanoatrazine

Atrazine was banned by the European Union in 2004, but is still used in many countries. Agricultural research employing nanotechnology has been developed in order to reduce the impacts to the environment and nontarget organisms. Nanoatrazine was developed as a carrier system and have been considered efficient in weed control. However, its toxicity must be verified with nontarget organisms. In this context, the aim of the present study was to investigate ecotoxicological effects of solid lipid nanoparticles (empty and loaded with atrazine) and atrazine on Chironomus sancticaroli larvae, evaluating the endpoints: mortality, mentum deformity, development rate and biochemical biomarkers. The contaminant concentrations used were 2, 470, 950, and 1900 μg L^-1 in acute (96 h) and 2 μg L^-1 in subchronic (10 days) bioassays. An environmentally relevant concentration of atrazine (2 μg L^-1) presented toxic and lethal effects towards the larvae. The nanoparticles loaded with atrazine showed toxic effects similar to free atrazine, causing mortality and biochemical alterations on the larvae. The nanoparticle without atrazine caused biochemical alterations and mortality, indicating a possible toxic effect of the formulation on the larvae. In the acute bioassay, most concentrations of nanoparticles loaded with atrazine were not dose dependent for the endpoint mortality. Only the atrazine concentration of 470 μg L^-1 was statistically significant to endpoint mentum deformity. The atrazine and nanoparticles (with and without atrazine) did not affect larval development. The results indicate that Chironomus sancticaroli was sensitive to monitor nanoatrazine, presenting potential to be used in studies of toxicity of nanopesticides.

What types of enzyme activities are useful biomarkers of bifenthrin exposure on Chironomus sp. (Diptera, Chironomidae) larvae under laboratory and field-based microcosm conditions?

Bifenthrin is a second generation synthetic pyrethroid insecticide that is widely used in Australia and worldwide. It is frequently found in urban freshwater sediments at concentrations likely to impact biota as it is highly toxic to fish and macroinvertebrates, such as chironomids. Our main goal was to evaluate if oxidative stress and hydrolase enzymes are useful biomarkers of effect of synthetic pyrethroids exposure under different scenarios. Chironomus tepperi larvae (5 days old) were exposed to sub-lethal sediment concentrations of bifenthrin for 5 days under controlled laboratory conditions. A field-based microcosm exposure with bifenthrin-spiked sediments (using the same concentrations as the laboratory exposure) was carried out at a clean field site for four weeks to allow for colonization and development of resident chironomid larvae. At the end of both experiments, Chironomus larvae (C. tepperi in the laboratory exposures and C. oppositus in the microcosm exposures) were collected and oxidative stress enzymes (Glutathione-s-Transferase, Glutathione Reductase and Glutathione Peroxidase) and hydrolase enzymes (Acetylcholinesterase and Carboxylesterase) were measured. Only the Glutathione Peroxidase activity was significantly impacted in larvae from the laboratory exposure. On the contrary, significant changes were observed in all the measured enzymes from the field-based microcosm exposure. This is likely because exposure was throughout the whole life cycle, from egg mass to fourth instar, showing a more realistic exposure scenario. Furthermore, this is the first time that changes in oxidative stress and hydrolase enzymes have been shown to occur in Australian non-biting midges exposed under field-based microcosm conditions. Thus, this study demonstrated the usefulness of these enzymes as biomarkers of effect following bifenthrin exposure in microcosms. It also highlights the importance of using a range of different biochemical endpoints to get a more holistic understanding of pesticide effects and the pathways involved.

Accumulation of As, Cd, Pb, and Zn in sediment, chironomids and fish from a high-mountain lake: First insights from the Carnic Alps

Though mountain lakes are generally much less influenced by human activities than other habitats, anthropogenic threats can still alter their natural condition. A major source of global environmental pollution in mountain ecosystems is trace element contamination. For this study we investigated for the first time the accumulation of As, Cd, Pb, and Zn in sediment, Diptera Chironomidae (prey), and bullhead Cottus gobio (predator) in a typical high-mountain lake (Dimon Lake) in the Carnic Alps. Significant differences in trace element levels were observed between sediment, Diptera Chironomidae, and C. gobio liver and muscle samples (Kruskal-Wallis test; p < .03 for all elements). As and Pb levels were highest in sediment, Cd and Zn levels were highest in Diptera Chironomidae, and the lowest values for all elements were measured in C. gobio muscle and liver. Bioaccumulation factor values were much higher in Diptera Chironomidae than fish muscle and liver, with the highest values recorded for Cd (5.16) and Zn (4.37). Trophic transfer factor values were very low for all elements in fish muscle and liver, suggesting a biodilution effect along the food chain. Further studies are needed to expand on these first findings that provide useful insights to inform environmental monitoring and policy in remote high-mountain lakes.

Is developmental instability in chironomids a sensitive endpoint for testing uranium mine-affected sediments?

There is increasing interest in effects of radionuclides on non-human species, but methods for studying such effects are not well developed. The aims of the current study were to investigate the effects of uranium mine-affected sediments on non-biting midge Chironomus riparius and to compare sensitivity of different endpoints. The midge larvae were exposed in controlled laboratory conditions to sediments from two ponds downstream from an abandoned uranium mine and a reference pond not receiving water from the mining site. Quartz sand was used as an additional control. Developmental effects were assessed by evaluating emergence of adult midges, body mass, and fluctuating asymmetry (FA) in the length of wing upper vein. FA has been suggested to be a sensitive indicator of developmental instability, but the results of previous studies are inconsistent. In the present study, no difference in FA was observed between the treatment groups, but time to emergence was significantly delayed in the contaminated sediments. The approach used in this study (laboratory experiments with sediments from a contaminated site) avoids confounding due to uncontrolled environmental variables and adaptation to long-term contamination, which may mask effects on natural populations. Using this approach, we found no effects on FA of wing length. Time to emergence, in contrast, was found to be a more sensitive endpoint.

Exposure to heavy metal-contaminated sediments disrupts gene expression, lipid profile, and life history traits in the midge Chironomus riparius

Despite the concern about anthropogenic heavy metal accumulation, there remain few multi-level ecotoxicological studies to evaluate their effects in fluvial ecosystems. The toxicity of field-collected sediments exhibiting a gradient of heavy metal contamination (Cd, Pb, and Zn) was assessed in Chironomus riparius. For this purpose, larvae were exposed throughout their entire life cycle to these sediments, and toxic effects were measured at different levels of biological organization, from the molecular (lipidomic analysis and transcriptional profile) to the whole organism response (respiration rate, shape markers, and emergence rate). Alterations in the activity of relevant genes, as well as an increase of storage lipids and decrease in membrane fluidity, were detected in larvae exposed to the most contaminated sediments. Moreover, reduced larval and adult mass, decrease of larval respiration rate, and delayed emergence were observed, along with increased mentum and mandible size in larvae and decreased wing loading in adults. This study points out the deleterious effects of heavy metal exposure at various levels of biological organization and provides some clues regarding the mode of toxic action. This integrative approach provides new insights into the multi-level effects on aquatic insects exposed to heavy metal mixtures in field sediments, providing useful tools for ecological risk assessment in freshwater ecosystems.

Use of Larval Morphological Deformities in Chironomus plumosus (Chironomidae: Diptera) as an Indicator of Freshwater Environmental Contamination (Lake Trasimeno, Italy)

The mentum deformity incidence in Chironomus plumosus larvae to assess the environmental contamination level in Lake Trasimeno, Central Italy, was investigated. The survey lasted from May 2018 to August 2019. Fifty-one samplings were carried out: 34 in the littoral zone and 17 in the central zone. The deformity assessment was based on 737 and 2767 larval specimens of C. plumosus collected from the littoral and central zones, respectively. Comparison of the larval morphometric variables between normal and deformed specimens highlighted that the deformities did not cause alterations of the larval growth. The deformity incidence amounted to 7.22% in the whole Trasimeno’s ecosystem, reaching 8.28% in the littoral zone and 6.94% in the central zone. Among the different seasonal cohorts, the spring cohort had overall the highest deformity value (11.41%). The deformity type assessment protocol highlighted that the most common deformity type was “round/filed teeth” (64%). The results of this 2018–2019 survey revealed a low deformity incidence, within the background range of relatively low-impacted freshwaters. Comparison with previous investigations (2000–2010) of the same habitat showed a clear decrease of the deformity incidence. This study further contributes to the evaluation of the mentum deformity in chironomids that represent an indicator endpoint of the anthropogenic contamination level in freshwaters.

A Re-Evaluation of Chironomid Deformities as an Environmental Stress Response: Avoiding Survivorship Bias and Testing Noncontaminant Biological Factors

Larval deformities have been observed in chironomids, and are thought to be associated with aquatic contaminant exposure. However, in laboratory assays, deformities have not been linked with contaminants in the absence of potential confounding variables including mortality, which introduces a survivorship bias. There is also a paucity of data on noncontaminant causes. In addition, power analyses are rarely undertaken, meaning that effect sizes detectable are usually uncertain. We therefore aimed to clarify factors associated with deformities, by running survivorship bias-free (i.e., sublethal) assays, assessing contaminant (copper and imidacloprid) and noncontaminant (malnutrition) stressors, and considering natural biological (metamorphosis) factors in Chironomus tepperi. We included a posteriori power analyses for all tests. Our assays found no significant association between tested factors and deformity rate. Power analyses indicated that the stressor experiment had moderate power to detect deformity effects. The metamorphosis assay had relatively lower power (due to an unexpectedly high control deformity rate), highlighting the importance of power tests in these types of evaluations. These results, in conjunction with others recently published, raise doubts as to the causal effects of environmental stressors on deformity incidence. By avoiding survivorship bias, and by testing noncontaminant factors and statistical power, we present a more holistic methodology, to resolve ongoing uncertainty in this area. We also discuss possible future directions for chironomid deformity research, and concerns regarding survivorship bias in ecotoxicology. Environ Toxicol Chem 2019;38:1658-1667. © 2019 SETAC.

Biological, biochemical and genotoxic effects of Sb in the midge Chironomus sancticaroli Strixino and Strixino, 1981 (Diptera: Chironomidae)

In aquatic systems, antimony (Sb) is found in the water column and associated with sediment particles being bioavailable to organisms. Consequently, toxic effects have been detected in benthic invertebrates, but the toxicity after Sb exposure in Chironomidae have not been investigated. Were investigated DNA damage, activities of cholinesterase (ChE), alpha and beta esterase (EST-α, EST-β), glutathione S-transferase (GST), catalase (CAT), and superoxide dismutase (SOD) and lipid peroxidation after acute (48 h) and subchronic exposure (8 d). We also investigated the effects of subchronic (8 d) on development of larvae and chronic (25 d) Sb exposure on emergence and size of adults of Chironomus sancticaroli. Were analyze Sb nominal concentrations ranged from 0.5 to 800 μg.L^-1. Genotoxic effects occurred at higher concentrations upon acute (50, 800 μg.L^-1) and subchronic exposure (50 μg.L^-1). Acute exposure increased ChE, EST-α, EST-β, and GST activities. Subchronic Sb exposure increased EST-α activity at 0.2 μg.L^-1 and GST activity at 5 μg.L^-1. CAT activity increased at all concentrations while increasing lipid peroxidation levels were observed (1 μg.L^-1, 5 μg.L^-1 and 50 μg.L^-1), indicating oxidative stress. All concentrations of Sb delayed larval development and decreased the number of emerging adults. At high concentrations (50, 500, 800 μg.L^-1), the emerging adults were smaller. In conclusion, these varying genotoxic, biochemical and biological effects of Sb make a notable impact on the reproduction and population dynamics of C. sancticaroli.

Chironomus riparius exposure to field-collected contaminated sediments: From subcellular effect to whole-organism response

The toxicity of three field-collected sediments differentially contaminated with pesticides, heavy metals, phtalates and polycyclic aromatic hydrocarbons (PAHs), was assessed in Chironomus riparius. For this purpose, C. riparius larvae were exposed throughout their entire life cycle to sediments collected in three sites along the Saulx river in France, and the toxic effects were measured at different levels of biological organization: from the molecular (lipidomic analysis and transcriptional variations) to the whole organism response (respiration rate, shape markers and emergence rate). In the sediment characterized by an intermediate level of contamination with PAHs and phtalates, we detected an increase of the cell stress response and delayed emergence of males. In the group exposed to the most contaminated sediment with PAHs, phtalates and pesticides, genes related to endocrine pathways, cell stress response and biotransformation processes were overexpressed, while female wing shape was affected. Field-collected sediment exposure did not induce significant effects on mentum shape markers or on the lipid profile. The present study provides new insights into the multilevel effects of differentially contaminated sediments in insects. This integrative approach will certainly contribute to improved assessment of the risk that complex mixtures of pollutants pose to the aquatic ecosystem.

Impacts of suspended sediment and metal pollution from mining activities on riverine fish population-a review

Mining activities are responsible for the elevated input levels of suspended sediment and hazardous metals into the riverine ecosystem. These have been shown to threaten the riverine fish populations and can even lead to localized population extinction. To date, research on the effects of mining activities on fish has been focused within metal contamination and bioaccumulation and its threat to human consumption, neglecting the effects of suspended sediment. This paper reviews the effects of suspended sediment and metal pollution on riverine ecosystem and fish population by examining the possibilities of genetic changes and population extinction. In addition, possible assessments and studies of the riverine fish population are discussed to cope with the risks from mining activities and fish population declines.

Incidence of deformities and variation in shape of mentum and wing of Chironomus columbiensis (Diptera, Chironomidae) as tools to assess aquatic contamination

Constantly, aquatic ecosystems are under pressure by complex mixtures of contaminants whose effects are not always easy to evaluate. Due to this, organisms are sought in which early warning signs may be detected upon the presence of potentially toxic xenobiotic substances. Thereby, the study evaluated the incidence of deformities and other morphometric variations in the mentum and wing of Chironomus columbiensis exposed to water from some of the Colombian Andes affected by mining, agriculture, and cattle raising. Populations of C. columbiensis were subjected throughout their life cycle (24 days) for two generations (F₁ and F₂). Five treatments were carried out in controlled laboratory conditions (water from the site without impact, site of mining mercury, mining mercury + cyanide, cattle raising, and agriculture) and the respective control (reconstituted water). Thereafter, the percentage of deformities in the mentum was calculated, and for the morphometric analysis 29 landmarks were digitized for the mentum and 12 for the wing. As a result, four types of deformities were registered in the C. columbiensis mentum, like absence of teeth, increased number of teeth, fusion and space between teeth, none of them detected in the individuals from the control. Additionally, the highest incidence of deformity in F₁ occurred in the treatment of mining mercury, while for F₂ this took place in the treatments of mining mercury + cyanide, cattle raising and agriculture. Differences were also found with respect to the morphometric variations of the mentum and wing of C. columbiensis among the control and the treatments with water from the creeks intervened. The treatments of mining mercury + cyanide and agriculture had the highest morphological variation in the mentum and wing of C. columbiensis. The results suggest that the anthropogenic impacts evaluated generate alterations in the oral apparatus of the larval state of C. columbiensis and in the adult state provoke alterations in the wing shape (increased width and reduced basal area). These deformities may be related to multiple stress factors, among them the xenobiotics metabolized by the organisms under conditions of environmental contamination.

Prodiamesa olivacea Meigen and Prodiamesa bureshi Michailova (Diptera, Chironomidae, Prodiamesinae) as a candidate for assessing the genotoxicity of trace metals in fluvial sediments

The genome response, realized by structure chromosome rearrangements in the polytene chromosomes of two sibling species Prodiamesa bureshi Michailova and Prodiamesa olivacea Mg., was studied. The larvae of the species were collected in May and September, 2016, from Biała Przemsza River, a metal-mine-affected site in southern Poland, where Zn, Cd, and Pb concentrations in the sediment exceeded many times the reference data and those from unpolluted sites. The water had high contents of different major ions and nutrients. A high spectrum of somatic chromosome aberrations was detected in the salivary gland chromosomes of both species, which defined a high somatic index (from 1.2 to 7), indicating the sensitivity of both genomes to anthropogenic stress. The cells with somatic rearrangements of both species were significantly higher (P. bureshi: G = 25.636, P < 0.001 May, G = 32.722, P < 0.001 September; P. olivacea: G = 47.863, P < 0.001 May, G = 38.742, P < 0.001 September) than the control. Both species from polluted and unpolluted sites showed a high frequency of ectopic conjugations, as between arms B, CD (centromere regions), and E (NOR). Some deformities of mentum and mandibles of P. bureshi (20%) and P. olivacea (35%) were detected. We postulate that the appearances of somatic chromosome aberrations are more sensitive indicators of genotoxicity in the studied species than changes in external morphology. The sensitivity of the P. olivacea and P. bureshi genomes shows that these species are good candidates for detecting the presence of genotoxic compounds in aquatic basins and evaluating their genotoxic effects.

Benzo(a)pyrene Exposure Causes Genotoxic and Biochemical Changes in the Midge Larvae of Chironomus sancticaroli Strixino & Strixino (Diptera: Chironomidae)

Benzo(a)pyrene (BaP) is a carcinogenic polycyclic aromatic hydrocarbon, also found in nature due to human activities. BaP adheres to sediments showing toxic effects on benthic organisms, including midge larvae of the family Chironomidae. We tested for toxic effects of benzo(a)pyrene on Chironomus sancticaroli Strixino & Strixino 1981 using biochemical and genotoxic biomarkers, to identify changes in metabolic and antioxidant pathways, besides neurotoxic and DNA damage. Enzyme activity was compared by exposing larvae to four nominal concentrations (0.47, 2.13, 3.41, and 4.73 μg l^-1) and DNA damage to two concentrations (0.47 and 4.73 μg l^-1), after exposure at 24, 48, 72, and 96 h. BaP caused neurotoxic effect, showing acetylcholinesterase alterations at different treatments. Changes in the biotransformation pathway were detected, with an increased activity of alpha and beta esterase in 48 h and reduction of glutathione-S-transferase activity in all periods at the highest concentrations. Damage to the antioxidant system was observed by the increase of the superoxide dismutase and reduction of the catalase, in 48 h. Genotoxicity was detected by an increased DNA damage at 48 and 72 h. The lowest concentration (0.47 μg l^-1), even presenting low mortality, also altered the biochemical parameters of the larvae. Thus, these results indicate that BaP causes metabolic, neurotoxic, and genotoxic effects on C. sancticaroli, even at low concentrations and short-term exposure. BaP can cause damage of immature invertebrates, and the ecological dynamics can be affected, since these organisms have trophic importance in the aquatic environment.

Wing shape-mediated carry-over effects of a heat wave during the larval stage on post-metamorphic locomotor ability

Two key insights to better assess the ecological impact of global warming have been poorly investigated to date: global warming effects on the integrated life cycle and effects of heat waves. We tested the effect of a simulated mild (25 °C) and severe (30 °C) heat wave experienced during the larval stage on the flight ability of the damselfly Ischnura elegans. To get a mechanistic understanding of how heat stress may translate into reduced post-metamorphic flight ability, we evaluated the hypothesized mediatory role of adult size-related traits, and also tested alternative pathways operating through changes in wing shape and two flight-related traits (both relative fat and flight muscle contents). Exposure to a heat wave, and particularly the severe one, shortened the larval stage, reduced adult size-related traits and modified the wing shape but did not significantly affect emergence success, relative fat content and relative flight muscle mass. Notably, the heat wave negatively affected all components of flight ability. Unexpectedly, the heat wave did not reduce flight ability through reducing size. Instead, we identified a novel size-independent mechanism bridging metamorphosis to link larval environment and adult flight ability in males: through affecting wing shape. The present study advances mechanistic insights in the still poorly understood coupling of life stages across metamorphosis. Additionally, our results underscore the need for integrative studies across life stages to understand the impact of global warming.

A Meta-Analysis Evaluating the Relationship between Aquatic Contaminants and Chironomid Larval Deformities in Laboratory Studies

Chironomid larval deformities have been widely investigated as an aquatic pollution toxicity end point. Field chironomid surveys often show a spatial association between contaminants and deformities, suggesting contaminants cause deformities. However, over 40 years of laboratory assays have not been able to confirm this causality. We therefore conducted a review of the literature and meta-analysis, in order to (A) assess whether trends across assays indicated dose-response effects, (B) characterize the consistency of results, and (C) investigate whether experimental issues and publication bias were contributing to inconsistency and/or reducing confidence in results. The experimental issues we investigated were extraneous nonchemical laboratory stressors (which may mask or interact with chemical effects), and mortality (which can confound deformity results). Our meta-analysis of the most commonly tested chemicals suggested dose-response effects for copper, but not lead or zinc. However, we also found substantial inconsistency across studies. Both mortality and extraneous stressors were potentially contributing to this inconsistency, reducing confidence in most published data. We observed no evidence of publication bias. We conclude that any causal link between contaminants and deformities remains uncertain, and suggest improved experimental and data reporting procedures to better assess this relationship.

Increase in developmental instability in a field-collected Chironomus population maintained under laboratory conditions

In order to be a relevant indicator of exposure towards teratogenic stressors, morphological defects should not be passed on to the next generation. In this study, we compare morphological variations in Chironomids collected from a contaminated river stretch with those of their progeny, reared in uncontaminated sediment under laboratory conditions. We focused on mentum defects (deformities, fluctuating asymmetry and mean shape change), measured by geometric morphometrics. We observed no significant variation in deformity rate between the parental generation and its progeny. On the contrary, we observed a significant increase in fluctuating asymmetry and a significant decrease in mentum centroid size in the offspring. Our results suggest that shape defects are not caused by direct exposure to teratogenic stressors alone. We propose four hypotheses to explain this: (a) teratogenic contaminants are present in egg-clutches, (b) contaminants at the sampling site have mutagenic effects, (c) costs of tolerance, and (d) contamination-induced genetic impoverishment.