Jean David | Orsay - Academia.edu (original) (raw)
Papers by Jean David
Active and inactive mariner elements from natural and laboratory populations of Drosophila simula... more Active and inactive mariner elements from natural and laboratory populations of Drosophila simulans were isolated and sequenced in order to assess their nucleotide variability and to compare them with previously isolated mariner elements from the sibling species Drosophila mauritiana and Drosophila sechelliu. The active elements of D. simulans are very similar among themselves (average 99.7% nucleotide identity), suggesting that the
Phenotypic plasticity of wing size and shape of Drosophila simulanswas analyzed across the entire... more Phenotypic plasticity of wing size and shape of Drosophila simulanswas analyzed across the entire range of viable developmental temperatures with Procrustes geometric morphometric method. In agreement with previous studies, size clearly decreases when temperature increases. Wing shape variation was decomposed into its allometric (24%) and nonallometric (76%) components, and both were shown to involve landmarks located throughout the entire wing
In five Indian localities, it was possible to collect D. melanogaster in two different types of h... more In five Indian localities, it was possible to collect D. melanogaster in two different types of habitats, namely ordinary domestic and alcohol rich ones. Tolerance and utilization capacity of several alcohols and of acetic acid were analyzed in a total of 10 local populations. Results on two other species (D. repleta and D. immigrans) were also available from one place. In each locality, the population from alcohol rich habitat proved to be more tolerant to all the investigated products and also to be more capable of using them as a resource. Alcohols toxicity increased with increasing carbon chain length and secondary alcohols were more toxic than primary ones. Utilization capacity of all products was relatively independent of their toxicity. Especially acetic acid, the toxicity of which was low and similar to that of ethanol, was always a fairly poor resource. From a genetic point of view, tolerance and utilization capacity appeared as two relatively independent traits. Natural selection, which is responsible for the genetic differentiation of local populations, is likely to act simultaneously on both traits.
Most animal species exhibit sexual size dimorphism (SSD). SSD is a trait difficult to quantify fo... more Most animal species exhibit sexual size dimorphism (SSD). SSD is a trait difficult to quantify for genetical purposes since it must be simultaneously measured on two kinds of individuals, and it is generally expressed either as a difference or as a ratio between sexes. Here we ask two related questions: What is the best way to describe SSD, and is it possible to conveniently demonstrate its genetic variability in a natural population? We show that a simple experimental design, the isofemale-line technique (full-sib families), may provide an estimate of genetic variability, using the coefficient of intraclass correlation. We consider two SSD indices, the female-male difference and the female/male ratio. For two size-related traits, wing and thorax length, we found that both SSD indices were normally distributed. Within each family, the variability of SSD was estimated by considering individual values in one sex (the female) with respect to the mean value in the other sex (the male). In a homogeneous sample of 30 lines of Drosophila melanogaster, both indices provided similar intraclass correlations, on average 0.21, significantly greater than zero but lower than those for the traits themselves: 0.50 and 0.36 for wing and thorax length respectively. Wing and thorax length were strongly positively correlated within each sex. SSD indices of wing and thorax length were also positively correlated, but to a lesser degree than for the traits themselves. For comparative evolutionary studies, the ratio between sexes seems a better index of SSD since it avoids scaling effects among populations or species, permits comparisons between different traits, and has an unambiguous biological significance. In the case of D. melanogaster grown at 25°C, the average female/male ratios are very similar for the wing (1.16) and the thorax (1.15), and indicate that, on average, these size traits are 15-16% longer in females.
Variation of size-related traits and of abdomen pigmentation was investigated in D. melanogaster ... more Variation of size-related traits and of abdomen pigmentation was investigated in D. melanogaster and D. simulans by transferring cultures from 258C to 178C at regular daily intervals. In most cases regular sigmoid curves were obtained, which were adjusted to a logistic model. For wing length, the thermosensitive period (TSP) extended during the last larval instar and most of the pupal stage, with an inflection point (IP) at 5.24 AE 0.24 days. Pigmentation of the last abdomen segments (5-7) in females exhibited a shorter and later TSP (IP at 7.21 AE 0.13 days) extending in the first day of adult life. In anterior segments (2-4) variations were less regular and our data suggest that TSP might extend during the first two days of adult life, at least in males. Significant differences among species were observed for size and pigmentation, but not for TSPs. #
When grown and kept at extreme constant temperatures, Zaprionus indianus males are sterile and do... more When grown and kept at extreme constant temperatures, Zaprionus indianus males are sterile and do not produce viable sperm. This phenomenon, already investigated in two Drosophila species, might be a general feature in drosophilids. On the high temperature side, sterility thresholds were similar in Z. indianus and D. melanogaster. On the low temperature side, Z. indianus was much more sensitive to cold. This might explain why Z. indianus is restricted to tropical and subtropical climates, while D. melanogaster also proliferates in temperate places. After returning to a middle, permissive temperature, males recovered fertility. The time to recover was always longer than in D. melanogaster, and the number of progeny much smaller in all cases. Such differences may be due to anatomical and functional divergences, and specially the longer sperm length in Z. indianus. r
Genetica, 1999
Drosophila kikkawai is known to be polymorphic for a single autosomal locus controlling abdomen p... more Drosophila kikkawai is known to be polymorphic for a single autosomal locus controlling abdomen pigmentation in females. Two strains homozygous at this locus (Abdomen pigmentation, Abp) were established from a polymorphic Indian population: one was homozygous (DD) for the dark allele, the other (LL) for the light allele. A Mendelian analysis of crosses at 25 degrees C confirmed the occurrence of a major locus, with dominance of the D allele. Phenotypic variation of pigmentation according to growth temperature was then analyzed in DD and LL male and female flies, and in reciprocal F1. A slight difference was found between reciprocal F1--females from a dark mother were darker but not at all temperatures. In females, the D allele exhibited an antero-posterior gradient of increasing expression from segment 2-7, with dominance over L and an increased expression at low temperatures. In males, abdomen pigmentation was uniformly light in segments 2-5, the D allele being repressed by the sex...
Genetica, 2000
We analyzed natural populations of Zaprionus indianus in 10 Indian localities along a south-north... more We analyzed natural populations of Zaprionus indianus in 10 Indian localities along a south-north transect (latitude: 10-31 degrees 3 N). Size traits (body weight, wing length and thorax length) as well as a reproductive trait (ovariole number) followed a pattern of clinal variation, that is, trait value increased with latitude. Wing/thorax ratio, which is inversely related to wing loading, also had a positive, but non-significant correlation with latitude. By contrast, bristle numbers (sternopleural and abdominal) exhibited a non-significant but negative correlation with latitude. Sex dimorphism, estimated as the female/male ratio, was very low in Z. indianus, contrasting with results already published in other species. Genetic variations among populations were also analyzed according to other geographic parameters (altitude and longitude) and to climatic conditions from each locality. A significant effect of altitude was found for size traits. For abdominal bristles, a multiple re...
Genetica, 2002
Numerous different criteria may be used for analysing species thermal adaptation. We compared mal... more Numerous different criteria may be used for analysing species thermal adaptation. We compared male sterility thresholds in the two most investigated cosmopolitan siblings, D. melanogaster and D. simulans. A survey of various populations from Europe and North Africa evidenced consistent differences between the two species, and a detailed analysis was made on flies from Marrakech. Sharp sterility thresholds were observed in both species but at different temperatures: D. simulans appeared more tolerant to cold than its sibling (difference 1 degrees C) but more sensitive to heat (difference 1.5 degrees C). When transferred to an optimum temperature of 21 degrees C, D. simulans males, sterilized by a low temperature, recovered more rapidly than males of D. melanogaster; the reverse was true on the high temperature side. The analysis of progeny number also revealed the better tolerance of D. simulans males to cold but a lesser tolerance to heat. From these observations, we might expect th...
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](Médecine sciences : M/S, 2007
In previous studies, the relationship between developmental temperature and phenotypic or genetic... more In previous studies, the relationship between developmental temperature and phenotypic or genetic variability has been mainly investigated using different constant temperatures. Natural conditions, however, are characterized by daily thermal cycles, sometimes resulting in a periodic daily stress. Using the isofemale line technique, we examined the effects of daily cycles on body size in two French populations of Drosophila melanogaster. We
Question: Daily thermal cycles are the rule under natural conditions, and may be very stressful. ... more Question: Daily thermal cycles are the rule under natural conditions, and may be very stressful. Are there specific effects of such cycling regimes upon a phenotypic bilateral trait, sternopleural bristle number?
MOLECULAR PHYLOGENETICS AND EVOLUTION, 2008
A molecular phylogeny for the drosophilid genus Zaprionus was inferred using a mitochondrial (CO-... more A molecular phylogeny for the drosophilid genus Zaprionus was inferred using a mitochondrial (CO-II) and a nuclear (Amyrel) gene using 22 available species. The combined molecular tree does not support the current classification, dubbed phylogenetic, based entirely upon a morphocline of forefemoral ornamentation. For species for which DNA was not available, phylogenetic positioning was only assigned using morphological characters. In order to avoid conflict between DNA and morphology in the combined analyses (supermatrix method), we developed a new method in which few morphological characters were sampled according to an a priori homoplasy assessment on the consensus molecular tree. At each internal node of the tree, a number of synapomorphies was determined, and species with no molecular sequences were grafted thereon. Analogously to tree vocabulary, we called our method 'morphological grafting'. New species groups and complexes were then defined in the light of our findings. Further, divergence times were estimated under a relaxed molecular clock, and historical biogeography was reconstructed under a maximum likelihood model. Zaprionus appears to be of recent origin in the Oriental region during the Late Miocene ($10 MYA), and colonization of Africa started shortly after ($7 MYA) via the maritime route of the Indian Ocean Islands. Most of the morphological and ecological diversification took place, later, in Western Africa during the Quaternary cyclic climatic changes. Furthermore, some species became recent invaders, with one, Zaprionus indianus, has successfully invaded South and North America during the last decade.
Journal of Zoological Systematics and Evolutionary Research, 2003
Five morphometrical traits (wing and thoraxlength, ovariole number, and thoracic and female abdom... more Five morphometrical traits (wing and thoraxlength, ovariole number, and thoracic and female abdomen pigmentation) were investigated in laboratory stocks of 20 species belonging to the Drosophila obscura group (subgenus Sophophora). These species originated from four biogeographical regions and represent all five of the presently recognized, taxonomic subgroups. Size-related traits (wing and thorax length) were highly variable across species, and interspecific
Mitochondrial DNA
Zaprionus indianus is an Afrotropical drosophilid species that has expanded its geographical rang... more Zaprionus indianus is an Afrotropical drosophilid species that has expanded its geographical range in the Palearctic region and the Americas during the second half of the last century. It has invaded Egypt within the past two decades from East Africa or Asia and became a dominant species in the drosophilid fauna therein, but the exact date of introduction and source of the propagule remain unknown. Here, we investigate the genetic structure of eight geographical populations within and around the Nile Delta using mitochondrial DNA sequences of the cox2 gene and chromosomal inversion polymorphism. A very low level of genetic variability was detected for both markers, mainly attributed to the introduction bottleneck. Nonetheless, both indicate a significant population structure, with a southeastern-northwestern cline. Demographic history analysis suggested northwestern populations to be younger (expanding in ca. 1992) than southeastern ones (expanding in ca. 1985). The In(II)A polymorp...
Trends in Genetics, 1988
Drosophila melanogaster natural populations show considerable show considerable genetic variation... more Drosophila melanogaster natural populations show considerable show considerable genetic variation in different geographicc regions. The nature of this variation.
Proceedings of the Royal Society B: Biological Sciences, 1990
The occurrence of active, or autonomous, mariner elements was investigated by crossing white-peac... more The occurrence of active, or autonomous, mariner elements was investigated by crossing white-peach mutant Drosophila simulans females with wild-type males from various geographic origins. From a total of 194 experimental crosses only 17 failed to produce progeny with eye mosaicism (MOS, i.e. pigmented spots in otherwise white-peach eyes). Therefore, active mariner elements inducing somatic excision of the copy inserted at the white locus are abundant in all populations sampled. In the experimental crosses the frequency of mosaic offspring ranged from 0 to 100%, showing that the phenotypic expression is highly variable. The MOS phenotype, measured by the number of spots on the eyes, is quite variable within the progeny of single crosses. Although a difference was observed in the average MOS score (percentage of mosaic flies) between northern and southern populations of France, there was no indication of long range variation between geographic populations. Neither was there a systematic difference between recently collected populations and samples kept several years as isofemale lines.
Proceedings of the National Academy of Sciences, 1989
Alcohol dehydrogenase (Adh) (alcohol:NAD' oxidoreductase, EC 1.1.1.1) gene frequencies and ethano... more Alcohol dehydrogenase (Adh) (alcohol:NAD' oxidoreductase, EC 1.1.1.1) gene frequencies and ethanol tolerance in Drosophila melanogaster are known to exhibit long-range latitudinal variations on different continents; this has led to the argument that the clines are adaptive. Accordingly, tropical populations are characterized both by a low frequency of Adh-F and by a low ethanol tolerance. In the urban area of Brazzaville (Congo) under an equatorial African climate, an original genetic structure of local populations has been found: Adh-F frequency varies from 3% to 90% when countryside and brewery populations are compared. This variation is accompanied by an increase of ethanol tolerance (from 6% to 13% alcohol). Such differences, which have remained stable for the past 3 years, were observed between collection sites <1 km apart. Two other enzyme loci exhibited a correlated variation with Adh-F-i.e., an increase of the S allele of glycerol-3-phosphate dehydrogenase (NAD+)
Active and inactive mariner elements from natural and laboratory populations of Drosophila simula... more Active and inactive mariner elements from natural and laboratory populations of Drosophila simulans were isolated and sequenced in order to assess their nucleotide variability and to compare them with previously isolated mariner elements from the sibling species Drosophila mauritiana and Drosophila sechelliu. The active elements of D. simulans are very similar among themselves (average 99.7% nucleotide identity), suggesting that the
Phenotypic plasticity of wing size and shape of Drosophila simulanswas analyzed across the entire... more Phenotypic plasticity of wing size and shape of Drosophila simulanswas analyzed across the entire range of viable developmental temperatures with Procrustes geometric morphometric method. In agreement with previous studies, size clearly decreases when temperature increases. Wing shape variation was decomposed into its allometric (24%) and nonallometric (76%) components, and both were shown to involve landmarks located throughout the entire wing
In five Indian localities, it was possible to collect D. melanogaster in two different types of h... more In five Indian localities, it was possible to collect D. melanogaster in two different types of habitats, namely ordinary domestic and alcohol rich ones. Tolerance and utilization capacity of several alcohols and of acetic acid were analyzed in a total of 10 local populations. Results on two other species (D. repleta and D. immigrans) were also available from one place. In each locality, the population from alcohol rich habitat proved to be more tolerant to all the investigated products and also to be more capable of using them as a resource. Alcohols toxicity increased with increasing carbon chain length and secondary alcohols were more toxic than primary ones. Utilization capacity of all products was relatively independent of their toxicity. Especially acetic acid, the toxicity of which was low and similar to that of ethanol, was always a fairly poor resource. From a genetic point of view, tolerance and utilization capacity appeared as two relatively independent traits. Natural selection, which is responsible for the genetic differentiation of local populations, is likely to act simultaneously on both traits.
Most animal species exhibit sexual size dimorphism (SSD). SSD is a trait difficult to quantify fo... more Most animal species exhibit sexual size dimorphism (SSD). SSD is a trait difficult to quantify for genetical purposes since it must be simultaneously measured on two kinds of individuals, and it is generally expressed either as a difference or as a ratio between sexes. Here we ask two related questions: What is the best way to describe SSD, and is it possible to conveniently demonstrate its genetic variability in a natural population? We show that a simple experimental design, the isofemale-line technique (full-sib families), may provide an estimate of genetic variability, using the coefficient of intraclass correlation. We consider two SSD indices, the female-male difference and the female/male ratio. For two size-related traits, wing and thorax length, we found that both SSD indices were normally distributed. Within each family, the variability of SSD was estimated by considering individual values in one sex (the female) with respect to the mean value in the other sex (the male). In a homogeneous sample of 30 lines of Drosophila melanogaster, both indices provided similar intraclass correlations, on average 0.21, significantly greater than zero but lower than those for the traits themselves: 0.50 and 0.36 for wing and thorax length respectively. Wing and thorax length were strongly positively correlated within each sex. SSD indices of wing and thorax length were also positively correlated, but to a lesser degree than for the traits themselves. For comparative evolutionary studies, the ratio between sexes seems a better index of SSD since it avoids scaling effects among populations or species, permits comparisons between different traits, and has an unambiguous biological significance. In the case of D. melanogaster grown at 25°C, the average female/male ratios are very similar for the wing (1.16) and the thorax (1.15), and indicate that, on average, these size traits are 15-16% longer in females.
Variation of size-related traits and of abdomen pigmentation was investigated in D. melanogaster ... more Variation of size-related traits and of abdomen pigmentation was investigated in D. melanogaster and D. simulans by transferring cultures from 258C to 178C at regular daily intervals. In most cases regular sigmoid curves were obtained, which were adjusted to a logistic model. For wing length, the thermosensitive period (TSP) extended during the last larval instar and most of the pupal stage, with an inflection point (IP) at 5.24 AE 0.24 days. Pigmentation of the last abdomen segments (5-7) in females exhibited a shorter and later TSP (IP at 7.21 AE 0.13 days) extending in the first day of adult life. In anterior segments (2-4) variations were less regular and our data suggest that TSP might extend during the first two days of adult life, at least in males. Significant differences among species were observed for size and pigmentation, but not for TSPs. #
When grown and kept at extreme constant temperatures, Zaprionus indianus males are sterile and do... more When grown and kept at extreme constant temperatures, Zaprionus indianus males are sterile and do not produce viable sperm. This phenomenon, already investigated in two Drosophila species, might be a general feature in drosophilids. On the high temperature side, sterility thresholds were similar in Z. indianus and D. melanogaster. On the low temperature side, Z. indianus was much more sensitive to cold. This might explain why Z. indianus is restricted to tropical and subtropical climates, while D. melanogaster also proliferates in temperate places. After returning to a middle, permissive temperature, males recovered fertility. The time to recover was always longer than in D. melanogaster, and the number of progeny much smaller in all cases. Such differences may be due to anatomical and functional divergences, and specially the longer sperm length in Z. indianus. r
Genetica, 1999
Drosophila kikkawai is known to be polymorphic for a single autosomal locus controlling abdomen p... more Drosophila kikkawai is known to be polymorphic for a single autosomal locus controlling abdomen pigmentation in females. Two strains homozygous at this locus (Abdomen pigmentation, Abp) were established from a polymorphic Indian population: one was homozygous (DD) for the dark allele, the other (LL) for the light allele. A Mendelian analysis of crosses at 25 degrees C confirmed the occurrence of a major locus, with dominance of the D allele. Phenotypic variation of pigmentation according to growth temperature was then analyzed in DD and LL male and female flies, and in reciprocal F1. A slight difference was found between reciprocal F1--females from a dark mother were darker but not at all temperatures. In females, the D allele exhibited an antero-posterior gradient of increasing expression from segment 2-7, with dominance over L and an increased expression at low temperatures. In males, abdomen pigmentation was uniformly light in segments 2-5, the D allele being repressed by the sex...
Genetica, 2000
We analyzed natural populations of Zaprionus indianus in 10 Indian localities along a south-north... more We analyzed natural populations of Zaprionus indianus in 10 Indian localities along a south-north transect (latitude: 10-31 degrees 3 N). Size traits (body weight, wing length and thorax length) as well as a reproductive trait (ovariole number) followed a pattern of clinal variation, that is, trait value increased with latitude. Wing/thorax ratio, which is inversely related to wing loading, also had a positive, but non-significant correlation with latitude. By contrast, bristle numbers (sternopleural and abdominal) exhibited a non-significant but negative correlation with latitude. Sex dimorphism, estimated as the female/male ratio, was very low in Z. indianus, contrasting with results already published in other species. Genetic variations among populations were also analyzed according to other geographic parameters (altitude and longitude) and to climatic conditions from each locality. A significant effect of altitude was found for size traits. For abdominal bristles, a multiple re...
Genetica, 2002
Numerous different criteria may be used for analysing species thermal adaptation. We compared mal... more Numerous different criteria may be used for analysing species thermal adaptation. We compared male sterility thresholds in the two most investigated cosmopolitan siblings, D. melanogaster and D. simulans. A survey of various populations from Europe and North Africa evidenced consistent differences between the two species, and a detailed analysis was made on flies from Marrakech. Sharp sterility thresholds were observed in both species but at different temperatures: D. simulans appeared more tolerant to cold than its sibling (difference 1 degrees C) but more sensitive to heat (difference 1.5 degrees C). When transferred to an optimum temperature of 21 degrees C, D. simulans males, sterilized by a low temperature, recovered more rapidly than males of D. melanogaster; the reverse was true on the high temperature side. The analysis of progeny number also revealed the better tolerance of D. simulans males to cold but a lesser tolerance to heat. From these observations, we might expect th...
Médecine sciences : M/S, 2007
In previous studies, the relationship between developmental temperature and phenotypic or genetic... more In previous studies, the relationship between developmental temperature and phenotypic or genetic variability has been mainly investigated using different constant temperatures. Natural conditions, however, are characterized by daily thermal cycles, sometimes resulting in a periodic daily stress. Using the isofemale line technique, we examined the effects of daily cycles on body size in two French populations of Drosophila melanogaster. We
Question: Daily thermal cycles are the rule under natural conditions, and may be very stressful. ... more Question: Daily thermal cycles are the rule under natural conditions, and may be very stressful. Are there specific effects of such cycling regimes upon a phenotypic bilateral trait, sternopleural bristle number?
MOLECULAR PHYLOGENETICS AND EVOLUTION, 2008
A molecular phylogeny for the drosophilid genus Zaprionus was inferred using a mitochondrial (CO-... more A molecular phylogeny for the drosophilid genus Zaprionus was inferred using a mitochondrial (CO-II) and a nuclear (Amyrel) gene using 22 available species. The combined molecular tree does not support the current classification, dubbed phylogenetic, based entirely upon a morphocline of forefemoral ornamentation. For species for which DNA was not available, phylogenetic positioning was only assigned using morphological characters. In order to avoid conflict between DNA and morphology in the combined analyses (supermatrix method), we developed a new method in which few morphological characters were sampled according to an a priori homoplasy assessment on the consensus molecular tree. At each internal node of the tree, a number of synapomorphies was determined, and species with no molecular sequences were grafted thereon. Analogously to tree vocabulary, we called our method 'morphological grafting'. New species groups and complexes were then defined in the light of our findings. Further, divergence times were estimated under a relaxed molecular clock, and historical biogeography was reconstructed under a maximum likelihood model. Zaprionus appears to be of recent origin in the Oriental region during the Late Miocene ($10 MYA), and colonization of Africa started shortly after ($7 MYA) via the maritime route of the Indian Ocean Islands. Most of the morphological and ecological diversification took place, later, in Western Africa during the Quaternary cyclic climatic changes. Furthermore, some species became recent invaders, with one, Zaprionus indianus, has successfully invaded South and North America during the last decade.
Journal of Zoological Systematics and Evolutionary Research, 2003
Five morphometrical traits (wing and thoraxlength, ovariole number, and thoracic and female abdom... more Five morphometrical traits (wing and thoraxlength, ovariole number, and thoracic and female abdomen pigmentation) were investigated in laboratory stocks of 20 species belonging to the Drosophila obscura group (subgenus Sophophora). These species originated from four biogeographical regions and represent all five of the presently recognized, taxonomic subgroups. Size-related traits (wing and thorax length) were highly variable across species, and interspecific
Mitochondrial DNA
Zaprionus indianus is an Afrotropical drosophilid species that has expanded its geographical rang... more Zaprionus indianus is an Afrotropical drosophilid species that has expanded its geographical range in the Palearctic region and the Americas during the second half of the last century. It has invaded Egypt within the past two decades from East Africa or Asia and became a dominant species in the drosophilid fauna therein, but the exact date of introduction and source of the propagule remain unknown. Here, we investigate the genetic structure of eight geographical populations within and around the Nile Delta using mitochondrial DNA sequences of the cox2 gene and chromosomal inversion polymorphism. A very low level of genetic variability was detected for both markers, mainly attributed to the introduction bottleneck. Nonetheless, both indicate a significant population structure, with a southeastern-northwestern cline. Demographic history analysis suggested northwestern populations to be younger (expanding in ca. 1992) than southeastern ones (expanding in ca. 1985). The In(II)A polymorp...
Trends in Genetics, 1988
Drosophila melanogaster natural populations show considerable show considerable genetic variation... more Drosophila melanogaster natural populations show considerable show considerable genetic variation in different geographicc regions. The nature of this variation.
Proceedings of the Royal Society B: Biological Sciences, 1990
The occurrence of active, or autonomous, mariner elements was investigated by crossing white-peac... more The occurrence of active, or autonomous, mariner elements was investigated by crossing white-peach mutant Drosophila simulans females with wild-type males from various geographic origins. From a total of 194 experimental crosses only 17 failed to produce progeny with eye mosaicism (MOS, i.e. pigmented spots in otherwise white-peach eyes). Therefore, active mariner elements inducing somatic excision of the copy inserted at the white locus are abundant in all populations sampled. In the experimental crosses the frequency of mosaic offspring ranged from 0 to 100%, showing that the phenotypic expression is highly variable. The MOS phenotype, measured by the number of spots on the eyes, is quite variable within the progeny of single crosses. Although a difference was observed in the average MOS score (percentage of mosaic flies) between northern and southern populations of France, there was no indication of long range variation between geographic populations. Neither was there a systematic difference between recently collected populations and samples kept several years as isofemale lines.
Proceedings of the National Academy of Sciences, 1989
Alcohol dehydrogenase (Adh) (alcohol:NAD' oxidoreductase, EC 1.1.1.1) gene frequencies and ethano... more Alcohol dehydrogenase (Adh) (alcohol:NAD' oxidoreductase, EC 1.1.1.1) gene frequencies and ethanol tolerance in Drosophila melanogaster are known to exhibit long-range latitudinal variations on different continents; this has led to the argument that the clines are adaptive. Accordingly, tropical populations are characterized both by a low frequency of Adh-F and by a low ethanol tolerance. In the urban area of Brazzaville (Congo) under an equatorial African climate, an original genetic structure of local populations has been found: Adh-F frequency varies from 3% to 90% when countryside and brewery populations are compared. This variation is accompanied by an increase of ethanol tolerance (from 6% to 13% alcohol). Such differences, which have remained stable for the past 3 years, were observed between collection sites <1 km apart. Two other enzyme loci exhibited a correlated variation with Adh-F-i.e., an increase of the S allele of glycerol-3-phosphate dehydrogenase (NAD+)