Daphnia Longicephala Research Articles

Allelochemical run-off from the invasive terrestrial plant Impatiens glandulifera decreases defensibility in Daphnia

Invasive species are a major threat for native ecosystems and organisms living within. They are reducing the biodiversity in invaded ecosystems, by outcompeting native species with e. g. novel substances. Invasive terrestrial plants can release allelochemicals, thereby reducing biodiversity due to the suppression of growth of native plants in invaded habitats. Aside from negative effects on plants, allelochemicals can affect other organisms such as mycorrhiza fungi and invertebrates in terrestrial ecosystems. When invasive plants grow in riparian zones, it is very likely that terrestrial borne allelochemicals can leach into the aquatic ecosystem. There, the often highly reactive compounds may not only elicit toxic effects to aquatic organisms, but they may also interfere with biotic interactions. Here we show that the allelochemical 2-methoxy-1,4-naphthoquinone (2-MNQ), produced by the ubiquitously occurring invasive terrestrial plant Impatiens glandulifera, interferes with the ability of Daphnia to defend itself against predators with morphological defences. Daphnia magna and Daphnia longicephala responded with morphological defences induced by chemical cues released by their corresponding predators, Triops cancriformis or Notonecta sp. However, predator cues in combination with 2-MNQ led to a reduction in the morphological defensive traits, body- and tail-spine length, in D. magna. In D. longicephala all tested inducible defensive traits were not significantly affected by 2-MNQ but indicate similar patterns, highlighting the importance to study different species to assess the risks for aquatic ecosystems. Since it is essential for Daphnia to adapt defences to the current predation risk, a maladaptation in defensive traits when simultaneously exposed to allelochemicals released by I. glandulifera, may therefore have knock-on effects on population dynamics across multiple trophic levels, as Daphnia is a key species in lentic ecosystems.

Distinct cell proliferation patterns underlying the development of defensive crests in Daphnia longicephala

The freshwater crustacean Daphnia is well known for its expression of morphological defenses in the presence of predators. Research into this phenomenon has mostly centered on the ecology and evolution of Daphnia defenses; information is limited on the cellular mechanisms that underlie site-specific tissue growth. We aimed to determine these cellular mechanisms, specifically those associated with the development of defensive crests in D. longicephala. With the help of a cell-proliferation assay we monitored changes in the epidermal tissue of naïve and predator-exposed D. longicephala. Based on our results, we propose that cell division is delayed in favor of cell growth, which results in crest formation. Further, we identify specific regions of proliferative activity in a time-dependent manner. Defense development starts in the ventral region, before extending in the cranial and then dorsal directions. We demonstrate that these cellular changes begin as early as 2 h after predator exposure. Our results provide new insights into the cellular processes underlying morphological defense expression in Daphnia.

Brain volume increase and neuronal plasticity underly predator-induced morphological defense expression in Daphnia longicephala

Predator-induced phenotypic plasticity describes the ability of prey to respond to an increased predation risk by developing adaptive phenotypes. Upon the perception of chemical predator cues, the freshwater crustacean Daphnia longicephala develops defensive crests against its predator Notonecta spec. (Heteroptera). Chemical predator perception initiates a cascade of biological reactions that leads to the development of these morphological features. Neuronal signaling is a central component in this series, however how the nervous system perceives and integrates environmental signals is not well understood. As neuronal activity is often accompanied by functional and structural plasticity of the nervous system, we hypothesized that predator perception is associated with structural and functional changes of nervous tissues. We observe structural plasticity as a volume increase of the central brain, which is independent of the total number of brain cells. In addition, we find functional plasticity in form of an increased number of inhibitory post-synaptic sites during the initial stage of defense development. Our results indicate a structural rewiring of nerve-cell connections upon predator perception and provide important insights into how the nervous system of prey species interprets predator cues and develops cost–benefit optimized defenses.

Prey capture analyses in the carnivorous aquatic waterwheel plant (Aldrovanda vesiculosa L., Droseraceae)

We investigated the predator-prey interactions between an Australian ecotype of the carnivorous waterwheel plant (Aldrovanda vesiculosa, Droseraceae) and its potential natural prey, the water flea Daphnia longicephala (Daphniidae), which also occurs in Australia. A. vesiculosa develops snap-traps, which close within ~10–100 ms after mechanical triggering by zooplankton prey. Prey capture attempts (PCAs) were recorded via high-speed cinematography in the laboratory. From 14 recorded PCAs, nine were successful for the plant (the prey was caught), and five were unsuccessful (prey could escape), resulting in a capture rate of ~64%. The prey animals’ locomotion behaviour (antenna beat frequency and movement type) in trap vicinity or inside the open traps is very variable. Traps were mainly triggered with the second antennae. During trap closure, the animals moved only very little actively. A flight response in reaction to an initiated trap closure was not observed. However, several animals could escape, either by having a “lucky” starting position already outside the triggered trap, by freeing themselves after trap closure, or by being pressed out by the closing trap lobes. According to our observations in the successful PCAs, we hypothesize that the convex curvature of the two trap lobes (as seen from the outside) and the infolded trap rims are structural means supporting the capture and retention of prey. Our results are discussed in a broader biological context and promising aspects for future studies are proposed.

Plastic waste interferes with chemical communication in aquatic ecosystems

Environmental pollution with plastic waste has gained increasing attention, as the contamination of aquatic habitats poses a challenge to these ecosystems. Plastic waste has direct negative effects on animals such as reduced growth rate, fecundity or life span. However, the indirect effects of plastic waste, which has the ability to sorb chemicals from the surrounding media, on chemical communication have yet to be investigated. Chemical communication is crucial for aquatic organisms, e.g., to avoid predation. The planktonic water flea Daphnia (Crustacea), an important link between trophic levels, relies on info-chemicals (kairomones) to assess its current predation risk and to form inducible defences. We show that plastic waste, composed of high-density polyethylene (HDPE) and polyethylene terephthalate (PET) interferes with the formation of inducible defences in Daphnia longicephala when exposed to a combination of kairomones of Notonecta glauca and plastic waste. D. longicephala shows a reduction in all defensive traits, including body length, crest width and time until primiparity, compared to exposure to solely kairomone conditioned media. Plastic waste in the absence of kairomones had no effect on defensive traits. Since it is vital to adjust these defences to the current predation risk, any misperception can have far-reaching ecological consequences. Therefore, plastic waste can have indirect effects on organisms, which may manifest at the community level.

Antibiofilm, anti cancer and ecotoxicity properties of collagen based ZnO nanoparticles

The use of natural biopolymers in the synthesis of nanomaterials can have a low cost and eco-friendly approach. ZnO nanoparticles synthesized through biological method has been reported to have biomedical applications to control pathogenic microbes as it is cost effective compared to commonly used physical and chemical methods. In this work we would like to report the “bioinspired” synthesis of ZnO nanopowders (ZnO-NPs) using type 1 collagen. Collagen based ZnO NPs (Cl-ZnO NPs) were bio-physically characterized by UV–vis Spectroscopy, XRD, FTIR, HR-TEM, EDX and Zeta potential analysis. HR-TEM recorded the presence of hexagonal wurtzite structure of Cl-ZnO NPs with particle size ranged between 20–50 nm. Further, Cl-ZnO NPs exhibited antibacterial and antibiofilm activity against Gram positive Streptococcus mutans, Gram negative Proteus vulgaris and fungi Candida albicans at 75 μg/ml. Moreover, the cytotoxicity assay demonstrated that the Cl-ZnO NPs was not toxic to murine (RAW 264.7) macrophage cells up to 75 μg/ml. However, it exhibited cytotoxicity against human liver cancer (HepG2) cells at 75 μg/ml. The HepG2 cell viability was significantly reduced at 75 μg/ml. In addition, the ecotoxicity of Cl-ZnO NPs on the freshwater micro crustacean Daphnia longicephala showed no mortality up to 250 μg/ml. The current study clearly demonstrated that the Cl-ZnO NPs had greater potential for antimicrobial and anticancer activities.

Predator-induced defences in Daphnia longicephala: location of kairomone receptors and timeline of sensitive phases to trait formation.

ABSTRACTThe freshwater crustacean Daphnia adapts to changing predation risks by forming inducible defences. These are only formed when they are advantageous, saving associated costs when the defence is superfluous. However, in order to be effective, the time lag between the onset of predation and the defence formation has to be short. Daphnia longicephala develop huge protective crests upon exposure to chemical cues (kairomones) from its predator the heteropteran backswimmer Notonecta glauca. To analyse time lags, we determined kairomone-sensitive stages and the developmental time frames of inducible defences. Moreover, we looked at additive effects that could result from the summation of prolonged kairomone exposure. Kairomones are perceived by chemoreceptors and integrated by the nervous system, which alters the developmental program leading to defence formation. The underlying neuronal and developmental pathways are not thoroughly described and surprisingly, the location of the kairomone receptors is undetermined. We show that D. longicephala start to sense predator cues at the onset of the second juvenile instar, defences develop with a time lag of one instar and prolonged kairomone exposure does not impact the magnitude of the defence. By establishing a method to reversibly impair chemosensors, we show the first antennae as the location of kairomone-detecting chemoreceptors. This study provides fundamental information on kairomone perception, kairomone-sensitive stages, developmental time frames and lag times of inducible defences in D. longicephala that will greatly contribute to the further understanding of the neuronal and developmental mechanisms of predator-induced defences in Daphnia.

Daphnia sniff out doom with first antennae

![Figure][1] Daphnia longicephala without and with defensive crest. Photo credit: Linda Weiss. Crustaceans have a reputation for vicious weapons and impenetrable defences. However, Linda Weiss from the University of Birmingham, UK, explains that one diminutive crustacean – the water flea

Daphnia longicephala neuropeptides: Morphological description of crustacean cardioactive peptide (CCAP) and periviscerokinins in the Ctenodaphnia central nervous system

The publication of the Daphnia genome has driven research in this ecologically relevant model organism in many directions. However, information on this organism’s physiology and the relevant controlling factors is limited. In this regard, especially neuropeptides are important biochemical regulators that control a variety of cellular processes, which in combination influence physiological conditions and allow the adaptation of the internal physiological state to external conditions. Thus, neuropeptides are prime in understanding an organism’s physiology. We here aimed to detect and describe the distribution of evolutionary conserved neuropeptides including the crustacean cardioactive peptide (CCAP) and peptides of the family periviscerokinins (PVKs) in the central nervous system and the periphery of the Daphnia longicephala head region. We were able to identify a large pair of CCAP immunoreactive cells within central nervous system. In addition, in the periphery we found CCAP immunoreactive cells in the epidermis of the head with processes indicating cuticular secretion. Furthermore, we were able to identify and describe a complex neuronal circuit of PVK neuropeptides in the central nervous system. The data obtained in this study will provide important background information for future investigations aiming to unravel the cellular, neuronal and physiological pathways in a highly adaptive organism such as Daphnia.

Two threats at once: encounters with predator cues alter host life-history and morphological responses to parasite spores

Parasites and predators are ubiquitous threats in every ecosystem. Host and prey species, respectively, have evolved effective protective mechanisms which are assumed to involve costs. In this study, we analyzed potential interactions between both threats. We exposed waterfleas (Daphnia longicephala) simultaneously to parasite spores (the yeast Metschnikowia) and cues from predatory notonectids (Notonecta glauca). In response to the parasite, D. longicephala had a delayed maturation time and produced less and smaller offspring, even though the parasite developed no spores. This suggests that hosts can successfully fight off the parasite invoking defensive costs. Some of these effects were altered or even reversed by the presence of predator cues. For example, time to maturity was further delayed when the Daphnia were exposed to both threats than under parasite stress alone. In addition, more offspring were produced in the presence of both threats, although parasites alone reduced their number. However, there was no effect of parasite exposure on the expression of morphological defenses. Our results imply that the impact of parasites on host species depends strongly on the presence of further threats. Similar types of experimental approaches may enhance our understanding of the effects of multiple stressors in natural systems.

Morphology of the Daphnia nervous system: A comparative study on Daphnia pulex, Daphnia lumholtzi, and Daphnia longicephala

The freshwater crustacean Daphnia is well known for its phenotypic plasticity, in which environmental cues are perceived by the nervous system and transformed into phenotypic adaptations beneficial under current conditions. Critical knowledge regarding the distribution and localization of neuronal antigens or neurotransmitters and differentially expressed proteins is sparse. Here, we applied immunohistochemical and histological-staining methods in combination with confocal laser scanning microscopy on whole mount preparations in Daphnia pulex, Daphnia longicephala, and Daphnialumholtzi. We document the nervous system, elements of the sensory system, and cell clusters with secretory characteristics in the Daphnia head. This is the first report on the nervous system of the species D.longicephala and D.lumholtzi. The methods established in this investigation will help to foster research on specific neuronal mechanisms in this rapidly advancing model system of life science research.

LC-MS/MS-based proteome profiling in Daphnia pulex and Daphnia longicephala: the Daphnia pulex genome database as a key for high throughput proteomics in Daphnia

BackgroundDaphniids, commonly known as waterfleas, serve as important model systems for ecology, evolution and the environmental sciences. The sequencing and annotation of the Daphnia pulex genome both open future avenues of research on this model organism. As proteomics is not only essential to our understanding of cell function, and is also a powerful validation tool for predicted genes in genome annotation projects, a first proteomic dataset is presented in this article.ResultsA comprehensive set of 701,274 peptide tandem-mass-spectra, derived from Daphnia pulex, was generated, which lead to the identification of 531 proteins. To measure the impact of the Daphnia pulex filtered models database for mass spectrometry based Daphnia protein identification, this result was compared with results obtained with the Swiss-Prot and the Drosophila melanogaster database. To further validate the utility of the Daphnia pulex database for research on other Daphnia species, additional 407,778 peptide tandem-mass-spectra, obtained from Daphnia longicephala, were generated and evaluated, leading to the identification of 317 proteins.ConclusionPeptides identified in our approach provide the first experimental evidence for the translation of a broad variety of predicted coding regions within the Daphnia genome. Furthermore it could be demonstrated that identification of Daphnia longicephala proteins using the Daphnia pulex protein database is feasible but shows a slightly reduced identification rate. Data provided in this article clearly demonstrates that the Daphnia genome database is the key for mass spectrometry based high throughput proteomics in Daphnia.

Inducible defenses: The relevance of chemical alarm cues in Daphnia

Many aquatic organisms use chemical cues to recognize predators and to activate inducible defenses. In zooplankton, most of these cues are thought to be kairomones released by specific predators. However, in several other organisms, e.g., fish and amphibians, alarm signals from conspecifics also provide reliable cues. We tested whether alarm substances also act as chemical cues in Daphnia and assessed their relevance compared with predator kairomones. Water-borne cues from macerated conspecifics altered morphology in all Daphnia species tested (Daphnia cucullata, Daphnia longicephala, and Daphnia lumholtzi). However, kairomones released by feeding predators had distinctly stronger effects. In D. cucullata, we tested for the relevance of predator diet and found that the increase in relative helmet length was most pronounced when the predator was fed with conspecifics instead of heterospecifics. Cross-species experiments with alarm substances also revealed that D. cucullata is more sensitive to info-chemicals from macerated conspecifics than to chemical cues from D. magna. Unspecific alarm cues together with cues released by predators consuming prey may form a blend of chemicals that indicates predation risk and activates inducible defenses in nature.

Inducible defences in Daphnia: responses to two closely related predator species.

The predator-induced responses of two species of Australian Daphnia, with contrasting distributions and life history patterns, to the kairomones of two species of Anisops predators, were measured. Daphnia longicephala produced a large crest and attained a larger size when exposed to both predators. D. carinata sl matured earlier than D. longicephala and did not produce a crest. Surprisingly, kairomones of both predators inhibited the production of ephippia in D. carinata sl. Anisops stali, the larger of the two predator species, induced a significantly larger crest size in D. longicephala, and larger brood size in both species compared with the smaller A. gratus, indicating a quantitative but not qualitative effect of predator species on inducible defences.

The effects of a pesticide on inducible phenotypic plasticity in Daphnia

Many species of zooplankton can detect chemical signals (kairomones) released by their predators and respond with defensive morphological and life-history changes. Daphnia longicephala were exposed to five different concentrations of the carbamate insecticide, carbaryl, in the presence and absence of kairomones released by Anisops gratus (Hemiptera: Notonectidae). In the absence of Anisops kairomone, there was a negative correlation between carbaryl concentration and length and brood size at maturity. Growth and reproduction were significantly impaired at carbaryl concentrations ⩾0.32 μg/litre. There was no effect of carbaryl on age at maturity and it did not induce crest growth in the absence of kairomone. In the presence of kairomone, D. longicephala developed a large crest, but took longer to reach maturity than control animals. A concentration of 3.2 μg/litre carbaryl decreased relative crest size of 3-day-old daphnids but did not affect crest size of adults. The Anisops kairomone dramatically altered the effects of carbaryl on the life-history responses of D. longicephala at maturity. There was a positive correlation between the concentration of carbaryl and age, length, and brood size at maturity. The effects of kairomone on life-history parameters are explained using a size threshold for maturation hypothesis.

Endosulfan-enhanced crest induction in Daphnia longicephala: evidence for cholinergic innervation of kairomone receptors

Daphnia longicephala were reared from early embryogenesis in the presence or absence of crest-inducing kairomones released by Anisops grants (Notonectidae) and from birth in one of five concentrations of the organochlorine pesticide, endosulfan (0,0.1,1.0,10 or 100 ug I*1). The morph- ology of the daphnids was measured 3 days after birth and on production of the first brood of eggs. The reproductive parameters, first brood size, age at first reproduction, mean egg volume and total egg volume, were also measured. Endosulfan significantly induced crest development in 3-day-old daphnids at 0.1,1.0 and 10 ug I1 in the presence and absence of Anisops kairomone, although crest size in the absence of kairomone was only marginally greater than controls. A concentration of 10 ug 1~' endosulfan significantly enhanced crest growth of kairomone-exp osed daphnids at maturity. The Anisops kairomone alone induced a large crest in D.longicephala, reduced first brood size, mean egg volume and total egg volume, and increased age at maturity. The coefficient of variation of mean egg volume was significantly reduced by Anisops kairomone. It is hypothesized that endosulfan enhances crest development by inhibition of y-aminobutyric acid (GABA), an inhibitory neurotransmitter at cholinergic nerve junctions.