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Strobilation is a well-organized metamorphosis process in scyphozoan jellyfish, through which the benthic polyp develops into the pelagic medusa. So far, knowledge on the molecular mechanisms behind the drastic morphological and physiological changes remains limited. In the present study, the metabolic profiles in polyp and strobila stages of jellyfish Rhopilema esculentum were examined using ultra-performance liquid chromatography coupled to a mass spectrometer. A total of 3 071 metabolites with putative annotation were detected, of which 167 were identified as differential metabolites between the polyp and strobila. Among the metabolites, 31 significantly decreased and 136 significantly increased in abundance in the strobila. Thyroxin, one of the previously proposed strobilation inducer of Aurelia, was not detected in this study. The indole-containing compounds are known for triggering strobilation in Discomedusae. Two indole derivatives and an indole-isomer containing metabolite were detected among the most significantly increased metabolites, which may be potential endogenous molecules for strobilation initiation. The membrane-associated phospholipids and the inflammation and oxidative stress-related eicosanoids were found to have significant changes. Although the functions of these metabolites in strobilation are not yet completely known, they provide some clues to the induction of the process of strobilation and metabolic responses that take place during strobilation. [ABSTRACT FROM AUTHOR]

Over the past decades, jellyfish occurred increasingly and abundantly in coastal areas worldwide. Usually, biomass of jellyfish, especially when they bloom, can be determined by visual counting. However, tiny individuals of jellyfish (e.g., planulae, polyps, and ephyrae) are difficult to detect in the field. In this study, species-specific quantitative real-time PCR assays (qPCR) (SYBR Green I) targeting the mitochondrial 16S rDNA (mt-16S rDNA) of jellyfish were developed and were used to estimate the distribution and seasonal fluctuations of four jellyfish species (Nemopilema nomurai, Cyanea nozakii, Rhopilema esculentum, and Aurelia coerulea) in Jiaozhou Bay (JZB), China in 2013. The mt-16S rDNA of A. coerulea and N. nomurai was detected in most of the survey months and it peaked in July (1.03×104 copies/L) and September (1.08×106 copies/L), respectively. The mt-16S rDNA of C. nozakii occurred from August to October only with monthly mean values of 7.18–46.17 copies/L and was mainly located from the middle part to the outer part of the bay. The mt-16S rDNA of R. esculentum was the least abundant among the four species and was detected in only one sample (B2 station in March), with a value of 88.49 copies/L. The Spearman correlation test revealed that phytoplankton biomass was significantly and positively correlated with the mt-16S rDNA abundance of A. coerulea (R=0.37, P<0.01) and negatively with the mt-16S rDNA of N nomurai (R=-0.36, P<0.01). The qPCR assay will enable the identification and quantification of jellyfish species in their whole life history and can be used as an approach in combination of the traditional jellyfish survey. [ABSTRACT FROM AUTHOR]

Strobilation is a unique asexual reproduction mode of scyphozoan jellyfish, through which benthic polyp develops into pelagic medusa. It is an orderly metamorphosis process triggered by environmental signals. However, the knowledges of molecular mechanisms under the drastic morphological and physiological changes are still limited. In this study, the transcriptomes from polyps to juvenile medusae at different stages were characterized by RNA-seq in scyphozoan jellyfish Rhopilema esculentum. Among 96,076 de novo assembled unigenes, 7090 differentially expressed genes (DEGs) were identified during the developmental stages. The co-expression pattern analysis of DEGs yielded 15 clusters with different expression patterns. Among them, a cluster with 388 unigenes was related to strobila. In this specific cluster, the GO terms related to "sequence-specific DNA binding transcription factor activity" and "sequence-specific DNA binding" were significantly enriched. Transcription factors, including segmentation protein even-skipped-like, segmentation polarity protein engrailed-like, homeobox proteins Otx-like, Twist-like and Cnox2-Pc-like, as well as genes such as RxR-like and Dmrtf-like, were identified to be potentially involved in strobilation. Their expression patterns and the other 11 TFs/genes involved in strobilation were confirmed with qRT-PCR methods. The present study pointed out the role of transcription factors in strobilation and produced a list of novel candidate genes for further studies. It could provide valuable information for understanding the molecular mechanisms of jellyfish strobilation. [ABSTRACT FROM AUTHOR]

Ten microsatellite markers were used to analyze the levels of genetic diversity and inbreeding in a hatchery release population of Rhopilema esculentum Kishinouye (Scyphozoa: Rhizostomatidae). A total of 85 alleles were detected in 600 individuals. Within-population levels of observed ( H ) and expected ( H ) heterozygosity ranged from 0.152 to 0.839 (mean=0.464) and from 0.235 to 0.821 (mean=0.618), respectively. The polymorphism information content (PIC) of each marker ranged from 0.207 to 0.795 with an average of 0.580, indicating that the hatchery population maintained a high level of genetic diversity. Inbreeding levels were estimated in the hatchery population and the inbreeding coefficient was 0.203. This result revealed that a certain level of inbreeding occurred within the population. Meanwhile, we also determined genetic diversity at the clone level. Several polyps from the same scyphistomae were genotyped at the ten microsatellite loci and there was virtually no difference in their genotypes. Furthermore, we calculated the probabilities of exclusion. When both parents were known, the average exclusion probability of ten loci was 99.99%. Our data suggest that the ten microsatellite markers can not only be used to analyze the identity of individuals but they can also be applied to parentage identification. Our research provides a theoretical basis and technical support for genetic diversity detection and reasonable selection of R. esculentum hatchery populations. These findings support the use of releasing studies and conservation of R. esculentum germplasm resources. [ABSTRACT FROM AUTHOR]

Jellyfish are sometimes considered as valueless because of their supposed low nutritive content. Here, we conducted feeding experiments on silver pomfret juveniles to evaluate the dietary value of jellyfish. Six treatments, including a starvation treatment (S) and five feeding treatments, with Aurelia aurita ( AA), Rhopilema esculentum ( RE), artificial diet (AD), both A. aurita and artificial diet ( A&A), and both R. esculentum and artificial diet ( R&A), were carried out to compare fish survival rates and growth performance. Fish with S treatment showed a 48% mortality rate and reduced body weight, whereas fish with AA and RE treatments showed no death and much increased body weight. Fish with A&A and R&A treatments exhibited a much faster growth than that with AD treatment. Further, the effects of diet on biochemical composition of silver pomfrets were explored. Monounsaturated fatty acid (MUFA), seven different fatty acids, and six different essential amino acids (EAAs) were showed to be good indicators to assess silver pomfrets' response to their prey. Our experiment indicated that the jellyfish, A. aurita and R. esculentum, can provide energy for silver pomfrets' metabolism and growth, and as supplemental food are suitable for rearing silver pomfret juveniles. [ABSTRACT FROM AUTHOR]

Fifteen polymorphic microsatellite loci were developed and characterized for Rhopilema esculentum using a (GT)-enriched genomic library. The numbers of alleles per locus ranged from 2 to 12, and the observed and expected heterozygosities varied from 0.0417 to 0.8750 and from 0.0086 to 0.7055, respectively. These markers will be helpful for QTL mapping, molecular breeding and investigation of population genetic diversity in R. esculentum. [ABSTRACT FROM AUTHOR]

The current study explored Aurelia aurita and Rhopilema esculentum consumption by silver pomfret juveniles, as well as their prey selection between the two jellyfish species. Silver pomfret juveniles weighing 1±0.1 g actively preyed on both the species. Their daily A. aurita consumption was 11.6 times their own body weights regardless of the size of A. aurita medusae. Their daily R. esculentum consumption was 13, 9.1, 5, and 4.1 times their own body weights when the R. esculentum medusae were 10, 20, 30, and 40 mm in bell diameter, respectively. The survival rates of the R. esculentum were higher than those of the A. aurita. When the R. esculentum medusae were more than 30 mm in bell diameter, their survival rate exceeded 92%. Silver pomfrets serve as a type of potential predators on A. aurita in coastal waters, and they have little influence on R. esculent um with a size exceeding 30 mm. Besides, A. aurita may be able to be used as fish prey in silver pomfret artificial breeding. [ABSTRACT FROM AUTHOR]

Amplified fragment length polymorphisms (AFLP) markers were developed to assess the genetic variation of populations and clones of Rhopilema esculentum Kishinouye (Scyphozoa, Rhizostomatidae). One hundred and seventy-nine loci from 56 individuals of two hatchery populations and two wild populations were genotyped with five primer combinations. The polymorphic ratio, Shannon's diversity index and average heterozygosity were 70.3%, 0.346 and 0.228 for the white hatchery population, 74.3%, 0.313, and 0.201 for the red hatchery population, 79.3%, 0.349, and 0.224 for the Jiangsu wild population, and 74.9%, 0.328 and 0.210 for the Penglai wild population, respectively. Thus, all populations had a relatively high level of genetic diversity. A specific band was identified that could separate the white from the red hatchery population. There was 84.85% genetic differentiation within populations. Individual cluster analysis using unweighted pair-group method with arithmetic mean (UPGMA) suggested that hatchery populations and wild populations could be divided. For the hatchery populations, the white and red populations clustered separately; however, for the wild populations, Penglai and Jiangsu populations clustered together. The genetic diversity at the clone level was also determined. Our data suggest that there are relatively high genetic diversities within populations but low genetic differentiation between populations, which may be related to the long-term use of germplasm resources from Jiangsu Province for artificial seeding and releasing. These findings will benefit the artificial seeding and conservation of the germplasm resources. [ABSTRACT FROM AUTHOR]