Pulling or drilling, does size or species matter? An experimental study of prey handling in Octopus dierythraeus ()

The influence of both predator and prey size on the shift from a pulling to a drilling predatory response was examined in the intertidal octopus Octopus dierythraeus, using an experimental program. Additionally, selective drilling, where particular regions of the prey are targeted, was examined for a variety of bivalve and gastropod prey. O. dierythraeus always initially attempted to pull bivalves apart. Shells that were eventually drilled were always subjected to significantly more pulling attempts than those that could be pulled apart, indicating that octopus are willing to expend more energy to access the flesh quickly. There was no defined threshold where bivalve size caused an octopus to switch from a pulling to a drilling response. Instead, there was a broad size range where the octopus could adopt either handling method and it varied for each individual. Octopus may only able to pull open bivalves before the molecular ratchet or ‘catch’ mechanism that many bivalves possess is engaged. This might explain the lack of a relationship between either octopus or bivalve size and the success of pulling, as it is likely that when the bivalves were presented to individual octopus they were either setting the ‘catch’ mechanism, or had already engaged it. O. dierythraeus demonstrated selective drilling on a variety of molluscan prey, with penetration sites differing between prey species. O. dierythraeus targeted the valve periphery, which was the thinnest part of the shell, therefore minimizing handling time. O. dierythraeus always drilled gastropods, but did not target the thinnest regions of the shells, with drill site varying according to the morphology of the prey. Elongate species with pronounced aperture lips were drilled in the apical region, close to the columella on the side of the opercula whereas nonelongate species were drilled immediately above the aperture. The location of drilling sites may represent a trade-off between targeting the most effective places to inject paralyzing secretions and the mechanically simplest places to drill.     

Age and growth rate determinations of an intertidal bivalve, Phacosoma japonicum, using internal shell increments

A venerid bivalve Phacosoma japonicum (Reeve) occurring commonly in the Japanese coastal area preserves periodic growth lines in the shell cross-section. Long-term shell growth patterns of this species have been traced for many individuals on the intertidal flat of the Seto Inland Sea, west Japan. Sclerochronological analysis of these individuals and specimens collected monthly shows that several growth cessation marks within their shells are formed during the winter of each year prior to spawning. Hence the marks were used for age and growth rate determinations. As large individuals showed little shell growth for more than two years after the formation of 7 or 8 annual increments, this species probably has a lifespan of more than ten years. Shell growth patterns of this species based on annual increments can be accurately approximated by a von Bertalanffy curve. The number of microgrowth increments formed during a year tends to decrease with age, although it varies markedly among specimens of the same age. Furthermore, even in summer during rapid shell growth, the microgrowth increments do not represent daily and/or sub-daily tidal rhythms in many specimens. The results of this study and those by several authors strongly suggest that the annual increments are the key for age and growth rate determinations of both living and fossil bivalve species.     

Purification of ribulose 1,5-bisphosphate carboxylase/oxygenase and of carboxysomes from Thiobacillus thyasiris the putative symbiont of Thyasira flexuosa (Montagu)

The bacterial symbionts of many marine invertebrates contain ribulose 1,5-bisphosphate (RuBP) carboxylase but apparently no carboxysomes, polyhedral bodies containing RuBP carboxylase. In the few cases where polyhedral bodies have been observed they have not been characterised enzymatically. Polyhedral bodies, 50–90 nm in diameter, were observed in thin cell sections of Thiobacillus thyasiris the putative symbiont of Thyasira flexuosa and RuBP carboxylase activity was detected in both soluble and particulate fractions after centrifugation of cell-free extracts. RuBP carboxylase purified 90-fold from the soluble fraction was of high molecular weight and consisted of large and small subunits, with molecular weights of 53,110 and 11,100 respectively. Particulate RuBP carboxylase activity was associated with polyhedral bodies 50–100 nm in diameter, as revealed by density gradient centrifugation and electron microscopy. Therefore, the polyhedral bodies were inferred to be carboxysomes. Native electrophoresis of isolated carboxysomes demonstrated a major band which comigrated with the purified RuBP carboxylase and three minor bands of lower molecular weight. Sodium dodecyl-sulphate (SDS) gel electrophoresis of SDS-dissociated carboxysomes demonstrated nine major polypeptides two of which were the large and small subunits of RuBP carboxylase. The RuBP carboxylase subunits represented 21% of the total carboxysomal protein. The most abundant polypeptide had a molecular weight of 40,500. Knowledge of carboxysome composition is necessary to provide an understanding of carboxysome function.Abbreviations FPLC fast performance liquid chromatography - IB isolation buffer - PAGE polyacrylamide gel electrophoresis - RuBP carboxylase - ribulose 1,5-bisphosphate carboxylase/oxygenase - SDS sodium dodecyl-sulphate     

福建永安丰海二叠系上部及三叠系底部的双壳类动物群*

系统研究了闽西永安丰海地区二叠系上部及三叠系下部的双壳类动物群面貌、层位及组合,并与国内外相当的地层进行了对比,阐明了该双壳动物群在二叠-三叠系界线划分中的地层意义.描述了15属24种(其中5新种)、5未定种.     

In vitro investigation of α-amylase release from the digestive cells of the bivalve mollusc Pecten maximus: effect of second messengers and biogenic amines

The (neuro)endocrine control of enzyme release from invertebrate digestive cells remains poorly understood. A tissue dissociation procedure was developed to investigate the regulatory mechanisms of -amylase discharge from the cells of the stomach-digestive gland complex of the scallop Pecten maximus. The validity of the experimental system was tested by increasing the intracellular concentration of second messenger analogues (N ⁶,2-o-dibutyryl-adenosine-3,5 cyclic monophosphate and the ionophore A23187) known to mimic the activity of naturally occurring secretagogues in vertebrates: N ⁶,2-o-dibutyryl-adenosine-3,5 cyclic monophosphate increased the time and dose-dependent release of -amylase in a similar way as in vertebrates. A23187 was also very effective in inducing enzyme discharge. Since the in vitro bioassay was shown to be functional and because axon terminals were previously seen in close contact to -amylase secreting cells, the effect of some classic neurotransmitters was explored. Only the cholinergic agonist carbachol and dopamine evoked a secretory response. Maximal stimulation of -amylase release was reached at 10^-5 mol·l^-1 carbachol; at the same concentration dopamine was less effective than carbachol. By contrast, serotonin was totally inactive. The in vitro bioassay should prove useful for the identification of regulatory molecules involved in the control of enzyme discharge and to study stimulus secretion coupling mechanisms in scallop digestive cells.Abbreviations DBcAMP N ⁶, 2-O-dibutyryl-adenosine-3,5 cyclic monophosphate - cAMP adenosine-3,5 cyclic monophosphate     

Ultrastructural studies on early events in fertilization of the bivalveLaternula limicola

Summary Ultrastructural studies on sperm-egg interaction at the time of fertilization inLaternula limicola were performed. The temporary-acrosome did not change morphologically while the sperm passed through the egg investments. At the onset of sperm entrance into the egg, however, the temporary-acrosome and mitochondria were eliminated from the sperm. Afterwards the sperm was engulfed by the egg surface without membrane fusion of the gametes. After entry the sperm nucleus was surrounded by four membranes: the plasma membranes of the egg and of the sperm, and the membranes of the sperm nuclear envelope. As the sperm nucleus differentiated into the male pronucleus, the plasma membranes of both the sperm and egg were initially vesiculated, then dispersed into the egg cytoplasm. Finally, the sperm nuclear envelope changed into the male pronuclear membrane accompanying sperm chromatin dispersion.     

Evidence for a Plastic Dual Circadian Rhythm in the Oyster Crassostrea gigas

Although a significant body of literature has been devoted to the chronobiology of aquatic animals, how biological rhythms function in molluscan bivalves has been poorly studied. The first objective of this study was to determine whether an endogenous circadian rhythm does exist in the oyster, Crassostrea gigas. The second objective was to characterize it in terms of robustness. To answer these questions, the valve activity of 15 oysters was continuously recorded for 2 mo in the laboratory under different entrainment and free-running regimes using a high-frequency noninvasive valvometer. The present work demonstrates the presence of a circadian rhythm in the oyster Crassostrea gigas. First, oysters were entrained by 12?L:12 D conditions. Then, free-running conditions (D:D and L:L) indicated that the most frequently observed period ranged from 20 to 28?h, the circadian range. That endogenous circadian rhythm was characterized as weak. Indeed, the period (τ) of the individual animals exhibited high plasticity in D:D and L:L, and the animals immediately followed a 4-h phase advance or delay. Additionally, C. gigas appeared as a dual organism: all oysters were nocturnal at the beginning of the laboratory experiment (January), whereas they were diurnal at the end (March). That shift was progressive. Comparison with a full-year in situ record showed the same behavioral duality as observed in the laboratory: the animals were nocturnal in autumn–winter and diurnal in spring–summer. The significant advantage of a plastic and dual circadian rhythm in terms of adaptability in a highly changing environment is discussed. (Author correspondence: d.tran@epoc.u-bordeaux1.fr)     

Hyperosmotic volume regulation in the gills of the ribbed mussel, Geukensia demissa: rapid accumulation of betaine and alanine

The content of betaine and alanine in gills of the ribbed mussel Geukensia demissa increases rapidly following transfer of the tissues from 250 to 1000 mOsm seawater (SW). Increases in alanine, proline and glycine account for most of the increase in the amino acid pool. The betaine content increases from 45 to 150 μmol/g dry weight within 12 h. Transfer of isolated gills from 250 to 1000 mOsm SW results in a temporary cessation of all ciliary activity. Within 20–40 min following transfer, ciliary activity has recovered. Recovery of ciliary activity precedes recovery of tissue hydration. The uric acid content of gills is unchanged by exposure to hyperosmotic media, suggesting that uric acid is not a store of nitrogen for alanine synthesis from pyruvate. In other organisms, the accumulation of betaine in response to hyperosmotic stress is a slow (days to weeks) process that probably involves changes in gene expression. The rapid, large increases in betaine reported here suggest that gene expression is not a factor in volume recovery by euryhaline bivalve tissues exposed to acute hyperosmotic stress.     

Effects of Bucephalus sp. (Trematoda: Bucephalidae) on Perna perna mussels from a culture station in Ratones Grande Island,Brazil

This study reports the prevalence of Bucephalus sp. in Perna perna populations from a culture station of southern Brazil and its effect on the mussel reproductive tissue and immune system. The prevalence of Bucephalus sp. in P. perna (n = 1871) was considered low (3.1%) and did not seasonally vary. Histological sections of the mantle of infected mussels revealed a marked (80%) reduction of the reproductive tissue that was severe even in mussels exhibiting a moderate infection degree. The total (THC) and differential (DHC) hemocyte counts were lower in infected mussels (3.9 x 10(6) hem/ml; granular hemocytes = 33%) as compared with non-infected animals (5.5 x 10(6) hem/ml; granular hemocytes = 40%). The plasma protein concentration did not vary upon infection. Hemocyte infiltration was significantly higher only in mussels with a very heavy infection degree. The parasite sporocysts were never seen encapsulated by the host hemocytes. Our results indicate that Bucephalus sp. promotes a severe castration in its host and apparently evades the mussel immune system.     

Growth variations in the bivalve<Emphasis Type="Italic"> Mya truncata</Emphasis>: a tool to trace changes in the Frisian Front macrofauna (southern North Sea)?

Annual monitoring of the benthic fauna living at the Frisian Front (southern North Sea) has shown a tenfold decrease in the dominant brittlestar Amphiura filiformis in 1993–1995. In search of evidence that this decline was caused by a change in benthic food supply, we analysed variations in the shell growth of the bivalve Mya truncata from the Frisian Front during the period of interest. For this purpose, the widths of the internal growth bands in the chondrophore of M. truncata were standardised and assigned to calendar years. Averaging the yearly band width in the period 1985–2000 among 25 individuals revealed low growth rates in 1986 and 1992. Growth of M. truncata quickly recovered after 1992, while A. filiformis densities remained at low levels. Moreover, the 1986 dip in M. truncata growth had no equivalent in A. filiformis density. We conclude that there is no direct coupling between fluctuations in density of A. filiformis and variations in growth of M. truncata. The data we collected during this study on the size and spatial distribution of M. truncata are discussed in the light of plans for the protection and conservation of long-lived benthic organisms in the North Sea. Communicated by E. Rachor