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Microscopic plastic items (microplastics) are ubiquitously present in aquatic ecosystems. With decreasing size their availability and potential to accumulate throughout food webs increase. However, little is known on the uptake of microplastics by freshwater invertebrates. To address this, we exposed species with different feeding strategies to 1, 10 and 90 µm fluorescent polystyrene spheres (3–3 000 particles mL −1 ). Additionally, we investigated how developmental stages and a co-exposure to natural particles (e.g., food) modulate microplastic ingestion. All species ingested microplastics in a concentration-dependent manner with Daphnia magna consuming up to 6 180 particles h −1 , followed by Chironomus riparius (226 particles h −1 ), Physella acuta (118 particles h −1 ), Gammarus pulex (10 particles h −1 ) and Lumbriculus variegatus (8 particles h −1 ). D. magna did not ingest 90 µm microplastics whereas the other species preferred larger microplastics over 1 µm in size. In C. riparius and D. magna , size preference depended on the life stage with larger specimens ingesting more and larger microplastics. The presence of natural particles generally reduced the microplastics uptake. Our results demonstrate that freshwater invertebrates have the capacity to ingest microplastics. However, the quantity of uptake depends on their feeding type and morphology as well as on the availability of microplastics.

The presence of microplastics (MPs) in the environment has generated global concerns. However, the explicit assessment of the effect of multiple anthropogenic activities on the existence of MPs in the freshwater system is scarcely reported. This study quantified anthropogenic activities and analyzed their relationship with MPs on a freshwater organism: the midge larvae (Diptera: Chironomidae). The study took place in an urban river and consisted of comparing the abundance and types of MPs. Our results highlight that, while industrial area was the most important variable contributing to the total MP concentration in midge larvae, residential area also influenced the concentration of microfibers in midge larvae. The impact of a residential area on the relative abundance of microfibers in each sample site was diluted by the proximity to an industrial area. In conclusion, we suggest that industrial areas are a potential source of MP pollution in river sediment, and midge larvae can be a good indicator of the MP concentrations in urban river systems. Quantifying anthropogenic activities can help discern their effects on MP concentration in a river system and promote management strategies.

Organisms use endogenous clocks to anticipate regular environmental cycles, such as days and tides. Natural variants resulting in differently timed behaviour or physiology, known as chronotypes in humans, have not been well characterized at the molecular level. We sequenced the genome of Clunio marinus , a marine midge whose reproduction is timed by circadian and circalunar clocks. Midges from different locations show strain-specific genetic timing adaptations. We examined genetic variation in five C. marinus strains from different locations and mapped quantitative trait loci for circalunar and circadian chronotypes. The region most strongly associated with circadian chronotypes generates strain-specific differences in the abundance of calcium/calmodulin-dependent kinase II.1 (CaMKII.1) splice variants. As equivalent variants were shown to alter CaMKII activity in Drosophila melanogaster , and C. marinus ( Cma )-CaMKII.1 increases the transcriptional activity of the dimer of the circadian proteins Cma- CLOCK and Cma- CYCLE, we suggest that modulation of alternative splicing is a mechanism for natural adaptation in circadian timing. Genomic and molecular analyses of Clunio marinus timing strains suggest that modulation of alternative splicing of Ca2+/calmodulin-dependent kinase II represents a mechanism for evolutionary adaptation of circadian timing. Night and day habits of a sea midge Kristin Tessmar-Raible and colleagues report the genome of Clunio marinus , a marine midge whose reproduction is timed to the tides by circadian and circalunar clocks. To identify genetic variation associated with timing differences, the authors report genetic mapping in a selection of C. marinus strains with a range of circadian and circalunar timing. They suggest that circalunar and circadian timing are regulated by separate pathways, do not find involvement of core clock genes, and implicate calcium/calmodulin-dependent kinase II.1 in the regulation of circadian timing.

The midge, Belgica antarctica , is the only insect endemic to Antarctica, and thus it offers a powerful model for probing responses to extreme temperatures, freeze tolerance, dehydration, osmotic stress, ultraviolet radiation and other forms of environmental stress. Here we present the first genome assembly of an extremophile, the first dipteran in the family Chironomidae, and the first Antarctic eukaryote to be sequenced. At 99 megabases, B. antarctica has the smallest insect genome sequenced thus far. Although it has a similar number of genes as other Diptera, the midge genome has very low repeat density and a reduction in intron length. Environmental extremes appear to constrain genome architecture, not gene content. The few transposable elements present are mainly ancient, inactive retroelements. An abundance of genes associated with development, regulation of metabolism and responses to external stimuli may reflect adaptations for surviving in this harsh environment. The Antarctic midge, Belgica antarctica , is the only insect endemic to Antarctica. Here, the authors sequence the B. antarctica genome, the smallest insect genome yet reported, and suggest that genes involved in development, metabolism and stimuli response may have had a role in how this insect adapted to survive in such a harsh environment.

We present here the first-ever fossil flies from the family Deuterophlebiidae. The recent adults have an exceptionally brief lifespan, with males surviving only two hours. Their distinctive features include a complete reduction of mouthparts, and wing venation characterized by a dense net of false veins replacing most of true veins. Due to this distinctive venation the phylogenetic position of Deuterophlebiidae was unclear, compounded by the absence of fossils that could shed light on the early development of these characters. Two new genera and species are described from Burmese amber, Protodeuterophlebia oosterbroeki Krzemiński, Krzemińska & Soszyńska, gen. et sp. nov. and Cretodeuterophlebia courtneyi , Krzemiński, Skibińska & Kopeć, gen. et sp. nov. They date back the age of the family to the mid-Cretaceous. Notably, the fossils reveal first false veins and reduced mouthparts, suggesting a short lifespan in these Cretaceous mountain midges. A comparative analysis of wing venation indicated the Hennigmatidae as a plausible ancestral group to the Deuterophlebiidae. A syninclusion of mayfly indicates the coexistence of these short-lived insects during the same flight period. This synchrony extends to their brief time in flight aligning with the flow of fluid resin. The occurrence of these simultaneous events is extremely low, emphasizing the significance of these findings.

Chironomids are important laboratory model organisms used to assess toxicity in freshwater environments. Cell and tissue features are not commonly used as chironomid markers to detect toxicity, but they could be extremely helpful in identifying acute and chronic effects of pollutants. The nervous system is an excellent cellular candidate since it is reactive to toxic substances. However, a detailed description of the chironomid nervous system is required prior to considering it as a candidate for a cellular toxicity marker. The present study describes the central ganglia, nerves, axons, and the neuromuscular system of Chironomus vitellinus (Freeman, 1961) to facilitate its use as a model organism in environmental studies. We find that the structure of the C. vitellinus central nervous system is identical to that observed in other Chironomus larvae. We then focused our study on the first abdominal segment and labeled the 31 hemi-segmental muscles according to a nomenclature based on their position and orientation. We also characterized their innervation and assigned the nerves a nomenclature based on their terminals’ location in the muscle tissue. Finally, we investigated the neuromuscular junctions (NMJs) throughout this segment and defined four types of NMJs illustrating their great variability in size and shape. We selected a model NMJ, VEL 2, and quantified its mean bouton number and muscle size. Together with documenting a neurobiological system that could be informative to insects’ comparative biology, these results could help establish the Chironomus NMJ as an aquatic toxicity marker.

Coastal ecosystems, such as lakes and lagoons, are unique and valuable water bodies whose proper functioning depends on hydrological connectivity with the sea or ocean. Human interventions, such as the construction of storm surge barriers, that block the periodic and free influx of seawater into lakes induce a permanent freshwater state. This study presents such disturbances, considered as environmental stressors, initiating changes in the assemblages of Chironomidae larvae inhabiting the bottom of Lake Jamno (southern coast of the Baltic Sea). Changes in the structure of this assemblages were assessed during a long-term study (2010–20), which considered two periods: a time of free seawater intrusion (FF) and seven years of blocked influx (BF). The findings indicate that, following the activation of storm surge barriers, the α-diversity of larvae consistently decreased throughout the lake. Concurrently, the density of Chironomidae larvae decreased by over 20%, although their biomass increased. In the last year of the study with functioning gates, the diversity of the studied insects was drastically reduced and was limited to only two genus: Chironomus sp. and Procladius sp., which serve as indicators of disturbances in aquatic ecosystems undergoing changes in line with deterministic chaos theory. The information provided indicates that periodic increases in salinity significantly affect the structure of Chironomidae larvae, though it should be considered as a component of several other parameters (EC, temperature, or nutrients).

The Antarctic midge, Belgica antarctica , is a unique insect endemic to Antarctica. It has a 2-year life cycle, with larvae overwintering in two different instars and adults emerging the following summer. This seasonality is crucial for adaptation to Antarctica’s harsh climates and ephemeral growing seasons; however, the underlying mechanisms remain unclear. We found that, under summer-like conditions, larvae could develop from egg to the fourth-instar larval stage without interruption, but they never pupated. Spontaneous developmental arrest at this stage suggests that they overwinter in obligate diapause, a genetically determined period of dormancy. The winter cold can terminate this diapause, and long-term cold exposure is more effective. Although this species can utilise two alternative cold tolerance strategies with diapause for overwintering, freezing was more successful than cryoprotective dehydration in allowing survival and developmental resumption in our experimental conditions. In contrast, the first three larval instars continued their development under the same conditions as the fourth-instar larvae. Although we do not exclude the possibility of facultative diapause, they likely overwinter in a quiescent state, an immediate developmental arrest in response to adversity, to maximise exploitation of the short Antarctic summer. Diapause and quiescence ensure developmental and reproductive success in this extremophile insect.

Deterministic and stochastic drivers in metacommunities of main chironomid taxa were identified by an analysis of the taxa’s local species richness (LSR), environmental and seasonal factors, and habitat species richness (HSR), in samples collected at the mid-European regional scale. Orthocladiinae LSR depended on Orthocladiinae HSR, while Chironomini LSR did not depend on Chironomini HSR. Environmental drivers and autumn (optionally with HSR) explained over 70% of Orthocladiinae LSR variance, while environmental factors (optionally with HSR) explained less than 40% of Chironomini LSR variance. In both taxa, stochastic processes dominated over deterministic ones because species random co-occurrence was more frequent than non-random co-occurrence. In each taxon, about 20% of species pairs were non-random. Yet, in the Orthocladiinae, no pairs, while in the Chironomini one third of pairs, were negatively associated. Only the Chironomini metacommunity was competitively structured. In the Orthocladiinae, deterministic drivers were more abiotic (higher number and greater impact of environmental factors, a seasonal factor, no negative species co-occurrences), while in the Chironomini, deterministic drivers were more biotic (negative species co-occurrences, competitive metacommunity structure, no seasonal factor, lower number and smaller impact of abiotic factors).

Water mites are diverse aquatic invertebrates that provide potentially important ecosystem and economic services as bioindicators and mosquito biocontrol; however, little is known about water mite digestive physiology, including their diet in nature. Water mites, much like their spider relatives, liquefy their prey upon consumption. This results in the absence of morphologically identifiable prey in water mite mid-gut. Previous studies have reported associations in the field of water mites with presumed prey and laboratory observations of water mites feeding on specific organisms offered for ingestion; however, the present work aims to determine what water mites have ingested in nature based on molecular studies of gut contents from freshly collected organisms from the field. To elucidate water mite prey, we used next-generation sequencing to detect diverse cytochrome oxidase I DNA barcode sequences of putative prey in the guts of 54 specimens comprising two species of Lebertia and a few specimens of Arrenurus (2) and Limnesia (1). To our knowledge this is the first molecular study of the diets of water mites as they feed in nature. While the presence of chironomid DNA confirmed previous observations of midge larvae as part of the diets of Lebertia , we also found the DNA of diverse organisms in all four species of water mites, including the DNA of mosquitoes in 6 specimens of Lebertia and a large number of previously unknown prey, especially from oligochaete worms. These studies thereby reveal a greater diversity of prey and a potentially broader significance than previously appreciated for water mites in aquatic food webs. Molecular studies like this can detect water mite predators of mosquito larvae and add knowledge of water mite predatory contributions to freshwater food webs.