Role of two contrasting ecosystem engineers (<Emphasis Type="Italic">Zostera noltii</Emphasis> and <Emphasis Type="Italic">Cymodocea nodosa</Emphasis>) on the food intake rate of <Emphasis Type="Italic">Cerastoderma edule</Emphasis>

Seagrasses are well known ecosystem engineers that can significantly influence local hydrodynamics and the abundance and biodiversity of macrobenthic organisms. This study focuses on the potential role of the seagrass canopy structure in altering the abundance of filter-feeding organisms by modifying the hydrodynamic driven food supply. We quantified the effect of two ecosystem engineers with contrasting canopy properties (i.e. Zostera noltii and Cymodocea nodosa) on the food intake rate of a suspension-feeding bivalve Cerastoderma edule living in these seagrass meadows. Field experiments were carried out in two seagrass beds (Z. noltii and C. nodosa) and bare sediment, located on sandflat characterised by a relatively high hydrodynamic energy from waves and currents. Results demonstrated that the filter-feeding rate was almost twofold increased when C. edule was inhabiting Z. noltii meadows (1.10 ± 0.24 μg Chl g Fresh Weight⁻¹) when compared to cockles living on the bare sediment (0.65 ± 0.14 μg Chl g FW⁻¹). Intermediate values were found within C. nodosa canopy (0.97 ± 0.24 μg Chl g FW⁻¹), but filter feeding rate showed no significant differences with values for Z. noltii meadows. There were no apparent correlations between canopy properties and filter-feeding rates. Our results imply that food refreshment within the seagrass canopies was enough to avoid food depletion. We therefore expect that the ameliorated environmental conditions within vegetated areas (i.e. lower hydrodynamic conditions, higher sediment stability, lower predation pressure…) in combination with sufficient food supply to prevent depletion within both canopies are the main factors underlying our observations.     

Integrating ecosystem engineering and food webs

Ecosystem engineering, the physical modification of the environment by organisms, is a common and often influential process whose significance to food web structure and dynamics is largely unknown. In the light of recent calls to expand food web studies to include non‐trophic interactions, we explore how we might best integrate ecosystem engineering and food webs. We provide rationales justifying their integration and present a provisional framework identifying how ecosystem engineering can affect the nodes and links of food webs and overall organization; how trophic interactions with the engineer can affect the engineering; and how feedbacks between engineering and trophic interactions can affect food web structure and dynamics. We use a simple integrative food chain model to illustrate how feedbacks between the engineer and the food web can alter 1) engineering effects on food web dynamics, and 2) food web responses to extrinsic environmental perturbations. We identify four general challenges to integration that we argue can readily be met, and call for studies that can achieve this integration and help pave the way to a more general understanding of interaction webs in nature. Synthesis All species are affected by their physical environment. Because ecosystem engineering species modify the physical environment and belong to food webs, such species are potentially one of the most important bridges between the trophic and non‐trophic. We examine how to integrate the so far, largely independent research areas of ecosystem engineering and food webs. We present a conceptual framework for understanding how engineering can affect food webs and vice versa, and how feedbacks between the two alter ecosystem dynamics. With appropriate empirical studies and models, integration is achievable, paving the way to a more general understanding of interaction webs in nature.     

Unroofed coronary sinus newly diagnosed in adult patients after corrected congenital heart disease

Patients with congenital heart disease corrected in early childhood may later in life present with cardiac symptoms caused by other associated congenital anomalies that were initially not diagnosed. Nowadays, several noninvasive imaging modalities are available for the visualisation of cardiac anatomy in great detail. We describe two patients with an unroofed coronary sinus, a rare congenital anomaly which could be diagnosed using a combination of modalities including echocardiography, cardiac CT and cardiac MRI.     

Interactions between Seagrass Complexity,Hydrodynamic Flow and Biomixing Alter Food Availability for Associated Filter-Feeding Organisms

Seagrass shoots interact with hydrodynamic forces and thereby a positively or negatively influence the survival of associated species. The modification of these forces indirectly alters the physical transport and flux of edible particles within seagrass meadows, which will influence the growth and survivorship of associated filter-feeding organisms. The present work contributes to gaining insight into the mechanisms controlling the availability of resources for filter feeders inhabiting seagrass canopies, both from physical (influenced by seagrass density and patchiness) and biological (regulated by filter feeder density) perspectives. A factorial experiment was conducted in a large racetrack flume, which combined changes in hydrodynamic conditions, chlorophyll a concentration in the water and food intake rate (FIR) in a model active filter-feeding organism (the cockle). Results showed that seagrass density and patchiness modified both hydrodynamic forces and availability of resources for filter feeders. Chlorophyll a water content decreased to 50% of the initial value when densities of both seagrass shoots and cockles were high. Also, filter feeder density controlled resource availability within seagrass patches, depending on its spatial position within the racetrack flume. Under high density of filter-feeding organisms, chlorophyll a levels were lower between patches. This suggests that the pumping activity of cockles (i.e. biomixing) is an emergent key factor affecting both resource availability and FIR for filter feeders in dense canopies. Applying our results to natural conditions, we suggest the existence of a direct correlation between habitat complexity (i.e. shoot density and degree of patchiness) and filter feeders density. Fragmented and low-density patches seem to offer both greater protection from hydrodynamic forces and higher resource availability. In denser patches, however, resources are allocated mostly within the canopy, which would benefit filter feeders if they occurred at low densities, but would be limiting when filter feeder were at high densities.     

Expression of miRNAs in ovine fetal gonads: potential role in gonadal differentiation

Background  

Gonadal differentiation in the mammalian fetus involves a complex dose-dependent genetic network. Initiation and progression of fetal ovarian and testicular pathways are accompanied by dynamic expression patterns of thousands of genes. We postulate these expression patterns are regulated by small non-coding RNAs called microRNAs (miRNAs). The aim of this study was to identify the expression of miRNAs in mammalian fetal gonads using sheep as a model.     

Production,maturity, reproductive cycle and fecundity of small-spotted catshark,Scyliorhinus canicula (Chondrichthyes: Scyliorhinidae) from the northern coast of Tunisia (Central Mediterranean)

Small-spotted catshark Scyliorhinus canicula (Linnaeus, 1758) is confronted since 2000 to a drastic decline of captures in Tunisian northern areas where it formerly was quantitatively and qualitatively very abundant. A study conducted in the area showed that males and females sexually matured between 400–478 mm and 364–471 mm total length (TL), respectively. The largest male and female were 521 mm and 531 mm TL, respectively and weighed 449 and 445.5 g, respectively. There was a not significant relationship total mass vs. TL between males and females. Conversely, the relationship of liver mass vs. TL significantly differed between sexes. Both HSI and GSI values did not present significant differences between males and females. There was a not significant relationship total mass vs. TL between males and females. Both male and female HSI reached high values in adults, significantly higher than those of sub-adults. Both male and female GSI values increased with TL of specimens; additionally, they showed significant differences between juveniles and sub-adults and also between sub-adults and adults. The OSI values were significantly different between juvenile and sub-adult females, and also between sub-adult and adult females. Monthly mean values of adult male and female HSI did not significantly vary throughout the year. Significant monthly changes were recorded in mean values of adult male however no significant changes were observed in monthly mean of GSI and OSI for adult females. Vitellogenic activity and production of egg cases permanently occurred throughout the year. The diameter of largest yolky oocytes ranged from 20.1 to 23.0 (mean = 21.43 ± 1.07) and weighed from 0.64 to 0.90 g (mean = 0.78 ± 0.09). Some measurements were taken on egg cases: length with horns ranged 42.5-55.7 mm with mean = 48.9 ± 2.9, width ranged 13.6–19.7 mm with mean = 16.50 ± 0.9, while the total mass of complete egg case ranged between 1.8 and 4.6 g, with mean = 2.4 ± 0.4. An annual fecundity estimation based on production of egg cases and oocytes during one year counted in adult females, enabled us to consider it between 40 and 240.     

Description of two different patients with abetalipoproteinemia: synthesis of a normal-sized apolipoprotein B-48 in intestinal organ culture

We describe here two patients, M. P. and S. L., with recessive abetalipoproteinemia. Analysis of restriction fragments of DNA from both patients using cDNA probes spanning the entire apolipoprotein B gene revealed no major insertions or deletions. Further, as defined by restriction fragment length polymorphism, abetalipoproteinemia, in these patients, did not appear associated with particular alleles of apolipoprotein B. Northern and dot blot analysis of intestinal mRNA of one patient (M. P.) revealed a normal-sized apolipoprotein B mRNA which was present in slightly reduced amounts. At the cellular level apolipoprotein B was detected in both intestinal and hepatic biopsies, of one patient (S. L.), by immunoenzymatic techniques using polyclonal and monoclonal antibodies to apolipoprotein B-48 and/or B-100. The level of apolipoprotein B-48 appeared to increase in the intestine after a fatty meal. In the other patient (M. P.), although no apolipoprotein B was detected in the enterocytes using similar immunoenzymatic techniques, organ culture experiments using [35S]methionine demonstrated the synthesis of a normal-sized apolipoprotein B-48 which appeared to be normally glycosylated. The glycosylation and processing of two intestinal membrane enzymes, sucrase-isomaltase and aminopeptidase N, were also normal. Although lipids and apolipoprotein B-48 were present intracellularly, no lipoprotein-like particles were observed by electron microscopy in the endoplasmic reticulum, the Golgi apparatus, or in the intercellular spaces of intestinal biopsies obtained in the fasted (M. P. and S. L.) or fed state (S. L.). The defect in these cases of abetalipoproteinemia, therefore, does not appear to involve the apolipoprotein B gene nor the synthesis or the glycosylation of the apolipoprotein but instead appears to involve some aspect of lipoprotein assembly or secretion.     

Importance of the alpha 3-fragment of complement C4 for the binding with C4b-binding protein.

The human regulatory complement component C4b-binding protein (C4BP) is a multimeric plasma protein, which regulates the classical pathway of the complement system. C4BP functions as a cofactor to factor 1 in the degradation of C4b and accelerates the decay rate of the C4b2a complex. Previously, we have demonstrated that monoclonal antibodies (C4-2 and 9) directed against the alpha'-chain of C4b inhibit the binding of C4b to C4BP. In order to identify the structural domain of C4b that binds C4BP, proteolytic fragments of C4 were generated with trypsin and Staphylococcus aureus V8 protease. Sodium dodecyl sulfate polyacrylamide gel electrophoresis, immunoblotting and amino acid sequence analysis of the proteolytic fragments reactive with the anti-C4 mAb's revealed that the residues Ala738-Arg826 of the alpha 3-fragment of C4b are important for the interaction with C4BP.     

6-phospho-alpha-D-glucosidase from Fusobacterium mortiferum: cloning, expression, and assignment to family 4 of the glycosylhydrolases.

The Fusobacterium mortiferum malH gene, encoding 6-phospho-alpha-glucosidase (maltose 6-phosphate hydrolase; EC 3.2.1.122), has been isolated, characterized, and expressed in Escherichia coli. The relative molecular weight of the polypeptide encoded by malH (441 residues; Mr of 49,718) was in agreement with the estimated value (approximately 49,000) obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis for the enzyme purified from F. mortiferum. The N-terminal sequence of the MalH protein obtained by Edman degradation corresponded to the first 32 amino acids deduced from the malH sequence. The enzyme produced by the strain carrying the cloned malH gene cleaved [U-14C]maltose 6-phosphate to glucose 6-phosphate (Glc6P) and glucose. The substrate analogs p-nitrophenyl-alpha-D-glucopyranoside 6-phosphate (pNP alphaGlc6P) and 4-methylumbelliferyl-alpha-D-glucopyranoside 6-phosphate (4MU alphaGlc6P) were hydrolyzed to yield Glc6P and the yellow p-nitrophenolate and fluorescent 4-methylumbelliferyl aglycons, respectively. The 6-phospho-alpha-glucosidase expressed in E. coli (like the enzyme purified from F. mortiferum) required Fe2+, Mn2+, Co2+, or Ni2+ for activity and was inhibited in air. Synthesis of maltose 6-phosphate hydrolase from the cloned malH gene in E. coli was modulated by addition of various sugars to the growth medium. Computer-based analyses of MalH and its homologs revealed that the phospho-alpha-glucosidase from F. mortiferum belongs to the seven-member family 4 of the glycosylhydrolase superfamily. The cloned 2.2-kb Sau3AI DNA fragment from F. mortiferum contained a second partial open reading frame of 83 residues (designated malB) that was located immediately upstream of malH. The high degree of sequence identity of MalB with IIB(Glc)-like proteins of the phosphoenol pyruvate dependent:sugar phosphotransferase system suggests participation of MalB in translocation of maltose and related alpha-glucosides in F. mortiferum.