Post-senescence reproductive rebound in Daphnia associated with reversal of age-related transcriptional changes.

A long-lived species of zooplankton microcrustaceans, Daphnia magna, sometimes exhibits late-life rebound of reproduction, briefly reversing reproductive senescence. Such events are often interpreted as terminal investments in anticipation of imminent mortality. We demonstrate that such post-senescence reproductive events (PSREs) neither cause nor anticipate increased mortality.

Short lifespan is one's fate, long lifespan is one's achievement: lessons from Daphnia.

Studies of longevity rely on baseline life expectancy of reference genotypes measured in standardized conditions. Variation among labs, protocols, and genotypes makes longevity intervention studies difficult to compare. Furthermore, extending lifespan under suboptimal conditions or that of a short-lived genotype may be of a lesser theoretical and translational value than extending the maximal possible lifespan.

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.

Diet effects on longevity, heat tolerance, lipid peroxidation and mitochondrial membrane potential in Daphnia.

The dietary supply of polyunsaturated fatty acids (PUFA) crucially affects animals' performance at different temperatures. However, the underlying physiological mechanisms are still insufficiently understood. Here, we analyzed lifespan and heat tolerance of four genotypes of Daphnia magna reared on either the green alga Scenedesmus obliquus that lacks long-chain (> C18) PUFA, or the heterokont alga Nannochloropsis limnetica that contains C20 PUFA, both either at saturating and near-starvation levels.

Lipofuscin, amyloids, and lipid peroxidation as potential markers of aging in Daphnia.

Accumulation of autofluorescent waste products, amyloids, and products of lipid peroxidation (LPO) are important hallmarks of aging. Until now, these processes have not been documented in Daphnia, a convenient model organism for longevity and senescence studies. We conducted a longitudinal cohort study of autofluorescence and Congo Red (CR) fluorescent staining for amyloids in four clones of D.

Inverse Lansing Effect: Maternal Age and Provisioning Affecting Daughters' Longevity and Male Offspring Production.

AbstractMaternal age effects on offspring life history are known in a variety of organisms, with offspring of older mothers typically having lower life expectancy (the Lansing effect). However, there is no consensus on the generality and mechanisms of this pattern. We tested predictions of the Lansing effect in several clones and observed clone-specific magnitude and direction of the maternal age effect on offspring longevity.

The interplay between prior selection, mild intermittent exposure, and acute severe exposure in phenotypic and transcriptional response to hypoxia.

Hypoxia has profound and diverse effects on aerobic organisms, disrupting oxidative phosphorylation and activating several protective pathways. Predictions have been made that exposure to mild intermittent hypoxia may be protective against more severe exposure and may extend lifespan. Here we report the lifespan effects of chronic, mild, intermittent hypoxia, and short-term survival in acute severe hypoxia in four clones of originating from either permanent or intermittent habitats.

Intelligent high-throughput intervention testing platform in Daphnia.

We present a novel platform for testing the effects of interventions on the life- and healthspan of a short-lived freshwater organism with complex behavior and physiology-the planktonic crustacean Daphnia magna. Within this platform, dozens of complex behavioral features of both routine motion and response to stimuli are continuously quantified over large synchronized cohorts via an automated phenotyping pipeline. We build predictive machine-learning models calibrated using chronological age and extrapolate onto phenotypic age.

Pluripotency factors determine gene expression repertoire at zygotic genome activation.

Awakening of zygotic transcription in animal embryos relies on maternal pioneer transcription factors. The interplay of global and specific functions of these proteins remains poorly understood. Here, we analyze chromatin accessibility and time-resolved transcription in single and double mutant zebrafish embryos lacking pluripotency factors Pou5f3 and Sox19b.

Lack of age-related respiratory changes in Daphnia.

Aging is a multifaceted process of accumulation of damage and waste in cells and tissues; age-related changes in mitochondria and in respiratory metabolism have the focus of aging research for decades. Studies of aging in nematodes, flies and mammals all revealed age-related decline in respiratory functions, with somewhat controversial causative role. Here we investigated age-related changes in respiration rates, lactate/pyruvate ratio, a commonly used proxy for NADH/NAD+ balance, and mitochondrial membrane potential in 4 genotypes of an emerging model organism for aging research, a cyclic parthenogen Daphnia magna.

Does geographic variation in thermal tolerance in Daphnia represent trade-offs or conditional neutrality?

Geographic variation in thermal tolerance in Daphnia seems to represent genetic load at the loci specifically responsible for heat tolerance resulting from conditional neutrality. We see no evidence of trade-offs between fitness-related traits at 25 °C vs. 10 °C or between two algal diets across Daphnia magna clones from a variety of locations representing the opposite ends of the distribution of long-term heat tolerance.

False and true positives in arthropod thermal adaptation candidate gene lists.

Genome-wide studies are prone to false positives due to inherently low priors and statistical power. One approach to ameliorate this problem is to seek validation of reported candidate genes across independent studies: genes with repeatedly discovered effects are less likely to be false positives. Inversely, genes reported only as many times as expected by chance alone, while possibly representing novel discoveries, are also more likely to be false positives.

Breaking free from thermodynamic constraints: thermal acclimation and metabolic compensation in a freshwater zooplankton species.

Respiration rates of ectothermic organisms are affected by environmental temperatures, and sustainable metabolism at high temperatures sometimes limits heat tolerance. Organisms are hypothesized to exhibit acclimatory metabolic compensation effects, decelerating their metabolic processes below Arrhenius expectations based on temperature alone. We tested the hypothesis that either heritable or plastic heat tolerance differences can be explained by metabolic compensation in the eurythermal freshwater zooplankton crustacean We measured respiration rates in a ramp-up experiment over a range of assay temperatures (5-37°C) in eight genotypes of representing a range of previously reported acute heat tolerances and, at a narrower range of temperatures (10-35°C), in with different acclimation history (either 10 or 25°C).

To the origin of Lake Baikal endemic gammarid radiations, with description of two new Eulimnogammarus spp.

Extraordinarily diverse morphologically and ecologically, Lake Baikal's two endemic gammaroidean amphipod clades are both firmly placed within the paraphyletic genus Gammarus, based both on morphological and molecular characters. However, the exact placement of the two Baikal clades remains elusive, making reconstruction of the ancestral state of Baikal endemic radiation difficult. We sequenced 2 mitochondrial and 3 nuclear genes from several species of each of the two clades aiming to represent early branches of the radiation.

Excessive Parallelism in Protein Evolution of Lake Baikal Amphipod Species Flock.

Repeated emergence of similar adaptations is often explained by parallel evolution of underlying genes. However, evidence of parallel evolution at amino acid level is limited. When the analyzed species are highly divergent, this can be due to epistatic interactions underlying the dynamic nature of the amino acid preferences: The same amino acid substitution may have different phenotypic effects on different genetic backgrounds.

Quantitative Proteomics Reveals Remodeling of Protein Repertoire Across Life Phases of Daphnia pulex.

Although the microcrustacean Daphnia is becoming an organism of choice for proteomic studies, protein expression across its life cycle have not been fully characterized. Proteomes of adult females, juveniles, asexually produced embryos, and the ephippia-resting stages containing sexually produced diapausing freezing- and desiccation-resistant embryos are analyzed. Overall, proteins with known molecular functions are more likely to be detected than proteins with no detectable orthology.

Rearing Temperature and Fatty Acid Supplementation Jointly Affect Lipid Fluorescence Polarization and Heat Tolerance in .

The homeoviscous adaptation hypothesis states that the relative abundance of polyunsaturated fatty acids (PUFAs) in membrane phospholipids of ectothermic organisms decreases with increasing temperatures to maintain vital membrane properties. We reared at 15°, 20°, and 25°C and increasing dietary concentrations of the long-chain PUFA eicosapentaenoic acid (EPA) to test the hypothesis that the well-documented increase in heat tolerance of high-temperature-reared is due to a reduction in body PUFA concentrations. Heat tolerance was assessed by measuring the time to immobility at a lethally high temperature ( at 37°C), and whole body lipid fluorescence polarization (FP) was used as an estimate of membrane fluidity.

Pou5f3, SoxB1, and Nanog remodel chromatin on high nucleosome affinity regions at zygotic genome activation.

The zebrafish embryo is transcriptionally mostly quiescent during the first 10 cell cycles, until the main wave of zygotic genome activation (ZGA) occurs, accompanied by fast chromatin remodeling. At ZGA, homologs of the mammalian stem cell transcription factors (TFs) Pou5f3, Nanog, and Sox19b bind to thousands of developmental enhancers to initiate transcription. So far, how these TFs influence chromatin dynamics at ZGA has remained unresolved.

The Trace Element Zinc in the Composition of Native Chorionic Gonadotropin.

Human chorionic gonadotropin (hCG) is a most important regulator of embryogenesis and spermatogenesis. Equally important for the development of the fetus is the trace element zinc, which is essential for sustainable fetal development. The involvement of hCG and zinc in the first trimester of pregnancy (embryogenesis) led us to question the possibility of their structural cooperation and inclusion in the native molecule chorionic gonadotropin and zinc atoms.

Net Evolutionary Loss of Residue Polarity in Drosophilid Protein Cores Indicates Ongoing Optimization of Amino Acid Composition.

Amino acid frequencies in proteins may not be at equilibrium. We consider two possible explanations for the nonzero net residue fluxes in drosophilid proteins. First, protein interiors may have a suboptimal residue composition and be under a selective pressure favoring stability, that is, leading to the loss of polar (and the gain of large) amino acids.

Antioxidant capacity, lipid peroxidation, and lipid composition changes during long-term and short-term thermal acclimation in Daphnia.

Examples of phenotypic plasticity-the ability of organisms of identical genotypes to produce different phenotypes in response to the environment-are abundant, but often lack data on the causative physiology and biochemistry. Phenotypes associated with increased protection against or reduced damage from harmful environments may, in fact, be downstream effects of hidden adaptive responses that remain elusive to experimental measurement or be obscured by homeostatic or over-compensatory effects. The freshwater zooplankton crustacean Daphnia drastically increases its heat tolerance as the result of acclimation to high temperatures, an effect often assumed to be based on plastic responses allowing better protection against oxidative stress.

Nuclear DNA content correlates with depth, body size, and diversification rate in amphipod crustaceans from ancient Lake Baikal, Russia.

Lake Baikal in Russia is a large, ancient lake that has been the site of a major radiation of amphipod crustaceans. Nearly 400 named species are known in this single lake, and it is thought that many more await description. The size and depth of Lake Baikal, in particular, may have contributed to the radiation of endemic amphipods by providing a large number of microhabitats for species to invade and subsequently experience reproductive isolation.

Transcriptome-based phylogeny of endemic Lake Baikal amphipod species flock: fast speciation accompanied by frequent episodes of positive selection.

Endemic species flocks inhabiting ancient lakes, oceanic islands and other long-lived isolated habitats are often interpreted as adaptive radiations. Yet molecular evidence for directional selection during species flocks radiation is scarce. Using partial transcriptomes of 64 species of Lake Baikal (Siberia, Russia) endemic amphipods and two nonendemic outgroups, we report a revised phylogeny of this species flock and analyse evidence for positive selection within the endemic lineages.

Functional genomics of acclimation and adaptation in response to thermal stress in Daphnia.

Background: Gene expression regulation is one of the fundamental mechanisms of phenotypic plasticity and is expected to respond to selection in conditions favoring phenotypic response. The observation that many organisms increase their stress tolerance after acclimation to moderate levels of stress is an example of plasticity which has been long hypothesized to be based on adaptive changes in gene expression. We report genome-wide patterns of gene expression in two heat-tolerant and two heat-sensitive parthenogenetic clones of the zooplankton crustacean Daphnia pulex exposed for three generations to either optimal (18°C) or substressful (28°C) temperature.