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35 results for “Daphnia pulex”
Different photoperiodic responses in diapause induction can promote the maintenance of genetic diversity via the storage effect in Daphnia pulex
<p>Understanding mechanisms that promote the maintenance of biodiversity (genetic and species diversity) has been a central topic in evolution and ecology. Previous studies have revealed that dormancy can contribute to coexistence of competing genotypes or species in fluctuating environments via the storage effect. However, they tended to focus on differences in reproductive success (e.g., seed yield) and diapause termination (e.g., germination) timing. Here we tested whether different photoperiodic responses in diapause induction can promote coexistence of two parthenogenetic (asexual) genotypes of <em>Daphnia pulex </em>in Lake Fukami-ike, Japan. Through laboratory experiments, we confirmed that short day length and low food availability induced the production of diapausing eggs. Furthermore, we found that one genotype tended to produce diapausing eggs in broader environmental conditions than the other. Terminating parthenogenetic reproduction earlier decreases total clonal production, but the early-diapausing genotype becomes advantageous by assuring reproduction in "short" years where winter arrival is earlier than usual. Empirically parameterized theoretical analyses suggested that different photoperiodic responses can promote coexistence via the storage effect with fluctuations of the growing season length. Therefore, timing of diapause induction may be as important as diapause termination timing for promoting the maintenance of genetic diversity in fluctuating environments.</p>
The maternal effects of dietary restriction on Dnmt expression and reproduction in two clones of Daphnia pulex
<p>The inheritance of epigenetic marks induced by environmental variation in a previous generation is broadly accepted as a mediator of phenotypic plasticity. Transgenerational effects linking maternal experiences to changes in morphology, gene expression, and life history of successive generations are known across many taxa. While the number of studies linking epigenetic variation to ecological maternal effects is increasing rapidly, few if any attempts have been made to investigate molecular mechanisms governing epigenetic functions in the context of ecologically relevant maternal effects. <em>Daphnia</em> make an ideal model for investigating molecular epigenetic mechanisms and ecological maternal effects because they will reproduce asexually in the lab. <em>Daphnia</em> are also known to have strong maternal effects, involving a variety of traits and environmental variables. Using two clones of <em>Daphnia</em> <em>pulex</em>, we investigated the plasticity of life history and DNA methyltransferase (Dnmt) gene expression with respect to food limitation within- and across-generations. We found strong evidence of genotypic variation of responses of life history and Dnmt expression to low food diets, both within- and across-generations. In general, effects of offspring diet were larger than either the direct maternal effect or offspring-maternal environment interactions, but the direction of the maternal effect was usually in the opposite direction of the within-generation effect. For both life history and Dnmt expression, we also found that when offspring had low food, effects of the maternal environment were stronger than when offspring had high food.</p>
Data from: Genetic variation in reproductive investment across an Ephemerality gradient in Daphnia pulex
<p>Species across the tree of life can switch between asexual and sexual reproduction. In facultatively sexual species, the ability to switch between reproductive modes is often environmentally dependent and subject to local adaptation. However, the ecological and evolutionary factors that influence the maintenance and turnover of polymorphism associated with facultative sex remain unclear. We studied the ecological and evolutionary dynamics of reproductive investment in the facultatively sexual model species, Daphnia pulex. We found that patterns of clonal diversity, but not genetic diversity varied among ponds consistent with the predicted relationship between ephemerality and clonal structure. Reconstruction of a multi-year pedigree demonstrated the coexistence of clones that differ in their investment into male production. Mapping of quantitative variation in male production using lab-generated and field-collected individuals identified multiple putative quantitative trait loci (QTL) underlying this trait, and we identified a plausible candidate gene. The evolutionary history of these QTL suggests that they are relatively young, and male limitation in this system is a rapidly evolving trait. Our work highlights the dynamic nature of the genetic structure and composition of facultative sex across space and time and suggests that quantitative genetic variation in reproductive strategy can undergo rapid evolutionary turnover.</p>
The maternal effects of dietary restriction on Dnmt expression and reproduction in two clones of Daphnia pulex
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Different photoperiodic responses in diapause induction can promote the maintenance of genetic diversity via the storage effect in Daphnia pulex
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Data from: Rare sexual reproduction by females of “obligate parthenogenetic” lineages of Daphnia cf. pulex
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Raw data for: Are standard test species still relevant? A comprehensive assessment of Daphnia pulex reared in laboratory and wild environments and their responses to organic ultraviolet filters
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Data from: Genetic variation in reproductive investment across an Ephemerality gradient in Daphnia pulex
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Data from: Evolution of asexual Daphnia pulex in Japan: variations and covariations of the digestive, morphological and life history traits
Background Several genetic lineages of obligate parthenogenetic Daphnia pulex, a common zooplankton species, have invaded Japan from North America. Among these, a lineage named JPN1 is thought to have started colonization from a single genotype several hundred to thousand years ago and subsequently produced many genotypes in Japan. To examine the phenotypic variations due to ecological drivers diverging the genotypes in new habitats, we measured heritability and variation in 17 traits, including life history, morphology and digestive traits, and the genetic distance among the D. pulex JPN1 genotypes in Japan. Results We found that most of the traits measured varied significantly among the genotypes and that heritability was highest in the morphological traits, followed by the digestive and life history traits. In addition, 93% of the variation in these traits was explained by the first three components in the principal component analysis, implying that variations of these heritable traits are not random but rather converged into a few directions. These relations among traits revealed the potential importance of predation pressures and food conditions as factors for diverging and selecting different genotypes. However, the magnitude of the difference in any single trait group did not correlate with the genetic distance. Conclusions Our findings show that the divergent traits evolved within D. pulex JPN1 without genetic recombination since their ancestral clone invaded Japan. Large variations and covariations of the phenotypic traits, irrespective of the genetic distance among the genotypes, support the view that the invasive success of D. pulex JPN1 was promoted by a genetic architecture that allowed for large phenotypic variations with a limited number of functionally important mutations without recombination.
Chaoborus induced defences in Daphnia pulex (raw images)
<p>Raw images of Daphnia pulex exposed to control conditions or predator cues from Chaoborus larvae (<a href="/api/files/e95ff93a-55d1-46c8-b548-83c68b3fb4d7/DAPCHA_raw_images_Daphnia.tar.gz?versionId=0c3fee60-e92d-4a62-97b5-c2e571040c75">DAPCHA_raw_images_Daphnia.tar.gz</a>)</p> <p>Raw images of microstage meters; each image is associated with one respective Daphnia image to allow for size estimation of animals (see above) (<a href="/api/files/e95ff93a-55d1-46c8-b548-83c68b3fb4d7/DAPCHA_raw_images_MicrostageMeter.tar.gz?versionId=a0408c06-f030-4252-913f-231bd7928838">DAPCHA_raw_images_MicrostageMeter.tar.gz</a>) </p> <p> </p> <p>File names are coded as below:</p> <p>*_BARCODEid_PONDid_CLONEid_MICROSCOPEstation_DATE.TIME</p>
UV radiation affects anti-predatory defense traits in Daphnia pulex
In aquatic environments prey perceive predator threats by chemical cues called kairomones, which can induce changes in their morphology, life histories and behavior. Predator-induced defenses have allowed for prey, such as Daphnia pulex, to avert capture by common invertebrate predators, such as Chaoborus sp. larvae. However, the influence of additional stressors, such as ultraviolet radiation (UVR), on the Daphnia-Chaoborus interaction is not settled as UVR may for instance deactivate the kairomone. In laboratory experiments, we investigated the combined effect of kairomones and UVR at ecologically relevant levels on induced morphological defenses of two D. pulex clones. We found that kairomones were not deactivated by UVR exposure. Instead, UVR exposure suppressed induced morphological defense traits of D. pulex juveniles under predation threat by generally decreasing the number of neckteeth and especially by decreasing the size of the pedestal beneath the neckteeth. UVR exposure also decreased the body length, body width, and tail spine length of juveniles, likely additionally increasing the vulnerability to Chaoborus predation. Our results suggest potential detrimental effects on fitness and survival of D. pulex subject to UVR-stress, with consequences on community composition and food web structure in clear and shallow water bodies.
Data from: Evolution of asexual Daphnia pulex in Japan: variations and covariations of the digestive, morphological and life history traits
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UV radiation affects anti-predatory defense traits in Daphnia pulex
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Data from: Transcriptional changes during Daphnia pulex development indicate that the maturation decision resembles a rate more than a threshold
Maturation is a critical developmental process, and the age and size at which it occurs have important fitness consequences. Although maturation is remarkably variable, certain mechanisms, including a minimum size or state threshold, are proposed to underlie the process across a broad diversity of taxa. Recent evidence suggests that thresholds may themselves be developmentally plastic, and in the crustacean Daphnia pulex it is unclear whether maturation follows a threshold or is a gradual process more akin to a rate. Changes in gene expression across four instars before and during maturation were compared in a cDNA microarray experiment. Developmental stage was treated statistically both as a discontinuous and a continuous variable, to determine whether genes showed gradual or discrete changes in expression. The continuous analysis identified a greater number of genes with significant differential expression (45) than the discontinuous analysis (11). The majority of genes, including those coding for histones, factors relating to transcription and cell cycle processes, and a putative developmental hormone showed continuous increases or decreases in expression from the first to the fourth instar, suggestive of a prolonged and gradual maturation process. Three genes coding for a fused Vitellogenin/super-oxide dismutase showed increases in expression following the second instar and coincided with the posited maturation threshold, but even their expression increased in a continuous fashion.
Data from: Offspring provisioning explains clone specific maternal age effects on life history and lifespan in the water flea, Daphnia pulex
Genetic inheritance underpins evolutionary theories of aging, but the role that nongenetic inheritance plays is unclear. Parental age reduces the life span of offspring in a diverse array of taxa but has not been explained from an evolutionary perspective. We quantified the effect that maternal age had on the growth and maturation decisions, life history, rates of senescence, and life span of offspring from three Daphnia pulex clones collected from different populations. We then used those data to test general hypotheses proposed to explain maternal age effects on offspring life span. Three generations of breeding from young or old mothers produced dramatic differences in the life histories of fourth-generation offspring, including significant reductions in life span. The magnitude of the effect differed between clones, which suggests that genetic and nongenetic factors ultimately underpin trait inheritance and shape patterns of aging. Older parents did not transmit a senescent state to their offspring. Instead, offspring from older ancestors had increased early-life reproductive effort, which resulted in an earlier onset of reproductive senescence, and an increased rate of actuarial senescence, which shortened their life span. Our results provide a clear example of the need to consider multiple inheritance mechanisms when studying trait evolution.
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 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.
Data from: Transcriptional changes during Daphnia pulex development indicate that the maturation decision resembles a rate more than a threshold
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