Silver nanoparticles adversely affect the swimming behavior of European Whitefish (Coregonus lavaretus) larvae within the low µg/L range.

The aim of this study was to determine the effects of silver nanoparticles (AgNPs; speciation: NM-300 K) in the lab on the behavior of larvae in European Whitefish (Coregonus lavaretus), a relevant model species for temperate aquatic environments during alternating light and darkness phases. The behavioral parameters measured included activity, turning rate, and distance moved. C. lavaretus were exposed to AgNP at nominal concentrations of 0, 5, 15, 45, 135, or 405 µg/L (n = 33, each) and behavior was recorded using a custom-built tracking system equipped with light sources that reliably simulate light and darkness. The observed behavior was analyzed using generalized linear mixed models, which enabled reliable detection of AgNP-related movement patterns at 10-fold higher sensitivity compared to recently reported standard toxicological studies. Exposure to 45 µg/L AgNPs significantly resulted in hyperactive response patterns for both activity and turning rates after an illumination change from light to darkness suggesting that exposure to this compound triggered escape mechanisms and disorientation-like behaviors in C. lavaretus fish larvae. Even at 5 µg/L AgNPs some behavioral effects were detected, but further tests are required to assess their ecological relevance. Further, the behavior of fish larvae exposed to 135 µg/L AgNPs was comparable to the control for all test parameters, suggesting a triphasic dose response pattern. Data demonstrated the potential of combining generalized linear mixed models with behavioral investigations to detect adverse effects on aquatic species that might be overlooked using standard toxicological tests.

Impact of wastewater-borne nanoparticles of silver and titanium dioxide on the swimming behaviour and biochemical markers of Daphnia magna: An integrated approach.

Due to their widespread use, silver (Ag) and titanium dioxide (TiO2) nanoparticles (NPs) are commonly discharged into aquatic environments via wastewater treatment plants. The study was aimed to assess the effects of wastewater-borne AgNPs (NM-300 K; 15.5 ±â€¯2.4 nm; 25-125 µg L-1) and TiO2NPs (NM-105; 23.1 ±â€¯6.2 nm; 12.5-100 µg L-1), from a laboratory-scale wastewater treatment plant, on Daphnia magna, at individual and subcellular level. For effect comparison, animals were also exposed to ASTM-dispersed NPs at the same nominal concentrations. The behaviour of D. magna was evaluated through monitoring of swimming height and allocation time for preferred zones after 0 h and 96 h of exposure. Biochemical markers of neurotransmission, anaerobic metabolism, biotransformation, and oxidative stress were subsequently determined. No 96-h EC50 (immobilization ≤ 4 %) could be obtained with wastewater-borne NPs and ASTM-dispersed TiO2NPs, whereas the ASTM-dispersed AgNPs resulted in an immobilization 96-h EC50 of 113.8 µg L-1. However, both wastewater-borne and ASTM-dispersed TiO2NPs, at 12.5 µg L-1, caused immediate (0 h) alterations on the swimming height. Allocation time analyses showed that animals exposed to ASTM-dispersed AgNPs spent more time on the surface and bottom at 0 h, and in the middle and bottom at 96 h. This pattern was not observed with ASTM-dispersed TiO2NPs nor with wastewater-borne AgNPs and wastewater-borne TiO2NPs. At the biochemical level, the more pronounced effects were observed with wastewater-borne AgNPs (e.g. induction of lactate dehydrogenase and glutathione S-transferase activities, and inhibition of catalase activity). This integrative approach showed that: (i) the behavioural and biochemical response-patterns were distinct in D. magna exposed to environmentally relevant concentrations of wastewater-borne and ASTM-dispersed NPs; (ii) the most pronounced effects on allocation time were induced by ASTM-dispersed AgNPs; and (iii) at the subcellular level, wastewater-borne AgNPs were more toxic than wastewater-borne TiO2NPs. This study highlights the need for the assessment of the effects of wastewater-borne NPs under realistic exposure scenarios, since processes in wastewater treatment plants may influence their toxicity.

Zebrafish larvae show negative phototaxis to near-infrared light.

Zebrafish larvae (Danio rerio) are among the most used model species to test biological effects of different substances in biomedical research, neuroscience and ecotoxicology. Most tests are based on changes in swimming activity of zebrafish larvae by using commercially available high-throughput screening systems. These systems record and analyse behaviour patterns using visible (VIS) and near-infrared (NIR) light sources, to simulate day (VIS) and night (NIR) phases, which allow continuous recording of the behaviour using a NIR sensitive camera. So far, however, the sensitivity of zebrafish larvae to NIR has never been tested experimentally, although being a critical piece of information for interpreting their behaviour under experimental conditions. Here, we investigated the swimming activity of 96 hpf (hours post fertilization) and 120 hpf zebrafish larvae under light sources of NIR at 860 nm and at 960 nm wavelength and under VIS light. A thermal source was simultaneously presented opposite to one of the light sources as control. We found that zebrafish larvae of both larval stages showed a clear negative phototactic response towards 860 nm NIR light and to VIS light, but not to 960 nm NIR light. Our results demonstrated that zebrafish larvae are able to perceive NIR at 860 nm, which is almost identical to the most commonly used light source in commercial screening systems (NIR at 850 nm) to create a dark environment. These tests, however, are not performed in the dark from the zebrafish´s point of view. We recommend testing sensitivity of the used test organism before assuming no interaction with the applied light source of commonly used biosensor test systems. Previous studies on biological effects of substances to zebrafish larvae should be interpreted with caution.

Symmetry is in the eye of the beeholder: innate preference for bilateral symmetry in flower-naïve bumblebees.

Bilateral symmetry has been considered as an indicator of phenotypic and genotypic quality supporting innate preferences for highly symmetric partners. Insect pollinators preferentially visit flowers of a particular symmetry type, thus leading to the suggestion that they have innate preferences for symmetrical flowers or flower models. Here we show that flower-naïve bumblebees (Bombus terrestris), with no experience of symmetric or asymmetric patterns and whose visual experience was accurately controlled, have innate preferences for bilateral symmetry. The presence of color cues did not influence the bees' original preference. Our results thus show that bilateral symmetry is innately preferred in the context of food search, a fact that supports the selection of symmetry in flower displays. Furthermore, such innate preferences indicate that the nervous system of naïve animals may be primed to respond to relevant sensory cues in the environment.