Rapid Adaptation And Molecular Mechanism Of Freshwater Clover Resistance To Microcystis

Prey should develop adaptive strategies as much as they can to reduce predation risks. Some adaptive strategies of prey are likely to harm or even kill consumers. Correspondingly, consumers had to develop adaptations (i.e., consumer offense) to overcome prey defenses. The most profitable systems in which to pursue the consequences of consumer offense should be those in which prey can have negative effects on consumer fitness. Although adaptations by consumers are less studied, interaction of cyanobacteria and cladocera is condiered as an ideal model to investigate predation affected by consumer offense.Cladocera species occur in lakes and ponds on every continent, where they consistently play a significant ecological role in food-web dynamics. Cladocera is a pelagic filter-feeding zooplankter with the potential for high population growth rate. Cladoceran food-web interactions, both as a primary consumer of phytoplankton and as a key food source for secondary consumers (e.g. fish, prawn), define it as a strong ecological interactor. Its combined effects on phytoplankton grazing and nutrient cycling, along with its role as a preferred prey species for secondary consumers, cause cladocera to occupy a uniquely significant position in the pelagic ecosystem of many lakes. Over the past 200 years, freshwaters around the world have been negatively impacted by nutrient inputs from agricultural, industrial, and urban development. One of the negative consequences of eutrophication is the proliferation of harmful cyanobacterial blooms, which represents one of the greatest threats to the quality, usage, ecological integrity, and sustainability of our water resources worldwide. When abundant, cyanobacteria can negatively affect herbivorous zooplankton as a result of poor food quality or toxic secondary metabolites. However, the generality of this negative correlation between cyanobacterial abundance and cladoceran fitness has recently been debated based on laboratory and field-based studies. To withstand toxic cyanobacteria, some cladocera species have evolved adaptations to enhance their ability to digest cyanobacterial toxins. Related studies have shown that adaptations in cladocera to toxic cyanobacteria occur across eutrophic lakes and that the effects of cladocera resistance on algal abundance can be as important as the presence or absence of cladocera. One of the major questions in evolutionary ecology is to understand how species have adapted to different environments and how the underlying changes in morphology, physiology and behavior relate to modifications in the corresponding genes. Therefore, the present research explored the rapid adaptation to cyanobacteria in cladocera species and its potential molecular mechanism.1. Effects of maternal consumption of nontoxic Microcystis on resistance to toxic Microcystis in Daphnia magnaCyanobacteria blooms often comprise both non-toxic and toxic species and strains. Populations of some zooplankton, including Daphnia, have been shown to adapt locally to toxic Microcystis through maternal effects. However, Microcystis populations vary spatially and temporally in the absolute and relative abundances of non-toxic and toxic genotypes. We examined variation in induction of tolerance to toxic cyanobacteria in offspring from two Daphnia magna clones (JS and AH) fed diets containing Scenedesmus by itself or in combination with either a non-toxic or a toxic clone of Microcystis aeruginosa. The diets containing Microcystis included relatively more cyanobacteria with each week of the three week experiment (week 1-10%, week 2-20%, week 3-40%). Daphnia neonates were collected from these three treatments at the end of the third week and fed a diet containing Scenedesmus and toxic Microcystis for three weeks before a suite of life-history, physiological, and biochemical measurements were made on the surviving animals.Neonates from mothers fed toxic and non-toxic Microcystis showed enhanced growth and reproduction compared to neonates produced from mothers fed only Scenedesmus. Our results showed that Daphnia magna neonates can be induced to tolerate toxic cyanobacteria when their mothers are fed diets containing non-toxic or toxic strains of cyanobacteria. Furthermore, elevated RNA-DNA ratio, superoxide dismutase activity and catalase activity in neonates fed diets containing non-toxic or toxic Microcystis clones suggested that the mechanisms behind these observations involved processes associated with metabolism and antioxidation. Our study shows that non-toxic cyanobacteria can induce tolerance to toxic cyanobacteria and further elucidates the general importance of maternal effects on cyanobacteria tolerance in herbivorous zooplankton.2. Effects of maternal warming on resistance to toxic Microcystis in two body-sized cladoceraElevated temperatures and nutrient can favor phytoplankton dominance by cyanobacteria, which can be toxic to zooplankton. This study focused on the effects of maternal exposure to elevated temperatures on the tolerance of zooplankton offspring to toxic cyanobacteria. Three different maternal thermal environments were used to examine population fitness in the offspring of two cladoceran species that vary in size, including the larger-sized Daphnia similoides and the smaller-sized Moina macrocopa, directly challenged by toxic Microcystis. Daphnia and Moina mothers exposed to elevated temperatures produced offspring that were more resistant to Microcystis. Interestingly, offspring from Moina fed toxic Microcystis performed better than Daphnia offspring, which could partially explain the dominance of small cladocerans during cyanobacterial blooms. Such findings may result from life-history optimization of mothers in different temperature environments.The present study emphasizes the importance of maternal effects on zooplankton resistance to cyanobacteria mediated through environmental warming and further highlights the complexities associated with the factors that influence zooplankton-cyanobacteria interactions.3. Arginine kinase in the cladoceran Daphnia magna:cDNA sequencing and expression in association with resistance to toxic MicrocystisPrevious chapters revealed that Daphnia had ability to resist toxic Microcystis, yet little is known about the physiology of zooplankton behind these phenomena. One possibility to induce more tolerance is to elevate energy production, thereby adding more energy allocation to detoxification expenditure. It is assumed that arginine kinase (AK) serves as a core in temporal and spatial adenosine triphosphate (ATP) buffering in cells with high fluctuating energy requirements. To test this hypothesis, we studied the energetic response of Daphnia magna exposed to a toxic strain of Microcystis aeruginosa, PCC7806. Arginine kinase of D. magna (Dm-AK) was successfully cloned. An ATP-gua PtransN domain which was described as a guanidine substrate specificity domain and an ATP-gua Ptrans domian which was responsible for binding ATP were both identified in Dm-AK. Phylogenetic analysis of AKs in a range of arthropod taxa suggested that Dm-AK was as dissimilar to other crustaceans as it was to insects. Dm-AK transcript level and ATP content in the presence of M. aeruginosa were significantly lower than those in the 100%Scenedesmus obliquus, whereas the two parameters in the neonates whose mothers had been previously exposed to M. aeruginosa were significantly higher than those of mother fed with pure S. obliquus. These findings of the study implied that Dm-AK might play an essential role in the coupling of energy production and utilization and the resistance against cyanobacterial blooms.4. Stress-responsive expression of a glutathione S-transferase (delta) gene Daphnia magna challenged by microcystin-producing and microcystin-free Microcystis aeruginosaPrevious In vitro experiments indicated that glutathione-S-transferase (GST) may act as the first step of detoxification in Daphnia by conjugating microcystins (MCs) with glutathione. The GST family is categorized into many classes, and different classes present distinct responses to MC detoxification. However, to date, the molecular mechanism of single class GST participation in buffering the toxic effects of MCs in Daphnia remain poorly known. In the present study, a full-length delta-GST cDNA of Daphnia magna (Dm-dGST) was isolated and characterized through bioinformatics. Differential gene expression studies revealed that short-term exposure to microcystin-producing (MP) M. aeruginosa increased Dm-dGST transcript levels. By contrast, long-term exposure to MP or microcystin-free (MF) M. aeruginosa decreased Dm-dGST transcript levels. Together with changes in three other antioxidation biomarkers (catalase, CuZn-and Mn-superoxide dismutase), we conclude that Dm-dGST could potentially biotransform MCs to reduce their toxicity. The present study highlights the importance of Dm-dGST in response to MC toxicity and may thus facilitate future research on the molecular mechanisms of MC tolerance in zooplankton under an increasing eutrophic world.5. Changes in iTRAQ-based proteomic profiling of the cladoceran Daphnia magna exposed to microcystin-producing (MP) and microcystin-free (MF) Microcystis aeruginosaThe mass occurrences of toxic cyanobacteria strongly affect freshwater zooplankton communities, especially the unselective filter feeder Daphnia. However, the molecular mechanisms of cyanobacterial toxicity remain poorly understood. This study is the first to combine the established body growth rate (BGR), which is an indicator of life-history fitness, with differential peptide labeling (iTRAQ)-based proteomics in Daphnia magna influenced by microcystin-producing (MP) and microcystin-free (MF) Microcystis aeruginosa. A significant decrease in BGR was detected when D. magna was exposed to MP or MF M. aeruginosa. Conducting iTRAQ proteomic analysis, we successfully identified and quantified 211 proteins with significant changes in expression. A cluster of orthologous groups revealed that M. aeruginosa-affected differential proteins were strongly associated with lipid, carbohydrate, amino acid, and energy metabolism. There parameters could potentially explain the reduced fitness based on the cost of substance metabolism.6. Transcriptome profiling of the cladoceran Daphnia similoides reveals genotype-specific gene expression signatures for Microcystis aeruginosa resistanceZooplankton populations may adapt to tolerate bloom-forming cyanobacteria in their diets. Essentially, tolerance can be induced a heritable genotype trait. Limited recent field observations suggest that the effect of different intraspecific genotypes has contrasting offensive ability to their toxic prey. However, the analysis of molecular mechanisms underlying these resistance difference is still in its early stages. The present study analysed the individual growth rate as well as transcriptome of tow clones of Daphnia similoides:Clone LS and Clone LM in response to toxin-producing Microcystis. A significant increase of individual fitness in Clone LS was detected compared to Clone LM. Using a high-throughput transcriptomic approach, we found five enhanced pathways:metabolic pathways, glutathione metabolism, mucin type O-Glycan biosynthesis, protein processing in endoplasmic reticulum and amino sugar and nucleotide sugar metabolism, which could explain why fitness in Clone LS is elevated based on energy budget considerations.