Phylogéographie des moules du complexe d'espèces "Mytilus edulis"

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Genetic relationships of Mytilus galloprovincialis Lmk. populations worldwide: evidence from nuclear -DNA markers

Allozyme surveys of genetic variation in Mytilus galloprovincialis Lmk. throughout the world have identified three groups within this species: a northeastern (NE) Atlantic group that also includes the M. galloprovincialis population of South Africa, a Mediterranean group that also includes the M. galloprovincialis populations from the eastern and the western coasts of the North Pacific, and an Australasian g roup. Hypotheses that have been proposed to account for the genetic differentiation patterns and disjunct, worldwide distribution of M. galloprovincialis include the recent introduction of this species into the Southern Hemisphere and the North Pacific through human agency, and an alternative hypothesis that each of the three groups is endemic. We used two nuclear-DNA markers (the polyphenolic adhesive protein gene Glu-5' and the first intron of the actin gene mac-1) to investigate in more depth the genetic relationships among M. galloprovincialis populations. Samples were taken between 1996 and 1999 from California, the NE Atlantic, the Mediterranean Sea, South Africa, Korea, Western Australia, Tasmania, and New Zealand. NE Atlantic M. edulis L. were used a s an outgroup. While all M. galloprovincialis samples were fixed, or nearly so, for the diagnostic G allele at locus Glu-5', correspondence analysis of mac-1 allele -frequency data highlighted the genetic distinctness of Australasian mussels relative to other M. galloprovincialis populations. The latter consisted of two differentiated groups (NE Atlantic and Mediterranean) as formerly reported at allozyme loci. Another sample, from Chile, was nearly identical to Mediterranean M. galloprovincialis. Nuclear-DNA data thus enforce the idea that M. galloprovincialis have probably been introduced from the Mediterranean to the North Pacific (and now Chile), and from the NE Atlantic to South Africa. We argue that Australasian mussels derive from a proto- M. galloprovincialis population introgressed by M. edulis-like genes, and should be considered as a regional subspecies of M. galloprovincialis

Genetic characterisation of Mytilus galloprovincialis Lmk. in North West Africa using nuclear DNA markers

International audienceThe genetic relationships among Mytilus galloprovincialis populations over their range in the northeastern Atlantic and the western Mediterranean were investigated using polymerase chain reaction (PCR)amplified nuclear DNA markers. We used long-range polyacrylamide gel electrophoresis for characterizing an intron-length polymorphism at the actin gene locus mac-1 in Mytilus. Sharp resolution was obtained with this technique, which revealed a high level of size polymorphism. It also allowed to discriminate between M. galloprovincialis and M. edulis. Mytilus populations sampled on the northwestern African coasts (Morocco, Western Sahara, and Mauritania) were M. galloprovincialis as formerly suggested on the basis of morphology and geographic location. A sample of the Padstow mussel reported as M. galloprovincialis according to allozyme and morphological data exhibited allele frequencies that were rather intermediate between M. galloprovincialis and M. edulis. Slight heterozygote deficiencies were possibly present within each sample as usually reported in bivalve populations. Additional PCRs using a second pair of primers showed that this could not be explained by the occurrence of null alleles that would have resulted from mis-priming during DNA amplification. Significant differentiation was observed between M. galloprovincialis from northwestern Africa and the reference M. galloprovincialis sample from the Mediterranean Sea, a result that is consistent with previous allozyme- and mitochondrial DNA-based reports of an abrupt genetic change between northeastern Atlantic / Alboran Sea and western Mediterranean M. galloprovincialis populations

The zone of sympatry and hybridization of Mytilus edulis and M. galloprovincialis, as revealed by intron length polymorphism at locus mac-1

International audienceIntron-size variation at the actin gene locus mac-1 was used to characterise mussel, Mytilus spp., populations in the ~2000-km wide zone of contact and hybridization ('hybrid zone') between M. edulis and M. galloprovincialis in western Europe. Twenty-five samples were collected in 1995-1999 in locations within the hybrid zone and from reference populations of each species. We used correspondence analysis on the matrix of allelic frequencies to determine which alleles are characteristic of each species, and to characterise samples along the genetic gradient between M. edulis and M. galloprovincialis. In the hybrid zone, some samples exhibited mac-1 allele frequencies that were typical of M. edulis; other samples were distributed along the M. edulis / M. galloprovincialis gradient and displayed variable levels of intergradation that were not correlated with geography. Some of the latter samples exhibited significant heterozygote deficiencies. The simple admixture hypothesis (Wahlund effect) could not be rejected for two-fifths of the samples. The hybrid zone thus appeared as a mosaic of populations which are either pure M. edulis, or hybrid between M. galloprovincialis and M. edulis, or a mixture of the foregoing with M. galloprovincialis individuals. These results were consistent with published allozyme data, suggesting that they can be extended to the entire nuclear genome. M. edulis mac-1 alleles were present at moderate frequency in Atlantic M. galloprovincialis, and at significantly lower frequency in some Mediterranean samples. This pattern was homogenous over a broad geographic range within each basin. It was not evident that introgression of M. edulis into M. galloprovincialis presently occurs south of the zone of contact. We propose that the distinctness of the Atlantic M. galloprovincialis population results from past introgression by M. edulis alleles

Genetics and taxonomy of Chilean smooth-shelled mussels, Mytilus spp. (Bivalvia: Mytilidae)

International audienceIt has been previously established that native smooth-shelled mussels in southern South America possess close evolutionary affinities with Northern-Hemisphere Mytilus edulis L. 1758 [McDonald et al., Mar. Biol. 111 (1991) 323-333]. This result has since been challenged by authors claiming that Chilean mussels should be considered a local subspecies of M. galloprovincialis Lmk. 1819. Moreover, morphological, physiological, ecotoxicological and molecular genetic studies on Chilean smooth-shelled mussels still frequently refer to 'M. chilensis' Hupé 1854, even though the previous discovery of alien M. galloprovincialis and considerable heterogeneity in shell morphology among samples collected along the Chilean shores raise concern that different Mytilus spp. species might have been included under 'M. chilensis'. Here we reviewed the molecular and morphological data available on smooth-shelled mussels from Chile in an attempt to clarify both their genetic composition and their taxonomic status. Using multivariate analysis on sample x allozyme-frequency matrices, we confirmed the widespread occurrence of the Southern-Hemisphere form of M. edulis along the shores from the North Patagonia region of Chile to the southern tip of the South American continent. The populations sampled in southern central Chile showed some evidence of slight introgression from Southern-Hemisphere M. galloprovincialis. Morphological characterization of a sample from Dichato in southern central Chile was consistent with its previous genetic identification as Mediterranean M. galloprovincialis. The occurrence of Southern-Hemisphere M. galloprovincialis in Punta Arenas at the southern tip of the South American continent was also reported. Southern-Hemisphere M. edulis, including native Chilean smooth-shelled Mytilus, should be assigned subspecific rank and named M. edulis platensis d'Orbigny 1846

Microsatellite markers for the Jaera albifrons species complex (marine isopods)

International audienceBackground: The Jaera albifrons complex contains five species of marine isopods (J. albifrons, J. praehirsuta, J. ischio-setosa, J. forsmani, and J. posthirsuta). These species, occurring on the shores of the North‑Atlantic Ocean, are partially reproductively isolated by barriers due to sexual isolation (mate choice), genetic incompatibilities, and ecological spe‑ cialization. Microsatellite loci would be useful for parentage‑based analyses of sexual selection and studies of genetic structure in the context of speciation. Findings: Twenty‑four microsatellite markers were developed for J. albifrons using pyrosequencing of enriched libraries. Patterns of polymorphisms were analyzed in 49 J. albifrons adult males sampled in two populations from Brittany (Western France). The average number of alleles per locus was 4.73 ± 2.45 and the average gene diversity was 0.55 ± 0.23. Most markers also successfully amplified in the three sibling species J. praehirsuta, J. ischiosetosa, and J. forsmani. Conclusions: These polymorphic and cross‑amplifiable markers will be useful for population genetics and parentage studies in the J albifrons complex

Isolation of 11 microsatellite markers in Crepidula convexa (Gastropoda, Calyptraeideae) for parentage analyses

International audienceCrepidula convexa, a calyptreid gastropod with direct embryonic development, changes sex from male to female in the course of its lifetime (protandry). Under sex-allocation theory, male reproductive success should be independent from age and size (a proxy used for age). However, this may be counterbalanced by female cryptic choice or gregarious behaviour. Eleven polymorphic microsatellite loci were thus developed to examine paternity of embryos and larvae. This set of loci appears suitable to carry out paternity analyses due to the high exclusion probability of unrelated males given the maternal genotype