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Tracking techniques are vital for the understanding of the biology and ecology of organisms. While such techniques have provided important information on the movement and migration of large animals, such as mammals and birds, scientific advances in understanding the individual behaviour and interactions of small (mm-scale) organisms have been hampered by constraints, such as the sizes of existing tracking devices, in existing tracking methods. By combining biology, chemistry and physics we here present a method that allows three-dimensional (3D) tracking of individual mm-sized aquatic organisms. The method is based on in-vivo labelling of the organisms with fluorescent nanoparticles, so-called quantum dots, and tracking of the organisms in 3D via the quantum-dot fluorescence using a synchronized multiple camera system. It allows for the efficient and simultaneous study of the behaviour of one as well as multiple individuals in large volumes of observation, thus enabling the study of behavioural interactions at the community scale. The method is non-perturbing - we demonstrate that the labelling is not affecting the behavioural response of the organisms - and is applicable over a wide range of taxa, including cladocerans as well as insects, suggesting that our methodological concept opens up for new research fields on individual behaviour of small animals. Hence, this offers opportunities to focus on important biological, ecological and behavioural questions never before possible to address.

Urbanization causes both changes in community composition and evolutionary responses, but most studies focus on these responses in isolation. We performed an integrated analysis assessing the relative contribution of intra- and interspecific trait turnover to the observed change in zooplankton community body size in 83 cladoceran communities along urbanization gradients quantified at seven spatial scales (50–3200 m radii). We also performed a quantitative genetic analysis on 12 Daphnia magna populations along the same urbanization gradient. Body size in zooplankton communities generally declined with increasing urbanization, but the opposite was observed for communities dominated by large species. The contribution of intraspecific trait variation to community body size turnover with urbanization strongly varied with the spatial scale considered, and was highest for communities dominated by large cladoceran species and at intermediate spatial scales. Genotypic size at maturity was smaller for urban than for rural D. magna populations and for animals cultured at 24°C compared with 20°C. While local genetic adaptation likely contributed to the persistence of D. magna in the urban heat islands, buffering for the phenotypic shift to larger body sizes with increasing urbanization, community body size turnover was mainly driven by non-genetic intraspecific trait change. This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences’.

Species of the genus Moina Baird (Cladocera: Moinidae) often dominate freshwater crustacean communities in temporary water bodies. Several species of Moina are used as food for fish larvae in aquaculture, as bioindicators in toxicological studies, and as common subjects for physiological studies. The aim of this paper is to estimate biodiversity of Moina in northern Eurasia using the standard DNA barcoding approach based on the cytochrome c oxidase subunit I (COI) gene. We analysed 160 newly obtained and 157 existing COI sequences, and found evidence for 21 phylogroups of Moina, some of which were detected here for the first time. Our study confirmed the opinion that the actual species diversity of cladocerans is several times higher than is presently accepted. Our results also indicated that Moina has the second richest species diversity among the cladoceran genera (with only Daphnia O. F. Mueller having a greater diversity of species). Our study strongly supports division of Moina into two faunistic groups: European-Western Siberian and Eastern Siberian-Far Eastern, with a transitional zone at the Yenisey River basin (Eastern Siberia). Here, we refrain from taxonomic descriptions of new species, as this requires a thorough morphological and taxonomic study for each putative taxon.

Abstract The use of autochthonous zooplankton species, along with standardized protocols, ensures the reliability and reproducibility of ecotoxicological assays, enabling the anticipation and more efficient diagnosis of the harmful effects of toxic agentes in aquatic environments. The objective of this study was to evaluate the viability of laboratory cultivation of Ceriodaphnia cornuta under physical and chemical conditions similar to those of freshwater environments in a semiarid region, aiming to minimize uncertainties regarding the adaptability of test organisms in ecotoxicological assays with environmental samples. To this end, individuals of the species C. cornuta were collected from reservoirs in a semiarid region of Brazil. Subsequently, experiments were conducted with acute and chronic exposures, using different values of pH, hardness, temperature, and luminosity, based on the averages found in aquatic environments of semiarid regions and those suggested by standardized norms. Ceriodaphnia cornuta showed the highest survival and reproduction rates in water with a pH between 7.5 and 7.9, hardness of 66mg CaCO3.L-1, temperature of 25 °C ±2, and luminosity between 3000 to 3500 lux, these values are above those standardized by the Brazilian standard, demonstrating a potential viability of its cultivation under conditions similar to those of neotropical semiarid regions for use as a test organism in quality analyses of these environments. Resumo A utilização de espécies zooplanctônicas autóctones, aliada a protocolos padronizados, garante a confiabilidade e a reprodutibilidade dos ensaios ecotoxicológicos, possibilitando a antecipação e o diagnóstico mais eficiente dos efeitos nocivos de agentes tóxicos em ambientes aquáticos. O objetivo deste estudo foi avaliar a viabilidade do cultivo laboratorial de Ceriodaphnia cornuta em condições físicas e químicas semelhantes às de ambientes de água doce em região semiárida, visando minimizar as incertezas quanto à adaptabilidade dos organismos-teste em ensaios ecotoxicológicos com amostras ambientais. Para tanto, indivíduos da espécie C. cornuta foram coletados em reservatórios de uma região semiárida do Brasil. Posteriormente, foram conduzidos experimentos com exposições agudas e crônicas, utilizando diferentes valores de pH, dureza, temperatura e luminosidade, com base nas médias encontradas em ambientes aquáticos de regiões semiáridas e naquelas sugeridas por normas padronizadas. C. cornuta apresentou as maiores taxas de sobrevivência e reprodução em água com pH entre 7.5 e 7.9, dureza de 66mg CaCO3.L-1, temperatura de 25 °C ±2 e luminosidade entre 3000 a 3500 lux. Esses resultados demonstraram uma potencial viabilidade de seu cultivo em condições semelhantes às das regiões semiáridas neotropicais para uso como organismo teste em análises de qualidade desses ambientes.

Water fleas (Crustacea: Cladocera) are recently regarded as models for phylogeographic studies, but most such publications are concerned the planktonic genera, first of all, Daphnia O.F. Müller. The aim of our article is to study the phylogeographic pattern of a very common littoral chydorid Pleuroxus truncatus (O.F. Müller) based on sequences of two mitochondrial (cytochrome oxidase (COI) and 16S) and two nuclear (18S and 28S) genes. All totality of the sequences could be subdivided into two major clades, A, having a predominantly European distribution with a single exclusion, and B, having a predominantly Asian distribution, but with few populations in European Russia; the clade B is subdivided into three subclades (B1–B3) with a moderate support. Earlier derived phylogroups (subclades B1 and B2) are distributed in south portion of Western Siberia. This pattern is known for previously studied daphniids. Estimations of the major clade (A and B) and subclade differentiation time in P. truncatus based on different methods lie in the interval of ca . 0.01–0.3 Mya. Therefore, the whole revealed pattern is very young, related to Late Pleistocene and more shallow as compared to previously studied daphniids. Probably, the total population of P. truncatus was not so strongly split by the unfavorable conditions during the Pleistocene cold phases.

We studied the seasonal Delta *d15N patterns in particulate organic matter (POM < 48 Delta *mm) and crustacean zooplankton collected from a moderately eutrophic lake. Time series of POM and zooplankton showed consistent differences in Delta *d15N values between POM and different zooplankton taxa, but similar trends of steadily increasing Delta *d15N values through summer with peak values in autumn. The observed annual range in Delta *d15N was over 25 in POM and almost 17 in cladocera. We relate these marked seasonal changes in Delta *d15N values to temporal variation in inorganic nitrogen source for pelagic primary production. Ammonium (NH4+) and nitrate (NO3-) showed distinct Delta *d15N values, ammonium being considerably 15N-enriched ( Delta *d15N values ~20-30 ) compared to nitrate (< 10 ). The peak Delta *d15N values in POM and zooplankton can hence be explained by a shift from nitrate uptake to ammonium uptake by phytoplankton, as ammonium concentrations in the Jyvasjarvi epilimnion increase after lake turnover in autumn. However, such elevated Delta *d15N values were not observed during the high NH4+ concentrations after spring lake turnover, suggesting that the phytoplankton spring bloom was primarily supported by nitrate. These apparent seasonal differences in nitrogen utilisation reflect variation in species composition of the phytoplankton community. We conclude that seasonal changes in nitrogen source for phytoplankton can produce considerable differences in their Delta *d15N values, which are transmitted up the food chain to crustacean zooplankton. This has important implications for many food web studies using nitrogen stable isotopes, especially when Delta *d15N values have to be assigned to a trophic baseline.

Many aquatic organisms respond phenotypically, through morphological, behavioral, and physiological plasticity, to environmental changes. The small-size cladoceran Bosminalongirostris, a dominant zooplankter in eutrophic waters, displayed reduced growth rates in response to the presence of a toxic cyanobacterium, Microcystisaeruginosa, in their diets. The magnitude of growth reduction differed among 15 clones recently isolated from a single population. A significant interaction between clone and food type indicated a genetic basis for the difference in growth plasticity. The variation in phenotypic plasticity was visualized by plotting reaction norms with two diets. The resistance of each clone to dietary cyanobacteria was measured as the relative change in growth rates on the \"poor\" diet compared with the \"good\" diet. The enhanced resistance to M. aeruginosa in B. longirostris was derived from both the reduced slope of reaction norms and the increased mean growth rates with two diets. The large clonal variation within a B. longirostris population may contribute to local adaptation to toxic cyanobacteria and influence ecosystem function via clonal succession.

The taxonomic status of the genus Bythotrephes Leydig (Crustacea: Cladocera) has been debated since the second half of the XIX century. The most widespread view of recent decades has been that Bythotrephes is a monotypic genus, which was support by preliminary molecular data. However, the recent detailed morphological revision of this genus clearly distinguishes at least seven species. Therefore, we performed a multi-lake survey in Central Europe to give new insight into the taxonomic status of Bythotrephes by combining genetic analysis with traditional morphology-based taxonomy. Based on the morphology we identified two species in Central Europe , B. brevimanus and B. lilljeborgi , as well as hybrid forms. For the genetic analysis, we used newly obtained 113 sequences of mtDNA COI gene of the 535-bp length Bythotrephes from Central Europe and sequences downloaded from GenBank. There were no significant differences between all analyzed sequences, which supports the hypothesis that Bythotrephes is a monotypic genus, with only one highly polymorphic species. On the other hand, the results of our work could point out that the COI gene is insufficient to evaluate the taxonomic status of Bythotrephes . Nonetheless, we have identified 29 new haplotypes of mtDNA COI, and one which was the same as the haplotype found in North America and Finland. Furthermore, this haplotype was the source variant from which most other haplotypes were derived.

Chydorus sphaericus is often a dominant cladoceran zooplankton species in water bodies experiencing harmful cyanobacterial blooms. However, its relationship with toxin-producing algae remains largely unexplored. In this study, the feeding behavior of C. sphaericus on colonial cyanobacteria and potentially toxic Microcystis was investigated in a temperate, shallow, eutrophic lake. Liquid chromatographic analyses of phytoplankton marker pigments in C. sphaericus gut content revealed that pigments characteristic of cyanobacteria (identified a zeaxanthin, echinenone, and canthaxanthin) comprised the majority of its diet. Among them, colonial cyanobacteria (marked by the pigment canthaxanthin) were the highly preferred food source despite their minor contribution to phytoplankton biomass. qPCR targeting Microcystis genus-specific mcyE synthase genes, which are involved in microcystin biosynthesis, indicated that potentially toxic strains of Microcystis were present in C. sphaericus gut content throughout its temporal and spatial presence in the lake. The results suggest that the common small cladoceran in eutrophic waters, C. sphaericus, has a close trophic interaction with colonial cyanobacteria (including Microcystis) and may represent an important vector for transferring toxigenic Microcystis to the food web, even under conditions of low Microcystis biomass in the lake water.

Knowledge of reproductive rates and life cycle of the Cladocera species is essential for population dynamic studies, secondary production and food webs, as well as the management and preservation of aquatic ecosystems. The present study aimed to understand the life cycle and growth of Alona iheringula Kotov & Sinev, 2004 (Crustacea, Anomopoda, Chydoridae), a Neotropical species, as well as its DNA barcoding, providing new information on the Aloninae taxonomy. The specimens were collected in the dammed portion of the Cabo Verde River (21°26'05″ S and 46°10'57″ W), in the Furnas Reservoir, Minas Gerais State, Brazil. Forty neonates were observed individually two or three times a day under controlled temperature (25±1°C), photoperiod (12 h light/12 h dark) and feeding (Pseudokirchneriella subcapitata at a concentration of 105 cells.mL-1 and a mixed suspension of yeast and fish feed in equal proportion). Individual body growth was measured daily under optical microscope using a micrometric grid and 40× magnification. The species had a mean size of 413(±29) µm, a maximum size of 510 µm and reached maturity at 3.24(±0.69) days of age. Mean fecundity was 2 eggs per female per brood and the mean number of eggs produced per female during the entire life cycle was 47.6(±6.3) eggs per female. The embryonic development time was 1.79(±0.23) days and the maximum longevity was 54 days. The species had eight instars throughout its life cycle and four instars between neonate and primipara stage. The present study using molecular data (a 461 bp smaller COI fragment) demonstrated a deep divergence in the Aloninae subfamily.