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468 results for “Daphnia”
Data from: 5α-cyprinol sulfate, a bile salt from fish, induces diel vertical migration in Daphnia
Prey are under selection to minimize predation losses. In aquatic environments many prey use chemical cues released by predators, which initiate predator-avoidance. A prominent example of behavioural predator-avoidance constitutes diel vertical migration (DVM) in the freshwater microcrustacean Daphnia spp., which is induced by chemical cues (kairomones) released by planktivorous fish. In a bioassay-guided approach using liquid chromatography and mass spectrometry we isolated the kairomone from fish incubation water and identified it as 5α-cyprinol sulfate inducing DVM in Daphnia at picomolar concentrations. The role of 5α-cyprinol sulfate in lipid digestion in fish explains why from an evolutionary perspective fish has not stopped releasing 5α-cyprinol sulfate despite the disadvantages for the releaser. The identification of the DVM-inducing kairomone enables investigating its spatial and temporal distribution and the underlying molecular mechanism of its perception. Furthermore, it allows to test if fish-mediated inducible defenses in other aquatic invertebrates are triggered by the same compound.
Data from: Do microplastic particles affect Daphnia magna at the morphological, life history and molecular level?
Microplastic particles are ubiquitous not only in marine but also in freshwater ecosystems. However, the impacts of microplastics, consisting of a large variety of synthetic polymers, on freshwater organisms remains poorly understood. We examined the effects of two polymer mixtures on the morphology, life history and on the molecular level of the waterflea Daphnia magna (three different clones). Microplastic particles of ~40 µm were supplied at a low concentration (1% of the food particles) leading to an average of ~30 particles in the digestive tract which reflects a high microplastic contamination but still resembles a natural situation. Neither increased mortality nor changes on the morphological (body length, width and tail spine length) or reproductive parameters were observed for adult Daphnia. The analyses of juvenile Daphnia revealed a variety of small and rather subtle responses of morphological traits (body length, width and tail spine length). For adult Daphnia, alterations in expression of genes related to stress responses (i.e. HSP60, HSP70 & GST) as well as of other genes involved in body function and body composition (i.e. SERCA) were observed already 48h after exposure. We anticipate that the adverse effects of microplastic might be influenced by many additional factors like size, shape, type and even age of the particles and that the rather weak effects, as detected in a laboratory, may lead to reduced fitness in a natural multi-stressor environment.
Data from: Evolutionary history of Daphnia drives divergence in grazing selectivity and alters temporal community dynamics of producers
Consumers with different seasonal life histories encounter different communities of producers during specific seasonal phases. If consumers evolve to prefer the producers that they encounter, then consumers may reciprocally influence the temporal composition of producer communities. Here we study the keystone consumer Daphnia ambigua, whose seasonal life history has diverged due to intraspecific predator divergence across lakes of New England. We ask whether grazing preferences of Daphnia have diverged also, and test whether any grazing differences influence temporal composition patterns of producers. We reared clonal populations of Daphnia from natural populations representing the two diverged life history types for multiple generations. We conducted short-term (24 hours) and long-term (27 days) grazing experiments in equal polycultures consisting of 3 diatom and 2 green algae species, treated with no consumer, Daphnia from lakes with anadromous alewife, or from lakes with landlocked alewife. After 24 hours, life history and grazing preference divergence in Daphnia ambigua drove significant differences in producer composition. However, those differences disappeared at the end of the 27-day experiment. Our results illustrate that, despite potentially more complex long-term dynamics, a multitrophic cascade of evolutionary divergence from a predator can influence temporal community dynamics at the producer level.
Data from: Impacts of dispersal on rapid adaptation and dynamic stability of Daphnia in fluctuating environments
Prior ecological research has shown that spatial processes can enhance the temporal stability of populations in fluctuating environments. Less explored is the effect of dispersal on rapid adaptation and its concomitant impact on population dynamics. For asexually reproducing populations, theory predicts that dispersal in fluctuating environments can facilitate asynchrony among clones and enhance stability by reducing temporal variability of total population abundance. This effect is predicted when clones exhibit heritable variation in environmental optima and when fluctuations occur asynchronously among patches. We tested this in the field using artificial ponds and metapopulations composed of a diverse assemblage of <i>Daphnia pulex</i> clones. We directly manipulated dispersal presence/absence and environmental fluctuations in the form of nutrient pulses. Consistent with predictions, dispersal enhanced temporal asynchrony among clones in the presence of nutrient pulses; this in turn stabilized population dynamics. This effect only emerged when patches experienced spatially asynchronous nutrient pulses (dispersal had no effect when patches were synchronously pulsed). Clonal asynchrony was driven by strong positive selection for a single clone that exhibited a performance advantage under conditions of low resource availability. Our work highlights the importance of dispersal as a driver of eco-evolutionary dynamics and population stability in variable environments.
Data from: How clonal are clones? A quest for loss of heterozygosity during asexual reproduction in Daphnia magna
Due to the lack of recombination, asexual organisms are predicted to accumulate mutations and show high levels of within-individual allelic divergence (heterozygosity) however, empirical evidence for this prediction is largely missing. Instead, evidence of genome homogenization during asexual reproduction is accumulating. Ameiotic crossover recombination is a mechanism that could lead to long genomic stretches of loss of heterozygosity (LOH) and unmasking of mutations that have little or no effect in heterozygous state. Therefore, LOH might be an important force for inducing variation among asexual offspring and may contribute to the limited longevity of asexual lineages. To investigate the genetic consequences of asexuality, here we used high-throughput sequencing of Daphnia magna for assessing the rate of LOH over a single generation of asexual reproduction. Comparing parthenogenetic daughters with their mothers at several thousand genetic markers generated by Restriction site Associated DNA (RAD) sequencing resulted in high LOH rate estimation that largely overlapped with our estimates for the error rate. To distinguish these two, we Sanger re-sequenced the top 18 candidate RAD-loci for LOH, and all of them proved to be false positives. Hence, even though we cannot exclude the possibility that short stretches of LOH occur in genomic regions not covered by our markers, we conclude that LOH does not occur frequently during asexual reproduction in D. magna and ameiotic crossovers are very rare or absent. This finding suggests that clonal lineages of D. magna will remain genetically homogeneous at least over time periods typically relevant for experimental work.
Data from: Calcium interacts with temperature to influence Daphnia movement rates
Predicting the ecological responses to climate change is particularly challenging, because organisms might be affected simultaneously by the synergistic effects of multiple environmental stressors. Global warming is often accompanied by declining calcium concentration in many freshwater ecosystems. Although there is growing evidence that these changes in water chemistry and thermal conditions can influence ecosystem dynamics, little information is currently available about how these synergistic environmental stressors could influence the behaviour of aquatic organisms. Here, we tested whether the combined effects of calcium and temperature affect movement parameters (average speed, mean turning frequency and mean-squared displacement) of the planktonic Daphnia magna, using a full factorial design and exposing Daphnia individuals to a range of realistic levels of temperature and calcium concentration. We found that movement increased with both temperature and calcium concentration, but temperature effects became considerably weaker when individuals were exposed to calcium levels close to survival limits documented for several Daphnia species, signalling a strong interaction effect. These results support the notion that changes in water chemistry might have as strong an effect as projected changes in temperature on movement rates of Daphnia, suggesting that even sublethal levels of calcium decline could have a considerable impact on the dynamics of freshwater ecosystems.
Evolutionary mechanisms underpinning fitness response to multiple stressors in Daphnia
<p>Multiple stressors linked to anthropogenic activities can influence how organisms adapt and evolve. So far, a consensus on how multiple stressors drive adaptive trajectories in natural populations has not been reached. Some meta-analysis reports show predominance of additive effects of stressors on ecological endpoints (e.g. fecundity, mortality), whereas others show synergistic effects more frequently. Moreover, it is unclear what mechanisms of adaptation underpin responses to complex environments.</p> <p>Here, we use populations of the crustacean <i>Daphnia magna</i> resurrected from different times in the past to investigate mechanisms of adaptation to multiple stressors, and to understand how historical exposure to environmental stress shapes adaptive responses of modern populations. Using common garden experiments on resurrected modern and historical populations, we investigate: i) whether exposure to one stress results in higher tolerance to a second stressor; ii) the mechanisms of adaptation underpinning long-term evolution to multistress (genetic evolution, plasticity, evolution of plasticity); and iii) the interaction effects of multiple stressors on fitness (synergism, antagonism, additivity). We measure the combined impact of different levels of resource availability (algae) and biocides on fitness-linked life history traits and interpret these results in light of historical environmental exposures. We show that exposure to one stressor can alter tolerance to a second stressors and that the interaction effect depends on the severity of either stressor. We also show that mechanisms of adaptation underpinning phenotypic evolution significantly differ in single stress and multistress scenarios. These adaptive responses are driven largely by synergistic effects on fecundity and size at maturity, and additive effects on age at maturity. Exposure to multiple stressors shifts the trade-offs among fitness-linked life history traits, with a stronger effect on <i>Daphnia </i>populations when low resource availability and high biocide levels are experienced. Our study indicates that mitigation interventions based on single stress analysis may not capture realistic threats.</p>
Eutrophic status influences the impact of pesticide mixtures and predation on Daphnia pulex populations
<p>Pesticides, nutrients, and ecological stressors such as competition or predation co-occur in freshwater ecosystems impacted by agricultural pollution. The extent to which combinations of these stressors affect aquatic populations and the role of nutrients availability in modulating these responses requires further understanding. In this study, we assessed how pesticides affecting different taxonomic groups and predation influence the response of Daphnia pulex populations under different trophic conditions. An outdoor experiment was designed following a factorial design, with the insecticide chlorpyrifos, the herbicide diuron, and predation by Notonecta sp. individuals as key stressors. The single impact of each of these stressors, and their binary and tertiary combinations were evaluated on D. pulex abundance and population structure under mesotrophic and eutrophic conditions for 21 days. Data were analysed using generalized linear mixed models estimated by means of a novel Bayesian shrinkage technique. Our study shows a significant influence of each of the evaluated stressors on D. pulex abundance, however, the impacts of the herbicide and predation were lower under eutrophic conditions as compared to the mesotrophic ones. We found that binary stressor interactions were generally additive in the mesotrophic scenario, except for the herbicide-predation combination, which resulted in synergistic effects. The impacts of the binary stressor combinations in the eutrophic scenario were classified as antagonistic, except for the insecticide-herbicide combination, which was additive. The tertiary interaction resulted in significant effects on several sampling dates, however, those were rather antagonistic and resembled the most important binary stressor combination in each trophic scenario. Our study shows that the impact of pesticides on freshwater populations depends on the predation pressure, and demonstrates that the combined effect of pesticides and ecological stressors is influenced by the food availability and organism fitness related to the trophic status of freshwater ecosystems.</p>
Figure 5 in Types of cladoceran species described by Sven Ekman in the Swedish Museum of Natural History, with redescription of Daphnia cavicervix Ekman, 1900 (Daphniidae, Anomopoda, Cladocera)
Figure 5. Daphnia cavicervix, adult male from unknown water body near Morro Chico, Chile. (A) Lateral view; (B) head; (C) dissected valve; (D, E) postero-ventral portion of valve; (F, G) postabdomen and its distal portion; (H, I) antenna I; (J) limb I; (K) ODL; (L) armature of seta of ODL; (M) IDL; (N) tip of copulatory hook; (O) inner-distal portion of limb II; (P) inner-distal portion of limb III. Scale bars: 0.1 mm.
Figure 1 in Species diversity and endemism in the Daphnia of Argentina: a genetic investigation
Figure 1. Collection sites for Argentine populations belonging to the subgenus Daphnia. Photographs are included for a single individual of each species. Species were identified based on genetic analyses (see text and Fig. 2). Animals are not shown to scale. In some cases, multiple collections of the same species within a small geographical region are not shown (see Appendix 1 for the complete list of collection localities).
Reproductive success and mortality of male and female Daphnia at different sex ratios
<p>This dataset contains data from Daphnia sexual reproduction experiments described in the paper: "<span><span><span><span>Galimov YR, Haag CR, Tukhbatullin AR, Tchabovsky AV</span></span></span></span> <span><span><span>2021. <span>Sex ratio effects on reproductive success of male and female Daphnia</span></span></span>. </span><i><span>Journal of Evolutionary Ecology</span></i> <span><span><span><span><span><span>". </span></span></span></span></span></span></p> <p class="western"><span><span><span><span><span><span><span><span><span><span><span><span>We compared reproductive success of male and female Daphnia in experimental populations with sex ratios varying from one male per 81 females to one male per one female. In males, reproductive success strongly and monotonically decreased with decreasing number of females per male. In females, in contrast, mating success and reproductive success were reduced only at the most female-biased sex ratio (1:81), when many females remained unmated and unfertilized, and then again at equal sex ratios, probably due to negative effects of high density or stress induced by numerous males. Our results suggest that mating competition and the opportunity for sexual selection may exist not only in males but, at least periodically, also in females.</span></span></span></span></span></span></span></span></span></span></span></span></p>
Figure 4 from: Geng X, Cheng R, Xiang T, Deng B, Wanga Y, Deng D, Zhang H (2016) The complete mitochondrial genome of the Chinese Daphnia pulex (Cladocera, Daphniidae). ZooKeys 615: 47-60. https://doi.org/10.3897/zookeys.615.8581
Figure 4 - Phylogenetic tree obtained by the maximum-likelihood (ML) method and bootstrap values (1000 repetitions) of the branches were indicated. Daphnia magna and Daphnia carinata were used as outgroups.
Figure 2 from: Geng X, Cheng R, Xiang T, Deng B, Wanga Y, Deng D, Zhang H (2016) The complete mitochondrial genome of the Chinese Daphnia pulex (Cladocera, Daphniidae). ZooKeys 615: 47-60. https://doi.org/10.3897/zookeys.615.8581
Figure 2 - Nucleotide compositions of the two Daphnia pulex from Chinese Chaohu (Ch) and North America (Na). CDS: protein-coding genes; 1st: first codon position; 2nd: second codon position; 3rd: third codon position; tRNA: tRNA genes; rRNA: rRNA genes; D-loop: A+T-rich region. In addition, stop codons were excluded.
Figure 1 from: Geng X, Cheng R, Xiang T, Deng B, Wanga Y, Deng D, Zhang H (2016) The complete mitochondrial genome of the Chinese Daphnia pulex (Cladocera, Daphniidae). ZooKeys 615: 47-60. https://doi.org/10.3897/zookeys.615.8581
Figure 1 - Structure of Chinese Daphnia pulex mitochondrial genome. COI, COII, COIII refer to the cytochrome oxidase subunits, Cytb refers to cytochrome b, ND1 - ND6 refer to NADH dehydrogenase components, and rrL and rrnS refer to rRNAs. tRNA genes are denoted by one letter symbol according to the IPUC-IUB single-letter amino acid codes. L1, L2, S1 and S2 denote tRNALeu(CUN), tRNALeu(UUR), tRNASer(AGN) and tRNASer(UCN), respectively. D-loop indicates A+T-rich region. Gene names outside the ring are coded on the majority strand while those inside are on the minority strand.
Daphnia magna life history data for caged and uncaged individuals (lab and mesocosm)
<p>Life history studies are often conducted in a laboratory environment where it is easy to assay individual animals. However, factors such as temperature, photoperiod, and nutrition vary greatly between laboratory and field environments, making it difficult to compare results. Consequently, there is a need to study individual life histories in the field, but this is currently difficult in systems such as Daphnia where it is not possible to mark and track individual animals. Here, we present a proof of principle study showing that field cages are a reliable method for collecting individual-level life history data in Daphnia magna. As a first step, we compared the life history of paired animals reared outside and inside cages to test the hypothesis that cages allow free-flow of algal food resources. We then used a semi-natural mesocosm setting to compare the performance of individual field cages versus glass jars re-filled with mesocosm water each day. We found that cages did not inhibit food flow, and that differences in life histories between three clones detected in the jar assays were also detectable using the much less labour-intensive field cages. We conclude that field cages are a feasible approach for collecting individual-level life history data in systems such as Daphnia where individual animals cannot be marked and tracked.</p>
Primary data used to calculate predator-induced morphological changes in two Daphnia species-associated clones
<p>The expression of inducible defences in reaction to an inconsistent predation pressure is especially well investigated in the freshwater keystone filter-feeder <i>Daphnia</i>. Out of their many inducible defences, which increase their fitness, the highest diversity of induced traits is found within their morphology. In recent time the focus of studies on these has switched, from the previously thoroughly covered large-scale defences, e.g., elongated/enlarged tail-spines, helmets and crests, to rather small-scale predator-induced changes. Inconspicuous spinules that cover the dorsal and ventral carapace margins have only rarely been featured in studies. We, therefore, tested two well-studied <i>Daphnia</i> species (<i>D. magna</i> and <i>D. longicephala</i>) for predator-induced changes concerning the spinules, i.e., their area of distribution relative to the body length (relative dorsal/ventral spinules-bearing area, relSBA) and their change in length (mean spinule length of the five central spinules along the dorsal/ventral carapace margin, mean SL). As invertebrate and vertebrate predators display differently built catching structures, those of invertebrate predators being more delicate, the defensive structures against these predator groups might vary accordingly. To test this, we exposed the daphnids to the vertebrate <i>Leucaspius delineatus</i> and a well co-studied predator of the respective <i>Daphnia</i> species, i.e., <i>Triops cancriformis</i> or <i>Notontecta maculata</i>. Our study discovered induced changes of the spinules' lengths and an area they cover. These changes of inconspicuous traits appear not only to be predator-dependent, but also <i>Daphnia</i>-specific. The inconspicuous morphological changes of <i>Daphnia</i>, in combination with the large scale defences, here measured pointers for the expression of inducible defences were the tail spines (relative tail spine length, relTSL) in both species and the crest in <i>D. longicephala</i>, and some ultrastructural defences<i> </i>are suspected to be rather specifically customised collective defences.</p>
Data from: Interplay between fungicides and parasites: tebuconazole, but not copper, suppresses infection in a Daphnia-Metschnikowia experimental model
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Data from: Daphnia invest in sexual reproduction when its relative costs are reduced
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Data from: Transcriptional changes during Daphnia pulex development indicate that the maturation decision resembles a rate more than a threshold
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Data for: Transgenerational plasticity in the eye size of Daphnia
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