Bone Morphogenetic Protein 2/4 in Mollusk, Haliotis diversicolor: Its Expression and Osteoinductive Function In Vitro

Bone morphogenetic proteins (BMPs), which are members of the superfamily of transforming growth factor-β (TGF-β), are known both in vitro and in vivo for their osteoinduction properties on the osteoblastic cells. Its role in the mollusk shell formation has also been gradually established. Using Haliotis diversicolor as a model, we characterized the HdBMP2/4 gene in the mantle tissue and showed its expression in the outer fold epithelium (particularly at the periostracal groove) the epithelial site which is involved in shell formation, both prismatic and nacreous layers. Shell notching experiments following gene analysis by qPCR revealed the upregulation of the HdBMP2/4 gene up to 3.2-fold than that of the control animals. In vitro treatments of the preosteoblastic cells, MC3T3-E1 with HdBMP2/4 synthetic peptide demonstrated the enhanced effect of many osteogenic genes that are known to regulate bone and shell biomineralization including ALP, Runx2, and OCN with 2-4 fold-change throughout 14 days of culture. In addition, the increased deposition of calcium-based mineral (as assessed by Alizarin red staining) of the treated cells was comparable to the ascorbic acid (Vit C) + glycerophosphate positive control which revealed the enhanced effect of HdBMP2/4 peptide on matrix biomineralization of the preosteoblastic cells. In conclusion, these results indicated the presence of the HdBMP2/4 gene in the mantle tissue at the site involved in shell formation and the effect of the HdBMP2/4 knuckle epitope peptide in osteoinduction in vitro.

Characterization and functional analysis of chitinase family genes involved in nymph-adult transition of Sogatella furcifera

Chitinase degrades chitin in the old epidermis or peritrophic matrix of insects, which ensures normal development and metamorphosis. In our previous work, we comprehensively studied the function of SfCht7 in Sogatella furcifera. However, the number and function of chitinase genes in S. furcifera remain unknown. Here, we identified 12 full-length chitinase transcripts from S. furcifera, which included nine chitinase (Cht), two imaginal disc growth factor (IDGF), and one endo-β-N-acetylglucosaminidase (ENGase) genes. Expression analysis results revealed that the expression levels of eight genes (SfCht3, SfCht5, SfCht6-1, SfCht6-2, SfCht7, SfCht8, SfCht10, and SfIDGF2) with similar transcript levels peaked prior to molting of each nymph and were highly expressed in the integument. Based on RNA interference (RNAi), description of the functions of each chitinase gene indicated that the silencing of SfCht5, SfCht10, and SfIDGF2 led to molting defects and lethality. RNAi inhibited the expressions of SfCht5, SfCht7, SfCht10, and SfIDGF2, which led to downregulated expressions of chitin synthase 1 (SfCHS1, SfCHS1a, and SfCHS1b) and four chitin deacetylase genes (SfCDA1, SfCDA2, SfCDA3, and SfCDA4), and caused a change in the expression level of two trehalase genes (TRE1 and TRE2). Furthermore, silencing of SfCht7 induced a significant decrease in the expression levels of three wing development-related genes (SfWG, SfDpp, and SfHh). In conclusion, SfCht5, SfCht7, SfCht10, and SfIDGF2 play vital roles in nymph-adult transition and are involved in the regulation of chitin metabolism, and SfCht7 is also involved in wing development; therefore, these genes are potential targets for control of S. furcifera.

PU14, a Novel Matrix Protein, Participates in Pearl Oyster, Pinctada Fucata, Shell Formation

Biomineralization is a widespread biological process, involved in the formation of shells, teeth, and bones. Shell matrix proteins have been widely studied for their importance during shell formation. In 2015, our group identified 72 unique shell matrix proteins in Pinctada fucata, among which PU14 is a matrix protein detected in the soluble fraction that solely exists in the prismatic layer. However, the function of PU14 is still unclear. In this study, the full-length cDNA sequence of PU14 was obtained and functional analyses of PU14 protein during shell formation were performed. The deduced protein has a molecular mass of 77.8 kDa and an isoelectric point of 11.34. The primary protein structure contains Gln-rich and random repeat units, which are typical characteristics of matrix protein and indicate its potential function during shell formation. In vivo and in vitro experiments indicated PU14 has prismatic layer functions during shell formation. The tissue expression patterns showed that PU14 was mainly expressed in the mantle tissue, which is consistent with prismatic layer formation. Notching experiments suggested that PU14 responded to repair and regenerate the injured shell. After inhibiting gene expression by injecting PU14-specific double-stranded RNA, the inner surface of the prismatic layer changed significantly and became rougher. Further, in vitro experiments showed that recombinant protein rPU14 impacted calcite crystal morphology. Taken together, characterization and functional analyses of a novel matrix protein, PU14, provide new insights about basic matrix proteins and their functions during shell formation.

Temperature-induced microstructural changes in shells of laboratory-grown Arctica islandica (Bivalvia)

Bivalve shells are increasingly used as archives for high-resolution paleoclimate analyses. However, there is still an urgent need for quantitative temperature proxies that work without knowledge of the water chemistry-as is required for δ18O-based paleothermometry-and can better withstand diagenetic overprint. Recently, microstructural properties have been identified as a potential candidate fulfilling these requirements. So far, only few different microstructure categories (nacreous, prismatic and crossed-lamellar) of some short-lived species have been studied in detail, and in all such studies, the size and/or shape of individual biomineral units was found to increase with water temperature. Here, we explore whether the same applies to properties of the crossed-acicular microstructure in the hinge plate of Arctica islandica, the microstructurally most uniform shell portion in this species. In order to focus solely on the effect of temperature on microstructural properties, this study uses bivalves that grew their shells under controlled temperature conditions (1, 3, 6, 9, 12 and 15°C) in the laboratory. With increasing temperature, the size of the largest individual biomineral units and the relative proportion of shell occupied by the crystalline phase increased. The size of the largest pores, a specific microstructural feature of A. islandica, whose potential role in biomineralization is discussed here, increased exponentially with culturing temperature. This study employs scanning electron microscopy in combination with automated image processing software, including an innovative machine learning-based image segmentation method. The new method greatly facilitates the recognition of microstructural entities and enables a faster and more reliable microstructural analysis than previously used techniques. Results of this study establish the new microstructural temperature proxy in the crossed-acicular microstructures of A. islandica and point to an overarching control mechanism of temperature on the micrometer-scale architecture of bivalve shells across species boundaries.

Novel globular C1q domain-containing protein (PmC1qDC-1) participates in shell formation and responses to pathogen-associated molecular patterns stimulation in Pinctada fucata martensii

The C1q protein, which contains the globular C1q (gC1q) domain, is involved in the innate immune response, and is found abundantly in the shell, and it participates in the shell formation. In this study, a novel gC1q domain-containing gene was identified from Pinctada fucata martensii (P. f. martensii) and designated as PmC1qDC-1. The full-length sequence of PmC1qDC-1 was 902 bp with a 534 bp open reading frame (ORF), encoding a polypeptide of 177 amino acids. Quantitative real-time PCR (qRT-PCR) result showed that PmC1qDC-1 was widely expressed in all tested tissues, including shell formation-associated tissue and immune-related tissue. PmC1qDC-1 expression was significantly high in the blastula and gastrula and especially among the juvenile stage, which is the most important stage of dissoconch shell formation. PmC1qDC-1 expression was located in the outer epithelial cells of mantle pallial and mantle edge and irregular crystal tablets were observed in the nacre upon knockdown of PmC1qDC-1 expression at mantle pallial. Moreover, the recombined protein PmC1qDC-1 increased the rate of calcium carbonate precipitation. Besides, PmC1qDC-1 expression was significantly up-regulated in the mantle pallial at 6 h and was significantly up-regulated in the mantle edge at 12 h and 24 h after shell notching. The expression level of PmC1qDC-1 in mantle edge was significantly up-regulated at 48 h after LPS stimulation and was significantly up-regulated at 12 h, 24 h and 48 h after poly I:C stimulation. Moreover, PmC1qDC-1 expression was significantly up-regulated in hemocytes at 6 h after lipopolysaccharide (LPS) and poly I:C challenge. These findings suggest that PmC1qDC-1 plays a crucial role both in the shell formation and the innate immune response in pearl oysters, providing new clues for understanding the shell formation and defense mechanism in mollusk.

Shells of the bivalve Astarte moerchi give new evidence of a strong pelagic-benthic coupling shift occurring since the late 1970s in the North Water polynya

Climate changes in the Arctic may weaken the currently tight pelagic-benthic coupling. In response to decreasing sea ice cover, arctic marine systems are expected to shift from a 'sea-ice algae-benthos' to a 'phytoplankton-zooplankton' dominance. We used mollusc shells as bioarchives and fatty acid trophic markers to estimate the effects of the reduction of sea ice cover on the food exported to the seafloor. Bathyal bivalve Astarte moerchi living at 600 m depth in northern Baffin Bay reveals a clear shift in growth variations and Ba/Ca ratios since the late 1970s, which we relate to a change in food availability. Tissue fatty acid compositions show that this species feeds mainly on microalgae exported from the euphotic zone to the seabed. We, therefore, suggest that changes in pelagic-benthic coupling are likely due either to local changes in sea ice dynamics, mediated through bottom-up regulation exerted by sea ice on phytoplankton production, or to a mismatch between phytoplankton bloom and zooplankton grazing due to phenological change. Both possibilities allow a more regular and increased transfer of food to the seabed. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Tracing key genes associated with the Pinctada margaritifera albino phenotype from juvenile to cultured pearl harvest stages using multiple whole transcriptome sequencing

BACKGROUND

Albino mutations are commonly observed in the animal kingdom, including in bivalves. In the black-lipped pearl oyster Pinctada margaritifera, albino specimens are characterized by total or partial absence of colouration resulting in typical white shell phenotype expression. The relationship of shell colour with resulting cultured pearl colour is of great economic interest in P. margaritifera, on which a pearl industry is based. Hence, the albino phenotype provides a useful way to examine the molecular mechanisms underlying pigmentation.

RESULTS

Whole transcriptome RNA-sequencing analysis comparing albino and black wild-type phenotypes at three stages over the culture cycle of P. margaritifera revealed a total of 1606, 798 and 187 differentially expressed genes in whole juvenile, adult mantle and pearl sac tissue, respectively. These genes were found to be involved in five main molecular pathways, tightly linked to known pigmentation pathways: melanogenesis, calcium signalling pathway, Notch signalling pathway, pigment transport and biomineralization. Additionally, significant phenotype-associated SNPs were selected (N = 159), including two located in the Pif biomineralization gene, which codes for nacre formation. Interestingly, significantly different transcript splicing was detected between juvenile (N = 1366) and adult mantle tissue (N = 313) in, e.g., the tyrosinase Tyr-1 gene, which showed more complex regulation in mantle, and the Notch1 encoding gene, which was upregulated in albino juveniles.

CONCLUSION

This multiple RNA-seq approach provided new knowledge about genes associated with the P. margaritifera albino phenotype, highlighting: 1) new molecular pathways, such as the Notch signalling pathway in pigmentation, 2) associated SNP markers with biomineraliszation gene of interest like Pif for marker-assisted selection and prevention of inbreeding, and 3) alternative gene splicing for melanin biosynthesis implicating tyrosinase.

The balancing act of Nipponites mirabilis (Nostoceratidae, Ammonoidea): Managing hydrostatics throughout a complex ontogeny

Nipponites is a heteromorph ammonoid with a complex and unique morphology that obscures its mode of life and ethology. The seemingly aberrant shell of this Late Cretaceous nostoceratid seems deleterious. However, hydrostatic simulations suggest that this morphology confers several advantages for exploiting a quasi-planktic mode of life. Virtual, 3D models of Nipponites mirabilis were used to compute various hydrostatic properties through 14 ontogenetic stages. At each stage, Nipponites had the capacity for neutral buoyancy and was not restricted to the seafloor. Throughout ontogeny, horizontally facing to upwardly facing soft body orientations were preferred at rest. These orientations were aided by the obliquity of the shell's ribs, which denote former positions of the aperture that were tilted from the growth direction of the shell. Static orientations were somewhat fixed, inferred by stability values that are slightly higher than extant Nautilus. The initial open-whorled, planispiral phase is well suited to horizontal backwards movement with little rocking. Nipponites then deviated from this bilaterally symmetric coiling pattern with a series of alternating U-shaped bends in the shell. This modification allows for proficient rotation about the vertical axis, while possibly maintaining the option for horizontal backwards movement by redirecting its hyponome. These particular hydrostatic properties likely result in a tradeoff between hydrodynamic streamlining, suggesting that Nipponites assumed a low energy lifestyle of slowly pirouetting in search for planktic prey. Each computed hydrostatic property influences the others in some way, suggesting that Nipponites maintained a delicate hydrostatic balancing act throughout its ontogeny in order to facilitate this mode of life.

Identification of a long non-coding RNA (LncMSEN2) from pearl oyster and its potential roles in exoskeleton formation and LPS stimulation

Long non-coding RNAs (lncRNAs) play regulatory roles in various biological processes, including exoskeleton formation and immune response. The exoskeleton-based mantle-shell defense system is an important defense mechanism in shellfish. In this study, we found a novel lncRNA, herein formally named, LncMSEN2, from the pearl oyster Pinctada fucuta martensii, and its sequence was validated via polymerase chain reaction (PCR). LncMSEN2 was highly expressed in mantle tissues, especially in the central region (P < 0.05), and was also expressed in the pearl sac as detected by quantitative real-time PCR. In situ hybridization experiments revealed that LncMSEN2 had a strong positive signal in the inner and outer epidermal cells of the mantle pallial and central regions. RNA interference experiments showed that interference of LncMSEN2 expression with dsRNA in mantle tissues led to an abnormal crystal structure of the nacre. In addition, LncMSEN2 expression significantly increased 6 h after lipopolysaccharide stimulation in mantle tissues (P < 0.05). These results indicated that LncMSEN2 may be a novel regulator of the mantle-shell defense system of pearl oyster.

Can prior exposure to stress enhance resilience to ocean warming in two oyster species?

Securing economically and ecologically significant molluscs, as our oceans warm due to climate change, is a global priority. South eastern Australia receives warm water in a strengthening East Australia Current and so resident species are vulnerable to elevated temperature and marine heat waves. This study tested whether prior exposure to elevated temperature can enhance resilience of oysters to ocean warming. Two Australian species, the flat oyster, Ostrea angasi, and the Sydney rock oyster, Saccostrea glomerata, were obtained as adults and "heat shocked" by exposure to a dose of warm water in the laboratory. Oysters were then transferred to elevated seawater temperature conditions where the thermal outfall from power generation was used as a proxy to investigate the impacts of ocean warming. Shell growth, condition index, lipid content and survival of flat oysters and condition of Sydney rock oysters were all significantly reduced by elevated seawater temperature in the field. Flat oysters grew faster than Sydney rock oysters at ambient temperature, but their growth and survival was more sensitive to elevated temperature. "Stress inoculation" by heat shock did little to ameliorate the negative effects of increased temperature, although the survival of heat-shocked flat oysters was greater than non-heat shocked oysters. Further investigations are required to determine if early exposure to heat stress can enhance resilience of oysters to ocean warming.

A computational framework for the morpho-elastic development of molluskan shells by surface and volume growth

Mollusk shells are an ideal model system for understanding the morpho-elastic basis of morphological evolution of invertebrates’ exoskeletons. During the formation of the shell, the mantle tissue secretes proteins and minerals that calcify to form a new incremental layer of the exoskeleton. Most of the existing literature on the morphology of mollusks is descriptive. The mathematical understanding of the underlying coupling between pre-existing shell morphology, de novo surface deposition and morpho-elastic volume growth is at a nascent stage, primarily limited to reduced geometric representations. Here, we propose a general, three-dimensional computational framework coupling pre-existing morphology, incremental surface growth by accretion, and morpho-elastic volume growth. We exercise this framework by applying it to explain the stepwise morphogenesis of seashells during growth: new material surfaces are laid down by accretive growth on the mantle whose form is determined by its morpho-elastic growth. Calcification of the newest surfaces extends the shell as well as creates a new scaffold that constrains the next growth step. We study the effects of surface and volumetric growth rates, and of previously deposited shell geometries on the resulting modes of mantle deformation, and therefore of the developing shell’s morphology. Connections are made to a range of complex shells ornamentations.

Molluska are the second most diversified phylum of the animal kingdom, and their evolutionary success can be partly attributed to the hard shell that provides both protection and support to the soft body. The distinctive anatomical features of these hard shells are their rich pigmentation patterns and complex structural ornamentations. While the pigmentation patterns are primarily of biochemical origin, the ornamentations result from mechanical deformation of the mantle due to growth induced forces. This mechanical basis of “growth and form” has been previously investigated using simplified morpho-mechanical models, but restricted to reduced geometric representations. Here we propose a three-dimensional computational framework coupling morphology, incremental surface growth by accretion, and morpho-elastic volume growth, to enable an improved representation of the growth and structural parameters controlling the evolution of these ornamentations. We study the effects of growth rates, and of previously deposited shell geometries on the resulting modes of mantle deformation, and present a “phase diagram” of morphogenesis in molluskan shells. Our main motivation for focusing on generic physical processes involved in development is that they may shape living beings in a predictive way and partly determine the spectrum of forms that have been and could have been generated during evolution.

Legacy of Multiple Stressors: Responses of Gastropod Larvae and Juveniles to Ocean Acidification and Nutrition

Ocean acidification poses a significant threat to calcifying invertebrates by negatively influencing shell deposition and growth. An organism's performance under ocean acidification is not determined by the susceptibility of one single life-history stage, nor is it solely controlled by the direct physical consequences of ocean acidification. Shell development by one life-history stage is sometimes a function of the pH or pCO₂ levels experienced during earlier developmental stages. Furthermore, environmental factors such as access to nutrition can buffer organismal responses of calcifying invertebrates to ocean acidification, or they can function as a co-occurring stressor when access is low. We reared larvae and juveniles of the planktotrophic marine gastropod Crepidula fornicata through combined treatments of nutritional stress and low pH, and we monitored how multiple stressors endured during the larval stage affected juvenile performance. Shell growth responded non-linearly to decreasing pH, significantly declining between pH 7.6 and pH 7.5 in larvae and juveniles. Larval rearing at pH 7.5 reduced juvenile growth as a carryover effect. Larval rearing at pH 7.6 reduced subsequent juvenile growth despite the absence of a negative impact on larval growth, demonstrating a latent effect. Low larval pH magnified the impact of larval nutritional stress on competence for metamorphosis and increased carryover effects of larval nutrition on juvenile growth. Trans-life-cycle effects of larval nutrition were thus modulated by larval exposure to ocean acidification.

Can shell alterations in limpets be used as alternative biomarkers of coastal contamination?

The present study evaluated the association among traditional biochemical biomarkers with biometric, morphometric, and elemental composition of Lottia subrugosa (patelliform gastropod) shells from three multi-impacted coastal areas in Brazil. The study was carried out in Todos os Santos Bay (TSB), Santos/São Vicente Estuarine System (SESS) and Paranaguá Estuarine Complex (CEP), using three sampling sites to seek contamination gradients in each area. Results showed that all biomarkers evaluated responded to environmental contamination, regardless the presence (SESS and CEP) or absence (TSB) of a gradient of contamination. The responses found using biometric and morphometric parameters were consistent with the traditional biomarkers of exposure and effects (lipid peroxidation and DNA damage). Indeed, changes in elemental composition of L. subrugosa shells suggest that exposure to contaminated environments is probably responsible for the alterations detected. Despite the simplicity and lower cost of biometric and morphometric analyzes, these parameters are influenced by natural environmental conditions from which biases may arise. Therefore, these tools should be evaluated through experimental studies before it can be used in future assessments. However, the findings from the present study were observed in three aquatic systems distributed over a wide range of latitudes, which indicates that gastropod shells reflect effects resulting from environmental contamination.

Cell type phylogenetics informs the evolutionary origin of echinoderm larval skeletogenic cell identity

The multiplicity of cell types comprising multicellular organisms begs the question as to how cell type identities evolve over time. Cell type phylogenetics informs this question by comparing gene expression of homologous cell types in distantly related taxa. We employ this approach to inform the identity of larval skeletogenic cells of echinoderms, a clade for which there are phylogenetically diverse datasets of spatial gene expression patterns. We determined ancestral spatial expression patterns of alx1, ets1, tbr, erg, and vegfr, key components of the skeletogenic gene regulatory network driving identity of the larval skeletogenic cell. Here we show ancestral state reconstructions of spatial gene expression of extant eleutherozoan echinoderms support homology and common ancestry of echinoderm larval skeletogenic cells. We propose larval skeletogenic cells arose in the stem lineage of eleutherozoans during a cell type duplication event that heterochronically activated adult skeletogenic cells in a topographically distinct tissue in early development.

Growth and morphogenesis of the gastropod shell

Gastropod shell morphologies are famously diverse but generally share a common geometry, the logarithmic coil. Variations on this morphology have been modeled mathematically and computationally but the developmental biology of shell morphogenesis remains poorly understood. Here we characterize the organization and growth patterns of the shell-secreting epithelium of the larval shell of the basket whelk Tritia (also known as Ilyanassa). Despite the larval shell's relative simplicity, we find a surprisingly complex organization of the shell margin in terms of rows and zones of cells. We examined cell division patterns with EdU incorporation assays and found two growth zones within the shell margin. In the more anterior aperture growth zone, we find that inferred division angles are biased to lie parallel to the shell edge, and these divisions occur more on the margin's left side. In the more posterior mantle epithelium growth zone, inferred divisions are significantly biased to the right, relative to the anterior-posterior axis. These growth zones, and the left-right asymmetries in cleavage patterns they display, can explain the major modes of shell morphogenesis at the level of cellular behavior. In a gastropod with a different coiling geometry, Planorbella sp., we find similar shell margin organization and growth zones as Tritia, but different left-right asymmetries than we observed in the helically coiled shell of Tritia These results indicate that differential growth patterns in the mantle edge epithelium contribute to shell shape in gastropod shells and identify cellular mechanisms that may vary to generate shell diversity in evolution.

Shell repair and the potential microbial causal in a shell disease of the pearl oyster Pinctada fucata

The pearl oyster Pinctada fucata is famous for producing luxurious pearls. As filter feeders, they are confronted with various infectious microorganisms. Despite a long history of aquaculture, diseases in P. fucata are not well studied, which limits the development of the pearl industry. We report here a shell disease in P. fucata and a study of the shell repair processes. Scanning electron microscopy (SEM) revealed that the nacreous layer gradually recovered from disordered CaCO₃ deposition, accompanied by a polymorphic transition from a calcite-aragonite mixture to an aragonite-dominant composition, as revealed by X-ray diffraction analysis. SEM also showed that numerous microbes were embedded in the abnormal shell layers. Similar indications were induced by a high concentration of microbes injected into the extrapallial space, suggesting the potential pathogenic effect of uncontrolled microbes. Furthermore, hemocytes were found to participate in pathogens resistance and might promote shell repair. These results further our understanding of pathogen-host interactions in pearl oysters and have implications for biotic control in pearl aquaculture.

Energy metabolism and survival of the juvenile recruits of the American lobster (Homarus americanus) exposed to a gradient of elevated seawater pCO2

The transition from the last pelagic larval stage to the first benthic juvenile stage in the complex life cycle of marine invertebrates, such as the American lobster Homarus americanus, a species of high economic importance, represents a delicate phase in these species development. Under future elevated pCO₂ conditions, ocean acidification and other elevated pCO₂ events can negatively affect crustaceans. This said their effects on the benthic settlement phase are virtually unknown. This study aimed to identify the effects of elevated seawater pCO₂ on stage V American lobsters exposed to seven pCO₂ levels. The survival, development time, metabolic and feeding rates, carapace composition, and energy metabolism enzyme function were investigated. Results suggested an increase in mortality, slower development and an increase in aerobic capacity with increasing pCO₂. Our study points to potential reduction in juvenile recruitment success as seawater pCO₂ increases, thus foreshadowing important socio-economic repercussions for the lobster fisheries and industry.

Sublethal effects of oil-contaminated sediment to early life stages of the Eastern oyster, Crassostrea virginica

The explosion of the Deepwater Horizon (DWH) oil drilling rig resulted in the release of crude oil into the Gulf of Mexico. This event coincided with the spawning season of the Eastern oyster, Crassostrea virginica. Although oil bound to sediments constitutes an important source of polycyclic aromatic hydrocarbon (PAH) exposure to benthic organisms, toxicity of sediment-associated DWH oil has not been investigated in any bivalve species. Here, we evaluated the sublethal effects of acute exposure of gametes, embryos and veliger larvae of the Eastern oyster to different concentrations of unfiltered elutriates of sediment contaminated with DWH oil. Our results suggest that gametes, embryos and veliger larvae are harmed by exposure to unfiltered elutriates of contaminated sediment. Effective concentrations for fertilization inhibition were 40.6 μg tPAH50 L^-1 and 173.2 μg tPAH50 L^-1 for EC20_1h and EC50_1h values, respectively. Embryo exposure resulted in dose-dependent abnormalities (EC20 and EC50 values were 77.7 μg tPAH50 L^-1 and 151 μg tPAH50 L^-1, respectively) and reduction in shell growth (EC20_24h value of 1180 μg tPAH50 L^-1). Development and growth of veliger larvae were less sensitive to sediment-associated PAHs compared to embryos. Fertilization success and abnormality of larvae exposed as embryos were the most sensitive endpoints for assessing the toxicity of oil-contaminated sediment. Bulk of measured polycyclic aromatic hydrocarbons were sediment-bound and caused toxic effects at lower tPAH50 concentrations than high energy water accommodated fractions (HEWAF) preparations from the same DWH oil. This study suggests risk assessments would benefit from further study of suspended contaminated sediment.

A comparison of the cuticular properties of the female ticks Ixodes pacificus and Amblyomma hebraeum (Acari: Ixodidae) throughout the feeding period

The mechanical properties of the cuticle of Ixodes pacificus (Ip) are compared to those of Amblyomma hebraeum (Ah) from our earlier work. The 10-fold size difference between the species is expected to lead to significant differences in mechanical properties, because cuticular stretch depends on high internal hydrostatic pressure during the rapid phase of engorgement. We demonstrate here: (1) The cuticle of partially fed Ip is less stiff and viscous than that of Ah. (2) A stretch-recoil cycle in both ticks consists of recoverable deformation (ESv) and permanent deformation (ESp); ESp is higher in Ip, and increases sharply during the slow phase of engorgement, but not in Ah. (3) Injected dopamine (DA) increases ESp and reduces all measures of stiffness and viscosity, suggesting that a catecholaminergic neurotransmitter plays a fundamental role in modulating mechanical properties of the cuticle. However, unlike Ah, DA's effect was not different from that of the control (1.2% NaCl). Mere insertion of the needle may have punctured the gut, causing the release of perhaps a catecholamine that increases ESp, an hypothesis supported by the fact that inserting a needle without any injection also caused an increase in ESp. (4) Stretch reduces ESp, but subjecting loops to pH 6.5 in vitro restores it. (5) Despite the smaller size of Ip, later onset of the rapid phase of engorgement, a thinner cuticle and different mechanical properties all reduce the internal pressure needed for stretch.

Mapping Genetic Loci for Quantitative Traits of Golden Shell Color, Mineral Element Contents, and Growth-Related Traits in Pacific Oyster (Crassostrea gigas)

Golden shell color and mineral content are important economic traits of Pacific oyster (Crassostrea gigas). In this study, we mapped a series of quantitative trait loci (QTLs) that control zinc (Zn) and magnesium (Mg) content, shell color and growth performance to two sex-averaged linkage maps from the FAM-A and FAM-B families. In total, ten QTLs were identified in seven linkage groups (LGs) in the FAM-B family, and seven QTLs were identified in four linkage groups in the FAM-A family. Two QTLs affecting the trait of golden shell color were identified in LG8 of the FAM-A and LG10 of the FAM-B families, which could explain 20.2 and 10.5% of the phenotypic variations, respectively. Two QTLs for Zn content were identified that could contribute to 17.9 and 34.44% of the phenotypic variations in FAM-A. Six QTLs for Zn and Mg contents were identified in four LGs (LG1, LG2, LG5, and LG9) in FAM-B, which explained 13.5-26.7% of the phenotypic variations. In addition, seven QTLs related to oyster growth were recognized in both FAM-A and FAM-B families accounting for 14.6-36.7% of the phenotypic variations. All of the DNA markers in QTL regions were blasted and 14 genes associated with above traits were identified. The mRNA expression of these genes was determined by quantitative RT-PCR. These QTLs and candidate genes could be used as potential targets for marker-assisted selection in C. gigas breeding.

Bivalve shell formation in a naturally CO2-enriched habitat: Unraveling the resilience mechanisms from elemental signatures

Marine bivalves inhabiting naturally pCO₂-enriched habitats can likely tolerate high levels of acidification. Consequently, elucidating the mechanisms behind such resilience can help to predict the fate of this economically and ecologically important group under near-future scenarios of CO₂-driven ocean acidification. Here, we assess the effects of four environmentally realistic pCO₂ levels (900, 1500, 2900 and 6600 μatm) on the shell production rate of Mya arenaria juveniles originating from a periodically pCO₂-enriched habitat (Kiel Fjord, Western Baltic Sea). We find a significant decline in the rate of shell growth as pCO₂ increases, but also observe unchanged shell formation rates at moderate pCO₂ levels of 1500 and 2900 μatm, the latter illustrating the capacity of the juveniles to partially mitigate the impact of high pCO₂. Using recently developed geochemical tracers we show that M. arenaria exposed to a natural pCO₂ gradient from 900 to 2900 μatm can likely concentrate HCO₃^- in the calcifying fluid through the exchange of HCO₃^-/Cl^- and simultaneously maintain the pH homeostasis through active removal of protons, thereby being able to sustain the rate of shell formation to a certain extent. However, with increasing pCO₂ beyond natural maximum the bivalves may have limited capacity to compensate for changes in the calcifying fluid chemistry, showing significant shell growth reduction. Findings of the present study may pave the way for elucidating the underlying mechanisms by which marine bivalves acclimate and adapt to high seawater pCO₂.

Ligament, hinge, and shell cross-sections of the Atlantic surfclam (Spisula solidissima): Promising marine environmental archives in NE North America

The Atlantic surfclam (Spisula solidissima) is a commercially important species in North American waters, undergoing biological and ecological shifts. These are attributed, in part, to environmental modifications in its habitat and driven by climate change. Investigation of shell growth patterns, trace elements, and isotopic compositions require an examination of growth lines and increments preserved in biogenic carbonates. However, growth pattern analysis of S. solidissima is challenging due to multiple disturbance lines caused by environmental stress, erosion in umbonal shell regions, and constraints related to sample size and preparation techniques. The present study proposes an alternative method for describing chronology. First, we analyzed growth patterns using growth lines within the shell and hinge. To validate the assumption of annual periodicity of growth line formation, we analyzed the oxygen isotope composition of the outer shell layer of two specimens (46°54'20"N; 56°18'58"W). Maximum δ¹⁸O_shell values occurred at the exact same location as internal growth lines in both specimens, confirming that they are formed annually and that growth ceases during winter. Next, we used growth increment width data to build a standardized growth index (SGI) time-series (25-year chronology) for each of the three parts of the shell. Highly significant correlations were found between the three SGI chronologies (p < 0.001; 0.55 < τ < 0.68) of all specimens. Thus, ligament growth lines provide a new method of determining ontogenetic age and growth rate in S. solidissima. In a biogeographic approach, the shell growth performance of S. solidissima in Saint-Pierre and Miquelon was compared to those in other populations along its distribution range in order to place this population in a temporal and regional context.

Heterochronic development of lateral plates in the three-spined stickleback induced by thyroid hormone level alterations

The three-spined stickleback Gasterosteus aculeatus is an important model for studying microevolution and parallel adaptation to freshwater environments. Marine and freshwater forms differ markedly in their phenotype, especially in the number of lateral plates, which are serially repeated elements of the exoskeleton. In fishes, thyroid hormones are involved in adaptation to salinity, as well as the developmental regulation of serially repeated elements. To study how thyroid hormones influence lateral plate development, we manipulated levels of triiodothyronine and thiourea during early ontogeny in a marine and freshwater population with complete and low plate phenotypes, respectively. The development of lateral plates along the body and keel was heterochronic among experimental groups. Fish with a low dosage of exogenous triiodothyronine and those treated with thiourea exhibited retarded development of bony plates compared to both control fish and those treated with higher a triiodothyronine dosage. Several triiodothyronine-treated individuals of the marine form expressed the partial lateral plate phenotype. Some individuals with delayed development of lateral plates manifested 1–2 extra bony plates located above the main row of lateral plates.

Delineating modern variation from extinct morphology in the fossil record using shells of the Eastern Box Turtle (Terrapene carolina)

Characterization of morphological variation in the shells of extant Eastern Box Turtles, Terrapene carolina, provides a baseline for comparison to fossil populations. It also provides an example of the difficulties inherent to recognizing intraspecific diversity in the fossil record. The degree to which variation in fossils of T. carolina can be accommodated by extant variation in the species has been disagreed upon for over eighty years. Using morphometric analyses of the carapace, I address the relationship between modern and fossil T. carolina in terms of sexual dimorphism, geographic and subspecific variation, and allometric variation. Modern T. carolina display weak male-biased sexual size dimorphism. Sexual shape dimorphism cannot be reliably detected in the fossil record. Rather than a four-part subspecific division, patterns of geographic variation are more consistent with clinal variation between various regions in the species distribution. Allometric patterns are qualitatively similar to those documented in other emydid turtles and explain a significant amount of shape variation. When allometric patterns are accounted for, Holocene specimens are not significantly different from modern specimens. In contrast, several geologically older specimens have significantly different carapace shape with no modern analogue. Those large, fossilized specimens represent extinct variation occupying novel portions of morphospace. This study highlights the need for additional documentation of modern osteological variation that can be used to test hypotheses of intraspecific evolution in the fossil record.

Expression characteristics and functional analysis of Krüppel-like factor 4 in adductor muscle and mantle of Zhikong scallop Chlamys farreri

Krüppel-like factor 4 (KLF4) is an important transcription factor involving in formation and maintenance of muscles in mammals. However, no data are available on KLF4 function in shellfish muscles which play vital roles in the movement, stress response, and physiology in shellfish. In the present study, we revealed that the Klf4 mRNA of Zhikong scallop Chlamys farreri was expressed in most tissues, which has high level in adductor muscle, mantle, kidney, and testis. Positive signals of the Klf4 mRNA and protein were visible in all skeletal muscle fibers of adductor muscle, and all the cells of C. farreri mantle. Furthermore, the knockdown of Klf4 mRNA in adductor muscle and mantle by means of in vivo RNA interference led to some different phenotypes, including disordered arrangement of muscle fibers in adductor muscle and mantle, abnormal structures of skeletal muscles, and reduced muscle fibers under endepidermis of mantle. Our findings demonstrated that Klf4 plays important roles in maintenance of muscle functions in C. farreri adductor muscle and mantle, and suggested that its regulatory way in skeletal muscle may be different from the smooth muscle in shellfish.

A novel rapid additive manufacturing concept for architectural composite shell construction inspired by the shell formation in land snails

State-of-the-art rapid additive manufacturing (RAM)-specifically fused filament fabrication (FFF)-has gained popularity among architects, engineers and designers for the quick prototyping of technical devices, the rapid production of small series and even the construction scale fabrication of architectural elements. The spectrum of producible shapes and the resolution of detail, however, are determined and constrained by the layer-based nature of the fabrication process. These aspects significantly limit FFF-based approaches for the prefabrication and in situ fabrication of free-form shells at the architectural scale. Snails exhibit a shell building process that suggests ways to overcome these limits. They produce a soft, pliable proteinaceous film-the periostracum-which later hardens and serves, among other functions, as a form-giving surface for an inner calcium carbonate layer. Snail shell formation behavior is interpreted from a technical point of view to extract potentially useful aspects for a biomimetic transfer. A RAM concept for the continuous extrusion of thin free-form composite shells inspired by the snail shell formation is presented.

Blue mussel shell shape plasticity and natural environments: a quantitative approach

Shape variability represents an important direct response of organisms to selective environments. Here, we use a combination of geometric morphometrics and generalised additive mixed models (GAMMs) to identify spatial patterns of natural shell shape variation in the North Atlantic and Arctic blue mussels, Mytilus edulis and M. trossulus, with environmental gradients of temperature, salinity and food availability across 3980 km of coastlines. New statistical methods and multiple study systems at various geographical scales allowed the uncoupling of the developmental and genetic contributions to shell shape and made it possible to identify general relationships between blue mussel shape variation and environment that are independent of age and species influences. We find salinity had the strongest effect on the latitudinal patterns of Mytilus shape, producing shells that were more elongated, narrower and with more parallel dorsoventral margins at lower salinities. Temperature and food supply, however, were the main drivers of mussel shape heterogeneity. Our findings revealed similar shell shape responses in Mytilus to less favourable environmental conditions across the different geographical scales analysed. Our results show how shell shape plasticity represents a powerful indicator to understand the alterations of blue mussel communities in rapidly changing environments.

Development and ultrastructure of the rigid dorsal and flexible ventral cuticles of the elytron of the red flour beetle, Tribolium castaneum

Insect exoskeletons are composed of the cuticle, a biomaterial primarily formed from the linear and relatively rigid polysaccharide, chitin, and structural proteins. This extracellular material serves both as a skin and skeleton, protecting insects from environmental stresses and mechanical damage. Despite its rather limited compositional palette, cuticles in different anatomical regions or developmental stages exhibit remarkably diverse physicochemical and mechanical properties because of differences in chemical composition, molecular interactions and morphological architecture of the various layers and sublayers throughout the cuticle including the envelope, epicuticle and procuticle (exocuticle and endocuticle). Even though the ultrastructure of the arthropod cuticle has been studied rather extensively, its temporal developmental pattern, in particular, the synchronous development of the functional layers in different cuticles during a molt, is not well understood. The beetle elytron, which is a highly modified and sclerotized forewing, offers excellent advantages for such a study because it can be easily isolated at precise time points during development. In this study, we describe the morphogenesis of the dorsal and ventral cuticles of the elytron of the red flour beetle, Tribolium castaneum, during the period from the 0 d-old pupa to the 9 d-old adult. The deposition of exocuticle and mesocuticle is substantially different in the two cuticles. The dorsal cuticle is four-fold thicker than the ventral. Unlike the ventral cuticle, the dorsal contains a thicker exocuticle consisting of a large number of horizontal laminae and vertical pore canals with pore canal fibers and rib-like veins and bristles as well as a mesocuticle, lying right above the enodcuticle. The degree of sclerotization appears to be much greater in the dorsal cuticle. All of these differences result in a relatively thick and tanned rigid dorsal cuticle and a much thinner and less pigmented membrane-like ventral cuticle.

Impact of cationic polystyrene nanoparticles (PS-NH2) on early embryo development of Mytilus galloprovincialis: Effects on shell formation

The potential release of nanoparticles (NPs) into aquatic environments represents a growing concern for their possible impact on aquatic organisms. In this light, exposure studies during early life stages, which can be highly sensitive to environmental perturbations, would greatly help identifying potential adverse effects of NPs. Although in the marine bivalve Mytilus spp. the effects of different types of NPs have been widely investigated, little is known on the effects of NPs on the developing embryo. In M. galloprovincialis, emerging contaminants were shown to affect gene expression profiles during early embryo development (from trocophorae-24 hpf to D-veligers-48 hpf). In this work, the effects of amino-modified polystyrene NPs (PS-NH₂) on mussel embryos were investigated. PS-NH₂ affected the development of normal D-shaped larvae at 48 hpf (EC₅₀ = 0.142 mg/L). Higher concentrations (5-20 mg/L) resulted in high embryotoxicity/developmental arrest. At concentrations ≅ EC₅₀, PS-NH₂ affected shell formation, as shown by optical and polarized light microscopy. In these conditions, transcription of 12 genes involved in different biological processes were evaluated. PS-NH₂ induced dysregulation of transcription of genes involved in early shell formation (Chitin synthase, Carbonic anhydrase, Extrapallial Protein) at both 24 and 48 hpf. Decreased mRNA levels for ABC transporter p-glycoprotein-ABCB and Lysozyme were also observed at 48 hpf. SEM observations confirmed developmental toxicity at higher concentrations (5 mg/L). These data underline the sensitivity of Mytilus early embryos to PS-NH₂ and support the hypothesis that calcifying larvae of marine species are particularly vulnerable to abiotic stressors, including exposure to selected types of NPs.

Construction of the First High-Density Genetic Linkage Map and Analysis of Quantitative Trait Loci for Growth-Related Traits in Sinonovacula constricta

The razor clam (Sinonovacula constricta) is an important aquaculture species, for which a high-density genetic linkage map would play an important role in marker-assisted selection (MAS). In this study, we constructed a high-density genetic map and detected quantitative trait loci (QTLs) for Sinonovacula constricta with an F₁ cross population by using the specific locus amplified fragment sequencing (SLAF-seq) method. A total of 315,553 SLAF markers out of 467.71 Mreads were developed. The final linkage map was composed of 7516 SLAFs (156.60-fold in the parents and 20.80-fold in each F₁ population on average). The total distance of the linkage map was 2383.85 cM, covering 19 linkage groups with an average inter-marker distance of 0.32 cM. The proportion of gaps less than 5.0 cM was on average 96.90%. A total of 16 suggestive QTLs for five growth-related traits (five QTLs for shell height, six QTLs for shell length, three QTLs for shell width, one QTL for total body weight, and one QTL for soft body weight) were identified. These QTLs were distributed on five linkage groups, and the regions showed overlapping on LG9 and LG13. In conclusion, the high-density genetic map and QTLs for S. constricta provide a valuable genetic resource and a basis for MAS.

Alteration of neurotransmission and skeletogenesis in sea urchin Arbacia lixula embryos exposed to copper oxide nanoparticles

The extensive use of copper oxide nanoparticles (CuO NPs) in many applications has raised concerns over their toxicity on environment and human health. Herein, the embryotoxicity of CuO NPs was assessed in the black sea urchin Arbacia lixula, an intertidal species commonly present in the Mediterranean. Fertilized eggs were exposed to 0.7, 10 and 20ppb of CuO NPs, until pluteus stage. Interferences with the normal neurotransmission pathways were observed in sea urchin embryos. In detail, evidence of cholinergic and serotoninergic systems affection was revealed by dose-dependent decreased levels of choline and N-acetyl serotonin, respectively, measured by nuclear magnetic resonance (NMR)-based metabolomics, applied for the first time to our knowledge on sea urchin embryos. The metabolic profile also highlighted a significant CuO NP dose-dependent increase of glycine, a component of matrix proteins involved in the biomineralization process, suggesting perturbed skeletogenesis accordingly to skeletal defects in spicule patterning observed previously in the same sea urchin embryos. However, the expression of skeletogenic genes, i.e. SM30 and msp130, did not differ among groups, and therefore altered primary mesenchyme cell (PMC) migration was hypothesized. Other unknown metabolites were detected from the NMR spectra, and their concentrations found to be reflective of the CuO NP exposure levels. Overall, these findings demonstrate the toxic potential of CuO NPs to interfere with neurotransmission and skeletogenesis of sea urchin embryos. The integrated use of embryotoxicity tests and metabolomics represents a highly sensitive and effective tool for assessing the impact of NPs on aquatic biota.

Brain regionalization genes are co-opted into shell field patterning in Mollusca

The 'brain regionalization genes' Six3/6, Otx, Pax2/5/8, Gbx, and Hox1 are expressed in a similar fashion in the deuterostome, ecdysozoan, and the cephalopod brain, questioning whether this holds also true for the remaining Mollusca. We investigated developmental Gbx-expression in representatives of both molluscan sister groups, the Aculifera and Conchifera. Gbx is expressed in the posterior central nervous system of an aculiferan polyplacophoran and solenogaster but not in a conchiferan bivalve suggesting that Gbx, together with Six3/6, Otx, Pax2/5/8, and Hox1, is involved in central nervous system regionalization as reported for other bilaterians. Gbx is, however, also expressed in the anterior central nervous system, i.e. the anlagen of the cerebral ganglia, in the solenogaster, a condition not reported for any other bilaterian so far. Strikingly, all Gbx-orthologs and the other 'posterior brain regionalization genes' such as Pax2/5/8 and Hox1 are expressed in the mantle that secretes shell(s) and spicules of mollusks (except cephalopods). In bivalves, the ancestral condition has even been lost, with Gbx and Pax2/5/8 not being expressed in the developing central nervous system anymore. This suggests an additional role in the formation of the molluscan shell field(s) and spicule-bearing cells, key features of mollusks.

Development of structural colour in leaf beetles

Structural colours in living organisms have been observed and analysed in a large number of species, however the study of how the micro- and nano-scopic natural structures responsible of such colourations develop has been largely ignored. Understanding the interplay between chemical composition, structural morphology on multiple length scales, and mechanical constraints requires a range of investigation tools able to capture the different aspects of natural hierarchical architectures. Here, we report a developmental study of the most widespread strategy for structural colouration in nature: the cuticular multilayer. In particular, we focus on the exoskeletal growth of the dock leaf beetle Gastrophysa viridula, capturing all aspects of its formation: the macroscopic growth is tracked via synchrotron microtomography, while the submicron features are revealed by electron microscopy and light spectroscopy combined with numerical modelling. In particular, we observe that the two main factors driving the formation of the colour-producing multilayers are the polymerization of melanin during the ecdysis and the change in the layer spacing during the sclerotisation of the cuticle. Our understanding of the exoskeleton formation provides a unique insight into the different processes involved during metamorphosis.

High resolution microscopy reveals significant impacts of ocean acidification and warming on larval shell development in Laternula elliptica

Environmental stressors impact marine larval growth rates, quality and sizes. Larvae of the Antarctic bivalve, Laternula elliptica, were raised to the D-larvae stage under temperature and pH conditions representing ambient and end of century projections (-1.6°C to +0.4°C and pH 7.98 to 7.65). Previous observations using light microscopy suggested pH had no influence on larval abnormalities in this species. Detailed analysis of the shell using SEM showed that reduced pH is in fact a major stressor during development for this species, producing D-larvae with abnormal shapes, deformed shell edges and irregular hinges, cracked shell surfaces and even uncalcified larvae. Additionally, reduced pH increased pitting and cracking on shell surfaces. Thus, apparently normal larvae may be compromised at the ultrastructural level and these larvae would be in poor condition at settlement, reducing juvenile recruitment and overall survival. Elevated temperatures increased prodissoconch II sizes. However, the overall impacts on larval shell quality and integrity with concurrent ocean acidification would likely overshadow any beneficial results from warmer temperatures, limiting populations of this prevalent Antarctic species.

Differential mantle transcriptomics and characterization of growth-related genes in the diploid and triploid pearl oyster Pinctada fucata

To explore the molecular mechanism of triploidy effect in the pearl oyster Pinctada fucata, two RNA-seq libraries were constructed from the mantle tissue of diploids and triploids by Roche-454 massive parallel pyrosequencing. The identification of differential expressed genes (DEGs) between diploid and triploid may reveal the molecular mechanism of triploidy effect. In this study, 230 down-regulated and 259 up-regulated DEGs were obtained by comparison between diploid and triploid libraries. The gene ontology and KEGG pathway analysis revealed more functional activation in triploids and it may due to the duplicated gene expression in transcriptional level during whole genome duplication (WGD). To confirm the sequencing data, a set of 11 up-regulated genes related to growth and development control and regulation were analyzed by RT-qPCR in independent experiment. According to the validation and annotation of these genes, it is hypothesized that the set of up-regulated expressed genes had the correlated expression pattern involved in shell building or other interactive probable functions during triploidization. The up- regulation of growth-related genes may support the classic hypotheses of 'energy redistribution' from early research. The results provide valuable resources to understand the molecular mechanism of triploidy effect in both shell building and producing high-quality seawater pearls.

Physical versus Biological Control in Bivalve Calcite Prisms: Comparison of Euheterodonts and Pteriomorphs

Multiple groups of bivalve molluscs produce calcitic shell layers, many of these broadly classified as "prismatic." Various pteriomorphian bivalves (such as oysters, pterioids, and mussels) secrete prismatic microstructures with high organic content and clear, strong biological control. However, we present the results of a detailed analysis by scanning electron microscopy (SEM), thermogravimetric analysis, and electron backscatter diffraction to characterize the calcitic prisms in two different clades within the euheterodont bivalves: the extant Chama arcana and the extinct rudists. These results show that the form of prisms constructed is both closely similar between the two taxa and significantly different from those of the pteriomorph bivalves. Most notably, C. arcana and the extinct rudists lack the clear organic outer envelopes and uniform polygonal, cross-sectional appearance. Instead, they form interdigitating crystals of very varied diameters, with some crystals encapsulating others. We advocate retaining the term "fibrillar prisms" to classify these euheterodont microstructures. These fibrillar prisms are more closely similar to abiotic speleothem deposits than to the calcitic prisms of pteriomorph bivalves. We argue that calcite prism growth in euheterodonts is dominated by abiotic constraints whereas, in pteriomorphs (such as oysters, pterioids, and mussels), it is under strong biological control.

Identification and Characterization of the Lysine-Rich Matrix Protein Family in Pinctada fucata: Indicative of Roles in Shell Formation

Mantle can secret matrix proteins playing key roles in regulating the process of shell formation. The genes encoding lysine-rich matrix proteins (KRMPs) are one of the most highly expressed matrix genes in pearl oysters. However, the expression pattern of KRMPs is limited and the functions of them still remain unknown. In this study, we isolated and identified six new members of lysine-rich matrix proteins, rich in lysine, glycine and tyrosine, and all of them are basic matrix proteins. Combined with four members of the KRMPs previously reported, all these proteins can be divided into three subclasses according to the results of phylogenetic analyses: KRMP1-3 belong to subclass KPI, KRMP4-5 belong to KPII, and KRMP6-10 belong to KPIII. Three subcategories of lysine-rich matrix proteins are highly expressed in the D-phase, the larvae and adult mantle. Lysine-rich matrix proteins are involved in the shell repairing process and associated with the formation of the shell and pearl. What's more, they can cause abnormal shell growth after RNA interference. In detail, KPI subgroup was critical for the beginning formation of the prismatic layer; both KPII and KPIII subgroups participated in the formation of prismatic layer and nacreous layer. Compared with different temperatures and salinity stimulation treatments, the influence of changes in pH on KRMPs gene expression was the greatest. Recombinant KRMP7 significantly inhibited CaCO₃ precipitation, changed the morphology of calcite, and inhibited the growth of aragonite in vitro. Our results are beneficial to understand the functions of the KRMP genes during shell formation.

Effects of aging on the food intake in the feeding behavior of Aplysia kurodai

In wild Aplysia, the birthdate of animals can typically not be determined. Therefore, we sought a reliable index of old age by taking into consideration the distinguished Japanese seasons. Large amounts of eggs and dead bodies were present on the coast during and after the second half of May (MayS). Body mass decreased after May. We roughly classified animals collected before and after the MayS as mature and old animals. Plots of internalized shell length (S) against body mass (B) gave distinct best-fit curves for mature and old animals. The B/S significantly decreased in the second half of June, suggesting that body mass decreases with age but shell length is maintained in each animal. Therefore, the collected animals were classified into mature and old animals using the best-fit curves for animals classified by the collection period. We examined the amount of food intake every 2 h up to 8 h after providing food. The amounts increased linearly, and the rate was significantly lower in old animals than in mature animals. The amount of 1-day food intake was also significantly lower in old animals. These results suggest that food intake may decline with age and this may cause mass loss in old animals.

Historical Biogeography of the Marine Snail Littorina saxatilis Inferred from Haplotype and Shell Morphology Evolution in NW Spain

The marine snail Littorina saxatilis exhibits extreme morphological variation between and within geographical regions and represents an excellent model for assessing local adaptation. Previous studies support the hypothesis of parallel evolution in sympatry of two morphologically different ecotypes (named as RB and SU) that co-inhabit different habitats from Galician rocky shores (NW Spain), and which are interrupted by sheltered areas inhabited by a different morph never studied before (named as SRB). Here, we use morphological and mitochondrial DNA (mtDNA) sequence data to test hypotheses on the origin and diversification of SRB snails and to assess their evolutionary relationships with RB and SU ecotypes. Our results show that the SRB morph displays the largest size and shell elongation and the smallest relative shell aperture, representing an extreme type of the RB vs. SU polymorphism, which has been linked to adaptation to sheltered ecological factors. Phylogenetic analysis shows that the SRB morph shares ancestry with RB and SU ecotypes, rejecting the hypothesis that the SRB morph marks relict populations from which these ecotypes evolved in Galician coasts. Our data support that genetic differentiation among SRB, RB and SU morphs results from a general pattern of restricted gene flow and isolation by distance linked to the colonization of Galician coasts by two independent mtDNA lineages, rather than from a random fragmentation of the initial distributional range. Therefore, the confinement of distinct lineages to specific geographical areas denote evident limits to the distances these snails can disperse. Morphological analysis indicates no association between mtDNA lineage and a specific morphotype, and suggests the independent gain of convergent morphological patterns within each mtDNA lineage in populations occupying contrasting habitats following the colonization of Galician coasts.

Irregularity of the Linear Growth of the Margaritifera margaritifera (Bivalvia: Margaritiferidae) Population of the Nemina River, Karelia

The dependence of shell growth in length and height during ontogeny has been studied in the pearl mussel Margaritifera margaritifera inhabiting the Nemina River (basin of Lake Onega, Karelia). It has been shown that the population is heterogenous based on the height-to-length ratio. It has been found that during ontogeny M. margaritifera from the studied population undergoes a constant change in the relative growth of the shell leading to either lengthening or rounding of the shell.

cDNA Microarray Analysis Revealing Candidate Biomineralization Genes of the Pearl Oyster, Pinctada fucata martensii

Biomineralization is a common biological phenomenon resulting in strong tissue, such as bone, tooth, and shell. Pinctada fucata martensii is an ideal animal for the study of biomineralization. Here, microarray technique was used to identify biomineralization gene in mantle edge (ME), mantle center (MC), and both ME and MC (ME-MC) for this pearl oyster. Results revealed that 804, 306, and 1127 contigs expressed at least three times higher in ME, MC, and ME-MC as those in other tissues. Blast against non-redundant database showed that 130 contigs (16.17 %), 53 contigs (17.32 %), and 248 contigs (22.01 %) hit reference genes (E ≤ -10), among which 91 contigs, 48 contigs, and 168 contigs could be assigned to 32, 26, and 63 biomineralization genes in tissue of ME, MC, and ME-MC at a threshold of 3 times upregulated expression level. The ratios of biomineralization contigs to homologous contigs were similar at 3 times, 10 times, and 100 times of upregulated expression level in either ME, MC, or ME-MC. Moreover, the ratio of biomineralization contigs was highest in MC. Although mRNA distribution characters were similar to those in other studies for eight biomineralization genes of PFMG3, Pif, nacrein, MSI7, mantle gene 6, Pfty1, prismin, and the shematrin, most biomineralization genes presented different expression profiles from existing reports. These results provided massive fundamental information for further study of biomineralization gene function, and it may be helpful for revealing gene nets of biomineralization and the molecular mechanisms underlining formation of shell and pearl for the oyster.

Characterization of the mantle transcriptome in bivalves: Pecten maximus, Mytilus edulis and Crassostrea gigas

The calcareous shells secreted by bivalve molluscs display diverse and species specific structural compositions, which indicates possible divergent biomineralization processes. Thus, studying multiple mollusc species will provide a more comprehensive understanding of shell formation. Here, the transcriptomes of the mantle tissues responsible for shell deposition were characterized in three commercially relevant bivalve species. Using high-throughput sequencing and bioinformatics tools, de novo transcriptome assemblies of mantle tissues were generated for the mussel Mytilus edulis, the oyster Crassostrea gigas and the scallop Pecten maximus. These transcriptomes were annotated, and contigs with similarity to proteins known to have shell formation roles in other species were identified. Comparison of the shell formation specific proteins in the three bivalves indicates the possibility of species specific shell proteins.

Oxygen Isotope Variability within Nautilus Shell Growth Bands

Nautilus is often used as an analogue for the ecology and behavior of extinct externally shelled cephalopods. Nautilus shell grows quickly, has internal growth banding, and is widely believed to precipitate aragonite in oxygen isotope equilibrium with seawater. Pieces of shell from a wild-caught Nautilus macromphalus from New Caledonia and from a Nautilus belauensis reared in an aquarium were cast in epoxy, polished, and then imaged. Growth bands were visible in the outer prismatic layer of both shells. The thicknesses of the bands are consistent with previously reported daily growth rates measured in aquarium reared individuals. In situ analysis of oxygen isotope ratios using secondary ion mass spectrometry (SIMS) with 10 μm beam-spot size reveals inter- and intra-band δ¹⁸O variation. In the wild-caught sample, a traverse crosscutting 45 growth bands yielded δ¹⁸O values ranging 2.5‰, from +0.9 to -1.6 ‰ (VPDB), a range that is larger than that observed in many serial sampling of entire shells by conventional methods. The maximum range within a single band (~32 μm) was 1.5‰, and 27 out of 41 bands had a range larger than instrumental precision (±2 SD = 0.6‰). The results from the wild individual suggest depth migration is recorded by the shell, but are not consistent with a simple sinusoidal, diurnal depth change pattern. To create the observed range of δ¹⁸O, however, this Nautilus must have traversed a temperature gradient of at least ~12°C, corresponding to approximately 400 m depth change. Isotopic variation was also measured in the aquarium-reared sample, but the pattern within and between bands likely reflects evaporative enrichment arising from a weekly cycle of refill and replacement of the aquarium water. Overall, this work suggests that depth migration behavior in ancient nektonic mollusks could be elucidated by SIMS analysis across individual growth bands.

Characterization of a Monoclonal Antibody Directed against Mytilus spp Larvae Reveals an Antigen Involved in Shell Biomineralization

The M22.8 monoclonal antibody (mAb) developed against an antigen expressed at the mussel larval and postlarval stages of Mytilus galloprovincialis was studied on adult samples. Antigenic characterization by Western blot showed that the antigen MSP22.8 has a restricted distribution that includes mantle edge tissue, extrapallial fluid, extrapallial fluid hemocytes, and the shell organic matrix of adult samples. Other tissues such as central mantle, gonadal tissue, digestive gland, labial palps, foot, and byssal retractor muscle did not express the antigen. Immunohistochemistry assays identified MSP22.8 in cells located in the outer fold epithelium of the mantle edge up to the pallial line. Flow cytometry analysis showed that hemocytes from the extrapallial fluid also contain the antigen intracellularly. Furthermore, hemocytes from hemolymph have the ability to internalize the antigen when exposed to a cell-free extrapallial fluid solution. Our findings indicate that hemocytes could play an important role in the biomineralization process and, as a consequence, they have been included in a model of shell formation. This is the first report concerning a protein secreted by the mantle edge into the extrapallial space and how it becomes part of the shell matrix framework in M. galloprovincialis mussels.

Seasonal Variation in Shell Calcification of Planktonic Foraminifera in the NE Atlantic Reveals Species-Specific Response to Temperature, Productivity, and Optimum Growth Conditions

Using shells collected from a sediment trap series in the Madeira Basin, we investigate the effects of seasonal variation of temperature, productivity, and optimum growth conditions on calcification in three species of planktonic Foraminifera. The series covers an entire seasonal cycle and reflects conditions at the edge of the distribution of the studied species, manifesting more suitable growth conditions during different parts of the year. The seasonal variation in seawater carbonate saturation at the studied site is negligible compared to other oceanic regions, allowing us to assess the effect of parameters other than carbonate saturation. Shell calcification is quantified using weight and size of individual shells. The size-weight scaling within each species is robust against changes in environmental parameters, but differs among species. An analysis of the variation in calcification intensity (size-normalized weight) reveals species-specific response patterns. In Globigerinoides ruber (white) and Globigerinoides elongatus, calcification intensity is correlated with temperature (positive) and productivity (negative), whilst in Globigerina bulloides no environmental forcing is observed. The size-weight scaling, calcification intensity, and response of calcification intensity to environmental change differed between G. ruber (white) and G. elongatus, implying that patterns extracted from pooled analyses of these species may reflect their changing proportions in the samples. Using shell flux as a measure of optimum growth conditions, we observe significant positive correlation with calcification intensity in G. elongatus, but negative correlation in G. bulloides. The lack of a consistent response of calcification intensity to optimum growth conditions is mirrored by the results of shell size analyses. We conclude that calcification intensity in planktonic Foraminifera is affected by factors other than carbonate saturation. These factors include temperature, productivity, and optimum growth conditions, but the strength and sign of the relationships differ among species, potentially complicating interpretations of calcification data from the fossil record.

Shaving a Shell: Effect of Manipulated Sculpture and Feeding on Shell Growth and Sculpture Development in Nucella lamellosa (Muricidae: Ocenebrinae)

Gastropod shell sculpture offers a novel tool for studying morphological patterning. Existing shell features may be manipulated experimentally to test how alteration affects subsequent shell growth and form. Axial sculpture occurs in many gastropod groups, and spacing of sculpture may be regular or irregular. But how gastropods control sculpture placement during shell growth is unknown. We studied the growth and positioning of axial lamellae in the muricid Nucella lamellosa, and compared these to the superficially similar axial varices seen in other muricids. First, we tested whether the feeding rate had any effect on the rate of addition or positioning of new lamellae. Second, we tested what effect previous shell sculpture had on lamellar placement, and shell growth in general, by removing all shell sculpture and allowing snails to grow over the "shaved" shell surface. Lamellar growth appeared to be relatively plastic; spacing was highly variable both within and among individual snails, and 1-2 weeks were required to complete the addition of a new lamella. Body growth rate was the primary determinant of lamellar growth; past lamellae had no effect on placement of new lamellae or rate of shell length increase. Feeding rate and body size affected only growth in shell length, and had no direct effect on spacing or on the rate of addition of new lamellae. The growth of axial lamellae in N. lamellosa differed from that of varices by exhibiting neither a) regular spacing nor b) a growth hiatus after completion of a lamella. Significantly, despite the obvious impediment of previous sculpture to future shell growth, removal of this sculpture had no observable effect on the rate of body growth or on any aspect of subsequent lamellar growth.

[Specific Features of Linear Growth Influencing Morphometric Parameters of the Shell in Margaritifera margaritifera (Bivalvia: Margaritiferidae)]

Interdependence of parameters of shell growth in length and height during ontogeny has been studied in the freshwater pearl mussel M. margaritifera. It has been shown that the results of determining the height-to-length ratio depend on at least two factors: shell corrosion in the apical (umbo) zone and regular, rhythmic deviation of this ratio from values expected from linear regression equation. The first factor may be taken into account by applying an individual correction for each specimen, thereby making the ratio of linear dimensions independent of mussel age and size. The calculation error caused by biological rhythms may be reduced by measuring the greatest possible number of annual rings (> or = 18). Factors accounting for alternation between periods of prevalent shell growth in length or in height are discussed.

[Biomineralization--precision of shape, structure and properties controlled by proteins]

ABSTRACT Biomineralization is the process of the formation of crystal structures that is under biological control. Living organisms produce structures such as bone, teeth, otoliths, otoconia or shells. Although the chemical composition of these tissues is similar to corresponding inorganic minerals, their structure and mechanical properties differ significantly. This may be because of how they are adapted for the functions they perform. The precise control of the formation of biominerals starting with the early nucleation stage influences how the final tissues are formed. The key factors which determine the size, shape, internal structure and properties of biominerals are proteins which control the nucleation and growth of the crystals. Biomineralization is a multi-step process involving protein-protein interactions, as well as interactions between proteins and inorganic fraction. Due to their specific properties, intrinsically disordered proteins (IDPs) perform a particularly important role in the control of the biomineralization process. This article contains an overview of biominerals that are naturally occurring and describes the structures and mineralization mechanisms of the most important of them. The main part of this work was dedicated to the role of proteins which control crystal growth.

Self-similar mesostructure evolution of the growing mollusc shell reminiscent of thermodynamically driven grain growth

Significant progress has been made in understanding the interaction between mineral precursors and organic components leading to material formation and structuring in biomineralizing systems. The mesostructure of biological materials, such as the outer calcitic shell of molluscs, is characterized by many parameters and the question arises as to what extent they all are, or need to be, controlled biologically. Here, we analyse the three-dimensional structure of the calcite-based prismatic layer of Pinna nobilis, the giant Mediterranean fan mussel, using high-resolution synchrotron-based microtomography. We show that the evolution of the layer is statistically self-similar and, remarkably, its morphology and mesostructure can be fully predicted using classical materials science theories for normal grain growth. These findings are a fundamental step in understanding the constraints that dictate the shape of these biogenic minerals and shed light on how biological organisms make use of thermodynamics to generate complex morphologies.