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.