Analysis of the meiotic segregation in intergeneric hybrids of tilapias

Tilapia species exhibit a large ecological diversity and an important propensity to interspecific hybridisation. This has been shown in the wild and used in aquaculture. However, despite its important evolutionary implications, few studies have focused on the analysis of hybrid genomes and their meiotic segregation. Intergeneric hybrids between Oreochromis niloticus and Sarotherodon melanotheron, two species highly differentiated genetically, ecologically, and behaviourally, were produced experimentally. The meiotic segregation of these hybrids was analysed in reciprocal second generation hybrid (F2) and backcross families and compared to the meiosis of both parental species, using a panel of 30 microsatellite markers. Hybrid meioses showed segregation in accordance to Mendelian expectations, independent from sex and the direction of crosses. In addition, we observed a conservation of linkage associations between markers, which suggests a relatively similar genome structure between the two parental species and the apparent lack of postzygotic incompatibility, despite their important divergence. These results provide genomics insights into the relative ease of hybridisation within cichlid species when prezygotic barriers are disrupted. Overall our results support the hypothesis that hybridisation may have played an important role in the evolution and diversification of cichlids

The challenges of animal biodiversity

The successful introduction of the term “biodiversity” is the expression of several recent changes in our perception and understanding of the diversity of living organisms. In this presentation we will evoke three aspects of these changes, with a focus on animal biodiversity. - The unexpected magnitude of the diversity of species. Today, the number of animal species is estimated by indirect methods to more than 10 millions, the very largest part being small size invertebrates. So, after three centuries of zoologist’s active investment, only 1.3 million animal species are today listed and about 10 000 new species are described every year. This “new frontier” implies a rethinking of our inventory strategies of biodiversity. Besides this effort of inventory, the development of cladistics by systematicians has permitted the setting up of true phylogenetic classification of species, leading for instance to radical changes in the classification of vertebrates. - The existence, in addition to the diversity of species, of other levels of organization that seems to be necessary to investigate for a better understanding and management of biodiversity. The analysis of within species diversity was until recently mainly limited to domestic species but can be done now in all species by molecular markers and in a near future by the sequencing of portions of the genome. At the supraspecific level, diversity of biocenosis and ecosystems deserve a double effort, one for his inventory with a focus on the “hot spots” of biodiversity, the other for his understanding, the key role of biodiversity in the functioning of ecosystems being still to be explored. - The perception of a severe erosion of this biodiversity, as a result of diverse human activities. We present the different approaches that can be used to measure this erosion and to compare it with past extinction rates, as estimated by paleontologists. The causes of this erosion are then presented: overexploitation, destruction of habitats and introduction of alien species. Taking the example of industrial fishing, we insist on the fact that indirect and non-intentional impacts can play a larger role than direct impacts. This could explain the failure of management strategies exclusively focused on exploited species. Then, we analyse the possible consequences of climate changes that are announced for the 21st century. We show that our knowledge of the diverse adaptation modes of biodiversity is still very limited, especially if the question to be answered is not “will biodiversity be able to adapt itself?” but “will the forthcoming adaptations be favourable or not to human life?”L’introduction et le succès du terme « biodiversité » a concrétisé plusieurs évolutions récentes dans notre perception et notre compréhension de la diversité des êtres vivants. Nous évoquerons dans cette présentation trois aspects de ces évolutions, en nous concentrant plus particulièrement sur la biodiversité animale : - l’ampleur insoupçonnée de la diversité spécifique. On évalue aujourd’hui, par des méthodes indirectes, le nombre d’espèces animales à plus de 10 millions, l’essentiel étant constitué d’invertébrés de très petite taille. Or, après trois siècles d’activités des zoologistes, seul 1,3 million d’espèces animales sont aujourd’hui recensées et environ 10 000 espèces nouvelles sont décrites chaque année. Cette « nouvelle frontière » oblige donc à repenser les stratégies d’exploration de la biodiversité. Outre cet effort d’inventaire, les systématiciens ont développé, avec la cladistique, des méthodes permettant une véritable classification phylogénétique du vivant, qui ont notamment bouleversé la classification des vertébrés. - L’existence d’autres niveaux d’organisation que celui de la diversité des espèces, niveaux dont la connaissance apparaît nécessaire pour comprendre et mieux gérer la biodiversité. La diversité intraspécifique, dont l’analyse a été jusqu’à récemment trop limitée aux espèces domestiques, peut maintenant être décrite dans toutes les espèces par les marqueurs moléculaires et sera bientôt enrichie par les possibilités de séquençage de portions du génome. Au niveau supraspécifique, la diversité des biocénoses et des écosystèmes mérite un double effort, d’inventaire d’une part, en particulier sur les « points chauds » de la biodiversité, de compréhension d’autre part, l’importance de cette diversité vis-à-vis du fonctionnement des écosystèmes restant en grande partie à documenter. - La perception d’une érosion forte de cette biodiversité sous l’action des différentes activités humaines. Nous présentons les différentes approches permettant de mesurer cette érosion et de la comparer aux taux d’extinction passés, estimés par les paléontologues. Les causes de cette érosion sont ensuite évoquées : surexploitation, destruction des habitats, introduction d’espèces. En prenant l’exemple de la pêche industrielle, nous insistons sur le fait que les impacts indirects et non intentionnels jouent sans doute un rôle plus important que les impacts directs, d’où l’échec des modes de gestion focalisés exclusivement sur les espèces exploitées. Enfin, nous analysons les conséquences possibles des changements climatiques annoncés pour le 21e siècle. Nous montrons que notre connaissance des différents modes d’adaptation de la biodiversité est aujourd’hui très limitée, en particulier si la question à résoudre n’est pas « la biodiversité peut-elle s’adapter ? » mais « les adaptations qui vont se réaliser seront-elles ou non favorables à la vie humaine ? »

Microsatellites Cross-Species Amplification across Some African Cichlids

The transfer of the genomic resources developed in the Nile tilapia, Oreochromis niloticus, to other Tilapiines sensu lato and African cichlid would provide new possibilities to study this amazing group from genetics, ecology, evolution, aquaculture, and conservation point of view. We tested the cross-species amplification of 32 O. niloticus microsatellite markers in a panel of 15 species from 5 different African cichlid tribes: Oreochromines (Oreochromis, Sarotherodon), Boreotilapiines (Tilapia), Chromidotilapines, Hemichromines, and Haplochromines. Amplification was successfully observed for 29 markers (91%), with a frequency of polymorphic (P95) loci per species around 70%. The mean number of alleles per locus and species was 3.2 but varied from 3.7 within Oreochromis species to 1.6 within the nontilapia species. The high level of cross-species amplification and polymorphism of the microsatellite markers tested in this study provides powerful tools for a wide range of molecular genetic studies within tilapia species as well as for other African cichlids

Vitamin A status of populations in three West african countries

Les résultats des enquêtes de consommation alimentaire et d'épidémiologie (clinique et biochimique) entreprises dans trois régions sub-sahéliennes ont mis en évidence l'existence de xérophtalmie au Burkina Faso, une déficience transitoire en vitamine A durant la saison humide au sud du Mali sans signes cliniques graves et un bon état en vitamine A en Casamanc

Enhanced individual selection for selecting fast growing fish: the "PROSPER" method, with application on brown trout (Salmo trutta fario)

Growth rate is the main breeding goal of fish breeders, but individual selection has often shown poor responses in fish species. The PROSPER method was developed to overcome possible factors that may contribute to this low success, using (1) a variable base population and high number of breeders (Ne > 100), (2) selection within groups with low non-genetic effects and (3) repeated growth challenges. Using calculations, we show that individual selection within groups, with appropriate management of maternal effects, can be superior to mass selection as soon as the maternal effect ratio exceeds 0.15, when heritability is 0.25. Practically, brown trout were selected on length at the age of one year with the PROSPER method. The genetic gain was evaluated against an unselected control line. After four generations, the mean response per generation in length at one year was 6.2% of the control mean, while the mean correlated response in weight was 21.5% of the control mean per generation. At the 4th generation, selected fish also appeared to be leaner than control fish when compared at the same size, and the response on weight was maximal (≈130% of the control mean) between 386 and 470 days post fertilisation. This high response is promising, however, the key points of the method have to be investigated in more detail

Analyse génétique de la croissance chez la truite arc-en-ciel (Salmo gairdneri Richardson)

Analyse génétique de la croissance chez la truite arc-en-ciel (Salmo gairdneri Richardson