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

Transcriptome analysis of different developmental stages of Daphnia similoides sinensis and screening of male sex determination candidate genes

Abstract Background: In the life history of Daphnia, the reproductive mode of parthenogenesis and sexual reproduction alternate in aquatic ecosystem, which are often affected by environmental and genetic factor. Although several functional genes on reproductive transition of Daphnia had been determined, molecular mechanism on the reproductive mode of Daphnia are still not known well, including differentially expressed genes in different developmental stages.Results: In this study, four developmental stages, juvenile female (JF), parthenogenetic female (PF), sexual female (SF) and male (M), of D. similoides sinensis were performed for transcriptome sequence, and candidate genes related to male sex determination were screened. A total of 110437 transcripts were obtained and assembled into 22996 unigenes. In the four developmental stages (JF, PF, SF and M), the number of unique unigenes is respectively 2863, 445, 437 and 586, and the number of common unigenes is 9708. The differentially expressed genes (DEGs) between male and other three female stages (M vs JF, M vs PF and M vs SF) were obtained. GO gene enrichment analysis showed that the up-regulated genes in male were mainly enriched in hydrolase activity and peptidase activity.Thirty-six candidate genes related to male sex determination in male were significantly higher expression than those in the other three stages, including one Doublesex (Dsx) gene, one laminin gene, five trypsin genes and one serine protease genes, and one chitin synthase gene and two chitinase genes. In addition, in D. similoides sinensis male, the relative expression levels of two genes (Dsx1, antp) related to male sex determination observed in other Daphnia species were also significantly higher than those in the other three stages. Conclusions: Our results showed that thirty-six candidate genes may involve in sex differentiation of D. similoides sinensis male, and it will provide a reference for further exploring the functional genes related to sex determination mechanism in Daphnia species. Moreover, according to previous investigations, we thought that the expression level of functional genes may be related to the development stages of organisms, and may be also affected by different Daphnia species.</jats:p

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

Effects of toxic Microcystis aeruginosa on the expression of Hox genes in Daphnia similoides sinensis

Lake eutrophication and cyanobacterial blooms have become worldwide environmental issues. Under cyanobacterial blooms (especially Microcystis), Daphnia spp. can transfer beneficial information to their offspring in order to improve adaptability. Hox genes are important regulatory factors of transcription in metazoans, and are involved in the growth and development of organisms. In this study, the effects of Microcystis aeruginosa on Hox gene expression in the mothers and offspring of Daphnia similoides sinensis were investigated using a mixed diet of M. aeruginosa and Scenedesmus obliquus, in two clones. There were significant differences in the survival rates of D. similoides sinensis under different food treatments. Our results suggest that the offspring produced by D. similoides sinensis mother pre-exposed to toxic M. aeruginosa had stronger adaptability to M. aeruginosa than those produced by previously unexposed mother. Additionally, Hox gene expressions of D. similoides sinensis had obvious differences between clones under stress of toxic M. aeruginosa.</jats:p