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V Bénassi

Publications and source records attributed to V Bénassi.

6 recordsLinked to original sources
PubMed2000

Evolutionary novelties in islands: Drosophila santomea, a new melanogaster sister species from São Tomé.

The finding of new melanogaster sister species may help us in understanding more about how the emergence of genetic novelties, particularly in insular habitats, can result in speciation. Here we report on the discovery of Drosophila santomea, which is the first melanogaster sibling found off West-equatorial Africa, on São Tomé, one of the Gulf of Guinea islands. Although the eight other melanogaster sister species are remarkably conservative in their morphology except for their terminalia, the new find has a morphological trait distinguishing it from all of these: a pure yellow body coloration of both sexes without the normal black abdominal banding. Evidence from the terminalia, polytene and mitotic chromosomes, period gene and allozymes are provided indicating that it is nonetheless the nearest relative of Drosophila yakuba with which it coexists on the island. The new find is a clear-cut taxon as shown by the production of sterile male hybrids, eventually with developmental defects, in both directions of cross with yakuba and by the existence of an altitudinal divide accompanied by a hybrid zone at mid-elevation on the island. Molecular and karyotypic data further support this conclusion. In contrast to the significant divergence of their nuclear DNAs, an intriguing similarity in their cytochrome b sequences was observed indicating a recent coalescence common to santomea, yakuba and also teissieri cytoplasms. These were shown to harbour the same Wolbachia endosymbiotic bacteria which could possibly be responsible for mitochondrial DNA hitchhiking across the species barrier.

Animals↗
PubMed1999

Partial sweeping of variation at the Fbp2 locus in a west African population of Drosophila melanogaster.

Departure of molecular variation from neutral equilibrium was studied in a highly recombining region of the Drosophila genome. A 2.2-kb region including the Fbp2 locus was sequenced for 10 chromosomes from a D. melanogaster sample from West Africa and for the related species D. simulans. Of the 33 variable sites present in the 1.3-kb transcription unit, 32 made up a single haplotype present in half of the D. melanogaster sample. This pattern significantly departed from predictions of the neutral drift-mutation equilibrium model. The major haplotype presented a diagnostic restriction site which was investigated in 226 chromosomes from three distant European and African populations. It was found at a high frequency (31%) in the population from which the sequenced sample originated, but was nearly absent from the other two (below 4%), suggesting that the major haplotype frequency resulted from a local selective sweep event. Partial sweeping of variation in regions of high recombination rates has previously been found for American and European populations of D. melanogaster. Our study shows that this phenomenon also occurs in African populations, which are in the ancestral range of this species.

Africa, Western↗
PubMed1998

Allele-specific population structure of Drosophila melanogaster alcohol dehydrogenase at the molecular level.

The history of the Drosophila melanogaster alcohol dehydrogenase (ADH) Fast/Slow polymorphism was studied by recording molecular variation and inversion polymorphism in 233 chromosomes from European and African populations. Silent molecular variation in the Slow allele was very different between standard chromosomes and chromosomes bearing the In(2L)t inversion. Within populations, inverted Slow haplotypes were more variable than standard Slow haplotypes. Between populations, geographical structure was almost nonexistent for inverted Slow haplotypes and highly significant for standard Slow. All Fast haplotypes occurred on standard chromosomes. They showed little variation within and between populations. They were highly significantly closer to standard Slow haplotypes from Europe. These results suggest that the current range of Fast and In(2L)t Slow haplotypes is recent and that an older genetic differentiation between populations was followed by allele-specific gene flow.

Alcohol Dehydrogenase↗
PubMed1995

Comparative population structuring of molecular and allozyme variation of Drosophila melanogaster Adh between Europe, west Africa and east Africa.

Restriction enzyme molecular variation in Drosophila melanogaster Adh was compared between three natural populations from Europe, West Africa and East Africa. The frequency distribution of silent variation in the slow allele was compatible with the neutral model in all three samples. The number of haplotypes in East Africa was significantly higher than in the other two populations. The largest divergence, as measured by Fst, was between the East African population and a group made up from the West African, the European, and previously studied American populations. We suggest that a split first occurred within African populations at least 44000 years ago. European populations separated from West Africa more recently, between the last glacial maximum and the post-glacial optimum, 18,000 to 8,000 years ago. We suggest that this species was domesticated recently relative to human evolution, possibly with the advent of agriculture. Population differentiation with respect to the two allozymes, fast and slow, does not follow the geographical pattern of silent variation. It opposes European to both African populations, and probably results from selection for adaptation to alcohol in recent temperate populations.

Africa↗
PubMed1993

Molecular variation of Adh and P6 genes in an African population of Drosophila melanogaster and its relation to chromosomal inversions.

Four-cutter molecular polymorphism of Adh and P6, and chromosome inversion polymorphism of chromosome II were investigated in 95 isogenic lines of an Ivory Coast population of Drosophila melanogaster, a species assumed to have recently spread throughout the world from a West African origin. The P6 gene showed little linkage disequilibrium with the In(2L)t inversion, although it is located within this inversion. This suggests that the inversion and the P6 locus have extensively exchanged genetic information through either double crossover or gene conversion. Allozymic variation in ADH was in linkage disequilibrium with In(2L)t and In(2R)NS inversions. Evidence suggests either that inversion linkage with the Fast allele is selectively maintained, or that this allele only recently appeared. Molecular polymorphism at the Adh locus in the Ivory Coast is not higher than in North American populations. New haplotypes specific to the African population were found, some of them connect the "WaS-like" haplotypes found at high frequencies in the United States to the other slow haplotypes. Their relation with In(2L)t supports the hypothesis that WaS recently recombined away from an In(2L)t chromosome which may be the cause of its divergence from the other haplotypes.

Africa, Western↗