Studies on the seasonal variations in the proximate composition of ascidians from the Palk Bay,Southeast coast of India

Objective:To investigate the seasonal fluctuations of the proximate composition of the ascidians muscle.Methods:The moisture content was estimated by drying 1 g of fresh tissue at a constant temperature at 105(?)for 24 h.The loss of weight was taken as moisture content.The total protein was estimated using the Biuret method.The total carbohydrate in dried sample was estimated spectrophotometrically following the phenol-sulphuric acid method.The lipid in the dried sample tissue was gravimetrically estimated following the chloroform-methanol mixture method.Ash content was determined gravimetrically by incinerating 1 g dried sample in muffle furnace at about 550℃for 6 h and results are expressed in percentage.Results:It was found very difficult to compare the monthly variations,as all the ten species,exhibited wide fluctuations in their proximate compositions.For the sake of convenience,average seasonal values were calculated by summing the monthly values.Conclusions:The proximate composition of the 10 commonly available ascidians showed high nutritive value and hence these groups especially solitary ascidians can be recommended for human consumption in terms of pickles,soup,curry and others after ensuring the safety of consumers.

Observations on the morphology of embryonic and larval development in Styela canopus Savigny

The morphological characters on different developmental phases of embryo and larva and the schedule of the whole early developmental process in Styela canopus were observed and described. The types of reproduction and early development as well as the morphology, of egg and larva in different ascidian species were compared. Styela canopus is oviparous. Its egg, 230.4 similar to 336.0 mum in diameter, is equipped with extraembryonic cell layers measured 43.2 similar to 63.0 mum thick. The early development of Styela canopus is typical urodele development, including fertilization, cleavage, gastrulation, tadpole in membrane, tadpole, initiating metamorphosis and juvenile. The tadpole of Styela canopus, with a length of 0.6 similar to 0. 9 mm, consists of trunk and tail. There are obvious notochord, ocellus and adhesive papillae in the tadpole. Under the water temperature of (25 +/- 0-5) degreesC and the salinity of 27.0, the larva was hatched after 9.5 similar to 11.0 h since the fertilization.

The determination of larval metamorphic competence of Styela canopus Savigny

The larvae of Styela canopus show the highest rates of settlement and metamorphosis when treated with 40 mM KCl-elevated seawater at 25 degreesC in temperature and 27.0 in salinity. Induced by 40 mM KCl-elevated seawater, it took Styela canopus larvae approximately 3 h after hatching to develop competence to settle and metamorphose. The present experiment shows that Styela canopus larvae is an ideal model organism for examining the efficiency of antifouling substance.

Context‑dependent antioxidant defense system(ADS)‑based stress memory in response to recurrent environmental challenges in congeneric invasive species

Marine ecosystems are facing escalating environmental fluctuations owing to climate change and human activities,imposing pressures on marine species.To withstand recurring environmental challenges,marine organisms,especially benthic species lacking behavioral choices to select optimal habitats,have to utilize well-established strategies such as the antioxidant defense system(ADS)to ensure their survival.Therefore,understanding of the mechanisms governing the ADS-based response is essential for gaining insights into adaptive strategies for managing environmental challenges.Here we conducted a com-parative analysis of the physiological and transcriptional responses based on the ADS during two rounds of'hypersalinity-recovery'challenges in two model congeneric invasive ascidians,Ciona robusta and C.savignyi.Our results demonstrated that C.savignyi exhibited higher tolerance and resistance to salinity stresses at the physiological level,while C.robusta demonstrated heightened responses at the transcriptional level.We observed distinct transcriptional responses,particularly in the utilization of two superoxide dismutase(SOD)isoforms.Both Ciona species developed physiological stress memory with elevated total SOD(T-SOD)and glutathione(GSH)responses,while only C.robusta demonstrated transcriptional stress memory.The regulatory distinctions within the Nrf2-Keap1 signalling pathway likely explain the formation disparity of transcriptional stress memory between both Ciona species.These findings support the'context-dependent stress memory hypothesis',emphasizing the emergence of species-specific stress memory at diverse regulatory levels in response to recurrent environmental challenges.Our results enhance our understanding of the mechanisms of environmental challenge manage-ment in marine species,particularly those related to the ADS.

Establishment of a developmental atlas and transgenetic tools in the ascidian Styela clava

The ascidian Styela clava is an ecologically important species that is distributed along coastal regions worldwide.It has a long history as a model animal for evolutionary and developmental biology research owing to its phylogenetic position between vertebrates and invertebrates,and its classical mosaic expression patterns.However,the standard developmental atlas and protocols and tools for molecular manipulation of this organism are inadequate.In this study,we established a standard developmental table and provided a web-based digital image resource for S.clava embryogenesis at each developmental stage from fertilized eggs to hatching larvae by utilizing confocal laser microscopy and 3D reconstruction images.It takes around 10 h for fertilized eggs to develop into swimming larvae and 20–30 min to complete the tail regression processes at the metamorphic stage.We observed that the notochord cells in S.clava embryos did not produce an extracellular lumen like Ciona robusta,but showed polarized elongation behaviors,providing us an ideal comparative model to study tissue morphogenesis.In addition,we established a chemical-washing procedure to remove the chorion easily from the fertilized eggs.Based on the dechorionation technique,we further realized transgenic manipulation by electroporation and successfully applied tissue-specific fluorescent labeling in S.clava embryos.Our work provides a standard imaging atlas and powerful genetic tools for investigating embryogenesis and evolution using S.clava as a model organism.

Morphogenesis: a focus on marine invertebrates

Morphogenesis is a process describing how the shapes of living tissues and bodies are created during development. Livingand fossil organisms exhibit enormously diverse tissue architecture and body forms, although the functions of organs areevolutionally conserved. Current knowledge reveals that relatively conserved mechanisms are applied to control developmentamong different species. However, the regulations of morphogenesis are quite diverse in detail. Animals in the oceandisplay a wide range of diversity of morphology suitable for their seawater environment. Nevertheless, compared with theintensive studies on terrestrial animals, research on marine animal morphogenesis is still insufficient. The increasing genomicdata and the recently available gene editing methods, together with the fast development of imaging techniques, quantitativeanalyses and biophysical models, provide us the opportunities to have a deeper understanding of the principles that drivethe diverse morphogenetic processes in marine animals. In this review, we summarize the recent studies of morphogenesisand evolution at molecular, cellular and tissue levels, with a focus on three model marine animals, namely ascidians, seaurchins and sea anemones.

Prepatellamide A, a new cyclic peptide from the ascidian Lissoclinum patella

A new cyclic peptide, prepatellamide A (1), along with three known cyclic peptides (2)— (4), was isolated from the ascidianLissoclinum patella. The structure of prepatellamide A was determined from one- and two-dimensional1H and13C NMR spectra. The known cyclic peptides were identified as patellamides A (2), B (3) and C (4).

Cultivation of gut microorganisms of the marine ascidian Halocynthia roretzi reveals their potential roles in the environmental adaptation of their host

It has long been known that abundant symbiotic bacteria exist in the tunic and gut of marine ascidians,and that these play crucial roles in host development,physiological metabolism,and environmental adaptation.However,the identity,roles and functions of these symbiotic bacteria are known for only a few strains.In this study,we isolated and cultivated 263 strains of microorganisms from the intestine of the marine ascidian Halocynthia roretzi through a combination of aerobic and anaerobic culture approaches.Most cultivated species,both aerobic and anaerobic,from ascidian stool samples belonged to the genus Bacillus based on 16S rDNA sequencing identification and phylogenetic assays.The distribution of cultured bacteria varied with seasonal changes in environmental conditions.To explore the functions of cultured bacteria,we screened out a strain of Serratia sp.whose extracts showed high antibacterial activity against aquatic pathogens.These findings revealed the potential roles of gut microorganisms in ascidian defense and environmental adaptation,thus providing insights into the interaction and co-evolution between gut bacteria and their hosts.