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M Veuille

Publications and source records attributed to M Veuille.

At least 19 recordsLinked to original sources
PubMed2000

Genetics and the evolutionary process.

Population genetics was put forward as a mathematical theory between 1918 and 1932 and played a leading part in the rediscovery of the concept of natural selection. As an autonomous science developing Mendel's laws at the population scale and a key element of the Darwinian theory of evolution, its dual status led its practioners to initially overlook some consequences of Mendelism not accounted for by the Darwinian theory, including random drift and the cost of selection. The latter were put forward on purely theoretical grounds in the 1950s, but their importance was acknowledged only when empirical data on protein evolution and enzyme polymorphism (since 1965) and on DNA variation (since 1983) were obtained. The neutralist/selectionist debate that ensued involved disagreement over the scientific method as well as over the mechanisms of molecular evolution. Population genetics has long assumed the existence of natural selection a priori. It has since recentred around the null hypothesis that molecular evolution is neutral. This new approach, applied to sequence comparison and to the study of linkage disequilibrium, is logically more justified, yet empirical observations derived from it paradoxically show the overwhelming importance of selective effects within genomes.

Animals↗
PubMed2000

Selective sweep near the In(2L)t inversion breakpoint in an African population of Drosophila melanogaster.

Chromosomal inversions largely inhibit recombination and may be associated with selective forces, such as hitch-hiking effects: the effect of positive selection on linked loci. A West African population of Drosophila melanogaster showed a high frequency (0.61) of the In(2L)t inversion. Departure from neutrality statistically associated with the inversion polymorphism was previously recorded at Su(H), a locus distant from the proximal breakpoint of the inversion. These results were consistent with hitch-hiking effects with recombination. The present sequence polymorphism survey involves a 1 kb fragment of the Vha68-1 locus located closer to the proximal breakpoint of the inversion. It shows a significant deficit of polymorphism with respect to divergence when compared with other loci studied in the same population, thus suggesting selective effects. Only 11 polymorphic sites are present in a sample of 20 chromosomes and these sites present a significant excess of rare-frequency variants. The major haplotype shows an unexpectedly high frequency. Our estimate of the background selection effect is not sufficient to account for the observed reduction of polymorphism. Intraspecific variation is structured between inverted and standard chromosomes; there are no shared polymorphisms but also no fixed differences between them. This pattern, together with that found on other loci previously studied near this inversion breakpoint, suggests hitch-hiking effects enhanced by the inversion.

Animals↗
PubMed2000

Sexual isolation of genetically differentiated sympatric populations of Drosophila melanogaster in Brazzaville, Congo: the first step towards speciation?

Two sympatric populations of Drosophila melanogaster were collected in the Brazzaville area in Congo, one from the suburban countryside and the other from a brewery located in the city. They were compared for several genetically determined traits including morphology, allozymes, microsatellites, cuticular hydrocarbons, and sexual behaviour. The two populations were similar to other African populations for morphological traits, but differed significantly from each other for all other characters. The countryside population resembled other African populations, whereas the urban population was consistently similar to European populations. Mating choice experiments showed incipient reproductive separation between the populations. In agreement with the hypothesis that D. melanogaster originated in Africa and spread to the rest of the world by invading human-modified habitats, we suggest that man-adapted fruit fly populations have returned 'back to Africa', and remained partially isolated from older native stocks.

Animals↗
PubMed2000

Fragmented forests, evolving flies: molecular variation in African populations of Drosophila teissieri.

Microsatellite variation from eight loci was studied in five populations of Drosophila teissieri, a fruit-fly found only in the rain forests of sub-Saharan Africa. Five noncontiguous rain forest sites (from Tanzania, Gabon and Ivory Coast) were sampled to measure the effects of historical forest fragmentation on population structure in an obligatory forest-dwelling species. The Ivory Coast and Gabon populations showed a wider range of alleles, different modal alleles and had a higher genetic diversity than the three East African populations. As could be expected, genetic differentiation (FST) was significantly correlated with physical distance, but the westernmost population (Ivory Coast) showed values that were intermediate between the central (Gabon) and Eastern (Tanzania) populations. A migration-drift equilibrium in a stable continuum of populations did not appear adequate to describe the observed distribution. It seems probable that the species has undergone abrupt changes involving isolation, merging and migration of populations, as a consequence of repeated waves of forest fragmentation and coalescence.

Africa↗
PubMed2000

Gene flow in a facultative apomictic poacea, the savanna grass Hyparrhenia diplandra.

The genetics of the poacea Hyparrhenia diplandra was studied in four natural populations from an ecological station in West Africa, where it makes up 80% of grasses from wet savanna and constitutes a dense continuum of randomly distributed individuals. DNA content and cytogenetical observations suggest it is an allotetraploid. Using two highly variable microsatellites (heterozygosity H = 0.615-0.616), we show that this species is an apomict with rare sexual reproduction events that account for approximately 0.5% of seeds pollinated in the wild. Hexaploid individuals were also produced, corroborating the observation of aberrant genotypes in the wild. The spatial extent of asexual clones in the field was low in comparison with the predominance of apomixis, thus indicating a low dispersal of seeds from their parent. Heterozygosity and departure from Hardy-Weinberg predictions were similar in the four populations, revealing a high apparent selfing rate s = 0.599 among sexually produced seeds. This is an overestimate since we could not distinguish true selfing from reciprocal outcrosses between neighboring individuals from the same apomictic clone. Gene flow by pollen could be substantial, possibly explaining the absence of isolation by distance in the studied area.

Africa, Western↗
PubMed1999

Selective sweep at the Drosophila melanogaster Suppressor of Hairless locus and its association with the In(2L)t inversion polymorphism.

The hitchhiking model of population genetics predicts that an allele favored by Darwinian selection can replace haplotypes from the same locus previously established at a neutral mutation-drift equilibrium. This process, known as "selective sweep," was studied by comparing molecular variation between the polymorphic In(2L)t inversion and the standard chromosome. Sequence variation was recorded at the Suppressor of Hairless (Su[H]) gene in an African population of Drosophila melanogaster. We found 47 nucleotide polymorphisms among 20 sequences of 1.2 kb. Neutrality tests were nonsignificant at the nucleotide level. However, these sites were strongly associated, because 290 out of 741 observed pairwise combinations between them were in significant linkage disequilibrium. We found only seven haplotypes, two occurring in the 9 In(2L)t chromosomes, and five in the 11 standard chromosomes, with no shared haplotype. Two haplotypes, one in each chromosome arrangement, made up two-thirds of the sample. This low haplotype diversity departed from neutrality in a haplotype test. This pattern supports a selective sweep hypothesis for the Su(H) chromosome region.

Animals↗
PubMed1999

Population structure among African and derived populations of Drosophila simulans: evidence for ancient subdivision and recent admixture.

Previous studies based on allozyme variation have found little evidence for genetic differentiation in Drosophila simulans. On the basis of DNA sequence variation at two nuclear loci in four African populations of D. simulans, we show that there is significant structure to D. simulans populations within Africa. Variation at one of the loci, vermilion, appears to be neutral and supports an eastern African origin for European and American populations. Samples from the West Indies, Europe, and North America had a nucleotide diversity lower than that of African populations at vermilion and show nonequilibrium haplotype distributions at both vermilion and G6pd, consistent with a hypothesis of recent bottleneck and possibly also admixture in the history of these populations. Directional selection, previously documented at G6pd, appears to have occurred within the coalescence time of the species, obscuring deep population history.

Africa↗
PubMed1999

Directional substitution and evolution of nucleotide content in the cytochrome oxidase II gene in earwigs (dermapteran insects).

The cytochrome oxidase subunit II (COII) gene was sequenced for six dermapteran species. The nucleotide composition of this gene is biased in most animals. While the CG content of other insect orders is low (mean, 27.6%; range, 19.5%-33.1%), species from the Forficula genus showed unusually high values (mean, 42.4%; range, 37.3%-44.1%), mostly due to high CG frequencies at third codon positions: the mean CG content at these positions was around 45% (range, 43.9%-46.9%) for Forficula, compared with only 13.3% for other insects. This effect was so strong that in one species, Forficula lesnei, there was no significant difference between the frequencies of the four bases. During evolution, this loss of bias has involved a significant increase in the synonymous substitution rate and an increase of transitions over transversions compared with other insects. A strong directionality of substitutions has favored T-->C and A-->G changes. This phenomenon was also observed between two conspecific populations of Forficula auricularia. A species from a closely related genus, Anechura bipunctata, was intermediate between Forficula and other insects for these parameters, while two remotely related dermapteran species, Labidura riparia and Euborellia moesta, were similar to other insects. These results suggest that the evolution of Forficula DNA content has been both rapid and recent.

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↗
PubMed1997

Selection and methionine accumulation in the fat body protein 2 gene (FBP2), a duplicate of the Drosophila alcohol dehydrogenase (ADH) gene.

The Drosophila fat body protein 2 gene (Fbp2) is an ancient duplication of the alcohol dehydrogenase gene (Adh) which encodes a protein that differs substantially from ADH in its methionine content. In D. melanogaster, there is one methionine in ADH, while there are 51 (20% of all amino acids) in FBP2. Methionine is involved in 46% of amino acid replacements when Fbp2 DNA sequences are compared between D. melanogaster and D. pseudoobscura. Methionine accumulation does not affect conserved residues of the ADH-ADHr-FBP2 multigene family. The multigene family has evolved by replacement of mildly hydrophobic amino acids by methionine with no apparent reversion. Its short-term evolution was compared between two Drosophila species, while its long-term evolution was compared between two genera belonging respectively to acalyptrate and calyptrate Diptera, Drosophila and Sarcophaga. The pattern of nucleotide substitution was consistent with an independent accumulation of methionines at the Fbp2 locus in each lineage. Under a steady-state model, the rate of methionine accumulation was constant in the lineage leading to Drosophila, and was twice as fast as that in the calyptrate lineage. Substitution rates were consistent with a slight positive selective advantage for each methionine change in about one-half of amino acid sites in Drosophila. This shows that selection can potentially account for a large proportion of amino acid replacements in the molecular evolution of proteins.

Alcohol Dehydrogenase↗
PubMed1996

Length variation of CAG/CAA trinucleotide repeats in natural populations of Drosophila melanogaster and its relation to the recombination rate.

Eleven genes distributed along the Drosophila melanogaster chromosome 2 and showing exonic tandem repeats of glutamine codons (CAG or CAA) were surveyed for length variation in a sample of four European and African populations. Only one gene was monomorphic. Eight genes were polymorphic in all populations, with a total number of alleles varying between five and 12 for 120 chromosomes. The average heterozygozity per locus and population was 0.41. Selective neutrality in length variation could not be rejected under the assumptions of the infinite allele model. Significant population subdivision was found though no geographical pattern emerged, all populations being equally different. Significant linkage disequilibrium was found in four out of seven cases where the genetic distance between loci was < 1 cM and was negligible when the distance was larger. There is evidence that these associations were established after the populations separated. An unexpected result was that variation at each locus was independent of the coefficient of exchange, although the latter ranged from zero to the relatively high value of 6.7%. This would indicate that background selection and selective hitchhiking, which are thought to affect levels of nucleotide substitution polymorphism, have no effect on trinucleotide repeat variation.

Alleles↗
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↗
PubMed1995

Molecular basis of polymorphism at the esterase-5B locus in Drosophila pseudoobscura.

Sequence variation was studied in a 2.2-kb region encompassing the esterase-5B locus in Drosophila pseudoobscura from two California populations. In these populations, two common electrophoretic classes and many less frequent variants occur, and it was formerly shown by KEITH (1983) that allele frequencies differed from random distribution under an infinite allele model. Nucleotide polymorphisms were determined in 16 sequences representing 14 electrophoretic classes. There was no significant sequence differentiation between populations, and both synonymous and nonsynonymous polymorphisms are distributed homogeneously along the sequence. The data show that the two major electrophoretic classes are heterogeneous at the amino acid level with no diagnostic amino acid(s) distinguishing them. At the nucleotide level, members of one major class are more similar to members of other electrophoretic classes than they are to each other. It appears that random combinations of the neutral amino acid polymorphisms and other undefined physical properties of the proteins generate the different electrophoretic classes and maintain considerable variation at Est-5B.

Amino Acid Sequence↗