Purpuratus Larvae Research Articles

Scallop larvae resistant to a pathogenic Vibrio harbor host-associated bacteria with probiotic potential

The breeding of the scallop Argopecten purpuratus is threatened by mass mortality events mostly caused by bacterial pathogens of the genus Vibrio affecting larvae and spat cultivated in hatcheries. A strong genetic basis for the resistance of A. purpuratus larvae to vibriosis has been demonstrated, which is associated with an efficient energy metabolism and immunocompetence. However, various factors, including the microbiota composition, have a notable impact on the outcome of an infection in numerous animal models, affecting their resistance. In this context, we aimed to explore the possible contribution of host-associated bacteria to the resistance of scallop larvae to Vibrio bivalvicida VPAP30. To achieve this, we isolated culturable bacteria from four scallop families displaying contrasted resistance to VPAP30 infection. We taxonomically assigned 75 bacterial isolates by 16S rDNA sequencing, and we found that 34 isolates were exclusively associated with resistant larvae. Then, 8 isolates were pre-selected as potential probiotics based on their exclusivity to the resistant families and bibliographic records of their use. Results highlighted three isolates displaying potential, belonging to the genera Psychrobacter, Hydrogenophaga, and Shewanella. The three isolates displayed in vitro antagonistic activity against VPAP30 and a protective effect on scallop veliger larvae against infection. We observed three main aspects of this protective effect: scallop larvae pretreated with each of the three probiotic candidates showed (i) no mortality after 24 h infection, (ii) an earlier induction of immune pattern recognition receptors, and (iii) no increase in total Vibrio spp. counts after infection with VPAP30. The findings demonstrated that scallop larvae resistant to vibriosis carry distinct bacteria possessing probiotic properties suitable for the rearing of scallop larvae. This study reinforces the significance of host resistance-related microorganisms as a potential source for discovering novel endogenous probiotics with biotechnological applications.

Identification of miRNAs in sea urchin Strongylocentrotus purpuratus larvae response to pH stress

MicroRNAs (miRNAs) are a class of small, endogenous, non-coding RNAs that regulate gene expression through transcriptional repression of messenger RNA. They play significant roles in many physiological and biochemical processes in eukaryotes. Ocean acidification can impact the development, survival, growth and physiology of many marine organisms. Here, we performed miRNA transcriptome analysis of the sea urchin Strongylocentrotus purpuratus larvae exposed to CO2-driven seawater acidification. We generated 10.6 and 10.8 million clean reads from the malformed S. purpuratus larva after CO2 treatment and the larvae with the normal bone development respectively. A total of 682 conserved and 17 novel miRNAs were identified. Target genes of the differential expression miRNAs were also predicted, which contained growth-related genes (collagenase, collagen and HSP70-binding protein 1), spicule formation-related gene (carbonic anhydrase transcript variant X1) and skeletogenesis-related genes (breast carcinoma amplified sequence 2). Target genes of the differentially expressed miRNAs were used to perform KEGG pathway analysis and were found to be involved in the proteasome and oxidative phosphorylation. These results provide a relatively large number of miRNAs transcriptome resource and provide a foundation for further analyses on the functional and molecular mechanisms of S. purpuratus larvae impacted by ocean acidification.

Neuropeptidergic Systems in Pluteus Larvae of the Sea Urchin Strongylocentrotus purpuratus: Neurochemical Complexity in a "Simple" Nervous System.

The nervous system of the free-living planktonic larvae of sea urchins is relatively “simple,” but sufficiently complex to enable sensing of the environment and control of swimming and feeding behaviors. At the pluteus stage of development, the nervous system comprises a central ganglion of serotonergic neurons located in the apical organ and sensory and motor neurons associated with the ciliary band and the gut. Neuropeptides are key mediators of neuronal signaling in nervous systems but currently little is known about neuropeptidergic systems in sea urchin larvae. Analysis of the genome sequence of the sea urchin Strongylocentrotus purpuratus has enabled the identification of 38 genes encoding neuropeptide precursors (NP) in this species. Here we characterize for the first time the expression of nine of these NP genes in S. purpuratus larvae, providing a basis for a functional understanding of the neurochemical organization of the larval nervous system. In order to accomplish this we used single and double in situ hybridization, coupled with immunohistochemistry, to investigate NP gene expression in comparison with known markers (e.g., the neurotransmitter serotonin). Several sub-populations of cells that express one or more NP genes were identified, which are located in the apica organ, at the base of the arms, around the mouth, in the ciliary band and in the mid- and fore-gut. Furthermore, high levels of cell proliferation were observed in neurogenic territories, consistent with an increase in the number of neuropeptidergic cells at late larval stages. This study has revealed that the sea urchin larval nervous system is far more complex at a neurochemical level than was previously known. Our NP gene expression map provides the basis for future work, aimed at understanding the role of diverse neuropeptides in control of various aspects of embryonic and larval behavior.

Onset of feeding in juvenile sea urchins and its relation to nutrient signalling

ABSTRACTThe purple sea urchin, Strongylocentrotus purpuratus, has been the focus of extensive ecological and developmental research over the years. Strongylocentrotus purpuratus larvae transition into the juvenile stage after an extensive planktonic period. The metamorphic transition is characterized by dramatic changes in morphology and physiology of the juvenile compared to the larval form and mechanisms underlying this process, especially the early days post-settlement, remain poorly understood. We used SEM and phalloidin stain analysis as well as whole mount in situ hybridization to gain a detailed understanding of juvenile development in relation to nutrient signalling [insulin-like growth factor (IIS), FoxO (forkhead box, sub-group ‘O’) and TOR (target of rampamycin), also known as IIS/TOR/FoxO signalling]. Our results show that the majority of juvenile feeding features are fully developed only after 8-days of juvenile development, leaving an extensive period of nutritional stress. We found that FoxO gene expression increases during that time period and is localized in juvenile tube feet, potentially associated with sensory structures involved in nutrient signalling. Our data complement existing work on sea urchin juvenile development and shed new light on the perimetamorphic period of Strongylocentrotus purpuratus, with respect to nutrient signalling and the potential stressful pre-feeding period of juvenile sea urchins.

Competition between mussels at the rocky intertidal zone of La Lobería, Río Negro, Argentina

Competitive interactions between individuals from a single or different species can regulate population densities and individual growth. Two mussel species, Brachidontes rodriguezii and Perumytilus purpuratus , coexist in the rocky intertidal zone of La Loberia, Rio Negro Province, Argentina. The aim of this study was to analyse the effect of intra- and interspecific competition in the growth and mortality of both bivalve species. An experiment was conducted to evaluate the intra- and interspecific competition using asbestos cement plates of 10 x 10 cm varying mussel densities. The results showed a trend toward decreasing size of B. rodriguezii with increasing density of conspecifics and when it coexists with P. purpuratus , but only the width of P. purpuratus showed significant increase in presence of B. rodriguezii . Mortality of B. rodriguezii and P. purpuratus did not significantly differ between treatments. Limited supply of P. purpuratus larvae or local tidal conditions that differentially affect each species could be leading to weak competition between both mussels species, thus allowing their coexistence.

Histamine is a modulator of metamorphic competence in Strongylocentrotus purpuratus (Echinodermata: Echinoidea).

BackgroundA metamorphic life-history is present in the majority of animal phyla. This developmental mode is particularly prominent among marine invertebrates with a bentho-planktonic life cycle, where a pelagic larval form transforms into a benthic adult. Metamorphic competence (the stage at which a larva is capable to undergo the metamorphic transformation and settlement) is an important adaptation both ecologically and physiologically. The competence period maintains the larval state until suitable settlement sites are encountered, at which point the larvae settle in response to settlement cues. The mechanistic basis for metamorphosis (the morphogenetic transition from a larva to a juvenile including settlement), i.e. the molecular and cellular processes underlying metamorphosis in marine invertebrate species, is poorly understood. Histamine (HA), a neurotransmitter used for various physiological and developmental functions among animals, has a critical role in sea urchin fertilization and in the induction of metamorphosis. Here we test the premise that HA functions as a developmental modulator of metamorphic competence in the sea urchin Strongylocentrotus purpuratus.ResultsOur results provide strong evidence that HA leads to the acquisition of metamorphic competence in S. purpuratus larvae. Pharmacological analysis of several HA receptor antagonists and an inhibitor of HA synthesis indicates a function of HA in metamorphic competence as well as programmed cell death (PCD) during arm retraction. Furthermore we identified an extensive network of histaminergic neurons in pre-metamorphic and metamorphically competent larvae. Analysis of this network throughout larval development indicates that the maturation of specific neuronal clusters correlates with the acquisition of metamorphic competence. Moreover, histamine receptor antagonist treatment leads to the induction of caspase mediated apoptosis in competent larvae.ConclusionsWe conclude that HA is a modulator of metamorphic competence in S. purpuratus development and hypothesize that HA may have played an important role in the evolution of settlement strategies in echinoids. Our findings provide novel insights into the evolution of HA signalling and its function in one of the most important and widespread life history transitions in the animal kingdom - metamorphosis.

Species-specific effects of fluid shear on grazing by sea urchin larvae: comparison of experimental results with encounter-model predictions

Small-scale turbulence can alter the rate of plankton predator–prey encounters. Encounter models predict that prey ingestion by slow-swimming zooplankton is enhanced at low levels of turbulence. We investigated whether small-scale turbulence increases ingestion for the slow-swimming, suspension-feeding pluteus larvae of the white urchin Lytechinus pictus and the purple urchin Strongylocentrotus purpuratus. Model predictions of the critical level of turbulence, ecr, above which encounters due to turbulence are greater than those due to behavior (swimming or suspension feeding) alone, were experimentally tested using shortand long-term grazing treatments. Because urchin larvae are smaller than the smallest eddy scales of turbulence and thus experience turbulence as laminar shear, larvae were exposed to flow conditions using a simple laminar shear flow with dissipation rates, e, of 0, 0.1, 0.4, and 1 cm2 s–3. Short-term ingestion of beads by L. pictus larvae was unaffected by e < 1 cm2 s–3 but was 30% greater at this level, which was greater than ecr based on flow speeds produced in suspension feeding. Long-term flow treatments with algal prey had no significant effect on grazing or growth. Short-term ingestion of beads by S. purpuratus larvae was unaffected by e < ecr based on suspension feeding; the effect of long-term flow exposure on ingestion and growth could not be investigated because of high mortality, suggesting greater sensitivity to flow exposure compared to L. pictus. Experimental results are consistent with model predictions that ecr is high, and thus levels of turbulence in the ocean are not expected to significantly increase ingestion and reduce food limitation in suspension-feeding urchin larvae.

Egg size and the evolution of phenotypic plasticity in larvae of the echinoid genus Strongylocentrotus

Planktotrophic larvae grow by utilizing energy obtained from food gathered in the plankton. Morphological plasticity of feeding structures has been demonstrated in multiple phyla, in which food-limited larvae increase feeding structure size to increase feeding rates. However, before larvae can feed exogenously they depend largely on material contained within the egg to build larval structures and to fuel larval metabolism. Thus, the capacity for plasticity of feeding structures early in development may depend on egg size. Using the congeneric sea urchins Strongylocentrotus franciscanus and S. purpuratus, which differ in egg volume by 5-fold, I tested whether the degree of expression of feeding structure (larval arm length) plasticity is correlated with differences in the size of the egg. I experimentally manipulated egg size of S. franciscanus (the larger-egged species) by separating blastomeres at the 2-cell stage to produce half-sized larvae. I reared half-size and normal-size larvae under high and low food treatments for 20 days. I measured arm and body lengths at multiple ages during development and calculated the degree of plasticity expressed by larvae from all treatments. Control and unmanipulated S. franciscanus larvae (from ∼ 1.0 nl eggs) had significantly longer arms relative to body size and a significantly greater degree of plasticity than half-sized S. franciscanus larvae (from < 0.18 nl eggs), which in turn expressed a significantly greater degree of plasticity than S. purpuratus larvae (from ∼ 0.3 nl eggs). These results indicate that egg size affects larval arm length plasticity in the genus Strongylocentrotus; larger eggs produce more-plastic larvae both in an experimental and a comparative context. However, changes in egg size alone are not sufficient to account for evolved differences in the pattern of plasticity expressed by each species over time and may not be sufficient for the evolutionary transition from feeding to non-feeding.

Neuron‐specific expression of a synaptotagmin gene in the sea urchin Strongylocentrotus purpuratus

Interest in chordate evolution has emphasized a need for a better understanding of the comparative neuroanatomy of invertebrate deuterostomes. However, molecular and genetic approaches to neurobiological studies in these groups are hampered by a lack of neuron-specific molecular markers. A monoclonal antibody, 1E11, is neuron specific and is useful in identification of neural structures in larvae and adults of echinoderms, hemichordates, and urochordates. To identify a neuron-specific gene product, we have characterized the antigen recognized by 1E11. In immunoblots and immunoprecipitations of neural tissue from adult Strongylocentrotus purpuratus, 1E11 recognizes a 57-kDa band. Tandem mass spectrometry of trypsin digests of the 57-kDa band permitted peptide mass mapping and sequencing of five peptides. All of the sequenced peptides, and 12 additional mass-mapped peptides, are found within the open reading frame of a cDNA encoding synaptotagmin B (Sp-SynB). In situ RNA hybridizations with synaptotagmin B probes with S. purpuratus larvae reveal a pattern of expression that is similar to that revealed by the antibody 1E11. Antibodies produced against a bacterially expressed Sp-SynB protein recognize a 57-kDa protein and colocalize with 1E11. When a full-length Sp-SynB cDNA is expressed in chicken embryonic cells, the cells become immunoreactive to 1E11. We conclude that synaptotagmin B is a gene expressed in neurons that has conserved epitopes in other invertebrate deuterostomes.

Supplementation of EPA and DHA emulsions to a Dunaliella tertiolecta diet: effect on growth and lipid composition of scallop larvae, Argopecten purpuratus (Lamarck, 1819)

Hatchery-reared Argopecten purpuratus larvae were fed a Dunaliella tertiolecta-diet (DUN-diet) supplemented with 0%, 20% or 40% of a highly unsaturated fatty acid (HUFA) lipid emulsion (ICES Reference Emulsions), rich in docosahexaenoic acid (22:6 n−3, DHA) and eicosapentaenoic acid (20:5 n−3, EPA). A standard diet (ST-diet), consisting of a mixture of Isochrysis galbana (T-iso) and Chaetoceros neogracile was used as a positive control. The supplementation of 20% and 40% HUFA-emulsion to the DUN-diet led to a significantly better daily growth rate (136–177% as compared to DUN-diet) and a higher percentage of eyed-pediveliger larvae in comparison with the non-supplemented DUN-diet. Practically no eyed-larvae were present when fed with D. tertiolecta only, whereas 17% of the larvae developed an eyespot when fed a 20% HUFA-supplement. An increase of the lipid supplement from 20% to 40% further improved the larval performance, although the difference was not significant and less than compared with the changes between the non-supplemented DUN-diet and the DUN+20%-diet. The poor performance of larvae that received D. tertiolecta only was attributed to the depletion of the lipid reserves in the triglyceride fraction and possibly to the very low levels of saturated fatty acids 14:0 and 16:0, rather than to the low levels of EPA and DHA (in absolute terms). Limited biosynthesis of DHA from EPA as a precursor molecule is proposed. Despite similar relative and absolute fatty acid levels of DHA and EPA in larvae that received the ST-diet and the DUN+40%HUFA-diet, the former performed significantly better. Other factors such as the arachidonic acid (20:4 n−6) content and the n−3/ n−6 ratio are suggested to play a determining role.

Addition of inhibitor-producing bacteria to mass cultures of Argopecten purpuratus larvae (Lamarck, 1819)

Assays were carried out to test the feasibility of adding inhibitor-producing bacteria (IPB) to mass cultures of Argopecten purpuratus larvae with the aim of replacing the use of antibiotics to minimize deleterious effects of pathogenic bacteria in these cultures. Previously identified IPB ( Vibrio sp. C33 and Pseudomonas sp. 11) and a newly identified Bacillus sp. (strain B2) were employed in both summer and winter seasons in a commercial hatchery in northern Chile (23°40′S). Results demonstrated that addition of the selected bacterial cultures did not adversely affect the scallop larvae. In all tests, addition of IPB permitted completion of the pelagic larval phase without the use antibiotic treatment. Observations were also made on changes in the bacterial flora of the larvae upon addition of the IPB strains.

Selective incorporation of bacteria by Argopecten purpuratus larvae: implications for the use of probiotics in culturing systems of the Chilean scallop

Experiments on ingestion rates, colonization and impact of inhibitory producer substances bacteria (IPB) on larvae of Argopecten purpuratus, were carried out to evaluate potential use of bacteria as probiotics in cultures of this Chilean scallop. Three selected strains, named as 11, C33 and 77, obtained from larval cultures of A. purpuratus were tested at different concentrations and incubation times. After 6 h of incubation at a concentration of 10 6 cells ml −1, A. purpuratus larvae ingested cells of strains 11 and 77, but not those of C33. When comparing bacterial incorporation among these strains, the 77 became the dominant bacteria of the larval microflora, causing no differences in larval survival at different bacterial concentrations. Our results suggest that strain 77 appears as a potential probiotic for scallop larvae and hence, as a promising method to control and prevent infections in hatcheries systems.

Potential probiotic strains in the culture of the Chilean scallop Argopecten purpuratus (Lamarck, 1819)

This study reports on the search for naturally occurring bacteria which are able to promote the growth and survival of Argopecten purpuratus larvae by inhibiting the activity of other deleterious bacteria that flourish in hatchery cultures. A total of 506 bacterial isolates, obtained from laboratory and hatchery sources, were evaluated for the production of substances inhibitory to a Vibrio anguillarum-related (VAR) larval pathogen, of which 11 (2.2%) were found positive. One of these strains ( Vibrio sp.), when used as a pre-treatment, protected the scallop larvae against subsequent experimental infection with the VAR pathogen.

Effects of different feeding regimens on larval growth and the energy budget of juvenile Chilean scallops, Argopecten purpuratus Lamarck

Effects of continuous and discontinuous feeding regimens on growth and survival of Argopecten purpuratus larvae and the partitioning of energy in juveniles are presented. Larvae from a single cohort were cultured under three feeding regimens: (1) fed once a day, (2) fed twice a day and (3) fed continuously, while keeping the total daily amount of food equal for each treatment. Larvae cultured under the continuous feeding regimen had faster growth and higher survival than those fed discontinuously. Early juveniles from a single cohort of larvae were cultured under the same conditions as larvae. Organic weight, energy content, filtration rate, oxygen consumption and excretion rate were measured after 16 days under these regimens. Maximal increase in shell length and in ash-free dry weight was attained by those juveniles fed continuously. No significant difference in energy content was found between the three groups of individuals. Juveniles fed continuously showed a higher metabolic rate than those fed once or twice a day. Ingestion rate and ammonia excretion did not differ significantly among individuals in the three feeding regimens. Results indicate there is better assimilation of food in both larvae and juveniles under a continuous feeding regimen.

Pathogenicity studies on a Vibrio anguillarum-related (VAR) strain causing an epizootic in Argopecten purpuratus larvae cultured in Chile

DAO Diseases of Aquatic Organisms Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials DAO 22:135-141 (1995) - doi:10.3354/dao022135 Pathogenicity studies on a Vibrio anguillarum-related (VAR) strain causing an epizootic in Argopecten purpuratus larvae cultured in Chile Riquelme C, Hayashida G, Toranzo AE, Vilches J, Chavez P A Vibrio anguillarum-related (VAR) strain, isolated in pure culture from an epizootic in a commercial hatchery producing Argopecten purpuratus, was characterized, and its potential pathogenicity to veliger larvae of A. purpuratus determined. Experimental challenges indicated that the bacterium affects larval survival at concentrations of 104 to 108 cells ml-1. The effect of water quality and temperature on pathogenicity was also evaluated. Larval survival in seawater filtered through 5 um pore-size membranes was 45.6%, whereas using seawater passed through 1 and 0.2 um filters, larval survival increased to 66.4 and 80.4% respectively. Temperature also affected pathogenicity as larval survival at 15*C for 24 h was 69.3% but decreased to 30 and 26.9% at 20 and 25*C, respectively. Toxic activity was found in cell-free supernatant of bacterial culture. Larval survival was reduced to 68.9 and 36.4% after 20 and 40% (v/v) of supernatant, respectively, was added to the rearing water. These results suggest that exotoxins produced by the VAR strain play an important role in its pathogenicity for scallop larvae. Argopecten purpuratus . Larvae . Vibrio anguillarum-related (VAR) . Pathogenicity . Exotoxins Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in DAO Vol. 22, No. 2. Publication date: June 15, 1995 Print ISSN:0177-5103; Online ISSN:1616-1580 Copyright © 1995 Inter-Research.