Multiple introductions promote range expansion of the mollusc Cyclope neritea (Nassariidae) in France: evidence from mitochondrial sequence data.

Since the 1970s, the nassariid gastropod Cyclope neritea has been extending its range north along the French Atlantic coasts from the Iberian Peninsula. This may be due to natural spread because of the recent warming of the northeastern Atlantic. However, human-mediated introductions related to shellfish culture may also be a probable explanation for this sudden range expansion. To examine these two hypotheses, we carried out a comprehensive study based on mitochondrial gene sequences (cytochrome oxidase I) of the five recently colonized French bays as well as 14 populations located in the recognized native range of the species. From a total of 594 individuals, we observed 29 haplotypes to split into three divergent clades. In the native range, we observed a low molecular diversity, strong genetic structure and agreement between geography and gene genealogies. Along the French coasts, we observed the opposite: high genetic diversity and low genetic structure. Our results show that recurrent human-mediated introductions from several geographical areas in the native range may be a source for the French Atlantic populations. However, despite the low dispersal ability of C. neritea, the isolation-by-distance pattern in France suggested that this gastropod may have been present (although unnoticed) on the French Atlantic coasts before the 1970s. As C. neritea shows characteristics of a cryptogenic species, the classification of Atlantic populations as either native or introduced is not straightforward. Cryptogenic species should be studied further to determine the status of new populations close to their recognized native range.

[Rapid determination of sex in Myocastor coypus embryos in the first stage of gestation]. / Détermination rapide du sexe chez des embryons de ragondin, Myocastor coypus, dès les premiers stades de gestation.

The early knowledge of the sex may be crucial for the understanding of many features of ecological and evolutive biology, including offspring sex-ratio adjustment and evolution of breeding systems. In coypu (Myocastor coypus), significant variation in birth sex-ratios can be observed and selective abortion of entire litters is one of the cited mechanisms. In order to determine the sex of coypu embryos in the earlier stages of gestation (second week), we developed a molecular technique based on PCR amplification of a region of the Sry gene. These method used the combination of two sets of primers: one specific of the Y-chromosome; the other one, autosomal, is a positive control for amplification. Because of the direct amplification of embryo lysate without DNA extraction, the present sexing technique is rapid, relatively simple and inexpensive, and presents numerous advantages for the study at population scale.

[Presence if a new oyster predator, Ocinebrellus inornatus (Recluz, 1851), in the shellfish culture bay of Marennes-Oleron]. / Présence d'un nouveau prédateur de l'huître creuse, Ocinebrellus inornatus (Récluz, 1851), dans le bassin conchylicole de Marennes-Oléron.

The muricid gastropod, Ocinebrellus inornatus, originates from the coasts of the Korean Sea and southern Japan. This species has been regularly sampled in the bay of Marennes-Oléron (France) since spring 1997, and allowed us to validate the taxonomic status of a previous report of the species in the bay in April 1995. O. inornatus was sampled only in the bay of Marennes-Oléron and has not been observed in the other areas along the Charente-Maritime coast. O. inornatus lives mainly in the same biotope as the local muricid Ocenebra erinacea (i.e. the level of Fucus serratus between MLWN and ELWS) Now, this alien species seems to be very well settled in the bay of Marennes-Oléron, where it causes damage to the farming oyster beds. In the areas of highest densities of Ocinebrellus inornatus, the local species Ocenebra erinacea is observed in comparatively reduced numbers. The probable causes of introduction of O. inornatus in the bay are discussed.

Concerted evolution in the GAPDH family of retrotransposed pseudogenes.

In murine rodents the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) multigene family includes more than 300 retroprocessed pseudogenes. Its single functional gene encodes GAPDH, an enzyme of glycolysis. Because of its manageable size, this family is a good model for the study of genome cohesion and evolution. By sequence comparison of several GAPDH pseudogenes in Rattus norvegicus and Mus musculus, we have obtained evidence that (i) the GAPDH family still generates new pseudogenes; we note in each species the beginning of a process of species-specific evolution since the pseudogenes of one genus on average cluster more with one another than they do with those of the other genus, and (ii) the GAPDH family contains diversified subfamilies. These findings suggest a certain level of transcription and transposition of the pseudogenes independent of the functional gene which may result from various mechanisms. The homogenization we observe may be due to the pseudogenes themselves (concerted evolution in a strict sense), which explains the occurrence of long-term homogenization of old sequences and subfamily groupings.