Core-shell nanospheres behind the blue eyes of the bay scallop Argopecten irradians.

The bay scallop Argopecten irradians (Mollusca: Bivalvia) has dozens of iridescent blue eyes that focus light using mirror-based optics. Here, we test the hypothesis that these eyes appear blue because of photonic nanostructures that preferentially scatter short-wavelength light. Using transmission electron microscopy, we found that the epithelial cells covering the eyes of A. irradians have three distinct layers: an outer layer of microvilli, a middle layer of random close-packed nanospheres and an inner layer of pigment granules. The nanospheres are approximately 180 nm in diameter and consist of electron-dense cores approximately 140 nm in diameter surrounded by less electron-dense shells 20 nm thick. They are packed at a volume density of approximately 60% and energy-dispersive X-ray spectroscopy indicates that they are not mineralized. Optical modelling revealed that the nanospheres are an ideal size for producing angle-weighted scattering that is bright and blue. A comparative perspective supports our hypothesis: epithelial cells from the black eyes of the sea scallop Placopecten magellanicus have an outer layer of microvilli and an inner layer of pigment granules but lack a layer of nanospheres between them. We speculate that light-scattering nanospheres help to prevent UV wavelengths from damaging the internal structures of the eyes of A. irradians and other blue-eyed scallops.

Robustness of Adamussium colbecki shell to ocean acidification in a short-term exposure.

Atmospheric pCO2 has increased since the industrial revolution leading to a lowering of the ocean surface water pH, a phenomenon called ocean acidification (OA). OA is claimed to be a major threat for marine organisms and ecosystems and, particularly, for Polar regions. We explored the impact of OA on the shell mechanical properties of the Antarctic scallop Adamussium colbecki exposed for one month to acidified (pH 7.6) and natural conditions (unmanipulated littoral water), by performing Scanning Electron Microscopy, nanoindentation and Vickers indentation on the scallop shell. No effect of pH could be detected either in crystal deposition or in the mechanical properties. A. colbecki shell was found to be resistant to OA, which suggests this species to be able to face a climate change scenario that may threat the persistence of the endemic Antarctic species. Further investigation should be carried out in order to elucidate the destiny of this key species in light of global change.

Bending and branching of calcite laths in the foliated microstructure of pectinoidean bivalves occurs at coherent crystal lattice orientation.

Foliated calcite is widely employed by some important pteriomorph bivalve groups as a construction material. It is made from calcite laths, which are inclined at a low angle to the internal shell surface, although their arrangement is different among the different groups. They are strictly ordered into folia in the anomiids, fully independent in scallops, and display an intermediate arrangement in oysters. Pectinids have particularly narrow laths characterized by their ability to change their growth direction by bending or winding, as well as to bifurcate and polyfurcate. Electron backscatter analysis indicates that the c-axes of laths are at a high, though variable, angle to the growth direction, and that the laths grow preferentially along the projection of an intermediate axis between two a-axes, although they can grow in any intermediate direction. Their main surfaces are not particular crystallographic faces. Analyses done directly on the lath surfaces demonstrate that, during the bending/branching events, all crystallographic axes remain invariant. The growth flexibility of pectinid laths makes them an excellent space-filling material, well suited to level off small irregularities of the shell growth surface. We hypothesize that the exceptional ability of laths to change their direction may be promoted by the mode of growth of biogenic calcite, from a precursor liquid phase induced by organic molecules.

Application of monoclonal antibody against granulocytes of scallop Chlamys farreri on granulocytes occurrence at different developmental stages and antigenic cross-reactivity of granulocytes in five other bivalve species.

A monoclonal antibody (MAb) 6H7 raised specifically against granulocytes of scallop (Chlamys farreri) was employed to observe granulocyte occurrence successively in blastulae, gastrulae, trochophore larvae, D-shape larvae, umbo-veliger larvae and creeping larvae of C. farreri by immunohistochemistry assay contrasted with H&E stain using semi-thin sections. Moreover, the reactivity of the MAb with granulocytes of C. farreri, Bay scallop Argopecten irradians, Japanese scallop Patinopecten yessoensis, Blue mussel Mytilus edulis, Pacific oyster Crassostrea gigas and Manila clam Ruditapes philippinarum, was detected by immunofluorescence assay (IFA) with differential interference contrast and fluorescent microscopy and flow cytometric immunofluorescence assay (FCIFA). The results showed that positive signals were first observed at D-shape larval stage, about 28 h post fertilization, after that, umbo-veliger larvae exhibited the positive cells with a diameter of 3-5 µm distributed in velum, digestive gland and esophagus. Then in creeping larvae, the number of positive cells increased with average diameter of 5-7 µm, and widely distributed in foot, digestive gland, gills and adductor muscles. No positive signal was found in blastulae, gastrulae and trochophore larvae. The results of IFA and FCIFA showed MAb 6H7 reacted to granulocytes of C. farreri, A. irradians, P. yessoensis and C. gigas, and the positive percentage reactivity were 53 ± 2.5%, 15 ± 2.5%, 12 ± 2.1% and 19 ± 2.1%, respectively, however, no cross-reaction was detected in hemocytes of R. philippinarum and M. edulis.

Development of a monoclonal antibody specific to granulocytes and its application for variation of granulocytes in scallop Chlamys farreri after acute viral necrobiotic virus (AVNV) infection.

A monoclonal antibody (MAb 6H7) specific to granulocytes of scallop Chlamys farreri was produced by immunising mice with separated granulocytes as an antigen. Characterised using a flow cytometric immunofluorescence assay, MAb 6H7 reacted to granulocytes by 87.1% of total positive haemocytes. At the ultrastructural level, MAb 6H7 demonstrated epitope in cytoplasmic granules of granulocytes. Western blotting analysis indicated that a peptide of 155 kDa was recognised by MAb 6H7. It was therefore used to investigate granulocyte variation in C. farreri after acute viral necrobiotic virus (AVNV) infection using an enzyme-linked immunosorbent assay. The result illustrated that granulocytes varied greatly by AVNV infection, and their amount significantly increased on day 1 post-injection, then decreased on days 2, 3 and 4, thereafter, rebounded and approached to a second peak on day 6, finally went down gradually to the control level on day 8.

[Effect of temperature stress on activities of nitric oxide synthase and tyrosine hydroxylase in the central nervous system of bivalve molluscs].

Effects of temperature stress on nitric oxide synthase (NOS) and tyrosine hydroxylase (TH) activities in CNS of two species of bivalve molluscs Mizuchopecten yessoensis and Chlamys farreri nipponensis (Pectinidae) were studied using NADPH-diaphorase histochemistry and ummunocytochemistry. General and specific peculiarities in distribution and relative content ofNOS- and TH-positive neurons in nervous ganglia were revealed in norm and under stress at 30 degrees C for 10, 30, and 60 min. The initial stress stage (for 10 min) has been shown to be accompanied by an increase of the relative content of TH-positive neurons in some CNS areas of both mollusc species. In Chlamys farreri nipponensis under normal conditions, the presence of NOS in the CNS and its significant activation under temperature stress might have possibly been an important neuroprotective component of stress reaction in some mollusc species.

The 7-stranded structure of relaxed scallop muscle myosin filaments: support for a common head configuration in myosin-regulated muscles.

Isolated relaxed myosin filaments from the myosin-regulated scallop striated adductor muscle have been reconstructed using electron microscopy and single particle analysis of negatively stained filaments. Three-dimensional reconstruction using 7-fold rotational symmetry but without imposed helical symmetry confirmed that the myosin head array is a 7-stranded, right-handed long-pitch 24/1 helix (or left-handed short-pitch 10/1 helix) with the whole structure having an axial repeat of 1440A. Reconstruction using the full helical symmetry revealed details of the myosin head density distribution within the head crowns in the relaxed scallop myosin filament. The resulting density distribution can best be explained by an arrangement in which the two heads from the same myosin molecule interact together within each crown in a compact parallel fashion along the filament axis. The configuration is consistent with the published configuration of the two heads within vertebrate smooth muscle myosin molecules observed in two-dimensional crystals of smooth muscle myosin and in the structure of tarantula myosin filaments. All these three muscle types are myosin-regulated, providing further support for a general motif of intramolecular interacting-heads structure in the relaxed state of myosin-regulated muscles as was proposed earlier by Woodhead et al. [Woodhead, J.L., Zhao, F.-Q., Craig, R., Egelman, E.H., Alamo, L., Padron, R.. 2005. Atomic model of a myosin filament in the relaxed state. Nature 436, 1195-1199]. However, the orientation of the Wendt structure is different from that found by Woodhead in that the outer head projects outwards and the inner head lies closer to the filament backbone, as in earlier work done on the insect flight muscle myosin filaments [AL-Khayat, H.A., Hudson, L., Reedy, M.K., Irving, T.C., Squire, J.M., 2003. Myosin head configuration in relaxed insect flight muscle: X-ray modelled resting crossbridges in a pre-powerstroke state are poised for actin binding. Biophys. J. 85, 1063-1079]. Possible species specific details that may differ between the scallop and the tarantula myosin filaments are also discussed.

Pathogenicity of a highly exopolysaccharide-producing Halomonas strain causing epizootics in larval cultures of the Chilean scallop Argopecten purpuratus (Lamarck, 1819).

Mass mortalities of larval cultures of Chilean scallop Argopecten purpuratus have repeatedly occurred in northern Chile, characterized by larval agglutination and accumulation in the bottom of rearing tanks. The exopolysaccharide slime (EPS) producing CAM2 strain was isolated as the primary organism from moribund larvae in a pathogenic outbreak occurring in a commercial hatchery producing larvae of the Chilean scallop Argopecten purpuratus located in Bahía Inglesa, Chile. The CAM2 strain was characterized biochemically and was identified by polymerase chain reaction amplification of 16S rRNA as Halomonas sp. (Accession number DQ885389.1). Healthy 7-day-old scallop larvae cultures were experimentally infected for a 48-h period with an overnight culture of the CAM2 strain at a final concentration of ca. 10(5) cells per milliliter, and the mortality and vital condition of larvae were determined by optical and scanning electron microscopy (SEM) to describe the chronology of the disease. Pathogenic action of the CAM2 strain was clearly evidenced by SEM analysis, showing a high ability to adhere and detach larvae velum cells by using its "slimy" EPS, producing agglutination, loss of motility, and a posterior sinking of scallop larvae. After 48 h, a dense bacterial slime on the shell surface was observed, producing high percentages of larval agglutination (63.28 +/- 7.87%) and mortality (45.03 +/- 4.32%) that were significantly (P < 0.05) higher than those of the unchallenged control cultures, which exhibited only 3.20 +/- 1.40% dead larvae and no larval agglutination. Furthermore, the CAM2 strain exhibited a high ability to adhere to fiberglass pieces of tanks used for scallop larvae rearing (1.64 x 10(5) cells adhered per square millimeters at 24 h postinoculation), making it very difficult to eradicate it from the culture systems. This is the first report of a pathogenic activity on scallop larvae of Halomonas species, and it prompts the necessity of an appraisal on biofilm-producing bacteria in Chilean scallop hatcheries.

Size- and age-dependent changes in adductor muscle swimming physiology of the scallop Aequipecten opercularis.

The decline of cellular and especially mitochondrial functions with age is, among other causes, held responsible for a decrease in physiological fitness and exercise capacity during lifetime. We investigated size- and age-related changes in the physiology of exercising specimens of the short lived swimming scallop Aequipecten opercularis (maximum life span 8 to 10 years) from the Isle of Man, UK. A. opercularis swim mainly to avoid predators, and a decrease in swimming abilities would increase the risk of capture and lower the rates of survival. Bigger (older) individuals were found to have lower mitochondrial volume density and aerobic capacities (citrate synthase activity and adenylates) as well as less anaerobic capacity deduced from the amount of glycogen stored in muscle tissue. Changes in redox potential, tissue pH and the loss of glutathione in the swimming muscle during the exercise were more pronounced in young compared to older individuals. This indicates that older individuals can more effectively stabilize cellular homeostasis during repeated exercise than younger animals but with a possible fitness cost as the change in physiology with age and size might result in a changed escape response behaviour towards predators.