Interaction strength between a predator and dangerous prey: Sinistrofulgur predation on Mercenaria

The lack of direct empirical evidence of predator evolution in response to prey adaptation is a fundamental weakness of the arms race analogy of predator-prey coevolution. I examined the interaction between the predatory busyconine whelk Sinistrofulgur sinistrum and its bivalve prey Mercenaria mercenaria to evaluate whether reciprocal adaptation was likely in this predator-prey system. Thick-lipped whelks use their shell lip to chip open the shell of their prey, often resulting in breakage to their own shell. Thus, hard-shelled prey, such as Mercenaria, may be considered dangerous because they are able to inflict damage to the predator as a consequence of the interaction. The strength of interaction between whelks and their bivalve prey was viewed by regressing predator performance (the incidence of shell breakage in encounters with prey) on prey phenotype (a function of size). Interaction with Mercenaria of varying sizes has strong and predictable consequences (r²=0.946; p=0.028) for Sinistrofulgur. Predators that select large, thick bivalve prey increase the likelihood that their shell lip will be broken in the process of attempting to open their prey. Ecological consequences of feeding-induced breakage may include reduced growth rate, reproductive success, and survivorship. These results suggest that natural selection should favor predator phenotypes that reduce feeding-induced breakage when interactions with damage-inducing prey occur.     

Microtexture of larval shell of oyster,Crassostrea nippona: A FIB-TEM study

The initial formation and subsequent development of larval shells in marine bivalve, Crassostrea nippona were investigated using the FIB-TEM technique. Fourteen hours after fertilization (the trochophore stage), larvae form an incipient shell of 100–150 nm thick with a columnar contrast. Selected-area electron diffraction analysis showed a single-crystal aragonite pattern with the c-axis perpendicular to the shell surface. Plan-view TEM analysis suggested that the shell contains high density of {110} twins, which are the origin of the columnar contrast in the cross-sectional images. 72 h after fertilization (the veliger stage), the shell grows up to 1.2–1.4 μm thick accompanying an additional granular layer between the preexisting layer and embryo to form a distinctive two-layer structure. The granular layer is also composed of aragonite crystals sharing their c-axes perpendicular to the shell surface, but the crystals are arranged with a flexible rotation around the c-axes and not restricted solely to the {110} twin relation. No evidence to suggest the existence of amorphous calcium carbonate (ACC) was found through the observation. The well-regulated crystallographic properties found in the present sample imply initial shell formation probably via a direct deposition of crystalline aragonite.     

Growth and shell morphology of three mytilidae (Bivalvia) species from the Sea of Japan

The growth and shell morphology of bivalve mollusks Crenomytilus grayanus, Mytilus coruscus, and Modiolus modiolus from the Sea of Japan are examined. The changes in body proportions and shell form in the ontogenesis of C. grayanus, M. coruscus, and M. modiolus are different even in the cases when the mussels develop in similar environmental conditions. Rapid growth shapes a well-streamlined and flat form of shell; slow growth leads to the formation of a massive and convex form. The parameters of the Bertalanffy growth curve for each species are calculated. The differences are discussed from the standpoint of functional morphology and spatial distribution patterns of mytilids in the coastal areas of the sea.     

Alternative predation tactics of a tropical naticid gastropod

Aquarium observations of naticid gastropods from Hong Kong show that different species attack their bivalve prey in different ways. Natica gualteriana and Glossaulax didyma appeared always to use conventional modes of boring, i.e., through one shell valve, before consuming the prey, but some larger prey of C. didyma with incomplete borings were consumed after having apparently suffocated before boring was complete. In contrast, Polinices tumidus prey may be side-bored, edge-bored (i.e., through the commisure of the valves) or suffocated and consumed without boring. The frequency of each of these modes of attack vary with different prey species. Non-boring prédation, in aquarium experiments, accounted for 14.7–54.9% of attacks with different species of prey. Suffocated prey were found to be enwrapped in a thick, viscous coat of mucus, which in partially consumed prey showed a round hole overlying the ventral shell gape marking the entrance hole made by the proboscis. The observations reveal considerable flexibility in predation behaviour in this tropical naticid and have important implications in the interpretation of naticid prédation rates in recent and fossil dead shell assemblages.     

Characteristics of shell microstructure and growth analysis of the Antarctic bivalve <Emphasis Type="Italic">Laternula elliptica</Emphasis> from Lützow-Holm Bay,Antarctica

Growth performance of the Antarctic bivalve Laternula elliptica was examined both by shell microstructural observation and by applying a fluorescent substance, tetracycline, as a shell growth marker. The shell was composed of two calcareous layers: the thick outer layer was homogeneous or granular in structure and the thin inner layer was nacreous. The architecture of Antarctic L. elliptica was different from that of temperate L. marilina, and the ratio of thickness between the outer and inner layers appeared to be different. The growth rate of the nacreous layer was analyzed to be very low. High correlations were found between the major axis of chondrophore and both shell length and shell dry weight, respectively. It is suggested that the chondrophore is an appropriate growth indicator, and combining the information of growth increments with the fluorescent method may be useful in estimating the bivalve growth performance in the Antarctic sea.     

A Bivalve Biomineralization Toolbox

Mollusc shells are a result of the deposition of crystalline and amorphous calcite catalyzed by enzymes and shell matrix proteins (SMP). Developing a detailed understanding of bivalve mollusc biomineralization pathways is complicated not only by the multiplicity of shell forms and microstructures in this class, but also by the evolution of associated proteins by domain co-option and domain shuffling. In spite of this, a minimal biomineralization toolbox comprising proteins and protein domains critical for shell production across species has been identified. Using a matched pair design to reduce experimental noise from inter-individual variation, combined with damage-repair experiments and a database of biomineralization SMPs derived from published works, proteins were identified that are likely to be involved in shell calcification. Eighteen new, shared proteins likely to be involved in the processes related to the calcification of shells were identified by the analysis of genes expressed during repair in Crassostrea gigas, Mytilus edulis, and Pecten maximus. Genes involved in ion transport were also identified as potentially involved in calcification either via the maintenance of cell acid–base balance or transport of critical ions to the extrapallial space, the site of shell assembly. These data expand the number of candidate biomineralization proteins in bivalve molluscs for future functional studies and define a minimal functional protein domain set required to produce solid microstructures from soluble calcium carbonate. This is important for understanding molluscan shell evolution, the likely impacts of environmental change on biomineralization processes, materials science, and biomimicry research.     

Assembly of the head of bacteriophage P22: X-ray diffraction from heads,proheads and related structures

We have used electron microscopy and small-angle X-ray diffraction to study the three principal structures found in the head assembly pathway of Salmonella phage P22. These structures are, in order of their appearance in the pathway: proheads, unstable filled heads (which lose their DNA and become empty heads upon isolation), and phage. In addition, we can convert proheads to an empty head-like form (the empty prohead) in vitro by treating them with 0.8% sodium dodecyl sulfate at room temperature.We have shown that proheads are composed of a shell of coat protein with a radius of 256 Å, containing within it a thick shell or a solid ball (outer radius 215 Å) of a second protein, the scaffolding protein, which does not appear in phage. The three other structures studied are all about 10% larger than proheads, having outer shells with radii of about 285 Å. Empty heads and empty proheads appear identical by small-angle X-ray diffraction to a resolution of 25 Å, both being shells about 40 Å thick. Phage appear to be made up of a protein shell identical to that in empty heads and empty proheads, within which is packed the DNA.Some details of the DNA packing are also revealed by the diffraction pattern of phage. The inter-helix distance is about 28 Å, and the hydration is about 1.5 g of water per g of DNA. Certain aspects of the pattern suggest that the DNA interacts in a specific mariner with the coat protein subunits on the inside edge of the protein shell.Thus, the prohead-to-head transformation involves, in addition to the loss of an internal scaffold and its replacement by DNA, a structural transition in the outer shell. Diffraction from features of the surface organization in these structures indicates that the clustering of the coat protein does not change radically during the expansion. The fact that the expansion occurs in vitro during the formation of empty proheads shows that it is due to the bonding properties of the coat protein alone, although it could be triggered in vivo by DNA -protein interactions. The significance of the structural transition is discussed in terms of its possible role in the control of head assembly and DNA packaging.     

Ocean Warming,More than Acidification,Reduces Shell Strength in a Commercial Shellfish Species during Food Limitation

Ocean surface pH levels are predicted to fall by 0.3–0.4 pH units by the end of the century and are likely to coincide with an increase in sea surface temperature of 2–4°C. The combined effect of ocean acidification and warming on the functional properties of bivalve shells is largely unknown and of growing concern as the shell provides protection from mechanical and environmental challenges. We examined the effects of near-future pH (ambient pH –0.4 pH units) and warming (ambient temperature +4°C) on the shells of the commercially important bivalve, Mytilus edulis when fed for a limited period (4–6 h day⁻¹). After six months exposure, warming, but not acidification, significantly reduced shell strength determined as reductions in the maximum load endured by the shells. However, acidification resulted in a reduction in shell flex before failure. Reductions in shell strength with warming could not be explained by alterations in morphology, or shell composition but were accompanied by reductions in shell surface area, and by a fall in whole-body condition index. It appears that warming has an indirect effect on shell strength by re-allocating energy from shell formation to support temperature-related increases in maintenance costs, especially as food supply was limited and the mussels were probably relying on internal energy reserves. The maintenance of shell strength despite seawater acidification suggests that biomineralisation processes are unaffected by the associated changes in CaCO₃ saturation levels. We conclude that under near-future climate change conditions, ocean warming will pose a greater risk to shell integrity in M. edulis than ocean acidification when food availability is limited.     

Features of the shell morphology of Mytilus trossulus (Bivalvia: Mytilidae) in the fouling of the alga Sargassum pallidum (Phaeophyceae: Sargassaceae)

The features of ontogenetic variation in the shell shape of the bivalve Mytilus trossulus were studied based on material that was collected from different biotopes in the Vostok Bay of the Sea of Japan in 2011. It was revealed that the mollusks had different shell shapes in rock populations and in foulings of artificial substrates but all the developmental changes fall within formerly recorded peculiarities. It is shown that significant deviations from the typical form of the shell are characteristic to mollusks from the fouling of thalli of the brown algae Sargassum pallidum that inhabit shallow water at surf-exposed rocky headlands. The mollusks from this biotope were characterized by numerous traces of deformations of the shell, an atypically skewed growth of the rear edge, and a significant excess (20–25%) of the width over the shell height. It was revealed that the recorded features of shell morphology are apparently associated with features of mussel habitation in an environment with active hydrodynamics.     

The Ramonalinids: a new family of mound‐building bivalves of the Early Middle Triassic

Abstract: Ramonalina n. gen. is a large thick‐shelled bivalve abundant in mounds preserved in the Gevanim Formation (late Anisian, Middle Triassic) of southern Israel. This bivalve was an edgewise‐recliner with a flattened anteroventral (functionally basal) surface and partially fused valves. It is the basis of a new family, the Ramonalinidae, which is descended from the myalinids through adaptation to edgewise positioning. Ligamental attachment was inadequate to hold valves together on large adults, resulting in valve displacement followed by shell secretion in the apical area that fused valves together and caused irregular growth on abapical areas. The ramonalinids formed large, nearly monospecific mounds on firm mud substrates in shallow marine waters. These are the largest Middle Triassic bivalve mounds known.     

Ocean Acidification Has Multiple Modes of Action on Bivalve Larvae

Ocean acidification (OA) is altering the chemistry of the world’s oceans at rates unparalleled in the past roughly 1 million years. Understanding the impacts of this rapid change in baseline carbonate chemistry on marine organisms needs a precise, mechanistic understanding of physiological responses to carbonate chemistry. Recent experimental work has shown shell development and growth in some bivalve larvae, have direct sensitivities to calcium carbonate saturation state that is not modulated through organismal acid-base chemistry. To understand different modes of action of OA on bivalve larvae, we experimentally tested how pH, P_CO2, and saturation state independently affect shell growth and development, respiration rate, and initiation of feeding in Mytilus californianus embryos and larvae. We found, as documented in other bivalve larvae, that shell development and growth were affected by aragonite saturation state, and not by pH or P_CO2. Respiration rate was elevated under very low pH (~7.4) with no change between pH of ~ 8.3 to ~7.8. Initiation of feeding appeared to be most sensitive to P_CO2, and possibly minor response to pH under elevated P_CO2. Although different components of physiology responded to different carbonate system variables, the inability to normally develop a shell due to lower saturation state precludes pH or P_CO2 effects later in the life history. However, saturation state effects during early shell development will carry-over to later stages, where pH or P_CO2 effects can compound OA effects on bivalve larvae. Our findings suggest OA may be a multi-stressor unto itself. Shell development and growth of the native mussel, M. californianus, was indistinguishable from the Mediterranean mussel, Mytilus galloprovincialis, collected from the southern U.S. Pacific coast, an area not subjected to seasonal upwelling. The concordance in responses suggests a fundamental OA bottleneck during development of the first shell material affected only by saturation state.     

ADAPTATIONS IN GRAMMYSIA OBLIQUA

The Grammysiidae are an important but little understood family of Paleozoic bivalves. Specimens of Grammysia obliqua (McCoy) from the Stonehouse Formation (Uppermost Silurian), Nova Scotia, permit interpretation of their functional morphology and autecology. Grammysia obliqua was an immobile, semi-infaunal, filter-feeding bivalve. It lived fixed by a byssus, with the shell inclined about 40° to the sediment-water interface. Though incapable of opening the shell, the animal maintained contact with the environment through byssal and dorsal-posterior gapes. This latter gape was in a peculiar position for a bivalve and required some anatomical adaptation, but it was functionally efficient for the animal's life attitude.     

Temperature and Food Influence Shell Growth and Mantle Gene Expression of Shell Matrix Proteins in the Pearl Oyster Pinctada margaritifera

In this study, we analyzed the combined effect of microalgal concentration and temperature on the shell growth of the bivalve Pinctada margaritifera and the molecular mechanisms underlying this biomineralization process. Shell growth was measured after two months of rearing in experimental conditions, using calcein staining of the calcified structures. Molecular mechanisms were studied though the expression of 11 genes encoding proteins implicated in the biomineralization process, which was assessed in the mantle. We showed that shell growth is influenced by both microalgal concentration and temperature, and that these environmental factors also regulate the expression of most of the genes studied. Gene expression measurement of shell matrix protein thereby appears to be an appropriate indicator for the evaluation of the biomineralization activity in the pearl oyster P. margaritifera under varying environmental conditions. This study provides valuable information on the molecular mechanisms of mollusk shell growth and its environmental control.     

Feeding behavior,ration and size structure of a population of the predatory gastropod <Emphasis Type="Italic">Cryptonatica janthostoma</Emphasis> in Vostok Bay,Sea of Japan

The relationships between the shell height of the predatory gastropod Cryptonatica janthostoma and the shell length of its typical prey, the bivalve Ruditapes philippinarum, and the diameter of the borehole on the prey shell resulting from a successful attack of the predator were experimentally found and assessed statistically. The shell height of C. janthostoma calculated retrospectively from the borehole diameter using the obtained relationships was 17–52 mm. The prey of C. janthostoma are burrowing bivalves, whose populations are affected by the predator to a varying degree. In populations of medium-sized mollusks (R. philippinarum, Protothaca euglypta, P. jedoensis, and others), C. janthostoma feeds on mollusks larger than 7–10 mm; in species with a shell length greater than 100 mm (Callista brevisiphonata, Saxidomus purpuratus), it eats specimens of 10–58 mm. C. janthostoma apparently has no effect on populations of small-sized mollusks (Anisocorbula venusta) and mollusks with an active avoidance response (Clinocardium californiense).     

Identification of a tyrosinase gene potentially involved in early larval shell biogenesis of the Pacific oyster Crassostrea gigas

The larval shell emerges early in embryogenesis of mollusks, but the detailed mechanisms of its biogenesis remain to be determined. In this study, we cloned a tyrosinase gene (cgi-tyr1) that potentially functioned in larval shell biogenesis from the Pacific oyster Crassostrea gigas, a worldwide bivalve species. Sequence analysis of cgi-tyr1 revealed that it had typical copper-binding domains and a signal peptide. Through whole mount in situ hybridization and an electron scanning microscopic observation, we detected the expression of cgi-tyr1 firstly in the saddle-shaped shell field in trochophores, indicating that cgi-tyr1 might participate in the biogenesis of the initial non-calcified shell of trochophores. In the following development to early D-veliger, cells in the central region of shell field exhibited no detectable cgi-tyr1 expression, and cgi-tyr1 expression was sustained only in the edge of the shell field and the hinge region, indicating that cgi-tyr1 might function fundamentally in shell growth from trochophore to early D-veliger. Unexpectedly, cgi-tyr1 expression was not detected after the D-veliger stage. This indicated that other molecules might function in later shell development. Our results suggested a role for a tyrosinase gene that specifically functioned in the initial phase of the larval shell biogenesis of C. gigas. This work would shed light on future studies on larval shell development and might be helpful to understand how the molluscan shell emerged during evolution.     

Shell form and growth of the bivalveScapharca broughtoni

Linear growth rates and age-related changes in shell form are analyzed in the bivalveScapharca broughtoni from several areas of Peter the Great Bay, Sea of Japan. Mollusks grow fast during the first 4 to 5 years of life; at the age of 10–12 years, the annual growth increment in shell size does not usually exceed 1–3 mm. Irrespective of habitat, the shell valve convexity ofS. broughtoni increases with age, but the most significant changes in shell form occur during the first year of life. The peculiarities of growth and age-related changes in shell form ofS. broughtoni are discussed from the standpoint of the functional morphology of burrowing bivalve mollusks, which, at the postlarval stage, change from an attached to a free-living mode of life.     

A novel role for dpp in the shaping of bivalve shells revealed in a conserved molluscan developmental program

During the molluscan evolution leading to the bivalves, the single dorsal shell was doubled. To elucidate the molecular developmental basis underlying this prominent morphological transition, we described the cell cleavage and expression patterns of three genes, brachyury, engrailed, and dpp in the Japanese spiny oyster Saccostrea kegaki, and examined the function of dpp in this species. The cleavage pattern of the S. kegaki embryo was nearly the same as the previously described pattern of other bivalve species, suggesting that the pattern itself is highly important for the establishment or the maintenance of the bivalve body plan. The expression pattern of a brachyury homolog in S. kegaki (SkBra) was similar to the pattern in gastopods even at the single cell level despite the deep divergence of gastropods and bivalves. Engrailed and dpp were previously found to be expressed around the shell anlagen in gastropods. Like that of gastropods, an engrailed homolog in S. kegaki (SkEn) was found to be expressed around the shell anlagen. However, the dpp homolog in S. kegaki (SkDpp) was expressed only in the cells along the dorsal midline. ZfBMP4 treatment experiments revealed the importance of dpp in establishing the characteristic shape of the bivalve shell anlagen.     

Shell form,growth and life span of <Emphasis Type="Italic">Astarte arctica</Emphasis> and <Emphasis Type="Italic">A. borealis</Emphasis> (Mollusca: Bivalvia) from the subtidal zone of northeastern Sakhalin

This study investigates changes in body proportions during ontogenesis of the bivalves Astarte arctica and A. borealis from the subtidal zone of northeastern Sakhalin. Marked differences in the shell form of bivalves were found. The shell of A. arctica is convex and compact, shell length and height are comparable, and shell width is more than 50% of shell height. A. borealis has a slightly elongate and flattened shell, its width is less than 50% of its height. Shell proportions can provide a reliable criterion for differentiating the species. Mollusks grow at nearly the same rate but attain different maximum sizes. Linear growth is described by Bertalanffy’s equation: L_t = 48.2[1 ? e ^{?0.4850(t ? 0.4396)}] for A. arctica and L_t = 53.1[1 ? e^{?0.4106(t ? 0.4253)}] for A. borealis. In northeastern Sakhalin, the life span of A. arctica is 7 years and of A. borealis, 8 years. By life span, the two bivalve species from Sakhalin slightly differ from their counterparts in other regions, particularly the arctic seas.     

Form and functional morphology of Raetellops pulchella (Bivalvia: Mactridae): an example of convergent evolution with anomalodesmatans

Abstract. The bivalve Raetellops pulchella is a highly specialized, deposit-feeding member of the Mactridae. Studies of its form and function provide an example of how the bivalve body plan can be modified to facilitate the exploitation of mud as a food resource, and help in understanding how this lifestyle has evolved. Adaptations to this lifestyle include an overall reduction in ctenidial size and loss of the descending lamellae of both outer demibranchs. This reduction is associated with the enlargement of the labial palps to process inhaled sediment. In the mantle cavity, a waste canal below the posterior mantle flaps facilitates pseudofeces removal. The midgut is long and capacious, presumably to cope with the large amounts of ingested organic material. In addition, individuals of R. pulchella have unusually thin, brittle, and rostrate shells, with narrow siphonal gapes. They possess a shell buttress in each valve extending from the hinge plate to above the posterior adductor muscle. This buttress functions to prevent the brittle shell valves from fracturing when adduction occurs. A buttress is also seen in some representatives of the Anomalodesmata; in particular, the situation in R. pulchella is most like that seen in individuals of the similarly deposit-feeding species Offadesma angasi (Anomalodesmata: Periplomatidae). I interpret the similar shell form of these deposit-feeding clams as an example of convergent evolution.