Ecologia molecular de ostras (Crassostrea spp. )do Atlântico Tropical / Molecular ecology of oysters (Crassostrea spp. ) from Tropical Atlantic

Crassostrea (Sacco, 1897) é o gênero mais importante do mundo de ostras de cultivo e consiste de 34 espécies distribuídas pelas regiões tropicais e temperadas do globo. C. gasar e C. rhizophorae são as duas espécies nativas que estão distribuídas ao longo de toda a costa do Brasil até o Caribe. C. gasar também ocorre na costa da Africa. Ainda que sua distribuição seja extensa e com disponibilidade abundante, o cultivo de ostras nativas no Brasil ainda é incipiente e a delimitação correta dos estoques mantém-se incerta. O sucesso do desenvolvimento da malacocultura, que é recomendada internacionalmente como forma sustentável de aquicultura, depende da resolução desses problemas. Assim, com o objetivo de determinar geneticamente seus estoques no Atlântico como também estimar sua história demográfica, dois diferentes marcadores moleculares foram empregados: sequências de DNA da região controle mitocondrial e loci de microssatélites espécie-especifícos, desenvolvidos no presente estudo. Foram sequenciados fragmentos da região controle de um total de 930 indivíduos de C. gasar e C. rhizophorae coletados em 32 localidades que incluíram o Caribe, a Guiana Francesa, a costa brasileira e a África. Também foram realizadas genotipagens de 1178 indivíduos, e ambas as espécies, com 9 e 11 loci de microssatélites para C. gasar e C. rhizophorae, respectivamente. Os dados genéticos foram analisados através de diferentes abordagens (índices de estruturação (FST) e de (Jost D), análise molecular de variância (AMOVA), análise espacial molecular de variância (SAMOVA), Bayesian Skyline Plots (BSP), análise fatorial de correspondência (AFC) e análise de atribuição Bayesiana (STRUCTURE)). Os resultados indicaram um padrão geral de estruturação, onde dois diferentes estoques foram detectados para ambas as espécies: grupos do norte e do sul, onde o Rio de Janeiro seria a região limitante entre os dois estoques. Os maiores valores dos índices de estruturação foram encontrados ...

Crassostrea (Sacco, 1897) is the most important genus of cultivated oysters in the world and consisting of 34 species distributed by tropical and temperate regions of the globe. C. gasar and C. rhizophorae are the two native species which have wide distribution along the entire Brazilian coast up to the Caribbean. C. gasar also occurs on coast of Africa. Despite its extensive distribution and abundant availability, cultivation of those oysters in Brazil is incipient, and the correct delimitation of the existing stocks is still uncertain. The successful development of malacoculture which is recommended internationally as an environmentally sustainable form of aquaculture depends on the resolution of these issues. Thus, in order to genetically determinate their stocks in the Atlantic and to estimate their demographic history, two different molecular markers were employed: sequences of the mitochondrial DNA control region and species-specific microsatellite loci, developed in the present study. We have sequenced a fragment of the mitochondrial control region from a total of 930 individuals of C. gasar and C. rhizophorae collected in 32 localities including the Caribbean, French Guyana, Brazilian coast and Africa. We have also genotyped 1178 individuals of both species with 9 and 11 loci of microsatellites for C. gasar and C. rhizophorae, respectively. Genetic data were analyzed with different approaches (fixation (FST) and differentiation (Jost D) indices, analysis of molecular variance (AMOVA), spatial analysis of molecular variance (SAMOVA), Bayesian Skyline Plots (BSP), factorial correspondence analysis (AFC) and Bayesian attribution analysis (STRUCTURE)). The results indicated a general structure pattern, where two different stocks were detected for both species: north and south groups, where Rio de Janeiro would be the limited region between them. Higher values of fixation indices were found for C. gasar, indicating that this species would be more ...

Molecular identification, phylogeny and geographic distribution of Brazilian mangrove oysters (Crassostrea)

Oysters (Ostreidae) manifest a high degree of phenotypic plasticity, whereby morphology is of limited value for species identification and taxonomy. By using molecular data, the aim was to genetically characterize the species of Crassostrea occurring along the Brazilian coast, and phylogenetically relate these to other Crassostrea from different parts of the world. Sequencing of the partial cytochrome oxidase c subunit I gene (COI), revealed a total of three species of Crassostrea at 16 locations along the Brazilian coast. C. gasar was found from Curuçá (Pará state) to Santos (São Paulo state), and C. rhizophorae from Fortim (Ceará state) to Florianópolis (Santa Catarina state), although small individuals of the latter species were also found at Ajuruteua beach (municipality of Bragança, Pará state). An unidentified Crassostrea species was found only on Canela Island, Bragança. Crassostrea gasar and C. rhizophorae grouped with C. virginica, thereby forming a monophyletic Atlantic group, whereas Crassostrea sp. from Canela Island was shown to be more similar to Indo-Pacific oysters, and either arrived in the Atlantic Ocean before the convergence of the Isthmus of Panama or was accidentally brought to Brazil by ship.

Microsatellites within genes and ESTs of the Pacific oyster Crassostrea gigas and their transferability in five other Crassostrea species

We developed 15 novel polymorphic microsatellites for the Pacific oyster Crassostrea gigas by screening genes and expressed sequence tags (ESTs) found in GenBank. The number of alleles per locus ranged from two to 24 with an average of 8.7, and the values of observed heterozygosity (Ho) and expected heterozygosity (He) ranged from 0.026 to 0.750 and from 0.120 to 0.947, respectively. No significant pairwise linkage disequilibrium was detected among loci and eight loci conformed to Hardy-Weinberg equilibrium. Transferability of the markers was examined on five other Crassostrea species and all the markers were amplified successfully in at least one species. These new microsatellites should be useful for population genetics, parentage analysis and genome mapping studies of C. gigas and closely related species. The nine markers identified from known genes are expected to be especially valuable for comparative mapping as type I markers.

Chromosomal organization of simple sequence repeats in the Pacific oyster (Crassostrea gigas): (GGAT)(4), (GT)(7) and (TA)(10) chromosome patterns.

Chromosome identification is essential in oyster genomic research. Fluorescence in situ hybridization (FISH) offers new opportunities for the identification of oyster chromosomes. It has been used to locate satellite DNAs, telomeres or ribosomal DNA sequences. However, regarding chromosome identification, no study has been conducted with simple sequence repeats (SSRs). FISH was used to probe the physical organization of three particular SSRs, (GGAT)(4), (GT)(7) and (TA)(10) onto metaphase chromosomes of the Pacific oyster, Crassostrea gigas. Hybridization signals were observed in all the SSR probes, but the distribution and intensity of signals varied according to the oligonucleotide repeat. The intercalary, centromeric and telomeric bands were observed along the chromosomes, and for each particular repeat every chromosome pair presented a similar pattern, allowing karyotypic analysis with all the SSRs tested. Our study is the first in mollusks to show the application of SSR in situ hybridization for chromosome identification and karyotyping. This technique can be a useful tool for oyster comparative studies and to understand genome organization in different oyster taxa.