Trochophore Stage Research Articles

Sensitivity assessment of Biomphalaria glabrata (SAY, 1818) using reference substance sodium dodecyl sulfate for ecotoxicological analyzes.

Sodium dodecyl sulfate (SDS) is a surfactant used and recommended by regulatory agencies as a reference substance in ecotoxicological analyzes. In this work, acute toxicity assays were performed with adults and embryos of the freshwater snail Biomphalaria glabrata, an endemic organism with environmental and public health importance, to evaluate the effects of the surfactant and establish a sensitivity control chart. The organisms were exposed to SDS for 24 h to a range of concentrations, as well as a control group. Six assays were performed to establish the control chart for adults (with a median LC50 of 36.87 mg L-1) and differential sensitivity was observed at each embryonic stage (EC50 = blastulae 33.03, gastrulae 35.03, trochophore 39.71 and veliger 72.55 mg L-1). The following behavioral responses were observed in exposed adult snails: release of hemolymph and mucus, body outside the shell, and penile overexposure. Embryos at the blastulae and gastrulae stages were more sensitive, and teratogenic effects were accentuated in the trochophore stage. The difference in results obtained between adults and embryos underscore the importance of carrying out analyzes at different developmental stages. The serial assays established with SDS for B. glabrata demonstrated efficiency and constancy conditions in the assays with good laboratory practice standards. The wide distribution of Biomphalaria species in several countries, their easy maintenance and cultivation in the laboratory, in addition to ecological importance, make them economical alternatives for ecotoxicological assays.

Comparison of neurogenesis in bivalves with different types of development

The presence of different types of larvae within the same class suggests a broad ecological diversification. A clear comparison of bivalve larval nervous systems would give a broader view on evolutionary and ecological picture of the clade in question. The present study focused on the neurodevelopment in two bivalve species with different larval types: pericalymma of Acila insignis (Bivalvia: Protobranchia) and veliger of Spisula sybillae (Bivalvia: Autobranchia). It was shown that the pioneer dorsal and ventral neurons in S. sybillae appear at the trochophore stage. Subsequently, future three paired ganglia are developed on the nerve cords in pediveliger. In the pericalymma of A. insignis, serotonin- and FMRFamide-positive cells are found in the apical organ (AO), as well as two pairs of FMRFamide positive neurons are detected on dorsal and posterior part of pericalymma. A comparative analysis showed significant differences in the larval neuromorphology between veliger and pericalymma. In contrast to the S. sybillae veliger, the nervous system of the A. insignis pericalymma is simple, likely due to its different lifestyle. The larval nervous system in the species under study has features characteristic of Lophotrochozoa and Spiralia.

Regulatory role of ETS1 transcription factor in hemocytes proliferation in Anadara granosa

The ETS1 transcription factor is crucial in the process of biological development. In vertebrate, ETS1 plays a pivotal role in promoting endothelial cell proliferation and angiogenesis. However, the identity and function of ETS1 remains unclear in mollusks. In this study, an ETS1 homolog (named as AgETS1) was identified in blood clam Anadara granosa (synonym: Tegillarca granosa). The full length of the AgETS1 transcription factor is 1569 bp, consisting of 539 amino acids, including the Sterile Alpha Motif (SAM) domain, which can recognize and bind to sequence of GGAA. Tissue expression analysis of A. granosa showed that AgETS1 exhibits the highest expression level in the gill tissues (51.5-fold of that in hemocyte, p < 0.05). AgETS1 mRNA transcripts were predominantly expressed during larval development, from zygote to trochophore stage. Moreover, the expression levels of AgETS1 in blood clams with high hemoglobin concentration (hemocyte count >1.75 × 108 cells/mL) were significantly higher than that in blood clams with low hemoglobin concentration (hemocyte count <8.5 × 107 cells/mL) (p < 0.05). RNA interfering (RNAi) of AgETS1 induced a corresponding decrease in the number of hemocytes in the hemolymph and a reduction in EdU-marked proliferating cells in the gill tissue. These results indicated that the ETS1 actively regulated the proliferation of hemocytes in A. granosa.

Studies on embryo development and larval feeding of clam Paphia textile

The present study investigated the embryonic development, growth, metamorphosis, locomotory patterns, and feeding behaviors of Paphia textile larvae, offering dietary suggestions based on observed patterns. The larvae were subjected to a dietary regimen consisting of nine microalgae species at various developmental stages (1, 4, 7, 10, 13, and 16 days post-hatching). One hour after each feeding session, their feeding patterns were carefully documented. To assess digestion, larvae that had consumed the microalgae were filtered, rinsed, and placed in filtered seawater. The embryonic development of P. textile encompassed distinct stages, including the fertilized egg, emergence of the first and second polar bodies, progression through the 2–32 cell stage, morula stage, blastula stage, gastrula stage, trochophore stage, and ultimately the D-larvae stage. Movement patterns revealed that the larvae primarily utilized their cilia for locomotion and feeding. From a transverse perspective, they moved clockwise, tracing an irregular circular path. Vertically, they exhibited spiral movements, ascending or descending as needed. As they entered the late stage, they transitioned to using reciprocal expansion of their axe feet for crawling and filtering food through their gills. Throughout their development, the larvae were fed a variety of microalgae species, including Chlorella vulgaris, Nannochloropsis oculata, Pavlova viridis, Dicrateria zhanjiangensis, and Isochrysis galbana. At 4 days old, they began consuming Dunaliella salina, and at 7 days, they incorporated Platymonas subcordiformis into their diet. By 10 days of age, they had expanded their food choices to include Chaetoceros muelleri. However, it was noted that larvae frequently suffered from indigestion or incomplete digestion when fed excessive amounts of C. vulgaris and N. oculata. Therefore, it is recommended to commence the larval culture of P. textile using P. viridis, D. zhanjiangensis, and I. galbana as the primary dietary sources. Furthermore, a feeding strategy emphasizing small, frequent meals is recommended to promote optimal digestion and larval health.

Paternal heat exposure affects progeny larval development in green-lipped mussels Perna canaliculus

The green-lipped mussel Perna canaliculus is critically important to the New Zealand aquaculture industry. However, the rise in marine heatwave (MHW) events poses an emerging threat to this industry through summer mortality events. This study investigated the potential for paternally mediated transgenerational plasticity to improve offspring performance under heat stress. We simulated a week-long MHW event, exposing male P. canaliculus broodstock to elevated (22°C) or ambient (17.5°C) temperatures immediately prior to spawning, and evaluated the effects of paternal heat exposure on successful development, size and acute thermal tolerance of their larvae that were also reared under ambient or elevated (20°C) temperatures through to completion of the lecithotrophic trochophore stage. Elevated paternal and larval temperatures both increased incidence of abnormal development, reducing larval yield, while initial D-veliger shell length was predominantly influenced by developmental temperature, with longer shells formed at 20°C. Veligers from heat-exposed fathers raised under 20°C showed a small, but significant, elevation in lethal tolerance 50 (LT50), the temperature at which 50% of the larvae are predicted to die, when exposed to an additional 1 h heat-shock. These results indicate that paternal heat exposure over a relatively short period can influence offspring performance in this species. The paternal exposure investigated showed limited positive effects on offspring thermal tolerance, which may be outweighed by the negative impact on larval development. As MHWs are forecasted to continue accelerating, understanding transgenerational effects of heat stress will be critical for maintaining high-quality hatchery yields through broodstock selection and may inform wild population forecasting models.

Embryonic and Early Larval Development of the Pacific Razor Clam (Siliqua patula).

AbstractThe Pacific razor clam, Siliqua patula (Sugpiaq: Cingtaataq, Dixon, 1789), is vital to commercial, recreational, and subsistence fisheries across the Pacific Northwest Coast of North America. Despite the species' status as one of the most popular shellfish species harvested in the Pacific Northwest, British Columbia, and Alaska, its larval development has never been fully characterized. Generating a developmental times series, and describing development fully, is crucial for guiding targeted management, developing a mariculture strategy for the species, and providing a more pointed avenue for studies examining the response of S. patula to ocean change. This study presents the first photographic documentation of larval development in S. patula, including the timing of key transitions during embryogenesis and early larval development. Scanning electron microscopy revealed that the larval shell forms via a concretion, a process typically documented in early gastropod development. This novel characterization is pertinent, as it conveys the need for the inclusion of alternative bivalve development processes, such as a concretion, in bivalve research. This study also compared development in S. patula to a global assortment of bivalve species, including two other members of the Pharidae family, determining that the timing to D-veliger and trochophore stages was similar to the majority of bivalves surveyed. While bivalve response to climate change is a topic of great interest, not all species of concern have undergone comprehensive developmental assessments, a requisite benchmark for designing climate change studies that examine early life history sensitivity to such changes. This research supports the use of comprehensive developmental studies as prerequisites for designing climate change experimentation, establishes the necessity of high-magnification and high-resolution scanning electron microscopy within developmental assessments, and provides information about the development of a cornerstone bivalve species.

Hemocyte-like cells in larvae of the freshwater snail Biomphalaria glabrata (Mollusca: Panpulmonata)

Despite undergoing development within a germfree egg capsule, embryos and larvae of the freshwater snail Biomphalaria glabrata possess passive immune protection in the form of parentally-derived antimicrobial proteins in the perivitelline fluid. However, the point at which larvae begin to form their own internal defense system (IDS), which consists of both plasma proteins and hemocytes, is not known. In this study, hemocyte-like cells were observed in mechanically-disrupted late trochophores and veligers of the BS-90 strain of B. glabrata. These cells showed the properties of glass adherence, spreading, motility, and binding and phagocytosing polystyrene microspheres. No hemocyte-like cells were recovered from the early trochophore stage, and therefore their formation first occurs during subsequent maturation. Numbers of hemocyte-like cells increased during larval development. Although the functional significance of these cells is not known, they may represent the initial cellular component of the IDS.

The gastropod Lottia peitaihoensis as a model to study the body patterning of trochophore larvae.

The body patterning of trochophore larvae is important for understanding spiralian evolution and the origin of the bilateral body plan. However, considerable variations are observed among spiralian lineages, which have adopted varied strategies to develop trochophore larvae or even omit a trochophore stage. Some spiralians, such as patellogastropod mollusks, are suggested to exhibit ancestral traits by producing equal-cleaving fertilized eggs and possessing "typical" trochophore larvae. In recent years, we developed a potential model system using the patellogastropod Lottia peitaihoensis (= Lottia goshimai). Here, we introduce how the species were selected and establish sources and techniques, including gene knockdown, ectopic gene expression, and genome editing. Investigations on this species reveal essential aspects of trochophore body patterning, including organizer signaling, molecular and cellular processes connecting the various developmental functions of the organizer, the specification and behaviors of the endomesoderm and ectomesoderm, and the characteristic dorsoventral decoupling of Hox expression. These findings enrich the knowledge of trochophore body patterning and have important implications regarding the evolution of spiralians as well as bilateral body plans.

Monitoring the Reproduction and Development of Eggs in the Sea Hare Aplysia fasciata under Laboratory Conditions

This study looks at spawning patterns, egg mass shape, and embryo development to learn more about the reproductive biology of the A. fasciata species that lives in Libya's coastal waters. In June 2022, eight mature Aplysia fasciata collected from Tajura coast and kept into aquarium contain aerated seawater and marine algae (Ulva lactuca). After five days, a mating couple was seen in the aquarium, and, a mass of fertilized eggs were produced. The clusters eggs were transfer to new aquarium. After few hours, the eggs started development to embryo and at 10 day the egg masses colour changed to a brownish as the embryo developed to the trochophore stage and started to rotate inside capsules. After 16 day of spawning the trochophore broke the egg capsules to hatch as free swimming larvae (the veliger stage). Unfortunately, after 25 day of fertilized eggs all larvae died as veliger. Probably, the result of inadequate conditions for rearing or lack an availability of appropriate food. Whereas A. fasciata has never been recorded before in the Libyan waters.

Nuchal organs in the trochophore of Siboglinum fiordicum (Annelida, Siboglinidae).

Nuchal organs are epidermal sensory structures present in most annelids. Based on one of the interpretations, they serve in larval settlement. Siboglinids lack nuchal organs in adult and larval stages, however, larvae of some siboglinids inhabiting seeps and hydrothermal vents are capable of swimming up to 100 km away from their home hydrothermal field to colonize a new one. One question that remains is, what organ are siboglinid larvae using to search and locate suitable substrates? To determine if any nuchal organs are present in siboglinid larvae, we studied the head and sensory apparatus in successive larval stages in a frenulate, Siboglinum fiordicum (Webb, 1963), using transmission electron microscopy and immunocytochemistry. In the early trochophore stage, we found an unpaired dorsal organ lying proximal to the posterior prototroch. This organ consists of trochoblast- and "covering" cells. Trochoblasts exhibited serotonin-like immunoreactivity and likely correspond to ciliated supporting cells, where cilia and microvilli project into the olfactory chamber. The "covering" cells are characterized by the presence of large nuclei with numerous pores and thick processes that project into the olfactory chamber, forming the contacts with the trochoblast projections. We have shown for the first time the presence of a nuchal-like organ in annelids as early as the trochophore stage. The presence of this organ in siboglinid trochophores while they are still in the inside the female tube suggests that this structure might be associated with functions other than settlement, such as communication or initiation of the departure from her tube.

Cloning and Expression of Sox2 and Sox9 in Embryonic and Gonadal Development of Lutraria sieboldii

The Sox family plays essential roles as transcription factors in vertebrates; however, little is known about the Sox family in Lutraria sieboldii. L. sieboldii are pleasant to eat with a short growth cycle and have become one of the best bottom-seeded enrichment species in Guang Xi. In this study, Sox2 (named LsSox2) and Sox9 (named LsSox9) from L. sieboldii were cloned, and their expression patterns were analyzed. The length of the LsSox2 gene coding sequence was 1011 bp, encoding 336 amino acids, and LsSox9 was 1449 bp, encoding 482 amino acids. LsSox2 had its highest expression levels in the ovary, which were 356 times those in testis, whereas LsSox9 presented higher expression in testis, which was 6 times more highly expressed than in the ovary. LsSox2 exhibited the highest expression during the morula stage, which was 20 times that of the D-shaped larvae or zygote. LsSox9 exhibited two expression peaks, one at the four-cell stage and the other at the trochophore stage, while the lowest expression was in the zygote. LsSox9 was 73 times more highly expressed in the four-cell stage than in the zygote stage. During gonadal development, LsSox2 presented the highest expression in the mature ovary, which was 756 times more highly expressed than in mature testis. LsSox9 presented higher expression in testis at the emission stage which was 6 times more highly expressed than in the ovary. These results indicate that LsSox2 and LsSox9 may play important roles in embryonic and gonadal development.

Molecular basis of ocean acidification sensitivity and adaptation in Mytilus galloprovincialis

SummaryPredicting the potential for species adaption to climate change is challenged by the need to identify the physiological mechanisms that underpin species vulnerability. Here, we investigated the sensitivity to ocean acidification in marine mussels during early development, and specifically the trochophore stage. Using RNA and DNA sequencing and in situ RNA hybridization, we identified developmental processes associated with abnormal development and rapid adaptation to low pH. Trochophores exposed to low pH seawater exhibited 43 differentially expressed genes. Gene annotation and in situ hybridization of differentially expressed genes point to pH sensitivity of (1) shell field development and (2) cellular stress response. Five genes within these two processes exhibited shifts in allele frequencies indicative of a potential for rapid adaptation. This case study contributes direct evidence that protecting species’ existing genetic diversity is a critical management action to facilitate species resilience to climate change.

Phalloidin fluorescence and confocal microscopy reveal the musculature development of clam Ruditapes philippinarum.

Knowledge of early development in bivalves is of great importance to understand the function of animal organ systems and the evolution of phenotypic diversity. Manila clam (Ruditapes philippinarum) is an economically important bivalve living in marine intertidal zones. To determine the pattern of muscle development in the clams, we investigate the characteristics of musculature development utilizing phalloidin staining and confocal microscopy. Myofilaments first appear at the early trochophore stage, and gradually become orderly arranged during the transition from trochophore to veliger. For veliger, larval muscle system is mainly composed of dorsal velum retractors, medio-dorsal velum retractors, ventral velum retractors, ventral larval retractors and anterior and posterior adductor muscles. After metamorphosis, the muscle system of late veliger has been reconstructed, showing the irreversible shrink of velum retractor muscles, the rapid growth of wedge-shaped foot and mantle margins. One of the most striking changes in settled spats is the development of sophisticated architecture of foot musculature, which consists of transverse pedal muscles, anterior foot retractor and posterior foot retractor. These findings will not only provide the basis to understand the dynamic pattern of myogenesis in the burrowing bivalves, but also provide valuable information for comparative analysis of muscle development among bivalves.

Dinophiliformia early neurogenesis suggests the evolution of conservative neural structures across the Annelida phylogenetic tree.

Despite the increasing data concerning the structure of the adult nervous system in various Lophotrochozoa groups, the early events during the neurogenesis of rare and unique groups need clarification. Annelida are a diverse clade of Lophotrochozoa, and their representatives demonstrate a variety of body plans, lifestyles, and life cycles. Comparative data about the early development are available for Errantia, Sedentaria, Sipuncula, and Palaeoannelida; however, our knowledge of Dinophiliformia is currently scarce. Representatives of Dinophiliformia are small interstitial worms combining unique morphological features of different Lophotrochozoan taxa and expressing paedomorphic traits. We describe in detail the early neurogenesis of two related species: Dimorphilus gyrociliatus and Dinophilus vorticoides, from the appearance of first nerve cells until the formation of an adult body plan. In both species, the first cells were detected at the anterior and posterior regions at the early trochophore stage and demonstrated positive reactions with pan-neuronal marker anti-acetylated tubulin only. Long fibers of early cells grow towards each other and form longitudinal bundles along which differentiating neurons later appear and send their processes. We propose that these early cells serve as pioneer neurons, forming a layout of the adult nervous system. The early anterior cell of D. vorticoides is transient and present during the short embryonic period, while early anterior and posterior cells in D. gyrociliatus are maintained throughout the whole lifespan of the species. During development, the growing processes of early cells form compact brain neuropile, paired ventral and lateral longitudinal bundles; unpaired medial longitudinal bundle; and commissures in the ventral hyposphere. Specific 5-HT- and FMRFa-immunopositive neurons differentiate adjacent to the ventral bundles and brain neuropile in the middle trochophore and late trochophore stages, i.e. after the main structures of the nervous system have already been established. Processes of 5-HT- and FMRFa-positive cells constitute a small proportion of the tubulin-immunopositive brain neuropile, ventral cords, and commissures in all developmental stages. No 5-HT- and FMRFa-positive cells similar to apical sensory cells of other Lophotrochozoa were detected. We conclude that: (i) like in Errantia and Sedentaria, Dinophiliformia neurogenesis starts from the peripheral cells, whose processes prefigure the forming adult nervous system, (ii) Dinophiliformia early cells are negative to 5-HT and FMRFa antibodies like Sedentaria pioneer cells.

Molecular characterization, immune responses, and functional activities of manganese superoxide dismutase in disk abalone (Haliotis discus discus)

Superoxide dismutases (SODs) are metalloenzymes that convert superoxide radicals to H2O2 and O2. Although SODs have been extensively studied in mammals and other species, comparative studies in invertebrates, such as abalones, are lacking. Here, we aimed to characterize manganese superoxide dismutase in disk abalone (Haliotis discus discus) (AbMnSOD) by assessing its transcriptional levels at different embryonic developmental stages. Additionally, the temporal expression of AbMnSOD in different abalone tissues in response to bacterial, viral, and pathogen-associated molecular pattern (PAMP) stimuli was investigated. SOD activity was measured at various recombinant protein concentrations via the xanthine oxidase/WST-1 system. Cell viability upon exposure to H2O2, wound healing ability, and subcellular localization were determined in AbMnSOD-transfected cells. AbMnSOD was 681 bp long and contained the SOD-A domain. AbMnSOD expression was higher at the trochophore stage than at the other stages. When challenged with immune stimulants, AbMnSOD showed the highest expression at 6 h post-injection (p.i.) for all stimulants except lipopolysaccharides. In the gills, the highest AbMnSOD expression was observed at 6 h p.i., except for the Vibrio parahaemolyticus challenge. Recombinant AbMnSOD showed concentration-dependent xanthine oxidase activity. Furthermore, AbMnSOD-transfected cells survived H2O2-induced apoptosis and exhibited significant wound gap closure. As expected, AbMnSOD was localized in the mitochondria of the cells. Our findings suggest that AbMnSOD is an essential antioxidant enzyme that participates in regulating developmental processes and defense mechanisms against oxidative stress in hosts.

Transcriptional Responses of Flavin-Containing Monooxygenase Genes in Scallops Exposed to PST-Producing Dinoflagellates Implying Their Involvements in Detoxification

Flavin-containing monooxygenase (FMO) is one of the most prominent xenobiotic metabolic enzymes. It can catalyze the conversion of heteroatom-containing chemicals to polar, readily excretable metabolites and is considered an efficient detoxification system for xenobiotics. Bivalves can accumulate paralytic shellfish toxins (PSTs) produced by dinoflagellates, especially during outbreaks of harmful algal blooms. Exploring FMO genes in bivalves may contribute to a better understanding of the adaptation of these species and the mechanisms of PSTs bioavailability. Therefore, through genome screening, we examined the expansion of FMO genes in two scallops (Patinopecten yessoensis and Chlamys farreri) and found a new subfamily (FMO_like). Our expression analyses revealed that, in both scallops, members of the FMO_N-oxide and FMO_like subfamilies were mainly expressed from the D-stage larvae to juveniles, whereas the FMO_GS-OX subfamily genes were mainly expressed at and prior to the trochophore stage. In adult organs, higher expressions of FMOs were observed in the kidney and hepatopancreas than in other organs. After exposure to PST-producing algae, expression changes in FMOs occurred in hepatopancreas and kidney of both scallops, with more members being up-regulated in hepatopancreas than in kidney for Alexandrium catenella exposure, while more up-regulated FMOs were found in kidney than in hepatopancreas of C. farreri exposed to A. minutum. Our findings suggest the adaptive functional diversity of scallop FMO genes in coping with the toxicity of PST-producing algae.

Characterization of paramyosin protein structure and gene expression during myogenesis in Pacific oyster (Crassostrea gigas).

Paramyosin is a key component of thick filaments in invertebrate muscles. In this study, we isolated the full length cDNA of paramyosin from Pacific oyster (Crassostrea gigas), and determined its pattern of expression during myogenesis. The full length paramyosin (CgPM) cDNA contains an open reading frame (ORF) of 2586bp encoding a 861-amino acid protein. Sequence analysis revealed an assembly competence domain (ACD) and a heptad repeat (d-e-f-g-a-b-c) with 28-residue repeat zones in the CgPM primary structure, a characteristic of coiled-coil protein. Quantitative analysis of CgPM expression revealed a sharp increase in trochophore stage, and peaked at the D-shaped stage. Strong CgPM expression was found in smooth adductor muscle, followed by striated adductor muscle and mantle tissue. Whole-mount in situ hybridization (WISH) showed a restricted pattern of CgPM expression in adductor muscle, larval velum retractor and foot muscles at the umbo and eyed larval stages. These data indicate that CgPM is strongly expressed during larval myogenesis in C. gigas, which provides the basis for further functional studies of paramyosin in oyster to better understand the molecular and cellular mechanisms of muscle formation in mollusks.

Non-collinear Hox gene expression in bivalves and the evolution of morphological novelties in mollusks

Hox genes are key developmental regulators that are involved in establishing morphological features during animal ontogeny. They are commonly expressed along the anterior–posterior axis in a staggered, or collinear, fashion. In mollusks, the repertoire of body plans is widely diverse and current data suggest their involvement during development of landmark morphological traits in Conchifera, one of the two major lineages that comprises those taxa that originated from a uni-shelled ancestor (Monoplacophora, Gastropoda, Cephalopoda, Scaphopoda, Bivalvia). For most clades, and bivalves in particular, data on Hox gene expression throughout ontogeny are scarce. We thus investigated Hox expression during development of the quagga mussel, Dreissena rostriformis, to elucidate to which degree they might contribute to specific phenotypic traits as in other conchiferans. The Hox/ParaHox complement of Mollusca typically comprises 14 genes, 13 of which are present in bivalve genomes including Dreissena. We describe here expression of 9 Hox genes and the ParaHox gene Xlox during Dreissena development. Hox expression in Dreissena is first detected in the gastrula stage with widely overlapping expression domains of most genes. In the trochophore stage, Hox gene expression shifts towards more compact, largely mesodermal domains. Only few of these domains can be assigned to specific developing morphological structures such as Hox1 in the shell field and Xlox in the hindgut. We did not find traces of spatial or temporal staggered expression of Hox genes in Dreissena. Our data support the notion that Hox gene expression has been coopted independently, and to varying degrees, into lineage-specific structures in the respective conchiferan clades. The non-collinear mode of Hox expression in Dreissena might be a result of the low degree of body plan regionalization along the bivalve anterior–posterior axis as exemplified by the lack of key morphological traits such as a distinct head, cephalic tentacles, radula apparatus, and a simplified central nervous system.

Broodstock conditioning, spawning, embryonic and early larval development of a novel baby clam species for aquaculture in the southeast Pacific: Tawera elliptica (Lamarck, 1818)

Tawera elliptica is a small size (baby) clam with an export fishery in southern Chile. The species is dioecious with external fertilization and without sexual dimorphism. The aim of this work was to optimize broodstock conditioning, induce spawning and describe embryonic development until the early larval stage in a hatchery. Broodstock were conditioned at 3 treatments (with/without sand; water circulation) for 48 days. The clams were fed with a mixed diet of macroalgae, with a daily ration of 250,000 cells/ml. Broodstock response was quantified using condition index and gonad development stages (histological techniques). For spawning induction, physical and biological methods were tested. The best response was achieved in males with physical induction. Histological analysis showed that the water circulation system treatment exhibited the highest percentage of maximum maturity. A fertilization ratio of 500:1 sperm:oocyte was used. The incubation was carried out in 3-L containers with filtered seawater at 10.7 ± 0.9°C without aeration. Observations, measurements and the duration of each embryonic and larval stage were recorded. The oocyte has a prominent gelatinous layer (= jelly coat) that disappears between the gastrula and trochophore stages. The status of the D-larval stage was reached at 107 h post fertilization with a mean valve length of 91.4 ± 8.9 µm. This is the first record of the complete embryonic development of this baby clam until the early larval stage and the conditioning in a water circulation system for 48 days are suitable for the species.

The Molecular Basis of Ocean Acidification Sensitivity and Adaptation in &lt;i&gt;Mytilus galloprovincialis&lt;/i&gt;

One challenge in global change biology is to identify the mechanisms underpinning physiological sensitivities to environmental change and to predict their potential to adapt to future conditions. Using ocean acidification as the representative stressor, molecular pathways associated with abnormal larval development of a globally distributed marine mussel are identified. The targeted developmental stage was the trochophore stage, which is, for a few hours, pH sensitive and is the main driver of developmental success. RNA sequencing and in situ RNA hybridization were used to identify processes associated with abnormal development, and DNA sequencing was used to identify which processes evolve when larvae are exposed to low pH for the full duration of their larval stage. Trochophores exposed to low pH exhibited 43 differentially expressed genes. Thirteen genes, none of which have previously been identified in mussel trochophores, including three unknown genes, were expressed in the shell field. Gene annotation and in situ hybridization point to two core processes associated with the response to low pH: development of the trochophore shell field and the cellular stress response. Encompassing both of these processes, five genes demonstrated changes in allele frequency that are indicative of rapid adaptation. Thus, genes underpinning the most pH-sensitive developmental processes also exhibit scope to adapt via genetic variation currently maintained in the mussel population. These results provide evidence that protecting species’ existing genetic diversity is a critical management action to maximize the potential for rapid adaptation under a changing environment.