Paratectonatica tigrina employs three predatory tactics against bivalve prey: wall-drilling, edge-drilling and non-drilling (suffocation) tactics. In this study, we conducted laboratory experiments to examine the predator–prey interactions between the naticid gastropod P. tigrina and two species of bivalve prey, Ruditapes philippinarum and Meretrix lusoria, and to investigate how predatory tactics differ for the bivalve species. Predation success increased with the shell weight ratio between predator and prey, however, there was no significant difference among prey species. The shell weight ratio significantly differed (P < 0.05) between predatory tactics against R. philippinarum, but not against M. lusoria, implying that P. tigrina determines its predatory tactics based on the shell weight ratio for R. philippinarum. However, we observed that feeding duration was not influenced by shell weight ratio or prey species, even though data were separated for each predatory tactic. These results suggest that there is no difference in feeding efficiency based on shell weight ratio between prey species and between predatory tactics. Paratectonatica tigrina may alter its predatory tactics suitably depending on the prey species and the relative size difference, despite the same feeding efficiency.

Germ plasm-related structures (GPRS) are known to accompany meiotic cell differentiation but their dynamics are still poorly understood. In this study, we analyzed the ultrastructural mechanisms of GPRS transformation during oogenesis and spermatogenesis of the bivalve mollusc Ruditapes philippinarum (Manila clam), exploring patterns of GPRS activity occurring at meiosis onset, sex-specific difference/similarity of such patterns, and the involvement of mitochondria during GPRS-assigned events. In the two sexes, the zygotene–pachytene stage of meiosis is anticipated by three shared steps. First, the dispersion of germ plasm granules containing the germ line determinant VASA occurs. Second, the VASA protein deriving from germ plasm granules enters neighbouring mitochondria and appears to induce mitochondrial matter release, as supported by cytochrome B localization outside the mitochondria. Third, intranuclear VASA entrance occurs and the protein appears involved in chromatin reorganization, as supported by VASA localization in synaptonemal complexes. In spermatogenesis, these three steps are sufficient for the normal course of meiosis. In oogenesis, these are followed by the action of ‘germ plasm granule formation complex’, a novel type of structure that appears alternative to the Balbiani body. The possibility of germ plasm involvement in reproductive technologies is also suggested.

The introduction of the Manila clam into British coastal waters in the 1980s was contested by conservation agencies. While recognizing the value of the clam for aquaculture, the government decided that it posed no invasive risk, as British sea temperatures would prevent naturalization. This proved incorrect. Here we establish the pattern of introduction and spread of the species over the first 30 years of its presence in Britain. We report archival research on the sequence of licensed introductions and examine their relationship in time and space to the appearance of wild populations as revealed in the literature and by field surveys. By 2010 the species had naturalized in at least 11 estuaries in southern England. These included estuaries with no history of licensed introduction. In these cases activities such as storage of catch before market or deliberate unlicensed introduction represent the probable mechanisms of dispersal. In any event naturalization is not an inevitable consequence of introduction and the chances of establishment over the period in question were finely balanced. Consequently in Britain the species is not currently aggressively invasive and appears not to present significant risk to indigenous diversity or ecosystem function. However it is likely to gradually continue its spread should sea surface temperatures rise as predicted.

Quantitative real-time polymerase chain reaction (qPCR) is probably the most used method for gene expression quantification because of its high sensitivity and specificity. Nevertheless, this technology can undergo experimental errors and variations. Normalization of the results using a reference gene is therefore necessary to minimize these variations. As the study of immune genes in bivalve mollusks has increased in the last years, the establishment of adequate and stable reference genes for bivalves is strongly required. We analyzed the behavior of four putative reference genes: ribosomal RNA 18S, actin, elongation factor 1 − α and α-tubulin. The suitability of these four genes as internal control for qPCR was evaluated in mussel (Mytilus galloprovincialis) and clam (Ruditapes philippinarum) hemocytes after bacterial challenge. Four independent approaches (BestKeeper, GeNorm, NormFinder and DeltaCt ) were used to assess the suitable genes for stable expression. For these particular circumstances, the most stable gene in hemocytes was elongation factor 1 − α for mussels and α-tubulin for clams.

Although clam populations in France are known to be infected with protozoans of the genus Perkinsus, no molecular characterization was previously performed on these parasites. Considering that several members of this genus have been associated with mortalities of molluscs worldwide, a study was undertaken in order to characterize these parasites in France. For that purpose, clams, Ruditapes philippinarum and R. decussatus, collected from different production areas and found to be infected with Perkinsus sp. in thioglycolate culture medium, were selected for PCR-RFLP tests and sequencing. Perkinsus olseni was detected in all the investigated areas and results also suggested the presence of P. chesapeaki in Leucate, a lagoon on the Mediterranean coast and in Bonne Anse in Charente Maritime, on the Atlantic coast. Clonal cultures from both detected species were produced in order to describe and compare in vitro stages. Differences in size between both Perkinsus spp. were noticed especially for schizonts and zoosporangia. Lastly, in situ hybridization tests allowed confirmation of the presence of both species in the same R. decussatus population and even in same clams. This is the first detection of P. chesapeaki in Ruditapes species and outside North America, which questions its introduction into Europe.

A large number of Red Sea species are colonizing the eastern Mediterranean Sea after the opening of the sea-level Suez Canal in 1869, mainly following the Levantine and Anatolian coasts and then spreading westwards, at least in part, by shipping transport of larvae, juveniles, or adult specimens. Two of them are Cerithium scabridum and Fulvia fragilis, well established along the Italian coasts, where new large and stable populations have formed. Some other species, such as Anadara demiri, were accidentally introduced through shipping in our seas and have found good conditions to survive and develop. New distributional and ecological data about these alien molluscs are given and all the species found in association are listed to improve understanding of their living biocoenosis. The presence of a further lessepsian mollusc and of an intentionally introduced species, Brachidontes pharaonis and Ruditapes philippinarum, was also confirmed respectively from Vibo Valentia harbour and from the Gulf of Naples and the Gulf of Taranto. The nomenclature used is based on the CLEMAM Database (last research on 9 January 2008).

Adult, healthy Manila clams, Ruditapes philippinarum, were inoculated in the laboratory with different, possibly pathogenic bacteria species to study the cellular immune responses. Challenging the clams with Vibrio P1, the causative agent of brown ring disease, induced significant increased total hemocyte counts three days post-challenge. The triggering role of the number of bacteria in the inoculum suggested a threshold for inducing the host response. In addition, a significant decrease of hyalinocytes and an increase of granulocytes revealed a modification in hemocyte population balance. No response was observed in individuals that received either heat killed-Vibrio P1, V. anguillarum or V. pelagius. These experiments demonstrate in R. philippinarum the influence of bacterial parameters on the selective induction of host immunodefence mechanisms. The biological processes by which intra-pallial inoculation of Vibrio P1 stimulates the internal defence system of the host has not yet been identified but the role of some bacterial factors (toxins, adherence capacity) is discussed.

Several virulence factors involved in the potential pathogenic capacity of Vibrio P1, the causative agent of brown ring disease (BRD) affecting cultured Manila clam adults (Ruditapes philippinarum), have been evaluated in comparison with other strains of several Vibrio species isolated from diseased clams. The importance of bacterial cell surface associated properties as virulence factors has been studied considering both non-specific and specific bacterial adhesion to clams. Vibrio P1 showed moderate hydrophobicity, but high affinity to bind to Congo Red dye and the presence of appendages, characterized as fimbriaeor pili. All the strains of Vibrio P1 secreted haemolysis and cytotoxins, and were also strong exotoxin producers. The presence of a large 49.2-MDa plasmid in all the strains of Vibrio P1 may be used as an epidemiological marker, but its involvement in pathogenic mechanisms has not yet been established. Although in some Vibrio strains, iron-acquisition systems play an essential role in their pathogenicity, they do not seem to be an important factor in Vibrio P1, since this pathogen lacks siderophore-mediated iron transport mechanisms.

La palourde japonaise présente un grand polymorphisme de coloration de la coquille. Bien que ce polymorphisme soit connu depuis longtemps, son hérédité n'a jamais été analysée. Cette étude a pour but, hormis la connaissance fondamentale du déterminisme génétique des caractères de la coloration, de permettre de produire des individus homozygotes pour la coloration. Ceux-ci pourront être utilisés comme marqueurs génétiques dans des expériences au laboratoire. La coloration est définie par trois caractères, l'asymétrie, l'ornementation et la couleur de fond. Les palourdes à coloration asymétrique sont totalement ou partiellement dépigmentées, à l'exception d'une bande postérieure sur la valve gauche. Les palourdes à coloration symétrique sont pigmentées sur les deux valves. Quatre séries de croisements ont permis l'analyse de différents caractères, Asymétrie et Symétrie, et des ornementations Vague [V] et Zébré [Z]. Les résultats suggèrent que la coloration est contrôlée par au moins deux gènes. Le caractère d'asymétrie est contrôlé par un gène à deux allèles, asymétrie (A) dominante et symétrie (S) récessive. Quelquesindividus asymétriques homozygotes ont été identifiés. Un phénotype Bigarré (Bi), est apparu dans les ségrégations du croisement V × V et des croisements Z × Z. Les résultats suggèrent que Vague et Zébré sont dominants sur Bigarré. Cependant, il existe d'autres ornementations (phénotype 1) et le gène codant pour l'ornementation serait ainsi multiallélique. Le déterminisme de la couleur n'est pas défini. Par contre, les observations montrent que la coloration n'est pas liée au sexe. Dans la majorité des croisements, les proportions observées pour l'asymétrie s'éloignent des rapports attendus selon les lois de Mendel. Cette différence est due à un déficit systématique en individus homozygotes symétriques qui n'a pu être expliqué.

Tetraploidy was induced in embryos of Ruditapes philippinarum by treating the eggs with cytochalasin B (CB). Two treatment times were found to be effective in inducing tetraploidy: 0 to 10 minutes after insemination (before formation of the first polar body) and 45 minutes after insemination (just before the first cleavage). Treatments, started 5 and 45 minutes after insemination, produced $64.4\pm7.8{\%}$ and $28.3\pm2.3{\%}$ tetraploid embryos, respectively, after 6 hours (on the average over 3 experiments). However, no tetraploids were detected in 4-month-old spat. Sperm entry delayed by the CB could be involved in induction of tetraploidy by early treatment.

In order to highlight the main factors accounting for the growth of clams in Marennes-Oléron Bay, three locations were investigated in 1984-85. First, factor analysis provided information on fluctuations of the environment. Second, principal components analysis was used to study ecological phenomena. The main axes explained the growth rate, which was included in an allometric model. Its properties were then studied by means of sensitivity analysis.