Combined effects of colonial size and concentration of Microcystis aeruginosa on the life history traits of Daphnia similoides

Microcystis colonial size and concentration have detrimental effects on life history traits of Daphnia, but their detailed interactions have remained unclear so far. Our experiments show that the interaction between Microcystis colonial size and concentration on maturation time, life expectancy, net reproductive rate and innate capacity of increase in Daphnia similoides was significant. In all groups, the survival rate of D. similoides was 100% within 8 days. This value then declined quickly in the large-colony groups and in the SH group of Microcystis. Colonial M. aeruginosa significantly reduced the maturation time and body length at maturity of D. similoides. The number of offspring at first reproduction per female in the SH group of Microcystis was significantly higher than those in other groups. Net reproductive rate of D. similoides in the SL group of Microcystis was significantly higher than those in other groups of Microcystis. The innate capacity of increase of D. similoides in small-colony Microcystis groups was significantly higher than that in the large-colony groups. The results suggested that the effect of smallcolony Microcystis on the reproduction of Daphnia was positive under lower concentration, while their toxicity was intensitied under higher concentration when small-colony Microcystis were by Daphnia as food

The complete mitochondrial genome of the Chinese Daphnia pulex (Cladocera, Daphniidae)

Daphnia pulex has played an important role in fresh-water ecosystems. In this study, the complete mitochondrial genome of Daphnia pulex from Chaohu, China was sequenced for the first time. It was accomplished using long-PCR methods and a primer-walking sequencing strategy with genus-specific primers. The mitogenome was found to be 15,306 bp in length. It contained 13 protein-coding genes, two rRNA genes, 22 tRNA genes and a typical control region. This research revealed an overall A+T content of 64.50%. All of the 22 typical animal tRNA genes had a classical clover-leaf structure except for trnS1, in which its DHU arm simply formed a loop. The lengths of small and large rRNA were 744 bp and 1,313 bp, respectively. The A+T-rich region was 723 bp in length, which is longer than that from the North American species (689 bp). In terms of structure and composition, many similarities were found between the Chinese and North American Daphnia pulex

Genetic Diversity of Daphnia pulex in the Middle and Lower Reaches of the Yangtze River.

Increased human activities and environmental changes may lead to genetic diversity variations of Cladocerans in water. Daphnia pulex are distributed throughout the world and often regarded as a model organism. The 16S rDNA, cytochrome c oxidase subunit I (COI), and 18S genes were used as molecular marks. The genetic diversity and phylogeny of D. pulex obtained from 10 water bodies in the middle and lower reaches of the Yangtze River were studied. For 16S rDNA, COI gene, and 18S gene, the A+T content (65.4%, 58.4%, and 54.6%) was significantly higher than the G+C content (34.6%, 41.6% and 45.4%). This result was consistent with higher A and T contents among invertebrates. Based on the genetic distances of 16S rDNA and COI genes, the genetic differences of D. pulex from 10 water bodies located in the middle and lower reaches of the Yangtze River in China was minimal (0%-0.8% for 16S rDNA and 0%-1.5% for COI gene). However, D. pulex evolved into two branches in the phylogenetic trees, which coincided with its geographical distribution. Compared with D. pulex from other countries, the average genetic distance of D. pulex obtained from 10 water bodies in the middle and lower reaches of the Yangtze River reached 9.1%-10.5%, thereby indicating that D. pulex may have evolved into different subspecies

Cloning and functional analysis of the molting gene CYP302A1 of Daphnia sinensis

Abstract Background Molting is an important physiological process in the growth and development of arthropoda, which is mainly regulated by juvenile hormone and ecdysone. CYP302A1 is a key enzyme which plays a critical role in the synthesis of ecdysone in insects, but it has not been identified in cladocera. Results The CYP302Al gene of Daphnia sinensis was cloned and its function was analyzed in this paper. The CYP302Al gene of D. sinensis was 5926 bp in full-length, with an open reading frame (ORF) of 1596 bp that encoded 531 amino acids (aa), a molecular weight of 60.82 kDa and an isoelectric point of 9.29. The amino acid sequence analysis revealed that there were five characteristic conserved regions of cytochrome P450 family (namely helix-C, helix-K, helix-I, PERF and heme-binding). In dsRNA mediated experiment, the expression level of CYP302A1 gene decreased significantly (knock-down of 56.22%) in the 5% Escherichia coli concentration treatment. In addition, the expression levels of EcR and USP and HR3 genes in the downstream were also significantly decreased, whereas that of FTZ-f1 gene increased significantly. In the 5% E. coli treatment, the molting time at maturity of D. sinensis prolonged, and the development of embryos in the incubation capsule appeared abnormal or disintegrated. The whole-mount in situ hybridization showed that the CYP302A1 gene of D. sinensis had six expression sites before RNA interference (RNAi), which located in the first antennal ganglion, ovary, cecae, olfactory hair, thoracic limb and tail spine. However, the expression signal of the CYP302A1 gene of D. sinensis disappeared in the first antennal ganglion and obviously attenuated in the ovary after RNAi. Conclusion The CYP302A1 gene played an important role in the ecdysone synthesis pathway of D. sinensis, and the knock-down of the gene affected the molting and reproduction of D. sinensis

The photograph of adult <i>D</i>. <i>pulex</i> female.

<p>The photograph of adult <i>D</i>. <i>pulex</i> female.</p

Analysis of molecular variance (AMOVA) based on the <i>16S</i> rDNA, <i>CO</i>I gene and <i>18S</i> gene sequences of <i>D</i>. <i>pulex</i> in the middle and lower reaches of Yangtze River.

<p>Analysis of molecular variance (AMOVA) based on the <i>16S</i> rDNA, <i>CO</i>I gene and <i>18S</i> gene sequences of <i>D</i>. <i>pulex</i> in the middle and lower reaches of Yangtze River.</p

Analysis of molecular variance (AMOVA) based on the <i>16S</i> rDNA and <i>CO</i>I gene sequences of <i>D</i>. <i>pulex</i> about the two groups (middle reach vs. lower reach) in the Yangtze River.

<p>Analysis of molecular variance (AMOVA) based on the <i>16S</i> rDNA and <i>CO</i>I gene sequences of <i>D</i>. <i>pulex</i> about the two groups (middle reach vs. lower reach) in the Yangtze River.</p

<i>18S</i> gene sequences of <i>Daphnia</i> and <i>Ceriodaphni</i>a from GenBank.

<p><i>18S</i> gene sequences of <i>Daphnia</i> and <i>Ceriodaphni</i>a from GenBank.</p

Origin and number of <i>D</i>. <i>pulex</i> species in this study.

<p>Origin and number of <i>D</i>. <i>pulex</i> species in this study.</p