Effects of an alien invertebrate species and wave action on prey selection by African black oystercatchers (Haematopus moquini)

Abstract Shorebirds foraging in the intertidal have been shown to exert a significant effect on assemblage level processes; this is particularly true of the oystercatcher–limpet–algae system. The African black oystercatcher (Haematopus moquini) is endemic to the southern African coastline, where it plays a significant role in ecosystem processes as a rocky‐shore predator, especially of mussels and limpets. This understanding was based on studies of a rocky shore environment that has since been considerably modified following invasion of an alien mussel (Mytilus galloprovincialis). This invasion has not only changed the relative proportions of different food types on the shore, but has also greatly increased overall food biomass. We tested the previous model that food selection by oystercatchers reflected prey abundance and that intake by male and female oystercatchers differed owing to bill morphology. We predicted that this difference would persist despite the changed nature of the food base. We also predicted that wave action would modify prey selection as a result of both its influence on prey behaviour and its impact on searching and handling times of the birds. Overall, both sexes consumed more limpets than expected by encounter rate alone, but contrary to prediction, the relative proportions of different prey types taken post invasion did not differ between the sexes. Dietary convergence is interpreted as a result of greatly increased food biomass on the shore, which is also reflected in increased oystercatcher densities since the invasion. Also contrary to prediction there was no evidence that waves acted as indirect modifiers of the interaction between oystercatchers and their prey. The results of this study indicate that models of trophic cascades will need to be altered in the event of a significant change in a trophic level, which then effects behavioural changes in the key predator.     

Switch between tyrosinase and catecholoxidase activity of scorpion hemocyanin by allosteric effectors

Phenoloxidases and hemocyanins have similar type 3 copper centers although they perform different functions. Hemocyanins are oxygen carriers, while phenoloxidases (tyrosinase/catecholoxidase) catalyze the initial step in melanin synthesis. Tyrosinases catalyze two subsequent reactions, whereas catecholoxidases catalyze only the second one. Recent results indicate that hemocyanins can also function as phenoloxidases and here we show for the first time that hemocyanin can be converted to phenoloxidase. Furthermore, its substrate specificity can be switched between catecholoxidase and tyrosinase activity depending on effectors such as hydroxymethyl-aminomethan (Tris) and Mg(2+)-ions. This demonstrates that substrate specificity is not caused by a chemical modification of the active site.     

Purification and functional characterization of lectin with phenoloxidase activity from the hemolymph of cockroach,Periplaneta americana

Lectins also identified as hemagglutinins are multivalent proteins and on account of their fine sugar‐binding specificity play an important role in immune system of invertebrates. The present study was carried out on the hemolymph lectin of cockroach, Periplaneta americana with appropriate screening and purification to understand its molecular as well as functional nature. The lectin from the hemolymph was purified using ion‐exchange chromatography. The approximate molecular weight of purified lectin was 340 kDa as determined by FPLC analysis. Rabbit erythrocytes were highly agglutinated with purified lectin from the hemolymph of P. americana. The hemagglutination activity (HA) of lectin was specifically inhibited by fucose. Glycoproteins also inhibited the HA activity of lectin. The amino acid sequences of the purified lectin revealed homology with amino acid sequences of allergen proteins from P. americana. Purified lectin showed the highest phenoloxidase activity against dopamine. The activators such as exogenous proteases and LPS from Escherichia coli and Salmonella minnesota significantly enhanced the PO activity of the purified lectin. Besides, the presence of copper and hemocyanin conserved domain in the purified lectin provided a new facet that insects belonging to the ancient clade such as cockroaches retained some traces of evolutionary resemblance in possessing lectin of ancient origin.     

A novel big protein TPRBK possessing 25 units of TPR motif is essential for the progress of mitosis and cytokinesis

Through the comprehensive analysis of the genomic DNA sequence of human chromosome 22, we identified a novel gene of 702 kb encoding a big protein of 2481 amino acid residues, and named it as TPRBK (TPR containing big gene cloned at Keio). A novel protein TPRBK possesses 25 units of the TPR motif, which has been known to associate with a diverse range of biological functions. Orthologous genes of human TPRBK were found widely in animal species, from insecta to mammal, but not found in plants, fungi and nematoda. Northern blotting and RT-PCR analyses revealed that TPRBK gene is expressed ubiquitously in the human and mouse fetal tissues and various cell lines of human, monkey and mouse. Immunofluorescent staining of the synchronized monkey COS-7 cells with several relevant antibodies indicated that TPRBK changes its subcellular localization during the cell cycle: at interphase TPRBK locates on the centrosomes, during mitosis it translocates from spindle poles to mitotic spindles then to spindle midzone, and through a period of cytokinesis it stays on the midbody. Co-immunoprecipitation assay and immunofluorescent staining with adequate antibodies revealed that TPRBK binds to Aurora B, and those proteins together translocate throughout mitosis and cytokinesis. Treatments of cells with two drugs (Blebbistatin and Y-27632), that are known to inhibit the contractility of actin–myosin, disturbed the proper intracellular localization of TPRBK. Moreover, the knockdown of TPRBK expression by small interfering RNA (siRNA) suppressed the bundling of spindle midzone microtubules and disrupted the midbody formation, arresting the cells at G₂ + M phase. These observations indicated that a novel big protein TPRBK is essential for the formation and integrity of the midbody, hence we postulated that TPRBK plays a critical role in the progress of mitosis and cytokinesis during mammalian cell cycle.     

Oligosaccharide structure of a functional unit RvH1-b of Rapana venosa hemocyanin using HPLC/electrospray ionization mass spectrometry

In the present study the structures of two glycopeptides (G1 and G1'), isolated from FU RvH(1)-b and two glycopeptides (G2 and G3), isolated from the structural subunit RvH(1) of Rapana venosa hemocyanin, were determined. To structurally characterize the site-specific carbohydrate heterogeneity and binding site of the N-linked glycopeptide(s), a combination of capillary reversed-phase chromatography and ion trap mass spectrometry was used. The amino acid sequences of glycopeptides G1 and G1' determined by Edman degradation and MS/MS sequencing demonstrated that the oligosaccharides are linked to N-glycosylation sites. Two peptides (a glycosylated (G1) and non-glycosylated one) were identified in this fraction and no linkage sites were observed in the latter one. Based on the sequencing of the glycosylated fractions G1, G1', G2 and G3, the carbohydrate structure Man(alpha1-6)Man(alpha1-3)Man(beta1-4)GlcNAc(beta1-4)[Fuc(alpha1-6)]GlcNAc-R could be identified for glycopeptides G1 and G3, and only the typical core structure Man(alpha1-6)Man(alpha1-3)Man(beta1-4)GlcNAc(beta1-4)GlcNAc-R was found for G1' and G2. The Fuc residue found in glycopeptides G1 and G3 is attached to N-acetyl-glucosamine of the carbohydrate core, as often found in other glycoproteins.     

Dispersal ability and invasion success of Crepidula fornicata in a single gulf: insights from genetic markers and larval-dispersal model

The success of an exotic species relies on many factors including dispersal capabilities and adaptation to novel environments. In particular, rapid spread from an initial point of introduction favours long-term establishment of exotic species, especially when large genetic diversity is maintained during the colonization phase. We here focused on the slipper limpet, Crepidula fornicata, a species native to the western Atlantic that has successfully invaded European bays and estuaries since the end of the nineteenth century following repeated introductions. Its settlement at high densities has major consequences on the macro-benthic fauna and flora. The aim of the present study was to analyse the ability of C. fornicata for rapid diffusion and long-distance dispersal, at the level of a large French gulf, namely the gulf of St-Malo (covering 120 km in latitude and 40 km in longitude) in the English Channel. The genetic architecture of 16 populations distributed all over this gulf was investigated using five microsatellite loci. Genetic diversity was found to be high and did not vary significantly with population density, population age or geographic location. Moreover, despite potential isolation among populations due to a strong tidal regime and the action of wind-induced currents, only weak barriers to gene flow were found across the gulf. These results were in agreement with results obtained from a simple 2D larval dispersal model. Both genetic data and the simulation model highlighted the potential for rapid and efficient spread of C. fornicata at a regional level.