Growth, survival and fluctuating asymmetry of Iceland scallops in a test of density-dependent growth in a natural bed

We report an experiment designed to test for overpopulation in an Iceland scallop, Chlamys islandica (O.F. Müller), slow-growing bed. Scallops were installed in pearl nets at the site of the scallop bed and in a nearby unpopulated site, near the bottom and far from the bottom. With this set-up, all groups, except that one near the bottom inside the bed, were free from potential overpopulation effects. In addition, there were two stocking densities to test for containment effects.Shell growth was higher at 2.0 m above the bottom, outside the scallop bed, than at the three other site and height combinations, which were not significantly different from each other. There was a borderline effect of site on soft tissue growth, which was probably slower at the donor site. We conclude that there was no evidence of overpopulation in the scallop bed. On both sites, soft tissue growth was slowest near the bottom, irrespective of group size, intermediate at 2.0 m height, high population density, and fastest at 2.0 m height, low population density. Survivorship was lower near the bottom, but was independent of site and of group size. Available data showed no sustained vertical patterns in phytoplankton concentration in the water column. These results suggest that food depletion occurred in the pearl nets, but that density-independent factors dominated density-dependent factors in the pearl nets near the bottom. Likely explanations involve the interaction between containment effects and current speed variations in the benthic boundary layer. Survivorship decreased with fluctuating asymmetry of the ears of the shells. Fluctuating asymmetry, therefore, may provide a means of including individual effects in growth experiments and forecasting the ability of spat to resist density-independent mortality agents.     

Gametogenic cycle and size at first sexual maturity in female Chlamys (Azumapecten) farreri farreri (Jones & Preston, 1904) (Bivalvia: Pectinidae) in western Korea

The gametogenic cycle and number of spawning seasons per year of the female Chlamys (Azumapecten) farreri farreri were investigated by qualitative and quantitative analyses, and also the size at 50% of group sexual maturity (the size of first sexual maturity) was calculated to inform natural living resource management. In qualitative histologic analysis, the gametogenic cycle of this species can be classified into five successive stages: early active stage, late active stage, ripe stage, partially spawned stage, and spent/inactive stage. The spawning season occurs annually from July to September. In quantitative statistical analysis using an image analysis system, the patterns of monthly changes in reproductive cells were shown to be maximum in June and then dropped sharply from July to September. From these data, it is apparent that the C. (A.) farreri farreri has a unimodal annual gametogenic cycle. Shell heights at 50% of group sexual maturity were estimated as 51.47?mm and was 100% for scallops over 61.0?mm.     

栉孔扇贝耗氧率和排氨率的研究

1999年 4～ 6月 ,采用室内实验生态学方法对栉孔扇贝的耗氧率和排氨率进行了研究 .结果表明 ,在适宜的温度范围内 ,栉孔扇贝的耗氧率和排氨率均与温度成正比 ,而与体重呈负相关关系 .在实验室温度 (8～ 2 8℃ )条件下 ,栉孔扇贝的耗氧率为 0 .48～ 9.0 9mg·g-1·h-1,排氨率为 0 .0 5～ 1 0 1mg·g-1·h-1.其中耗氧率在 2 3℃时达到最高值 ,2 8℃时开始下降 ,而排氨率则呈持续升高趋势 .栉孔扇贝的日常代谢明显高于标准代谢 ,耗氧率和排氨率平均值分别提高约 35 .8%和 75 .9% .     

Polypeptide from Chlamys farreri inhibits UVB-induced HaCaT cells apoptosis via inhibition CD95 pathway and reactive oxygen species

Polypeptide from Chlamys farreri (PCF) is a novel marine active product isolated from gonochoric Chinese scallop Chlamys farreri which has recently been found to be an effective antioxidant. In this study, we assessed the effect of PCF on UVB-induced intracellular signalling of apoptosis in HaCaT cells. Pre-treatment with PCF significantly inhibited UVB-induced apoptosis in HaCaT cells. PCF strongly reduced the intracellular reactive oxygen species (ROS) level followed by inhibiting the release of cytochrome c. The expression of CD95 and Fas-associating protein with death domain (FADD) was eliminated in a dose-dependent manner by PCF pre-treatment in UVB-irradiated HaCaT cells, followed by inhibition of cleavage of procaspase-8, whose activation induced cell apoptosis. Furthermore, pre-treatment with the ROS scavenger N-acetylcysteine (NAC) and the caspase-8 inhibitor z-IETD-fmk was found to effectively prevent UVB-induced apoptosis, suggesting that UVB-induced HaCaT cell apoptosis was partially due to generation of ROS and activation of the caspase-8 pathway. Consequently, the protective effect of PCF against UVB irradiation in HaCaT cells is exerted by suppression of generation of ROS followed by inhibition of cytochrome c release and inactivation of Fas-FADD-caspase-8 pathway, resulting in blockage of UVB-induced apoptosis.     

Preliminary study on a potential antibacterial peptide derived from histone H2A in hemocytes of scallop Chlamys farreri

Histone H2A is reported to participate in host defense response through producing novel antimicrobial peptides (AMPs) from its N-terminus in vertebrates and invertebrates, while the AMPs derived from H2A have not to our knowledge been reported in mollusca. In the present study, gene cloning, mRNA expression of H2A from scallop Chlamys farreri, and the recombinant expression of its N-terminus were conducted to investigate whether a similar mechanism exists in mollusca. The full-length DNA of H2A was identified by the techniques of homology cloning and genomic DNA walking. The full-length DNA of the scallop H2A was 696bp long, including a 5'-terminal untranslated region (UTR) of 90bp, a 3'-terminal UTR of 228bp with a stem-loop structure and a canonical polyadenylation signal sequence AATAAA, and an open reading frame of 375bp encoding a polypeptide of 125 amino acids. The mRNA expression of H2A in the hemocytes of scallop challenged by microbe was measured by semi-quantitative RT-PCR. The expression of H2A was not upregulated after stimulation, suggesting that H2A did not participate in immunity response directly. The DNA fragment of 117bp encoding 39 amino acids corresponding to the N-terminus of scallop H2A, which was homologous to buforin I in vertebrates, was cloned into Pichia pastoris GS115. The transformants (His(+) Mut(+)) containing multi-copy gene insertion were selected with increasing concentration of antibiotic G418. The peptide of 39 amino acids was expressed by induction of 0.5% methanol. The recombinant product exerted antibacterial activity against both Gram-positive (G(+)) and Gram-negative (G(-)) bacteria. The antibacterial activity toward G(+) bacteria was 2.5 times more than that against G(-) bacteria. The results elucidated that N-terminus of H2A was a potential AMP and provided a promising candidate for a new antibiotic screening. However, whether H2A is really involved in scallop immune response mechanisms needs to be further investigated.     

cDNA cloning and mRNA expression of heat shock protein 90 gene in the haemocytes of Zhikong scallop Chlamys farreri

Heat shock protein 90 (HSP90) is a highly conserved molecular chaperone contributing to the folding, maintenance of structural integrity and proper regulation of a subset of cytosolic proteins. The full-length cDNA of Zhikong scallop Chlamys farreri HSP90 (designated CfHSP90) was cloned by EST and rapid RACE techniques. It was of 2710 bp, including an open reading frame (ORF) of 2181 bp encoding a polypeptide of 726 amino acids with all the five HSP90 family signatures. BLAST analysis revealed that the CfHSP90 gene shared high similarity with other known HSP90 genes. Fluorescent real-time quantitative RT-PCR was used to examine the expression pattern of CfHSP90 mRNA in haemocytes of scallops exposed to Cd²⁺, Pb²⁺ and Cu²⁺ for 10 and 20 days, respectively. All the three heavy metals could induce CfHSP90 expression. There was a clear dose-dependent expression pattern of CfHSP90 after heavy metals exposure for 10 days or 20 days. Different concentrations of the same metal resulted in different effects on CfHSP90 expression. The results indicated that CfHSP90 responded to various heavy metal stresses with a dose-dependent expression pattern as well as exposure time effect, and could be used as a molecular biomarker in a heavy metal polluted environment.     

Intermediary metabolism and shell growth in the brachiopod Terebratalia transversa

Juvenile Terebratalia transversa (Brachiopoda) metabolize carbohydrates in the anterior-most marginal mantle at a rate of 0.46 μM glucose/g/hr (in vitro incubation of mantle in C¹⁴-glucose in a carrying medium of 10^-3 M non-radioactive glucose). The rate declines to 0.18μM glucose/g/hr in full-grown specimens. Carbohydrate metabolism in the marginal (anterior-most) mantle averages approximately 3.7 times greater than metabolism in (a portion of the ‘posterior’) mantle situated between the coelomic canals and the marginal mantle. This ratio remains constant in specimens of all sizes (i.e. an ontogenetic trend in the ratio is absent at p≤ 0.05). Organic acids are not detectable within the mantle (HPLC techniques) even after simulated anoxia (N₂ bubbling during mantle incubation). Glucose metabolism in vitro declines in both the marginal and ‘posterior’ mantles during anoxia and the metabolic ratio between marginal/‘posterior’ mantles becomes 1/1. We found no difference (at p≤ 0.05) in mean metabolic activity or in sue-related metabolic trends among populations from depths ranging between mean sea level and 70 m. However, the activity within the ‘posterior’ mantle was more variable in specimens from 70 m than in those from shallower habitats (10 m - mean sea level). The size of the specimens analyzed was most variable in the groups obtained from the shallowest habitats and least variable at 70 m depth. Our results may help define the energetics of fossil as well as living brachiopod shell growth. Brachiopod shell growth is known to be very slow relative to that of bivalves and our results indicate that this is a result of the animals' slow metabolism. The inflation of the valves in T. transversa is, in part, a function of the high ratio of intermediary metabolism in the marginal vs‘posterior’ mantle (i.e. parallels the relative growth rates at the shell margin vs‘posterior’ areas). We found that the bivalve, Chlamys hastata, which is commonly associated with T. transversa, has a lower ratio of metabolic activities in the ventral/dorsal mantle areas than the brachiopod has in the anterior/posterior. The difference produces a flatter shell in the bivalve in accord with allometric principles. The higher metabolic rate in the marginal vs‘posterior’ brachiopod mantle and its more pronounced decline with anaerobiosis is reflected in the greater definition of growth increments in the outer shell layer. Our results do not support recent generalizations that correlate shell thickness of a wide variety of invertebrates inversely with metabolic rate. Growth rate as determined from width of shell growth increments is a better index of metabolic rate. Although the genetic basis of glucose metabolism is unknown, the observed metabolic variability is consistent with suggestions that populations of marine organisms living in stable offshore environments are genetically more variable but morphologically more uniform than populations from shallow water. Furthermore, our results support suggestions that bivalved molluscs and brachiopods are very different metabolically, but the data are neutral with respect to theories of competitive exclusion of the two taxa throughout geologic history.     

An endo-(1→3)-β-d-glucanase from the scallop Chlamys albidus: catalytic properties, cDNA cloning and secondary-structure characterization

An endo-(1→3)-β-d-glucanase (L₀) with molecular mass of 37 kDa was purified to homogeneity from the crystalline style of the scallop Chlamys albidus. The endo-(1→3)-β-d-glucanase was extremely thermolabile with a half-life of 10 min at 37 °C. L₀ hydrolyzed laminaran with K_m ∼ 0.75 mg/mL, and catalyzed effectively transglycosylation reactions with laminaran as donor and p-nitrophenyl β d-glucoside as acceptor (K_m ∼ 2 mg/mL for laminaran) and laminaran as donor and as acceptor (K_m ∼ 5 mg/mL) yielding p-nitrophenyl β d-glucooligosaccharides (n = 2-6) and high-molecular branching (1→3),(1→6)-β-d-glucans, respectively. Efficiency of hydrolysis and transglycosylation processes depended on the substrate structure and decreased appreciably with the increase of the percentage of β-(1→6)-glycosidic bonds, and laminaran with 10% of β-(1→6)-glycosidic bonds was the optimal substrate for both reactions. The CD spectrum of L₀ was characteristic for a protein with prevailing β secondary-structural elements. Binding L₀ with d-glucose as the best acceptor for transglycosylation was investigated by the methods of intrinsic tryptophan fluorescence and CD. Glucose in concentration sufficient to saturate the enzyme binding sites resulted in a red shift in the maximum of fluorescence emission of 1-1.5 nm and quenching the Trp fluorescence up to 50%. An apparent association constant of L₀ with glucose (K_a = 7.4 × 10⁵ ± 1.1 × 10⁵ M⁻¹) and stoichiometry (n = 13.3 ± 0.7) was calculated. The cDNA encoding L₀ was sequenced, and the enzyme was classified in glycoside hydrolases family 16 on the basis of the amino acid sequence similarity.