Influence of 'Trichobilharzia regenti' (Digenea: Schistosomatidae) on the defence activity of 'Radix lagotis' (Lymnaeidae) haemocytes

Radix lagotis is an intermediate snail host of the nasal bird schistosome Trichobilharzia regenti. Changes in defence responses in infected snails that might be related to host-parasite compatibility are not known. This study therefore aimed to characterize R. lagotis haemocyte defence mechanisms and determine the extent to which they are modulated by T. regenti. Histological observations of R. lagotis infected with T. regenti revealed that early phases of infection were accompanied by haemocyte accumulation around the developing larvae 2–36 h post exposure (p.e.) to the parasite. At later time points, 44–92 h p.e., no haemocytes were observed around T. regenti. Additionally, microtubular aggregates likely corresponding to phagocytosed ciliary plates of T. regenti miracidia were observed within haemocytes by use of transmission electron microscopy. When the infection was in the patent phase, haemocyte phagocytic activity and hydrogen peroxide production were significantly reduced in infected R. lagotis when compared to uninfected counterparts, whereas haemocyte abundance increased in infected snails. At a molecular level, protein kinase C (PKC) and extracellular-signal regulated kinase (ERK) were found to play an important role in regulating these defence reactions in R. lagotis. Moreover, haemocytes from snails with patent infection displayed lower PKC and ERK activity in cell adhesion assays when compared to those from uninfected snails, which may therefore be related to the reduced defence activities of these cells. These data provide the first integrated insight into the immunobiology of R. lagotis and demonstrate modulation of haemocyte-mediated responses in patent T. regenti infected snails. Given that immunomodulation occurs during patency, interference of snail-host defence by T. regenti might be important for the sustained production and/or release of infective cercariae

An environmentally induced tidal periodicity of microgrowth increment formation in subtidal populations of the clam Ruditapes philippinarum

The periodicity of increment formation in the shell of the Manila clam Ruditapes philippinarum was investigated in the subtidal zone of the Auray River estuary (South Brittany, France). Calcein markings were performed at different periods between May and October 2007 using in situ benthic chambers tented by scuba divers. This study shows that shell microgrowth increments were well-defined and deposited with a tidal periodicity in the subtidal zone, providing the calendar base for high-resolution ecological studies and environmental reconstruction from these R. philippinarum shells. Endogenous rhythmicity in shell microgrowth increment formation and oxygen consumption was previously documented in this species from intertidal flats. Our study suggests that, in the subtidal zone, Manila clams' rhythmic activity may be controlled by such an endogenous process, synchronized by tidal cues. As in other bivalves, R. philippinarum is an osmoconformer euryhaline bivalve. The tidal rhythmicity of shell microgrowth increments in subtidal specimens of this species could be explained by a behavioral adaptation of valve closure at low tide to protect the clam from low salinities and/or to synchronize with food availability. Finally, large inter-individual variability in tidally associated growth rates and asynchronous growth breaks were observed, and could be due to genetic variability between individuals, asynchronous partial spawning events or predation

Effect of hypoxia on cod bioenergetics

International audienc

Coupling experimental and field-based approaches to decipher carbon sources in the shell of the great scallop, Pecten maximus (L.)

This research investigated how the carbon isotopic composition of food source (delta C-13(food)) and dissolved inorganic carbon (delta C-13(DIC)) influences the carbon isotopic composition of Pecten maximus shells (delta C-13(shell)) under both experimental and natural conditions. The objectives are to better understand the relationship between P. maximus and its environment, and to specifically distinguish conditions under which calcification is influenced by respired CO2 derived from food sources versus conditions in which calcification uses inorganic carbon from seawater. Laboratory experiment investigated carbon incorporation into shell carbonates by maintaining scallops under conditions where the stable carbon isotopic composition of food sources was considerably depleted (-54 parts per thousand), relative to values observed in the natural environment (-21 parts per thousand). Laboratory experiment ran for 78 days under three temperature conditions, 15 degrees C, 21 degrees C and 25 degrees C. A survey of the environmental parameters and stable carbon isotopic composition into shell carbonate of natural population of P. maximus was also realized during the same year in the Bay of Brest, France. Data collected from both laboratory experiment and the natural environment confirmed that both delta C-13(DIC) and delta C-13(food) influence delta C-13(shell) values and that organic carbon incorporation (C-M) averages about 10% (4.3-6.8% under experimental conditions and 1.9-16.6% in the natural environment). The shift in stable carbon isotopic composition from the uptake of depleted food sources under experimental conditions realized a marked divergence in the predicted equilibrium between calcium carbonate and ambient bicarbonate, relative to the natural environment. This offset was 1.7 +/- 0.6 parts per thousand for scallops in their natural environment and 2.5 +/- 0.5 and 3.2 +/- 0.9 parts per thousand for scallops under experimental conditions at water temperatures of 15 degrees C and 21 degrees C, respectively. The offset of 3 parts per thousand for scallops subjected to laboratory experiment could not be explained in light of growth rate but may be related to food supply and/or temperature. Food source and temperature effects may also explain the annual variation observed in C-M values measured from scallops in their natural environment. C-M estimation from the natural population of P. maximus varied seasonally from around 2% at the end of winter, to 12% in summer. The seasonal variation resembles variability in the carbon isotopic composition of the food sources throughout the year with an exception at the end of winter

Primary production and spatial distribution of subtidal microphytobenthos in a temperate coastal system, the Bay of Brest, France

The main objective of this study was to define the primary production and the spatial and temporal distribution of the subtidal microphytobenthic community in a temperate coastal ecosystem, the Bay of Brest. The productivity of the microphytobenthos (MPB) was estimated in winter, spring and late summer, by a series of in situ benthic chamber incubations. Oxygen (O-2) and dissolved inorganic carbon (DIC) fluxes were measured at the sediment-water interface in light and dark conditions to determine the net and gross primary production present. Functional regression of the O-2 and DIC data demonstrated that the community photosynthetic quotient (CPQ) for the benthic community was 1. A maximal gross production (P-max) of between 0.4 and 0.8 mmol O-2 mg chl a(-1) h(-1) was estimated for the MPB in the Bay. E-K values were low, ranging from 57.8 to 83.4 mu mol photons m(-2) s(-1) and can be considered an adaptation of the MPB to the reduced light levels reaching the sediment-water interface. Two sampling campaigns were undertaken in winter and late summer to measure the biomass of the benthic microalgal community in the Bay. Productivity estimates were combined with this biomass to give the MPB production in all areas of the Bay. Principal components analysis revealed that stations sampled were grouped primarily as a function of their depth, highlighting the importance above all of light availability, and their sediment type, with highest biomass concentrations found in bare muddy sediments. Hierarchical classification allowed the determination of four groups of stations in the Bay defined by their biotic and abiotic differences. The importance of the gastropod Crepidulafornicata in conditioning the benthic structural and biochemical environment was also highlighted. Geographical information systems based mapping allowed the representation of the spatial and temporal distribution of biomass and primary production and consequently a determination of the overall MPB production. Average seasonal production estimates for the Bay of Brest ranged from 57 in winter to 111 mg C m(-2) day(-1) in late summer and represented from 12-20% of total primary production

Generalized de Bruijn Words and the State Complexity of Conjugate Sets

International audienceWe consider a certain natural generalization of de Bruijn words, and use it to compute the exact maximum state complexity for the language consisting of the conjugates of a single word. In other words, we determine the state complexity of cyclic shift on languages consisting of a single word