Evolution of natural populations in the Drosophila melanogaster sigma virus system I. Languedoc (Southern France)

In natural populations of Drosophila melanogaster, sigma virus is usually present in a minority of individuals. The virus is transmitted transovarially but is not contagious from fly to fly. Two viral Types (I and II) are found in populations. One of them (Type II) is better adapted to an allele for resistance to the virus, present as a polymorphism in fly populations. Previous observations have led to the hypothesis that a viral Type II originating in central France might be invading populations. The study of Languedoc populations was undertaken to examine this hypothesis. Two striking phenomena were observed. The strong increase in Type II clones frequency (from 0.53 to 0.91) confirmed that there was invasion in this region. The frequency of infected flies also increased dramatically, at levels never observed elsewhere yet, which indicates that Languedoc should present some unusual characteristics. The epidemiological consequences of such a burst, in the case of a pathogenic virus would have to be taken into consideration. Significant changes in other viral characteristics, from 1983 to 1987, in Languedoc populations have also been documented.     

Evolution of natural populations in the Drosophila melanogaster sigma system II. Northern and Central France

A survey of French natural populations of Drosophila melanogaster has been systematically performed, concerning their status of infection by the sigma virus and the characteristics of viral clones. These investigations, which were not as extensive as those performed in the Languedoc region (Fleuriet et al., 1990) nevertheless give a good representation of the evolution of this system because of the long period involved (almost 20 years). Some trends were observed in all French populations such as (1) a decrease in the high efficiency of transmission by males (which is an important parameter for the viral invading ability); (2) high frequency of a best adapted viral Type. These high frequencies might be due to a recent invasion which is expected to spread to other European populations. However, the frequency of infected flies remained low in northern and central France, unlike in Languedoc. The complexity of this, apparently simple, system of two well-known coevolving organisms should once again be stressed. It is impossible with the known parameters to arrive at a general interpretation of observations made in Languedoc and the rest of France. These data may also throw some light on the structure of French wild populations of D. melanogaster which appear to be subdivided into local populations between which gene flow might be low.     

Influence of the population size on the frequency of flies infected by sigma virus in populations of Drosophila melanogaster

The frequency of flies infected by the hereditary, noncontagious rhabdovirus sigma has been followed in experimental populations bred from very few adults. The average frequency of infected flies decreased. These results suggest that overwinterning might be one of the factors responsible for the discrepancy between wild and laboratory populations; in France, previous experiments have shown that about 20% of the individuals in natural populations are infected by the sigma virus, while in laboratory populations set up from samples collected in the wild, virus is detectable in almost the whole population. The effect of winter on the frequency of infected flies might be twofold: first, it has been shown previously that infected flies seem to be more sensitive to overwintering than uninfected flies; second, the reduction of population size might reduce the ability of the population to make up for the decrease during the summer generations.     

Evolution of the Drosophila melanogaster-sigma virus system in a natural population from Tübingen

Summary In natural populations of D. melanogaster, usually, a minority of individuals are infected by a Rhabdovirus called sigma. This virus is not contagious but is vertically transmitted through the gametes. In D. melanogaster, a polymorphism for two alleles (O, permissive and P, restrictive) of a gene responsible for resistance to the virus is regularly observed in the wild. On the virus side two types are found, which differ in their sensitivity to the P allele: Type I is very sensitive, and Type II more resistant. Previous findings had led to the hypothesis that an invasion of Type II clones, starting from central France, might be spreading over European populations. This replacement of viral Type I by viral Type II in natural populations could be observed in Languedoc (southern France), where it led to a dramatic increase in the frequency of infected flies. The invasion hypothesis is confirmed by the data from samples collected at Tübingen, where the frequency of Type II clones increased from 0.27 to 0.93 over a 6-year period (1985–1991). However, over the same period, no increase in the frequency of infected flies was observed. The evolution of other viral characteristics is discussed.     

Pseudorascora parva (Teleostei, Cyprinidae), an invasive species, a new vector for the maintenance and dissemination of anguillicolosis in France?]

Pseudorasbora parva (Pisces, Cyprinidae) is an invasive species from eastern Asia. Known in France since 1983, it has only been observed since 1993 in the Rh?ne delta where large populations occur. 203 specimens of that fish species have been examined for L3-larvae of Anguillicola crassus. 35% of the fish were found to be infected.     

Les industries lithiques de trois occupations de plein air et leur place dans le contexte Moustérien du Languedoc méditerranéen : Le Cadénas (Bédarieux, Hérault), Les Cours (Plaissan, Hérault) et Le Serre du Coucouyon (La Capelle et Masmolène, Gard)

Mediterranean Languedoc is a vast region in Southern France where Mousterian occupations, mainly concentrated in the eastern sector, are numerous. The three lithic series of the open-air sites presented in this article are yet unpublished. The techno-economical approach used to analyse these three stone assemblages has brought to light variability in Neandertal behaviour concerning raw material collection and economy in sectors more or less rich in siliceous resources, and also concerning the different production systems used and their goals. Comparisons made with other Mousterian stone assemblages in Languedoc seem to indicate ties with certain sites from the Rhône Valley.     

High genetic diversity in French invasive populations of common ragweed, Ambrosia artemisiifolia, as a result of multiple sources of introduction

Ambrosia artemisiifolia is an aggressive North American annual weed, found particularly in sunflower and corn fields. Besides its economic impact on crop yield, it represents a major health problem because of its strongly allergenic pollen. Ragweed was imported inadvertently to Europe in the 18th century and has become invasive in several countries, notably in the Rhône Valley of France. It has recently expanded in both the Provence-Alpes-Côte-d’Azur and Bourgogne regions. As first steps towards understanding the causes and mechanisms of ragweed invasion, genetic variability of French and North American populations was analysed using microsatellites. Overall genetic variability was similar in North America and in the Rhône-Alpes region, but within-population levels of genetic variability were surprisingly lower in native than in invasive French populations. French populations also exhibited lower among-population differentiation. A significant pattern of isolation by distance was detected among North American populations but not among French populations. Assignment tests and distribution of rare alleles did not point to a single origin for all French populations, nor for all individuals within populations and private alleles from different North American populations were found in the same French populations. Indeed, within all French populations, individual plants were roughly equally assigned to the different North American populations. Altogether, these results suggest that the French invasive populations include plants from a mixture of sources. Reduced diversity in populations distant from the original area of introduction indicated that ragweed range expansion probably occurred through sequential bottlenecks from the original populations, and not from subsequent new introductions.     

Perpetuation of the hereditary sigma virus in populations of its host,Drosophila melanogaster. Geographical analysis of correlated polymorphisms

In natural populations of Drosophila melanogaster, about 10% of the individuals are infected by a virus, sigma, which is not contagious but is transmitted through gametes. These populations are also regularly polymorphic for two alleles, O and P, of a locus ref(2)P; the P allele interferes with the multiplication of the virus. Two viral Types are found in populations, differing in their sensitivity to the P allele. Many samples of flies have been collected in different parts of the world and for each of them, the P frequency has been measured and the viral Type determined. A clear geographical differentiation appears for both these traits; they present a mutual adaptation leading to relatively low frequencies of infected flies in natural populations. Most viruses are only known from highly selected laboratory strains. The observations reported in this paper give evidence of the self restraint exercised by the sigma virus at the population level; they indicate that the characteristics of wild viral clones are likely to differ from those of laboratory strains and also from one population to another.The sigma virus is comparable to other genetical elements, that can be more efficiently transmitted than a mendelian allele, such as transposable elements. The discussion illustrates some of the factors involved in the perpetuation of such elements in a population and points out the difficulty of taking them all into consideration in theoretical models dealing with their perpetuation.     

Effect of Climate-Related Change in Vegetation on Leaf Litter Consumption and Energy Storage by Gammarus pulex from Continental or Mediterranean Populations

As a consequence of global warming, it is important to characterise the potential changes occurring for some functional processes through the intra-specific study of key species. Changes in species distribution, particularly when key or engineer species are affected, should contribute to global changes in ecosystem functioning. In this study, we examined the potential consequences induced by global warming on ecosystem functioning in term of organic matter recycling. We compared consumption of leaf litter by some shredder populations (Gammarus pulex) between five tree species inhabiting continental (i.e., the northern region of the Rhône River Valley) and/or Mediterranean (i.e., the southern region of the Rhône River Valley) conditions. To consider any potential adaptation of the gammarid population to vegetation in the same climate conditions, three populations of the key shredder Gammarus pulex from the northern region and three from the southern region of the Rhône River Valley were used. We experimentally compared the effects of the geographical origin of both the gammarid populations and the leaf litter species on the shredding activity and the physiological state of animals (through body triglyceride content). This study demonstrated that leaf toughness is more important than geographical origin for determining shredder leaf litter consumption. The overall consumption rate of the gammarid populations from the southern region of Rhône Valley was much higher than that of the populations from the northern region, but no clear differences between the origins of the leaf litter (i.e., continental vs. Mediterranean) were observed. The northwards shift of G. pulex populations adapted to warmer conditions might significantly modify organic matter recycling in continental streams. As gammarid populations can demonstrate local adaptations to certain leaf species as a trophic resource, changes in riparian vegetation associated with climate change might locally affect the leaf litter degradation process by this shredder.     

Polymorphism of the Hereditary Sigma Virus in Natural Populations of DROSOPHILA MELANOGASTER

Previous studies have shown that, in natural French populations of Drosophila melanogaster, 10 to 20% of the flies are infected by the noncontagious, hereditary rhabdovirus sigma responsible for CO₂ sensitivity. These populations are also polymorphic for two alleles [ref(2)P^o and ref(2)P^p] of a gene for resistance to the sigma virus. Evidence is given here that two viral genetic types, differing in their response to the ref(2)P^p allele, are present in these populations of flies; the most common type is only slightly sensitive to the ref(2)P^p allele.     

Phylogeographical variation of chloroplast DNA in holm oak (Quercus ilex L.)

Variation in the lengths of restriction fragments (RFLPs) of the whole chloroplast DNA molecule was studied in 174 populations of Quercus ilex L. sampled over the entire distribution of this evergreen and mainly Mediterranean oak species. By using five endonucleases, 323 distinct fragments were obtained. From the 29 and 17 cpDNA changes identified as site and length mutations, respectively, 25 distinct chlorotypes were distinguished, mapped and treated cladistically with a parsimony analysis, using as an outgroup Q. alnifolia Poech, a closely related evergreen oak species endemic to Cyprus where Q. ilex does not grow. The predominant role of Q. ilex as maternal parent in hybridization with other species was reflected by the occurrence of a single very specific lineage of related chlorotypes, the most ancestral and recent ones being located in the southeastern and in the northwestern parts of the species’ geographical distribution, respectively. The lineage was constituted of two clusters of chlorotypes observed in the ‘ilex’ morphotyped populations of the Balkan and Italian Peninsulas (including the contiguous French Riviera), respectively. A third cluster was divided into two subclusters identified in the ‘rotundifolia’ morphotyped populations of North Africa, and of Iberia and the adjacent French regions, respectively. Postglacial colonization probably started from three distinct southerly refugia located in each of the three European peninsulas, and a contact area between the Italian and the Iberian migration routes was identified in the Rhône valley (France). Chlorotypes identical or related to those of the Iberian cluster were identified in the populations from Catalonia and the French Languedoc region, which showed intermediate morphotypes, and in the French Atlantic populations which possessed the ‘ilex’ morphotype, suggesting the occurrence of adaptive morphological changes in the northern part of the species’ distribution.     

Geographic distribution of surnames and genetic structure: the county of Ardeche at the beginning of the twentieth century

The analysis of the geographical distribution of surnames (whose transmission in the European societies is similar to that of the Y chromosome) allows to study in an exhaustive way the spatial and temporal human population structure and the influence of environmental variations on this structure. The genetic structure of the Ardèche county was analysed through a study of the surname characteristics (diversity, frequency, geographical dispersion, etc.) of individuals born between 1891 and 1915. The estimation of the intra-community average consanguinity and the inter-district genetic relationships reveals a clear differentiation between populations of the mountainous part (geographically isolated, highly inbred) and those of the Rh?ne valley (less isolated, weakly inbred). As predicted by the isolation by distance model, inter-population coefficients of kinship decreases as distance increases, confirming the presence of a spatial structure, characterized by neighborhood exchange and resulting from former migratory flow.     

The use of molecular markers for germplasm management in a French olive collection

With more than 100 accessions, the CBNMP olive collection includes a major part of the French germplasm. We used molecular markers to characterise all accessions and to study genetic relationships between cultivars. Firstly, 497 olive trees were genotyped using 32 RAPD markers. We identified 114 RAPD profiles and detected several cases of mislabelling, synonymy and homonymy. Secondly, for each RAPD profile, one tree was analysed using mtDNA RFLPs to determine the cytoplasmic lineage of each cultivar and using five nuclear SSR loci. French germplasm displayed ME1, MOM and MCK mitotypes with ME1 prevailing (84%). Based on SSR markers, we revealed a slight differentiation between French cultivars growing in the West and the East side of the Rh?ne Valley. This study allowed us to construct a molecular data-base for the reference collection and to analyse genetic diversity for further prospecting, and for introducing new olive accessions.     

Clinal and seasonal variations in initial retention capacity of virginDrosophila melanogaster females as a strategy for fitness

Summary The study of the first laboratory generation of isofemale lines ofDrosophila melanogaster, founded by wild flies collected in populations of various geographical origins, has shown that virgin females differ in their capacity to control egg deposition. This capacity to delay the ovulation process when no sexual partner is available is genetically determined. The present study shows that the frequency distribution of the various phenotypes varies progressively along a latitudinal cline from Afrotropical to European regions, or from neotropical to nearctic areas, while a few oriental populations appear off the cline. This variation in initial retention capacity, added to a similar variation in number of ovarioles conditioning a potential increase in fecundity for mated flies, induces variation in reactivity to insemination which may be an adaptation to a variable environment. Moreover, similar study of F1 virgin females from isofemale lines founded by wild flies collected in Spring, Summer and Autumn in two French populations over ten successive years revealed that seasonal genetic variations occur in this capacity to postpone egg-laying in case of non-insemination. The frequency of the different phenotypes follows cyclical seasonal variations. Long retention phenotypes are more frequent in Spring and Autumn samples, whereas short retention phenotypes, closer to the ancestral African type, are more common in Summer generations. This balancing selection temporarily modifies the genetic equilibrium of the population, enhancing its competitive ability. Temperature appears to be the primordial selective factor both in geographical and in seasonal variations.     

Comparison of bacterial indicators and sampling programs for drinking water systems

A total of 48 French villages were selected for a survey of water quality from February 1983 to June 1984 as part of an epidemiological study conducted in the rural area of the Rh?ne-Alpes region. Water samples were collected and analyzed on a weekly basis in each village. Bacteriological analysis of each water sample included enumeration of standard plate count bacteria, total and thermotolerant coliforms, and fecal streptococci. The water quality regulations are examined as to the analysis frequency, the volume of samples, and the relationship between the various bacterial indicators. Analyzing 300-ml, instead of 100-ml, samples tends to generate better information on single water samples. However, if many samples are analyzed over time from the same community, the value of using large volumes of water samples is diminished. The comparisons between bacterial indicators showed that the information obtained from the various indicators was very similar. However, fecal streptococci had a better predictive value of a negative test than coliforms with respect to the French standards.     

Long-term patterns of genomic P element content and P-M characteristics of Drosophila melanogaster in eastern Australia

A latitudinal cline in characteristics associated with the P DNA transposable element is well known in eastern Australian populations of Drosophila melanogaster. In order to survey the long-term patterns of P-M system characteristics and genomic P element content, we established 292 isofemale lines from 54 localities in 1996-1997 and evaluated them for gonadal dysgenesis (GD) sterility and the ratio of KP to full-size P elements (KP/FP ratio). The results were compared to those from collections made in 1983-1986 and 1991-1994. Over 10-14 years, 1) the cross A GD scores of the northern-middle populations declined dramatically; 2) the clinal pattern of the cross A* GD scores did not change; 3) the latitudinal pattern of the KP/FP ratio did not change. The results suggest that only a few P elements determine P-M characteristics and that there has been selection for genomes with fewer active P elements, but not for a great change in proportions of size classes.     

Genetic structure of fragmented populations of a threatened endemic percid of the Rhône river: Zingel asper

Zingel asper is an endemic percid of the Rh?ne basin considered to be critically endangered. This species was continuously distributed throughout the Rh?ne in 1900, but today only occupies 17% of its initial area. In the present study, five microsatellite loci were used to assess the level of genetic variability within and among populations localized in different sub-basins. Contrasting results were obtained for the three main populations from the Rh?ne. A reduced allelic diversity was observed for the two populations displaying the lowest patch sizes (length of the river system occupied); of these, a recent genetic bottleneck was detected for the population showing a particularly low density. However, the third population was characterized by a relatively large spatial extent, high local fish concentrations and an allelic diversity that was twice as high and associated with an equilibrium between mutation and drift. Thus, this population shows an apparently better evolutionary potential for long-term survival. Since 1930, a marked fragmentation of the whole Rh?ne system has appeared, related to the development of dams, and we assume that the significant genetic differentiation detected between the populations could mainly reflect the impact of this fragmentation. The high turnover of the Z. asper populations, and the major role of dispersal in population persistence (highlighted in a recent population dynamics study), indeed suggest that the differentiation observed could mainly have arisen from habitat fragmentation in recent history.     

Incidence of finger pattern types and pattern intensity in a Spanish population (Tierra de Campos)

The incidence of finger pattern types and the pattern intensity distribution in a Spanish sample (417 males and 416 females) drawn from the geographical area of Tierra de Campos have been studied. Sexual and bilateral differences for both dermatoglyphic traits were explored by means of chi 2-test and Mann-Whitney U-test, showing significant differences in all cases, excepting the sexual difference between left hands for pattern intensity. Kolmogorov test for distribution normality showed that pattern intensity was not normally distributed, being the distributions right skewed because of the low frequency of classes with fewer triradii. The results obtained in Tierra de Campos were compared with those observed in other Spanish and Portuguese populations, showing more heterogeneity in the pattern types than in pattern intensity. This could imply that arches account for the main source of variation between populations. Moreover, pattern type frequencies and pattern intensity in Tierra de Campos are, as expected, within the variation ranges of Southeuropean-Mediterranean populations and Caucasians as a whole, although the incidence of radial loops is located in the lower extremes of the corresponding variation ranges.     

Cytoplasmic Incompatibility in Australian Populations of Drosophila Melanogaster

In Drosophila melanogaster, weak incompatibility in crosses between infected and uninfected strains is associated with a Wolbachia microorganism. Crosses between infected males and uninfected females show a reduction (15-30%) in egg hatch. Progeny tests indicated that the infection is widespread in Australian D. melanogaster populations and that populations are polymorphic for the presence of the infection. The infection status of 266 lines from 12 populations along the eastern coast of Australia was determined by 4',6-diamidino-2-phenylindole (DAPI) staining of embryos. All populations contained both infected and uninfected flies. Infection frequencies varied between populations but there was no discernible geographical pattern. Laboratory experiments indicated that the infection was not associated with a reduction in fecundity as in Drosophila simulans. Incompatibility levels could not be increased by laboratory selection on isofemale lines. Factors contributing to the persistence of the infection in D. melanogaster populations are discussed.     

On the maintenance of the polymorphism at the ref(2)P locus in populations of Drosophila melanogaster

Polymorphism for two alleles of the ref(2)P locus is a very constant feature of French natural populations of Drosophila melanogaster. One of these alleles interferes with the multiplication of the hereditary sigma virus in the fly. An equilibrium, quite similar to the natural one, has been observed previously in experimental populations, whether the sigma virus is present or not. Evidence is given that one of the selection components involved in the maintenance of this equilibrium affects adult stages when flies have not suffered severe larval competition. In conditions of severe larval competition, a maternal effect seems to be involved in the differential egg-to-adult viability of heterozygotes.