Invasive Species Mediate Insecticide Effects on Community and Ecosystem Functioning.

Anthropogenic activities increase pesticide contamination and biological invasions in freshwater ecosystems. Understanding their combined effects on community structure and on ecosystem functioning presents challenges for an improved ecological risk assessment. This study focuses on an artificial stream mesocosms experiment testing for direct and indirect effects of insecticide (chlorantraniliprole - CAP) exposure on the structure of a benthic macroinvertebrate freshwater community and on ecosystem functioning (leaf decomposition, primary production). To understand how predator identity and resource quality alter the community responses to chemical stress, the mediating effects of an invasive predator species (crayfish Procambarus clarkii) and detritus quality (tested by using leaves of the invasive Eucalyptus globulus) on insecticide toxicity were also investigated. Low concentrations of CAP reduced the abundance of shredders and grazers, decreasing leaf decomposition and increasing primary production. Replacement of autochthonous predators and leaf litter by invasive species decreased macroinvertebrate survival, reduced leaf decomposition, and enhanced primary production. Structural equation modeling (SEM) highlighted that CAP toxicity to macroinvertebrates was mediated by the presence of crayfish or eucalypt leaf litter which are now common in many Mediterranean freshwaters. In summary, our results demonstrate that the presence of these two invasive species alters the effects of insecticide exposure on benthic freshwater communities. The approach used here also allowed for a mechanistic evaluation of indirect effects of these stressors and of their interaction on ecosystem functional endpoint, emphasizing the value of incorporating biotic stressors in ecotoxicological experiments.

Combined effects of insecticide exposure and predation risk on freshwater detritivores.

Insecticides usually present in low concentrations in streams are known to impair behaviour and development of non-target freshwater invertebrates. Moreover, there is growing awareness that the presence of natural stressors, such as predation risk may magnify the negative effects of pesticides. This is because perception of predation risk can by itself lead to changes on behaviour and physiology of prey species. To evaluate the potential combined effects of both stressors on freshwater detritivores we studied the behavioural and developmental responses of Chironomus riparius to chlorantraniliprole (CAP) exposure under predation risk. Also, we tested whether the presence of a shredder species would alter collector responses under stress. Trials were conducted using a simplified trophic chain: Alnus glutinosa leaves as food resource, the shredder Sericostoma vittatum and the collector C. riparius. CAP toxicity was thus tested under two conditions, presence/absence of the dragonfly predator Cordulegaster boltonii. CAP exposure decreased leaf decomposition. Despite the lack of significance for interactive effects, predation risk marginally modified shredder effect on leaf decomposition, decreasing this ecosystem process. Shredders presence increased leaf decomposition, but impaired chironomids performance, suggesting interspecific competition rather than facilitation. C. riparius growth rate was decreased independently by CAP exposure, presence of predator and shredder species. A marginal interaction between CAP and predation risk was observed regarding chironomids development. To better understand the effects of chemical pollution to natural freshwater populations, natural stressors and species interactions must be taken into consideration, since both vertical and horizontal species interactions play their role on response to stress.

Responses of Mytilus galloprovincialis in a Multi-Stressor Scenario: Effects of an Invasive Seaweed Exudate and Microplastic Pollution under Ocean Warming.

Microplastic pollution, global warming, and invasive species are known threats to marine biota, but the impact of their simultaneous exposure is still not well understood. This study investigated whether the toxic effects posed by the invasive red seaweed Asparagopsis armata exudate (2%) to the mussel Mytilus galloprovincialis are amplified by a 96 h exposure to increased temperature (24 °C) and polyethylene microplastics (PE-MPs, 1 mg/L). Biochemical (neurotoxicity, energy metabolism, oxidative stress, and damage) and physiological (byssal thread production) responses were evaluated. The number of produced byssus greatly decreased under concomitant exposure to all stressors. The antioxidant defences were depleted in the gills of mussels exposed to temperature rises and PE-MPs, regardless of exudate exposure, preventing oxidative damage. Moreover, the heat shock protein content tended to decrease in all treatments relative to the control. The increased total glutathione in the mussels' digestive gland exposed to 24 °C, exudate, and PE-MPs avoided oxidative damage. Neurotoxicity was observed in the same treatment. In contrast, the energy metabolism remained unaltered. In conclusion, depending on the endpoint, simultaneous exposure to A. armata exudate, PE-MPs, and warming does not necessarily mean an amplification of their single effects. Studies focusing on the impact of multiple stressors are imperative to better understand the underlying mechanisms of this chronic exposure.

Co-Exposure with an Invasive Seaweed Exudate Increases Toxicity of Polyamide Microplastics in the Marine Mussel Mytilus galloprovincialis.

Plastic pollution and invasive species are recognised as pervasive threats to marine biodiversity. However, despite the extensive on-going research on microplastics' effects in the biota, knowledge on their combination with additional stressors is still limited. This study investigates the effects of polyamide microplastics (PA-MPs, 1 mg/L), alone and in combination with the toxic exudate from the invasive red seaweed Asparagopsis armata (2%), after a 96 h exposure, in the mussel Mytilus galloprovincialis. Biochemical responses associated with oxidative stress and damage, neurotoxicity, and energy metabolism were evaluated in different tissues (gills, digestive gland, and muscle). Byssus production and PA-MP accumulation were also assessed. Results demonstrated that PA-MPs accumulated the most in the digestive gland of mussels under PA-MP and exudate co-exposure. Furthermore, the combination of stressors also resulted in oxidative damage at the protein level in the gills as well as in a significant reduction in byssus production. Metabolic capacity increased in both PA-MP treatments, consequently affecting the energy balance in mussels under combined stress. Overall, results show a potential increase of PA-MPs toxicity in the presence of A. armata exudate, highlighting the importance of assessing the impact of microplastics in realistic scenarios, specifically in combination with co-occurring stressors, such as invasive species.

Responses of benthic macroinvertebrate communities to a Bti-based insecticide in artificial microcosm streams.

Bioinsecticides based on the bacterium Bacillus thuringiensis subsp. israelensis (Bti) are increasingly being applied directly into aquatic compartments to control nuisance mosquitoes and blackflies and are generally considered environmentally friendly alternatives to synthetic insecticides. Bti-based insecticides are considered highly selective, being Diptera-specific, and supposedly decompose rapidly in the environment. Nevertheless, their safety to non-target species and freshwater ecosystems has been questioned by recent studies, which in fact document possible indirect effects in aquatic food webs such as the decrease of prey availability to predators. This work aimed to evaluate the potential effects of a Bti-based insecticide (VectoBac® 12AS) on a freshwater macroinvertebrate community and on stream ecological functions by using artificial microcosm streams. Artificial microcosm streams were colonized with a macroinvertebrate community plus periphyton collected in a stream together with Alnus glutinosa leaf packs. They were exposed for 7 days to different Bti treatments (0, 12, 120, 1200 µg/L), which are within the recommended concentrations of application in aquatic compartments for blackfly and mosquito control. Besides invertebrate community structure and abundance, effects were evaluated regarding leaf decomposition and primary production as measures of ecosystem functioning. Community structure was significantly altered in all Bti treatments after 7 days of exposure, mostly due to a decline in chironomids, followed by oligochaetes, which both belong to the deposit-feeders' functional group. Direct effects on oligochaetes are surprising and require further research. Also, reductions of leaf decomposition due to Bti-induced sublethal effects on shredders (reduced feeding) or mortality of chironomids (that can also feed on coarse organic matter) observed in our study, represent potential indirect effects of Bti in aquatic ecosystems. Our short-exposure experiment evidenced some negative effects on stream benthic invertebrate communities and on ecosystem functioning that must be considered whenever Bti is used in water bodies for blackfly or mosquito control programs.

Ocean Warming May Enhance Biochemical Alterations Induced by an Invasive Seaweed Exudate in the Mussel Mytilus galloprovincialis.

Ocean warming and biological invasions are among the most pervasive factors threatening coastal ecosystems with a potential to interact. Ongoing temperature rise may affect physiological and cellular mechanisms in marine organisms. Moreover, non-indigenous species spread has been a major challenge to biodiversity and ecosystem functions and services. The invasive red seaweed Asparagopsis armata has become successfully established in Europe. Its exudate has been considered deleterious to surrounding native species, but no information exists on its effect under forecasted temperature increase. This study evaluated the combined effects of temperature rise and A. armata exudate exposure on the native mussel Mytilus galloprovincialis. Oxidative stress, neurophysiological and metabolism related biomarkers were evaluated after a 96 h-exposure to exudate (0% and 2%) under present (20 °C) and warming (24 °C) temperature scenarios. Short-term exposure to A. armata exudate affected the oxidative stress status and neurophysiology of the mussels, with a tendency to an increasing toxic action under warming. Significant oxidative damage at protein level was observed in the digestive gland and muscle of individuals exposed simultaneously to the exudate and temperature rise. Thus, under a climate change scenario, it may be expected that prolonged exposure to the combined action of both stressors may compromise M. galloprovincialis fitness and survival.

Lethal and sublethal effects of the saline stressor sodium chloride on Chironomus xanthus and Girardia tigrina.

Salinization in freshwaters is gradually increasing as a result of human activities and climatic changes. Higher salt content causes stress for freshwater organisms. Sodium chloride (NaCl) is among the most frequently occurring salts in freshwater ecosystems. The objective of the present study was to investigate the lethal and sublethal effects of NaCl on freshwater ecosystems, using as test organism the dipteran Chironomus xanthus and the planarian Girardia tigrina. Acute tests showed that C. xanthus was more sensitive (48-h LC50 (median lethal concentration) of 2.97 g NaCl L-1) than G. tigrina (48-h LC50 of 7.77 g NaCl L-1). C. xanthus larvae growth rate (larvae length and head capsule width) was significantly reduced under exposure to concentrations as low as 0.19 g L-1 NaCl and higher. A delay in the emergence time (EmT50) was also demonstrated for the same concentration. Sublethal NaCl effects in G. tigrina included feeding inhibition (LOEC (lowest observed effect concentration) of 0.4 g L-1), reduced locomotion (LOEC = 0.2 g L-1), and 24-48-h blastema regeneration (LOEC = 0.2 g L-1 and 0.1 g L-1, respectively). The results demonstrated the toxicity of NaCl to C. xanthus and G. tigrina including sublethal effects that can result in negative consequences for populations in natural freshwaters under salinization.

Energetic costs and biochemical biomarkers associated with esfenvalerate exposure in Sericostoma vittatum.

Pyrethroid insecticides have been used for decades and their worldwide market continues to increase, despite their high toxicity to non-target insects. Recent studies reveal that it is essential to investigate the secondary mechanisms of action of type II pyrethroids to understand their cellular effects on invertebrates. The aim of this study was to evaluate the lethality, behaviour and physiological alterations and energetic costs in caddisfly larvae exposed to environmentally relevant concentrations of esfenvalerate (ESF). ESF caused both mortality and feeding inhibition of exposed caddisfly larvae: nominal ESF 96 h LC50 was 2.29 µg/L; feeding activity was impaired at concentrations equal or above 0.25 µg/L. At the cellular level, glutathione-S-transferase (GST) activity was increased on caddisfly larvae exposed to 0.25 and 0.5 µg/L ESF, which might contribute to prevent oxidative damage since levels of lipid peroxidation (LPO) were not altered. The energy budget of exposed caddisfly larvae was impaired by exposure to 0.25 µg/L ESF since sugar and protein contents decreased, while a decline of energy consumption was observed. The analysis of feeding, energy reserves and consumption data through structural equation modelling (SEM) allowed to quantify the direct and indirect effects of ESF exposure on bioenergetics of caddisfly larvae. SEM analysis showed a strong negative direct influence of ESF onto feeding activity, sugars content and energy consumption, highlighting a significant positive relationship between sugars and protein contents. These results show that energy expenditure is related to oxidative defense mechanisms induced by ESF stress that may lead to deleterious effects on growth and development.

Exposure to chlorantraniliprole affects the energy metabolism of the caddisfly Sericostoma vittatum.

Caddisflies have been included in ecotoxicological studies because of their sensitivity and ecological relevance. The present study aimed to assess the sublethal effects of an anthranilic diamide insecticide, chlorantraniliprole (CAP), to Sericostoma vittatum. Used worldwide, CAP is a persistent compound that has been found in surface waters at concentrations from 0.1 µg/L to 9.7 µg/L. It targets the ryanodine receptors, and the present ecotoxicological assessment focused on biomarkers related to neurotransmission, biotransformation, oxidative stress damage, and endpoints related to energy processing (feeding, energy reserves, and cellular metabolism). Six days of exposure trials revealed that feeding activity was significantly decreased in S. vittatum larvae exposed to 0.9 µg/L CAP. Concomitantly, a reduction in cellular metabolism and a significant decrease in protein content were also observed in caddisfly larvae exposed to CAP, suggesting metabolic depression. The results show that sublethal concentrations of CAP can cause detrimental sublethal effects on S. vittatum total glutathione content at concentrations as low as 0.2 µg/L. Bioenergetics can be used to assess physiological effects of contaminants, and the present results show that exposure to low, environmentally relevant, concentrations of CAP alter energy acquisition and metabolism in nontarget aquatic insects with potential population level effects. Environ Toxicol Chem 2017;36:1584-1591. © 2016 SETAC.

The role of genetic diversity and past-history selection pressures in the susceptibility of Chironomus riparius populations to environmental stress.

Natural populations experiencing intense selection and genetic drift may exhibit limited potential to adapt to environmental change. The present study addresses the following aspects of the "genetic erosion" hypothesis in the midge Chironomus riparius: does long-term mercury (Hg) contamination affect the Hg tolerance of midge populations inhabiting such impacted areas? If so, is there any fitness cost under changing environmental conditions? And does genetic impoverishment influence the susceptibility of C. riparius to cope with environmental stressful conditions? For this end, we tested the acute and chronic tolerance to Hg and salinity in four C. riparius populations differing in their levels of genetic diversity (assessed through microsatellite markers) and past-histories of Hg exposure. Results showed that the midge population collected from a heavily Hg-contaminated site had higher Hg tolerance compared to the population collected from a closely-located reference site suggesting directional selection for Hg-tolerant traits in its native environment despite no genetic erosion in the field. No increased susceptibility under changing environmental conditions of salinity stress was observed. Moreover, results also showed that populations with higher genetic diversity performed better in the partial life-cycle assays providing evidence on the key role that genetic diversity plays as mediator of populations' susceptibility to environmental stress. Our findings are discussed in terms of the suitability of C. riparius as a model organism in evolutionary toxicology studies as well as the validity of ecotoxicological assessments using genetically eroded laboratory populations.