Assessment of toxic effects of imidacloprid on freshwater zooplankton: An experimental test for 27 species.

The neonicotinoid pesticide imidacloprid has been used worldwide since 1992. As one of the most important chemicals used in pest control, there have been concerns that its run-off into rivers and lakes could adversely affect aquatic ecosystems, where zooplankton play a central role in the energy flow from primary to higher trophic levels. However, studies assessing the effects of pesticides at the species level have relied on a Daphnia-centric approach, and no studies have been conducted using species-level assessments on a broad range of zooplankton taxa. In the present study, we therefore investigated the acute toxicity of imidacloprid on 27 freshwater crustacean zooplankton (18 cladocerans, 3 calanoid copepods and 6 cyclopoid copepods). The experiment showed that a majority of calanoid copepods and cladocerans were not affected at all by imidacloprid, with the exception of one species each of Ceriodaphnia and Diaphasoma, while all six cyclopoid copepods showed high mortality rates, even at concentrations of imidacloprid typically found in nature. In addition, we found a remarkable intra-taxonomic variation in susceptibility to this chemical. As many cyclopoid copepods are omnivorous, they act as predators as well as competitors with other zooplankton. Accordingly, their susceptibility to imidacloprid is likely to cause different responses at the community level through changes in predation pressure as well as changes in competitive interactions. The present results demonstrate the need for species-level assessments of various zooplankton taxa to understand the complex responses of aquatic communities to pesticide disturbance.

Use of TLM derived models to estimate toxicity of weathered MC252 oil based on conventional chemical data and the potential impact of unresolved polar components.

Target lipid model (TLM) and toxic unit (TU) approaches were applied to ecotoxicity and chemistry data from low-energy WAFs (LE-WAFs) of source and weathered crude oils originating from the Deepwater Horizon oil spill. The weathered oils included artificially weathered oils and naturally weathered samples collected in the Gulf of Mexico after the spill. Oil weathering greatly reduced the concentrations of identified LE-WAF components, however, the mass of uncharacterized polar material (UPC) in the LE-WAFs remained largely unchanged during the weathering process. While the TLM-derived calculations displayed a significant decrease in toxicity (TUs) for the heavily weathered oils, copepod toxicity, expressed as LC10-based TUs, were comparable between LE-WAFs of fresh and weathered oils. The discrepancy between observed and predicted toxicity for the LE-WAFs of artificially weathered oils may be related to limitations by the chemical analyses or increased toxicity due to generation of new unknown compounds during the weathering process.

Comprehensive Transcriptome Analyses in Sea Louse Reveal Novel Delousing Drug Responses Through MicroRNA regulation.

The role of miRNAs in pharmacological responses through gene regulation related to drug metabolism and the detoxification system has recently been determined for terrestrial species. However, studies on marine ectoparasites have scarcely been conducted to investigate the molecular mechanisms of pesticide resistance. Herein, we explored the sea louse Caligus rogercresseyi miRNome responses exposed to delousing drugs and the interplaying with coding/non-coding RNAs. Drug sensitivity in sea lice was tested by in vitro bioassays for the pesticides azamethiphos, deltamethrin, and cypermethrin. Ectoparasites strains with contrasting susceptibility to these compounds were used. Small-RNA sequencing was conducted, identifying 2776 novel annotated miRNAs, where 163 mature miRNAs were differentially expressed in response to the drug testing. Notably, putative binding sites for miRNAs were found in the ADME genes associated with the drugs' absorption, distribution, metabolism, and excretion. Interactions between the miRNAs and long non-coding RNAs (lncRNAs) were also found, suggesting putative molecular gene regulation mechanisms. This study reports putative miRNAs correlated to the coding/non-coding RNAs modulation, revealing novel pharmacological mechanisms associated with drug resistance in sea lice species.

Effects of microplastics on marine copepods.

Microplastic contamination has been considered as a global environmental problem in marine ecosystem. Due to small size (< 5 mm) in overlapping with that of microalgae, microplastics can easily be ingested by a wide range of marine copepods both in the laboratory and in situ. Although many studies have reported adverse effects of microplastics on marine copepods, it still lacks a systematic overview about the bioavailability of microplastics and their potential ecological consequences. As copepods dominate zooplankton biomass and provide an essential trophic link in marine ecosystem, this review indicates the bioavailability and toxicity of microplastics in such taxon depend on the shape, size, abundance, and properties of plastics. Also, ours is purposed to tease out the possible molecular mechanisms behind. Microplastic ingestion is prevalent; they impede food intake, block the digestive tract, and cause physiological stress in copepods (e.g., immune responses, metabolism disorders, energy depletion, behavioral alterations, growth retardation, and reproduction disturbance). Notably, in response to microplastic exposure, the copepods show both species- and stage-specificity. Furthermore, microplastics can serve as vectors of organic contaminants (e.g., triclosan, chlorpyrifos, and dibutyl phthalate) and thus increase their toxicity in marine copepods, consequently aggravating the adverse impacts of microplastics in marine ecosystem. Given that most previous studies have partially used pristine microplastics and their short-term exposure might have undervalued their negative effects, more multigenerational mechanistic researches (for example, via an integration of omics-based technology and phenotypic trait analysis) are urgently required for numerous marine copepods exposed to environmental-characteristics plastics as demonstrated by aged microplastics at environmentally realistic concentrations and added with other environmental pollutants; thus it will not only provide mechanistic insights into the biological impacts of microplastics, but also help make the seawater-benchmark setting and ecological assessment for microplastic pollution in marine environment.

Fragrance materials (FMs) affect the larval development of the copepod Acartia tonsa: An emerging issue for marine ecosystems.

Fragrance materials (FMs) are used in a variety of detergents and cosmetics, including household and personal care products. Despite their widespread use and the growing evidence of their occurrence in surface waters worldwide, very little is known about their toxicity towards marine species, including a key component of the marine food webs such as copepods. Thus, we investigated the toxicity of six of the more long-lasting and stable commercial fragrances, including Amyl Salicylate (AMY), Oranger Crystals (ORA), Hexyl Salicylate (HEX), Ambrofix (AMB), Peonile (PEO), and Benzyl Salicylate (BZS), to assess their ability to impair the larval development of the calanoid copepod Acartia tonsa. FMs inhibited the development of A. tonsa significantly at concentrations by far lower than the effect-concentrations reported in the literature for aquatic species. The more toxic FMs were HEX (EC50 = 57 ng L-1), AMY (EC50 = 131 ng L-1) and ORA (EC50 = 766 ng L-1), while the other three compounds exerted toxic effects at concentrations higher than 1000 ng L-1 (LOEC at 1000 ng L-1 for PEO and BZS, and at 10,000 ng L-1 for AMB). Early life-stage mortality was unaffected by FMs at all the tested concentrations. A comparison with water concentrations of FMs reported in the literature confirmed that FMs, especially HEX and AMY, may act as contaminants of potential concern in many aquatic habitats, including urban areas and remote and polar environments.

Effects of a bacteria-produced algicide on non-target marine invertebrate species.

Harmful algal blooms (HABs) affect both freshwater and marine systems. Laboratory experiments suggest an exudate produced by the bacterium Shewanella sp. IRI-160 could be used to prevent or mitigate dinoflagellate blooms; however, effects on non-target organisms are unknown. The algicide (IRI-160AA) was tested on various ontogenetic stages of the copepod Acartia tonsa (nauplii and adult copepodites), the blue crab Callinectes sapidus (zoea larvae and megalopa postlarvae), and the eastern oyster Crassostrea virginica (pediveliger larvae and adults). Mortality experiments with A. tonsa revealed that the 24-h LC50 was 13.4% v/v algicide for adult females and 5.96% for early-stage nauplii. For C. sapidus, the 24-h LC50 for first-stage zoeae was 16.8%; results were not significant for megalopae or oysters. Respiration rates for copepod nauplii increased in the 11% concentration, and in the 11% and 17% concentrations for crab zoeae; rates of later stages and oysters were unaffected. Activity level was affected for crab zoeae in the 1%, 11%, and 17% treatments, and for oyster pediveliger larvae at the 17% level. Activity of later stages and of adult copepods was unaffected. Smaller, non-target biota with higher surface to volume could be negatively impacted from IRI-160AA dosing, but overall the taxa and stages assayed were tolerant to the algicide at concentrations required for dinoflagellate mortality (EC50 = ~ 1%).

Prescribing sea water quality criteria for arsenic, cadmium and lead through species sensitivity distribution.

Water quality standards are essential for regulation of contaminants in marine environment. Seawater quality criteria (SWQC) for arsenic (As), cadmium (Cd) and lead (Pb) have not been developed for India. The aim of this study is to derive the SWQC for the metals based on Species Sensitivity Distribution (SSD). Eight species of sensitive marine organisms belonging to five phyla were assessed for their sensitivity to toxicity of As, Cd and Pb. Median effective concentrations (EC50) and Median Lethal Concentrations (LC50) were derived from the acute toxicity bio-assays. No Observed Effect Concentrations (NOEC), Lowest Observed Effect Concentrations (LOEC) and chronic values were derived from chronic toxicity bio-assays. Diatoms were more sensitive to As with 96 h EC50 of 0.1 mg/l and copepods were more sensitive to Cd and Pb with 96 h EC50 of 0.019 mg/l and 0.05 mg/l respectively. Estimated NOECs ranged from 4.87 to 21.55 µg/l of As, 1.0 to 120 µg/l of Cd and 5.67 to 91.67 µg/l of Pb. Similarly, chronic values (µg/l) were in the range of 6.71-26.1, 1.38-170, and 7.67-91.67 of As, Cd and Pb respectively. The Criterion Maximum Concentration (CMC), Criterion Continuous Concentration (CCC) and Predicted No Effect Concentration (PNEC) values were prescribed as SWQC. The CMC (µg/l) of 19, 1.7 and 17 for As, Cd, and Pb were derived respectively for acute exposure during accidental marine outfalls. The CCC (µg/l) for As was 4.6, 1.1 for Cd and 5.9 for Pb are recommended as SWQC for protection of 95% of marine organisms. PNEC (µg/l) of 3.8 for As, 0.92 for Cd and 4.3 for Pb are suggested for highly disturbed ecosystems, shell fishing and mariculture uses of water bodies. These values are recommended as a baseline for site specific water quality criteria for the coastal waters of the country.

Effect of environmentally relevant concentrations of potentially toxic microplastic on coastal copepods.

Tire wear particles (TWP) are both abundant and potentially toxic types of microplastic (MP) in the coastal ocean. We tested the effects of TWP type (new tires, old tires, rubber granules from artificial turfs) and concentration (10-10,000 TWP L-1) on feeding, reproduction and fecal pellet production of two common coastal copepods at high (400 µg C L-1) and low (40 µg C L-1) food concentration consisting of a cryptophyte Rhodomonas sp. We did not observe any effect of TWP on copepods at environmentally relevant concentrations of <10 TWP L-1. At TWP concentrations that were >100 times higher than the MP concentrations measured in coastal waters, food concentration, copepod feeding mode, TWP concentration and TWP type interacted to influence copepod feeding and pellet production, while reproduction was unaffected. Our results suggest that TWP at the current measured concentrations in the ocean environment is not likely to be a threat to the common coastal copepods.

Hydrogen peroxide treatment and its impacts on Lepeophtheirus salmonis originating from the Bay of Fundy, Canada.

Hydrogen peroxide (H2 O2 ) is used to treat sea lice infections of farmed salmonids in the Atlantic and Pacific Oceans and issues with resistance to this treatment, and others are a major threat to the sustainability of the industry. The objectives of this study were to determine how H2 O2 exposure affects survival and antioxidant-related gene expression in salmon lice (Lepeophtheirus salmonis) collected from the Bay of Fundy, New Brunswick. The maximum recommended dose of H2 O2 is 1,800 mg/L, while the EC50 values (with 95% CI) for the population tested were 1,486 (457, 2,515) mg/L for males and 2,126 (984, 3,268) mg/L for females. Neither temperature nor pretreatment with emamectin benzoate (EMB) impacted survival after H2 O2 exposure. RT-qPCR was performed on pre-adult sea lice exposed to H2 O2 and showed that four genes classically involved in the response to oxidative stress were unchanged between treated and control groups. Seven genes were found to be significantly upregulated in males and one in females. This is the first report on the efficacy and molecular responses of Atlantic Canada sea lice to H2 O2 treatment.

Climate change and oil pollution: A dangerous cocktail for tropical zooplankton.

Climate change and oil pollution pose a major threat to tropical marine ecosystems and to the coastal communities relying on their resources. The Gulf of Guinea is severely affected by multiple human induced stressors, but the potential impacts of these on marine productivity remain unknown. We investigated the combined effects of heatwaves (climate stressor) and the polycyclic aromatic hydrocarbon pyrene (proxy for oil) on the copepod Centropages velificatus. We quantified survival, reproduction and fecal pellet production of females exposed to concentrations of 0, 10, 100 and 100+ nM (saturated) pyrene under simulated heatwaves of different thermal intensity (+3 °C and +5 °C above control treatment temperature). Thermal stress due to both moderate and intensive heatwaves resulted in reduced survival and egg production. The negative effects of pyrene were only measurable at the high pyrene concentrations. However, thermal stress increased the sensitivity of C. velificatus to pyrene, indicating a synergistic interaction between the two stressors. We document that the interaction of multiple stressors can result in cumulative impacts that are stronger than expected based on single stressor studies. Further research is urgently needed to evaluate the combined impact of climatic and anthropogenic stressors on the productivity of coastal ecosystems, particularly in the tropical areas.

Ingestion and impact of microplastics on arctic Calanus copepods.

Microplastics (MPs) are contaminants of emerging concern in the Arctic, but knowledge of their potential effects on Arctic plankton food webs remains scarce. We experimentally investigated ingestion and effects of MPs (20 µm polyethylene spheres) on the arctic copepods Calanus finmarchicus, C. glacialis and C. hyperboreus. These species dominate arctic zooplankton biomass and are relevant target species to investigate the potential impacts of MPs on the Arctic marine ecosystem. Females of each species were exposed to two concentrations of MPs (200 and 20,000 MPs L-1) in combination with different food (diatom) concentrations, reflecting high (3000-5000 cells mL-1, spring phytoplankton bloom) and low (50-500 cells mL-1, pre/post bloom) food conditions. MPs did not affect negatively fecal pellet production rates in any of the species at the studied exposure concentrations. However, egg production rates of copepods exposed to MPs were 8 times higher compared with the controls, which suggests that MP exposure can cause stress-induced spawning in arctic copepods. Microscopic examination of the fecal pellets confirmed ingested MPs in the three species (up to aprox. 1000 MPs cop-1 d-1). The number of MPs per pellet decreased exponentially with increasing food concentration. The daily ingestion of MPs per copepod was higher at low- food concentrations (250-500 cells mL-1). At our exposure conditions, the presence of MPs inside C. hyperboreus fecal pellets did not affect their sinking rates. Overall, our experimental research show that 1) acute exposure to virgin polyethylene MPs has a low impact on arctic Calanus species at environmentally relevant MP concentrations, independent of food availability, and 2) arctic copepods influence the environmental fate of plankton-sized MPs by exporting buoyant MPs from the surface layer to the sea floor via fecal pellets.

Deriving a Chronic Guideline Value for Nickel in Tropical and Temperate Marine Waters.

The absence of chronic toxicity data for tropical marine waters has limited our ability to derive appropriate water quality guideline values for metals in tropical regions. To aid environmental management, temperate data are usually extrapolated to other climatic (e.g., tropical) regions. However, differences in climate, water chemistry, and endemic biota between temperate and tropical systems make such extrapolations uncertain. Chronic nickel (Ni) toxicity data were compiled for temperate (24 species) and tropical (16 species) marine biota and their sensitivities to Ni compared. Concentrations to cause a 10% effect for temperate biota ranged from 2.9 to 20 300 µg Ni/L, with sea urchin larval development being the most sensitive endpoint. Values for tropical data ranged from 5.5 to 3700 µg Ni/L, with copepod early-life stage development being the most sensitive test. There was little difference in temperate and tropical marine sensitivities to Ni, with 5% hazardous concentrations (95% confidence interval) of 4.4 (1.8-17), 9.6 (1.7-26), and 5.8 (2.8-15) µg Ni/L for temperate, tropical, and combined temperate and tropical species, respectively. To ensure greater taxonomic coverage and based on guidance provided in Australia and New Zealand, it is recommended that the combined data set be used as the basis to generate a jurisdiction-specific water quality guideline of 6 µg Ni/L for 95% species protection applicable to both temperate and tropical marine environments. Environ Toxicol Chem 2020;39:2540-2551. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The effects of teflubenzuron on mortality, physiology and accumulation in Capitella sp.

The chitin synthesis inhibitor teflubenzuron (TFB) is a feed antiparasitic agents used to impede molting of the salmon lice, an ecto-parasite that severely affects the salmon industry. Low absorption of oral administered TFB may cause elevated concentrations in the feces discharged from the salmon into the benthic environment. The polychaete Capitella sp. are often dominant in such habitats and consume organic waste deposited on the sediment. In the present study, Capitella sp. were exposed to doses of TFB in salmon feed of 1, 2 and 4 g TFB kg-1 (0 g TFB kg-1 in control group) over an experimental period of 32 days. Cumulative mortality was 12%-15% in both treatment groups with 1 and 2 g TFB kg-1 and reached 27% in the group with 4 g TFB kg-1. Only the highest dose (4 g TFB kg-1) negatively affected feed intake, growth and respiration of the polychaetes while food conversion efficiency was not affected. At the end of the experiment, the concentrations of TFB in the Capitella sp. were high, in the range of 9.24-10.32 µg g-1 for the three treatment groups. It was suggested that a maximum level of absorption rate was reached, also for the lowest dose. High concentrations of TFB in the Capitella sp. might pose a risk to crustaceans that forage for polychaetes in the vicinity of fish farms. We conclude that the effects of TFB on Capitella sp. may therefore primarily be to the predators rather than the Capitella sp.

Short and long-term effects of low-sulphur fuels on marine zooplankton communities.

International shipping is responsible for the release of numerous contaminants to the air and the marine environment. In order to reduce airborne emissions, a global 0.5 % sulphur limit for marine fuels was implemented in January 2020. Recently, a new generation of so-called hybrid fuels that meet these new requirements have appeared on the market. Studies have shown that these fuels have physical properties that make conventional clean-up methods difficult, but few have studied their effects on marine life. We conducted short and long-term microcosm experiments with natural mesozooplankton communities exposed to the water accommodated fractions (WAFs) of the hybrid fuel RMD80 (0.1 % sulphur) and a Marine Gas Oil (MGO). We compared the toxicity of both fuel types in 48h short-term exposures, and studied the effects of the hybrid fuel on community structure over two generations in a 28-day experiment. The F0 generation was exposed for eight days and the F1 generation was raised for 22 days without exposure. GC-MS and GC-FID analysis of the WAFs revealed that the hybrid fuel was dominated by a mixture of volatile organic compounds (VOCs) and poly aromatic hydrocarbons (PAHs), whereas the MGO was mainly composed of VOCs. We observed significant short-term effects on copepod egg production from exposure to 25 % hybrid fuel WAF, but no effects from the MGO WAF at equivalent WAF dilution. In the long-term experiment with RMD80, the feeding rate was initially increased after exposure to 0.5-1.1 % hybrid fuel WAF, but this did not increase the copepod egg production. Significant change in community structure was observed after eight days in the F0 community at 0.5-3.3 % WAF. Indications of further alterations in species abundances was observed in the F1 community. Our results demonstrate that the MGO is a less toxic low-sulphur alternative to the hybrid fuel for marine zooplankton, and that a hybrid fuel spill could result in altered diversity of future generations of copepod communities.

Differential gene expression profile of male and female copepods in response to cadmium exposure.

In this study, the whole transcriptome and sex-specific differential gene expression of the copepod Pseudodiaptomus annandalei exposed to cadmium (Cd) were investigated. P. annandalei were exposed to 40 µg/L Cd from the naupliar stage to male and female adults. High-throughput transcriptome sequencing (RNA-seq) was performed with copepod samples using an Illumina Hiseq™ 2000 platform. TransDecoder analysis found 32,625 putative open reading frame contigs. At p-values of <0.001, a total of 4756 differentially expressed genes (DEGs) (2216 up-regulated and 2540 down-regulated genes) were found in male copepods. Whereas a total of 2879 DEGs (2007 up-regulated and 872 down-regulated genes) were found in female copepods. A few selected cellular stress response genes, involved in xenobiotic metabolism, energy metabolism, growth, and development as a result of Cd exposure in the copepods were discussed. The study showed that most of these processes were changed in a sex-specific manner, accounting for the different sensitivities of male and female copepods. Results suggest and reinforce that sex is an important factor to be considered in ecotoxicogenomics.

Combined effects of exposure to engineered silver nanoparticles and the water-soluble fraction of crude oil in the marine copepod Calanus finmarchicus.

While it is likely that ENPs may occur together with other contaminants in nature, the combined effects of exposure to both ENPs and environmental contaminants are not studied sufficiently. In this study, we investigated the acute and sublethal toxicity of PVP coated silver nanoparticles (AgNP) and ionic silver (Ag+; administered as AgNO3) to the marine copepod Calanus finmarchicus. We further studied effects of single exposures to AgNPs (nominal concentrations: low 15 µg L-1 NPL, high 150 µg L-1 NPH) or Ag+ (60 µg L-1), and effects of co-exposure to AgNPs, Ag+ and the water-soluble fraction (WSF; 100 µg L-1) of a crude oil (AgNP + WSF; Ag++WSF). The gene expression and the activity of antioxidant defense enzymes SOD, CAT and GST, as well as the gene expression of HSP90 and CYP330A1 were determined as sublethal endpoints. Results show that Ag+ was more acutely toxic compared to AgNPs, with 96 h LC50 concentrations of 403 µg L-1 for AgNPs, and 147 µg L-1 for Ag+. Organismal uptake of Ag following exposure was similar for AgNP and Ag+, and was not significantly different when co-exposed to WSF. Exposure to AgNPs alone caused increases in gene expressions of GST and SOD, whereas WSF exposure caused an induction in SOD. Responses in enzyme activities were generally low, with significant effects observed only on SOD activity in NPL and WSF exposures and on GST activity in NPL and NPH exposures. Combined AgNP and WSF exposures caused slightly altered responses in expression of SOD, GST and CYP330A1 genes compared to the single exposures of either AgNPs or WSF. However, there was no clear pattern of cumulative effects caused by co-exposures of AgNPs and WSF. The present study indicates that the exposure to AgNPs, Ag+, and to a lesser degree WSF cause an oxidative stress response in C. finmarchicus, which was slightly, but mostly not significantly altered in combined exposures. This indicated that the combined effects between Ag and WSF are relatively limited, at least with regard to oxidative stress.

Candidate genes for monitoring hydrogen peroxide resistance in the salmon louse, Lepeophtheirus salmonis.

BACKGROUND: Hydrogen peroxide (H2O2) is one of the delousing agents used to control sea lice infestations in salmonid aquaculture. However, some Lepeophtheirus salmonis populations have developed resistance towards H2O2. An increased gene expression and activity of catalase, an enzyme that breaks down H2O2, have been detected in resistant lice, being therefore introduced as a resistance marker in the salmon industry. In the present study the aim was to validate the use of catalase expression as a marker and to identify new candidate genes as additional markers to catalase, related to H2O2 resistance in L. salmonis. METHODS: A sensitive and an H2O2 resistant laboratory strain (P0 generation, not exposed to H2O2 for several years) were batch crossed to generate a cohort with a wide range of H2O2 sensitivities (F2 generation). F2 adult females were then exposed to H2O2 to separate sensitive and resistant individuals. Those F2 lice, the P0 lice and field-collected resistant lice (exposed to H2O2 in the field) were used in an RNA sequencing study. RESULTS: Catalase was upregulated in resistant lice exposed to H2O2 compared to sensitive lice. This was, however, not the case for unexposed resistant P0 lice. Several other genes were found differentially expressed between sensitive and resistant lice, but most of them seemed to be related to H2O2 exposure. However, five genes were consistently up- or downregulated in the resistant lice independent of exposure history. The upregulated genes were: one gene in the DNA polymerase family, one gene encoding a Nesprin-like protein and an unannotated gene encoding a small protein. The downregulated genes encoded endoplasmic reticulum resident protein 29 and an aquaporin (Glp1_v2). CONCLUSIONS: Catalase expression seems to be induced by H2O2 exposure, since it was not upregulated in unexposed resistant lice. This may pose a challenge for its use as a resistance marker. The five new genes associated with resistance are put forward as complementary candidate genes. The most promising was Glp1_v2, an aquaglyceroporin that may serve as a passing channel for H2O2. Lower channel number can reduce the influx or distribution of H2O2 in the salmon louse, being directly involved in the resistance mechanism.

Tackling the Molecular Drug Sensitivity in the Sea Louse Caligus rogercresseyi Based on mRNA and lncRNA Interactions.

Caligus rogercresseyi, commonly known as sea louse, is an ectoparasite copepod that impacts the salmon aquaculture in Chile, causing losses of hundreds of million dollars per year. This pathogen is mainly controlled by immersion baths with delousing drugs, which can lead to resistant traits selection in lice populations. Bioassays are commonly used to assess louse drug sensitivity, but the current procedures may mask relevant molecular responses. This study aimed to discover novel coding genes and non-coding RNAs that could evidence drug sensitivity at the genomic level. Sea lice samples from populations with contrasting sensitivity to delousing drugs were collected. Bioassays using azamethiphos, cypermethrin, and deltamethrin drugs were conducted to evaluate the sensitivity and to collect samples for RNA-sequencing. Transcriptome sequencing was conducted on samples exposed to each drug to evaluate the presence of coding and non-coding RNAs associated with the response of these compounds. The results revealed specific transcriptome patterns in lice exposed to azamethiphos, deltamethrin, and cypermethrin drugs. Enrichment analyses of Gene Ontology terms showed specific biological processes and molecular functions associated with each delousing drug analyzed. Furthermore, novel long non-coding RNAs (lncRNAs) were identified in C. rogercresseyi and tightly linked to differentially expressed coding genes. A significant correlation between gene transcription patterns and phenotypic effects was found in lice collected from different salmon farms with contrasting drug treatment efficacies. The significant correlation among gene transcription patterns with the historical background of drug sensitivity suggests novel molecular mechanisms of pharmacological resistance in lice populations.

Acute and chronic combined effect of polystyrene microplastics and dibutyl phthalate on the marine copepod Tigriopus japonicus.

Dibutyl phthalate (DBP) is a commonly used additive in plastic products, so it may potentially coexist with microplastics (MPs) in marine environment. The ingestion of MPs might affect the accumulation of DBP in marine organisms. In this study, the marine copepod Tigriopus japonicus was applied to study the combined effect of DBP and polystyrene microplastics (mPS) on the copepod through both acute mortality tests and chronic reproduction tests. The LC50 of DBP was 1.23 mg L-1 (95% CI: 1.11-1.35 mg L-1), while exposure to mPS didn't have significant lethal effect on the copepods. Adsorption to MPs led to decreased bioavailability of DBP, resulting in decreased toxicity of DBP. In contrast to the results of acute toxicity tests, DBP didn't affect the reproduction of the copepods at lower exposure concentrations, while mPS reduced the number of nauplii and extended the time to hatch. Similar as acute toxicity tests, antagonistic interaction was observed for mPS and DBP in chronic reproduction tests, which might be attributed to promoted aggregation of mPS at presence of DBP. Overall, antagonistic toxicity effect between the two pollutants was observed for both acute and chronic tests, but the mechanisms of the interaction between DBP and mPS were different. Results of the present study highlighted the importance of long-term exposure when evaluating the toxic effect of MPs and their combined effect with other chemicals.

Nicotinic acetylcholine receptors: Ex-vivo expression of functional, non-hybrid, heteropentameric receptors from a marine arthropod, Lepeophtheirus salmonis.

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels mostly located in the post-synaptic membrane of cholinergic synapses. The natural neurotransmitter is acetylcholine, but they are also the direct targets for neonicotinoids, chemicals widely used against ectoparasites, arthropod vectors and agricultural pests. There are significant concerns regarding adverse effects of neonicotinoids on beneficial insects. In arthropods, functional nAChRs made of α subunits have been expressed from Drosophila genes, and hybrid receptors (sometimes also referred to as chimeric receptors) using species-specific α subunits and vertebrate ß subunits have been expressed ex-vivo. Arthropod-specific nAChRs made of both α and ß subunits from the target species have not been expressed ex-vivo. The aim of the current study was to express such receptors in Xenopus oocytes using only genes from Lepeophtheirus salmonis, to characterize them and study their modulation. Genes encoding α and ß subunits of the nAChRs and three ancillary proteins, RIC-3, UNC-50 and UNC-74 were identified in the L. salmonis genome, subjected to RACE-PCR, cloned into an expression vector and the cRNA produced was then injected into Xenopus laevis oocytes. Co-expression of the ancillary proteins was essential for the successful expression of the L. salmonis nAChRs with both α and ß subunits. Two functional nAChRs were identified: Lsa-nAChR1 consisting of α1, α2, ß1 and ß2 subunits, reconstituted to one distinct receptor, while Lsa-nAChR2, consisting of α3, ß1 and ß2 subunits reconstitutes receptors with two distinct characteristics. Out of seven neonicotinoids tested, six worked as partial agonist of Lsa-nAChR1 while only three did so for Lsa-nAChR2. Four non-neonicotinoid compounds tested had no effect on either of the nAChRs. The study demonstrated that fully functional, non-hybrid nAChRs containing both α and ß subunits from an arthropod can be reconstituted ex-vivo by co-expression of essential ancillary proteins. Such models would be valuable for in-depth studies of effects by neonicotinoids and other compounds on target pests, as well as for studies of adverse effects on non-target arthropods.