Planktonic Crustaceans Research Articles

Trehalose mediates salinity-stress tolerance in natural populations of a freshwater crustacean

Salinization poses an increasing problem worldwide, threatening freshwater organisms and raising questions about their ability to adapt. We explored the mechanisms enabling a planktonic crustacean to tolerate elevated salinity. By gradually raising water salinity in clonal cultures from 185 Daphnia magna populations, we showed that salt tolerance strongly correlates with native habitat salinity, indicating local adaptation. A genome-wide association study (GWAS) further revealed a major effect of the Alpha,alpha-trehalose-phosphate synthase (TPS) gene, suggesting that trehalose production facilitates salinity tolerance. Salinity-tolerant animals showed a positive correlation between water salinity and trehalose concentrations, while intolerant animals failed to produce trehalose. Animals with a non-functional TPS gene, generated through CRISPR-Cas9, supported the trehalose role in salinity stress. Our study highlights how a keystone freshwater animal adapts to salinity stress using an evolutionary mechanism known in bacteria, plants, and arthropods.

Application of the Biological Toxicity Effect Ratio (BER) Method for Advancing Water Quality Criteria Derivation.

Water quality criteria (WQC) serve as a scientific foundation for pollutant risk assessment and control in aquatic ecosystems. The development of regionally differentiated WQC tailored to specific regional characteristics has become an emerging trend. However, the current WQC is constrained by a lack of regional species toxicity data. To address these limitations, this study proposes the biological toxicity effect ratio (BER) method, which indirectly reflects the toxicity sensitivity of the overall aquatic ecosystem through the toxicity information on a limited number of species, enabling rapid WQC prediction. Using the established WQC in China and the USA as a case study, we combined mathematical derivation and data validation to evaluate the BER method. Among various species-taxon groups of freshwater organisms, planktonic crustaceans demonstrated the highest predictive accuracy. Our analysis further revealed that species toxicity sensitivity and regional variability jointly influence the prediction accuracy. Regardless of the evaluation indexes, planktonic crustaceans emerged as the most suitable species-taxon group for the BER method. Additionally, the BER method is particularly applicable to pollutants with conserved mechanisms across species. This study systematically explores the feasibility of using the BER method and offers new insights for deriving regionally differentiated WQC.

Strain‐dependent and host genotype–dependent priority effects in gut microbiome assembly affect host fitness in Daphnia

AbstractThe arrival order of species can strongly influence the early assembly of ecological communities. Such events, known as priority effects, are documented in various ecological settings, but remain understudied within the context of the gut microbiome. Given the fundamental link between the gut microbiome and host health, exploring the potential role of priority effects in shaping the assembly and development of microbial communities within the gut becomes imperative. Using the freshwater planktonic crustacean Daphnia magna as a model system, we manipulated the immigration order of three bacterial strain pairs in two germ‐free genotypes and quantified gut microbiome composition and host fitness at two time points, namely day 8 and day 12. Priority effects were observed; however, their presence, amplitude, and direction (suppressive or facilitative) were found to be contingent on the identity of bacterial strain and host genotype. These findings were accompanied by notable differences in Daphnia life history traits across inoculation order treatments, shedding light on the tangible consequences of priority effects triggered by the sequence of bacterial strain arrival in the gut environment, for host fitness. Our results thus highlight the complex nature of priority effects in gut community assembly, their strain/genotype specificity, and their potential impact on the host.

Long-term balancing selection for pathogen resistance maintains trans-species polymorphisms in a planktonic crustacean

Balancing selection is an evolutionary process that maintains genetic polymorphisms at selected loci and strongly reduces the likelihood of allele fixation. When allelic polymorphisms that predate speciation events are maintained independently in the resulting lineages, a pattern of trans-species polymorphisms may occur. Trans-species polymorphisms have been identified for loci related to mating systems and the MHC, but they are generally rare. Trans-species polymorphisms in disease loci are believed to be a consequence of long-term host-parasite coevolution by balancing selection, the so-called Red Queen dynamics. Here we scan the genomes of three crustaceans with a divergence of over 15 million years and identify 11 genes containing identical-by-descent trans-species polymorphisms with the same polymorphisms in all three species. Four of these genes display molecular footprints of balancing selection and have a function related to immunity. Three of them are located in or close to loci involved in resistance to a virulent bacterial pathogen, Pasteuria, with which the Daphnia host is known to coevolve. This provides rare evidence of trans-species polymorphisms for loci known to be functionally relevant in interactions with a widespread and highly specific parasite. These findings support the theory that specific antagonistic coevolution is able to maintain genetic diversity over millions of years.

Adverse effects of the 5-alpha-reductase inhibitor finasteride on Daphnia magna: Endocrine system and lipid metabolism disruption

Finasteride, a steroid 5-alpha reductase inhibitor, is commonly used for the treatment of benign prostatic hyperplasia and hair loss. However, despite continued use, its environmental implications have not been thoroughly investigated. Thus, we investigated the acute and chronic adverse impacts of finasteride on Daphnia magna, a crucial planktonic crustacean in freshwater ecosystems selected as bioindicator organism for understanding the ecotoxicological effects. Chronic exposure (for 23 days) to finasteride negatively affected development and reproduction, leading to reduced fecundity, delayed first brood, reduced growth, and reduced neonate size. Additionally, acute exposure (< 24 h) caused decreased expression levels of genes crucial for reproduction and development, especially EcR-A/B (ecdysone receptors), Jhe (juvenile hormone esterase), and Vtg2 (vitellogenin), with oxidative stress-related genes. Untargeted lipidomics/metabolomic analyses revealed lipidomic alteration, including 19 upregulated and 4 downregulated enriched lipid ontology categories, and confirmed downregulation of metabolites. Pathway analysis implicated significant effects on metabolic pathways, including the pentose phosphate pathway, histidine metabolism, beta-alanine metabolism, as well as alanine, aspartate, and glutamate metabolism. This comprehensive study unravels the intricate molecular and metabolic responses of D. magna to finasteride exposure, underscoring the multifaceted impacts of this anti-androgenic compound on a keystone species of freshwater ecosystems. The findings emphasize the importance of understanding the environmental repercussions of widely used pharmaceuticals to protect biodiversity in aquatic ecosystems.

Трансформація оселищ і її вплив на зообіоту

The history of the use of the term “habitat” is considered. It is emphasized that this term refers to the habitat of a particular animal species or population and is determined by their ranges. The factors that lead to the destruction of habitats of many populations on the lowlands and in the highlands of the Ukrainian Carpathians are indicated. Attention is drawn to the degradation of mountain lakes and streams as habitats for aquatic hydrobionts. Among the factors that cause the destruction of habitats, the factors of both natural and anthropogenic origin are identified: climate change, absolute protection of territories, demutational processes, uncontrolled recreation activities, changes in traditional land use, water chemiсal composition and pollution, the appearance of invasive plants, urbanization, etc. The synergistic effect of these factors leads to rapid habitat change, and thus to the loss of adaptive capacity of individuals of different species to the changed conditions of their habi­tats. Among the objects of our study are such taxa as planktonic crustaceans (Cladocera), ants (Formicidae), lampreys (Cyclostomata), ray-finned fish (Actinopterygii), amphibians (Amphibia) and birds (Aves). It was found, in particular, that deciduous forest habitats are the most favorable for the existence of a significant diversity of ants. The mega-habitats for amphibians were identified as a complex of individual habitats that vary during the vegetation season and are connected by migration routes. The key habitat in Western Polissia, as an example, can be the Unychi wetland, which is home to a number of rare bird species. The nest-building behavior of birds under the influence of anthropogenic factors also undergoes changes - its species-specific appearance and composition of nesting materials are transformed in response to habitat pollution. In addition, the study showed that the use of invasive trees and shrubs for urban greenery has a negative impact on the diversity of urban bird fauna, as it paradoxically reduces the number of nesting and foraging habitats for birds. It is proposed to identify key habitats for the populations of rare and endangered animal species within the protected areas and on the non-protected ones, to indicate their locations and the type of management approach (protection, restoration, reconstruction, etc.).

TROPHIC SPECTRUM AND FORAGING MODE OF LISSOTRITON VULGARIS IN A TEMPORARY POND OF THE CITY OF RIVNE, UKRAINE

The article summarizes the state of research on the trophic spectrum and foraging mode of the common newt in Europe in general and in Ukraine in particular. It is concluded that the level and diversity of such studies abroad is high compared to Ukraine. The relevance of such studies in temporary ponds is determined. The article analyzes the trophic spectrum and feeding mode of the common newt in temporary pond in Rivne. The stomach contents samples of 46 individuals of L. vulgaris were obtained, in which 2309 trophic objects were found. Food of animal origin prevails in the trophic spectrum of L. vulgaris and makes up 97%. Food objects of plant origin make up only 1% and mineral partic les – 2%. It was found that the most abundant food items are the larvae of the lake flies (Chironomidae) – 53% and crustaceans (Cladocera: Daphniidae; Chydoridae; Copepoda: Cyclopidae; Ostracoda) – 46%. The diet of L. vulgaris is significantly dominated by objects originating from the aquatic environment – 98.2% of the total number. Individuals of this species will capture prey of quite different sizes. The smallest food objects of the studied newts are planktonic crustaceans Chydoridae: 0.3–0.5 mm, the largest are earthworms Lumbricidae: 150–200 mm. It was found that the food spectrum of the newt changes during the season and depends on the life cycles of prey. In spring, when the trophic resources of the temporary pond are limited, crustaceans, in particular daphnia (Daphnіidae) and shell crustaceans (Ostracoda), dominate in the diet of the newt. During this period, the consumption of shed skin fragments, plant fragments, grains of sand is higher and larvae of the lake flies (Chironomidae) are absent, but in the second decade of May they dominate (more than 70%) in the diet. It was found that L. vulgaris uses different foraging mode in different periods. The predominance of crustaceans (daphnia, cyclopes) in the diet at the beginning of the season indicates that newts use active foraging tactics. In late April-May, we observed a significant predominance of larvae of the lake flies, which indicates that L. vulgaris uses sit-and-wait foraging. It was found that the foraging behavior of the newt in temporary ponds in Rivne is labile and varies depending on environmental conditions and its trophic offer.

Preliminary hazard assessment of a new nature-inspired antifouling (NIAF) agent

A recently synthesized aminated 3,4-dioxygenated xanthone (Xantifoul2) was found to have promising antifouling (AF) effects against the settlement of the macrofouler Mytilus galloprovincialis larvae. Preliminary assessment indicated that Xantifoul2 has reduced ecotoxicological impacts: e.g., being non-toxic to the marine crustacea Artemia salina (<10 % mortality at 50 μM) and showing low bioconcentration factor in marine organisms. In order to meet the EU Biocidal Product Regulation, a preliminary hazard assessment of this new nature-inspired antifouling (NIAF) agent was conducted in this work. Xantifoul2 did not affect the swimming ability of the planktonic crustacean Daphnia magna, the growth of the diatom Phaeodactylum tricornutum, and the cellular respiration of luminescent Gram-negative bacteria Vibrio fischeri, supporting the low toxicity towards several non-target marine species. Regarding human cytotoxicity, Xantifoul2 did not affect the cell viability of retinal human cells (hTERT-RPE-1) and lipidomic studies revealed depletion of lipids involved in cell death, membrane modeling, lipid storage, and oxidative stress only at a high concentration (10 μM). Accelerated degradation studies in water were conducted under simulated sunlight to allow the understanding of putative transformation products (TPs) that could be generated in the aquatic ecosystems. Both Xantifoul2 and photolytic-treated Xantifoul2 in the aqueous matrix were therefore evaluated on several nuclear receptors (NRs). The results of this preliminary hazard assessment of Xantifoul2, combined with the high degradation rates in water, provide strong evidence of the safety of this AF agent under the evaluated conditions, and provide the support for future validation studies before this compound can be introduced in the market.

Benthic assemblages in relation to planktonic assemblages in a eutrophic, thermally stratified reservoir

Few studies have explored the relationship between benthic and planktonic assemblages in reservoirs, despite their role in food chains and maintaining ecological functions. Macroinvertebrates play a crucial role in food webs and contribute about 42% of whole-lake secondary productivity. Therefore, their status is vital for maintaining good ecological functions. In this study, we selected Nanwan Reservoir, a eutrophic thermally stratified reservoir in China, to evaluate the community of macroinvertebrates in different seasons and explore the relationships between macroinvertebrate assemblages and different planktonic groups, including phytoplankton, protozoans, rotifers, and planktonic crustaceans. Cyanophyta and Bacillariophyta dominated the phytoplankton assemblages, and their proportions varied with seasons. The bad community of macroinvertebrates in summer, autumn, and winter could be attributed to the excessive growth of Cyanophyta or other phytoplankton. Based on the results of partial least squares regression, an algorithm used for prediction, we determined that the excessive growth of algae, crustaceans, protozoans, and Cyanophyta was detrimental to the development of macroinvertebrates, and was indicative of high nutrient loads in the reservoir. However, the growth of Bacillariophyta, Chrysophyta, and Euglenophyta was advantageous to macroinvertebrate assemblages and indicated a better ecological condition of the reservoir. The results of partial least squares structural equation modeling demonstrated close associations between phytoplankton and both zooplankton and macroinvertebrates, indicating their interdependence in this reservoir system. Our study results imply that the status of macroinvertebrates can be predicted by the abundance of some planktonic assemblages, and cost savings from selecting one of the planktonic groups to monitor ecological conditions could be accomplished in future studies.

Taxonomic diversity of marine planktonic ‘y-larvae’ (Crustacea: Facetotecta) from a coral reef hotspot locality (Japan, Okinawa), with a key to y-nauplii

The enigmatic ‘y-larvae’ (Thecostraca: Facetotecta) are microscopic marine planktonic crustaceans that were discovered more than a century ago, yet to this day their adults remain unknown. Despite occurring locally in large diversities, and therefore presumably being of ecological importance, only 17 species have been described globally, rendering it practically impossible to identify any y-larval specimen from any locality. The fact that species have been based on different life stages (nauplii and/or cyprids) further hampers identification. Y-larvae include many forms with planktotrophic (feeding) nauplii and even more with lecithotrophic (non-feeding) nauplii. At one coral-reef locality on the shore of Sesoko Island (Okinawa, Japan), extensive fieldwork in 2018 and 2019 confirmed an enormous taxonomic diversity of y-larvae there. Here, we present morphological diagnoses and an identification key for 34 lecithotrophic y-naupliar types (or morphospecies), which will correspond minimally to the same number of species when described. As a temporary measure, all are referred to by alphabetical parataxonomic designations, except for three that have been formally described already within the genus Hansenocaris Itô, 1985. To this should be added an additional 7–9 planktotrophic y-naupliar morphospecies, which are only treated briefly. Most often, y-larval taxonomy has been based on the cyprid stage, but the large morphological diversity of y-nauplii suggests that nauplii are at least as important for taxonomy. Lecithotrophic y-nauplii display a multitude of body shapes, the form-evolution of which is discussed here with reference to a recent molecular phylogeny of Facetotecta partly based on material from the same site. An indirect estimate of the relative abundances of all 34 lecithotrophic y-naupliar morphospecies is presented, based on laboratory-reared final-instar specimens. This treatment is intended as a step towards a proper taxonomy and a revised classification of Facetotecta, which will involve detailed descriptions of both nauplii and cyprids. Until such work progresses, the present overview of the y-naupliar fauna of a single Okinawan locality known to be a hotspot of y-larval diversity is offered as a baseline for further surveys of Facetotecta elsewhere in the Indo-West Pacific and beyond.

Plant-Derived Products Selectively Suppress Growth of the Harmful Alga Prymnesium parvum

Prymnesium parvum is a harmful alga found in brackish waters worldwide whose toxins can be lethal to aquatic organisms. Established field methods to control blooms of this species, however, are unavailable. Earlier studies showed that various extracts of giant reed (Arundo donax) can suppress P. parvum growth and that ellipticine, an allelochemical present in giant reed, is a potent algicide against this species. The unintended effects of giant reed products on nontarget organisms, however, are not fully understood. This study determined the effects of giant reed leachate (aqueous extract of dried chips) and ellipticine on growth of P. parvum and the green microalga Chlorella sorokiniana; survival and reproduction of the planktonic crustacean Daphnia pulex; and hatching success, larval survival, and larval swimming behavior of the teleost fish Danio rerio. Leachate made with 3 g chips L−1 was lethally toxic to P. parvum and D. pulex, stimulated C. sorokiniana growth, and impaired D. rerio behavior. Leachate at 1 g L−1 fully suppressed P. parvum growth, had moderate effects on D. pulex reproductive output, and had no effects on D. rerio. Ellipticine at 0.01 mg L−1 irreversibly inhibited P. parvum growth, acutely but reversibly inhibited C. sorokiniana growth, slightly delayed D. pulex reproduction, and had no effects on D. rerio. These observations suggest that when applied at appropriate concentrations, natural products derived from giant reed can be used as tools to specifically control P. parvum growth with minimal effects on nontarget species.

Feeding and trophic interactions of plankton Crustaceans in the pelagic zone of the Azabachye Lake

Characteristics of feeding mechanisms, forage composition and methods of analysis of the diet of plankton crustacean are demonstrated based on reviewed and author’s data. Preferable forage species for the mass plankton crustaceans Cyclops scutifer and Daphnia galeata in the lake Azabachye were figured out using methods of population ecology. It is revealed, that reproduction of the cyclops and daphnia populations prospers due to Aulacoseira subarctica. In the periods of poor vegetation of the diatom the cyclops have been feeding on shell-less rotifers, and in particular years – on the diatoms of the genera Stephanodiscus. In the years of vigorous bloom of Bacillariophyta the daphnias filter small cells of diatom (S. minutulus) or blue-green (Gloeocapsa sp.) algae. In case of suggested similarity in the forage organisms between small numbered Eurytemora kurenkovi and abundant C. scutifer, there was no competition observed between the copepods. The main forage component for predator Leptodora kindti was juvenile D. galeata. It is concluded based on the analysis, that intense competition between plankton crustaceans does not raise in the Azabachye Lake.

Acute and chronic effects of triclosan on the behavior, physiology, and multigenerational characteristics of the water flea Moina macrocopa

Triclosan, a chlorinated biphenyl ether is widely used in industrial products and cosmetics due to its antibiotic activity. Although relatively levels of triclosan have been detected in aquatic ecosystems, limited information is available regarding the acute and chronic impacts of triclosan on aquatic invertebrates, especially planktonic crustaceans. In this study, we analyzed the acute (24 h) and chronic (14 days exposure across three generations) effects of different concentrations of triclosan [1/10 of the no observed effect concentration (NOEC), the NOEC, and 1/10 of the LC50] calculated from the 24 h acute toxicity value, on the water flea Moina macrocopa. In the acute exposure experiment, the 1/10 LC50 value of triclosan significantly reduced survival, feeding rate, thoracic limb activity, heart activity, and acetylcholinesterase activity. In response to the 1/10 LC50 value, intracellular reactive oxygen species increased along with elevated levels of malondialdehyde and glutathione. Enzymatic activities of catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase were significantly increased by the 1/10 LC50 value, suggesting active protection of the antioxidant defense system against oxidative stress. Chronic exposure to the 1/10 NOEC and NOEC values revealed multigenerational adverse impacts of triclosan. The second generation was found to be the most sensitive to triclosan, as the NOEC value significantly reduced the survival rate, body length, and the number of neonates per brood, along with a delayed hatching period. Taken together, these results indicate that even sublethal levels of triclosan can have detrimental effects on the water flea population's maintenance through intergenerational toxicity.

QSAR assessment of aquatic toxicity potential of diverse agrochemicals

ABSTRACT The fast-increasing number of commercially produced chemicals challenges the experimental ecotoxicity assessment methods, which are costly, time-consuming, and dependent on the sacrifice of animals. In this regard, Quantitative Structure-Property/Activity Relationships (QSPR/QSAR) have led the way in developing ecotoxicity assessment models. In this study, QSAR models have been developed using the pEC50 values of 82 diverse agrochemicals or agro-molecules against a planktonic crustacean Daphnia magna with easily interpretable 2D descriptors. Moreover, a link among octanol-water partition coefficient (KOW), bio-concentration factor (BCF), and critical body residue (CBR) has been addressed, and their imputation for the prediction of the toxicity endpoint (EC50) has been done with an objective of the advanced exploration of several ecotoxicological parameters for toxic chemicals. The developed partial least squares (PLS) models were validated rigorously and proved to be robust, sound, and immensely well-predictive. The final Daphnia toxicity model derived from experimental derived properties along with computed descriptors emerged better in statistical quality and predictivity than those obtained solely from computed descriptors. Additionally, the pEC50 and other important properties (log KOW, log BCF, and log CBR) for a set of external agro-molecules, not employed in model development, were predicted to show the predictive ability of the models.

Dataset of Contamination (2009–2022) Legacy Contaminants (PCB and DDT) in Zooplankton of Lake Maggiore (CIPAIS, International Commission for the Protection of Italian-Swiss Waters)

In this paper, we describe a 13-year (2009–2022) dataset of legacy POP concentrations (DDTtot and sumPCB14 from 2016 isomers and congeners concentrations are also reported) in the planktonic crustaceans of Lake Maggiore (≥450 µm size fraction). The data were collected in the framework of a monitoring program finalized to assess the presence of pollutants in the lake biota, including zooplankton organisms directly preyed by fish. The data report both concentration of DDTtot and sumPCB14 in the zooplankton and the standing stock density and biomass of the population in each season. The dataset allows for detecting changes in the concentration over the long term and within a year, thus providing evidence for the seasonal and the plurennial variations in the presence of these pollutants in the lake. They also provide a basis for further studies aimed at modeling paths and the fate of persistent organic pollutants, for which the amount of toxicants stocked in the zooplankton compartment linked to fish is a crucial estimate.

Acute and Chronic Effects of the Antifouling Booster Biocide Diuron on the Harpacticoid Copepod Tigriopus japonicus Revealed through Multi-Biomarker Determination

Diuron, an additive biocide in antifouling paints, is widely employed to curtail the attachment of organisms on submerged surfaces in aquatic structures. Despite the detection of diuron in aquatic ecosystems, information regarding its acute and chronic impacts on aquatic invertebrates, particularly planktonic crustaceans, remains limited. In this study, we analyzed the acute (24 h) and chronic (12 days exposure across three generations) effects of different concentrations of diuron (1/10 of the no observed effect concentration (NOEC), the NOEC, and 1/10 of the lethal concentration 50% (LC50), derived from the 24 h acute toxicity value of 1152 μg L−1) on the harpacticoid copepod Tigriopus japonicus. The acute exposure experiment indicated that the 1/10 LC50 value of diuron significantly reduced the copepod’s feeding rate and acetylcholinesterase activity. In response to the 1/10 LC50 value, the intracellular reactive oxygen species were elevated alongside increased malondialdehyde levels, while the glutathione content was depleted. The enzymatic activities of glutathione S-transferase, catalase, and superoxide dismutase were significantly enhanced by the 1/10 LC50 value, suggesting a proactive role of the antioxidant defense system against oxidative stress. Conversely, the activities of glutathione peroxidase and glutathione reductase enzymes were increased at the NOEC value, while their values were reduced by the 1/10 LC50 value. Chronic exposure to 1/10 NOEC and NOEC values revealed the adverse multigenerational effects of diuron. The second generation exhibited the most sensitivity to diuron, with the NOEC value notably reducing survival rate, body length, nauplius-to-adult development, neonates per brood count, and extending the reproduction period. Taken together, our findings underscore that even sublethal diuron levels can adversely impact copepod populations across generations through intergenerational toxicity.

Mercury concentrations in Antarctic zooplankton with a focus on the krill species, Euphausia superba

The Antarctic is the most isolated region in the world; nevertheless, it has not avoided the negative impact of human activity, including the inflow of toxic mercury (Hg). Hg deposited in the Antarctic marine environment can be bioavailable and accumulate in the food web, reaching elevated concentrations in high-trophic-level biota, especially if methylated. Zooplankton, together with phytoplankton, are critical for the transport of pollutants, including Hg to higher trophic levels. For the Southern Ocean ecosystem, one of the key zooplankton components is the Antarctic krill Euphausia superba, the smaller euphausiid Thysanoessa macrura, and the amphipod Themisto gaudichaudii – a crucial food source for most predatory fish, birds, and mammals. The main goal of this study was to determine the Hg burden, as well as the distribution of different Hg forms, in these dominant Antarctic planktonic crustaceans. The results showed that the highest concentrations of Hg were found in T. gaudichaudii, a typically predatory taxon. Most of the Hg in the tested crustaceans was labile and potentially bioavailable for planktivorous organisms, with the most dangerous methylmercury (MeHg) accounting for an average of 16 % of the total mercury. Elevated Hg concentrations were observed close to the land, which is influenced by the proximity to penguin and pinniped colonies. In areas near the shore, volcanic activity might be a possible cause of the increase in mercury sulfide (HgS) content. The total Hg concentration increased with the trophic position and ontogenetic stage of predation, specific to adult organisms. In contrast, the proportion of MeHg decreased with age, indicating more efficient demethylation or elimination. The Hg magnification kinetics in the study area were relatively high, which may be related to climate-change induced alterations of the Antarctic ecosystem: additional food sources and reshaped trophic structure.

Attachment and Release of Water Fleas' Ephippia on a Medium-Sized Waterfowl's Leg for Migration.

Planktonic crustaceans of the genus Daphnia live in aquatic environments. Although they lack walking and flying capabilities, they have developed adaptations that facilitate the dispersal of their dormant forms, ephippia, to cross terrestrial barriers and reach neighborhood water bodies. It increases the survival rate of their species. It is reported that one of the ways this spread occurs is the transport of their ephippia through waterfowls' legs. Yet, little is known about how these ephippia are initially attached to the waterfowls' legs. In this work, using the legs of American Pekin ducks as test samples, we found that a "coating" mechanism might play a significant role in this attachment and that surface tension-induced attraction might have a secondary effect on it. Furthermore, we demonstrated that, no matter whether a duck's leg was inserted into water at a high or low speed, an ephippium could be released from the leg.

Differential expression of gluconeogenesis-related transcripts in a freshwater zooplankton model organism suggests a role of the Cori cycle in hypoxia tolerance.

Gluconeogenesis (GNG) is the process of regenerating glucose and NAD+ that allows for continued ATP synthesis by glycolysis during fasting or in hypoxia. Recent data from C. elegans and crustaceans challenged with hypoxia show differential and tissue-specific expression of GNG-specific genes. Here we report differential expression of several GNG-specific genes in the head and body of a model organism, Daphnia magna, a planktonic crustacean, in normoxic and acute hypoxic conditions. We predict that GNG-specific transcripts will be enriched in the body, where most of the fat tissue is located, rather than in the head, where the tissues critical for survival in hypoxia, the central nervous system and locomotory muscles, are located. We measured the relative expression of GNG-specific transcripts in each body part by qRT-PCR and normalized them by either the expression of a reference gene or the rate-limiting glycolysis enzyme pyruvate kinase (PK). Our data show that of the three GNG-specific transcripts tested, pyruvate carboxylase (PC) showed no differential expression in either the head or body. Phosphoenolpyruvate carboxykinase (PEPCK-C), on the other hand, is upregulated in hypoxia in both body parts. Fructose-1,6-bisphosphatase (FBP) is upregulated in the body relative to the head and upregulated in hypoxia relative to normoxia, with a stronger body effect in hypoxia when normalized by PK expression. These results support our hypothesis that Daphnia can survive hypoxic conditions by implementing the Cori cycle, where body tissues supply glucose and NAD+ to the brain and muscles, enabling them to continuously generate ATP by glycolysis.

Effect of heavy metals on the energy metabolism in the brackish water flea Diaphanosoma celebensis

Heavy metals such as lead (Pb), cadmium (Cd), and arsenic (As) are of great concern in aquatic ecosystems because of their global distribution, persistence, and biomagnification via the food web. They can induce the expression of cellular protective systems (e.g., detoxification enzymes and antioxidant enzymes) to protect organisms from oxidative stress, which is a high-energy-consuming process. Thus, energy reserves (e.g., glycogen, lipids, and proteins) are utilized to maintain metabolic homeostasis. Although a few studies have suggested that heavy metal stress can modulate the metabolic cycle in crustaceans, information on changes in energy metabolism under metal pollution remains lacking in planktonic crustaceans. In the present study, the activity of digestive enzymes (amylase, trypsin, and lipase) and the contents of energy storage molecules (glycogen, lipid, and protein) were examined in the brackish water flea Diaphanosoma celebensis exposed to Cd, Pb, and As for 48 h. Transcriptional modulation of the three AMP-activated protein kinase (AMPK) and metabolic pathway-related genes was further investigated. Amylase activity was highly increased in all heavy metal-exposed groups, whereas trypsin activity was reduced in Cd- and As-exposed groups. While glycogen content was increased in all exposed groups in a concentration-dependent manner, lipid content was reduced at higher concentrations of heavy metals. The expression of AMPKs and metabolic pathway-related genes was distinct among heavy metals. In particular, Cd activated the transcription of AMPK-, glucose/lipid metabolism-, and protein synthesis-related genes. Our findings indicate that Cd can disrupt energy metabolism, and may be a potent metabolic toxicant in D. celebensis. This study provides insights into the molecular mode of action of heavy metal pollution on the energy metabolism in planktonic crustaceans.