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G Periquet

Publications and source records attributed to G Periquet.

45 records · Page 3Linked to original sources
PubMed1991

Distribution of hobo transposable elements in natural populations of Drosophila melanogaster.

Forty-six strains derived from American and French natural populations of Drosophila melanogaster were tested for the presence and activity of hobo elements by using Southern blotting and a gonadal dysgenesis assay. The oldest available strains exhibited weak detectable hybridization to the hobo-element probe and revealed neither hobo-activity potential nor hobo-repression potential. In contrast, all recently collected strains harbored hobo sequences and revealed a strong hobo-repression potential but no strong hobo-activity potential. On the basis of restriction-enzyme analysis, old strains appear to have numerous fragments hybridizable to hobo sequences, several probably conserved at the same locations in the genome of the tested strain and others dispersed. In recently isolated strains, and unlike the situation in the published sequence of the cloned hobo108 element, a PvuII site is present in the great majority of full-sized hobo elements and their deletion derivatives. When the genetic and molecular characteristics are considered together, the available evidence is consistent with the hypothesis of a worldwide hobo-element invasion of D. melanogaster during the past 50 years. Comparison of data from the I-R and P-M systems suggests that the putative invasion followed the introduction of the I element but preceded that of the P element. This hypothesis poses the problem of the plausibility of three virtually simultaneous element invasions in this species. Such a possibility might be due to a modification of the genetic structure of American populations of D. melanogaster during the first part of the 20th century.

Americas↗
PubMed1990

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.

Adaptation, Physiological↗
PubMed1990

Heterochromatin condensation and evolution of unique satellite-DNA families in two parasitic wasp species: Diadromus pulchellus and Eupelmus vuilleti (Hymenoptera).

Large quantities of satellite DNA families (15%-25% of the genome) were found in the DNA of two species of parasitic wasps, Diadromus pulchellus and Eupelmus vuilleti. In both species the satellite DNA was found to consist wholly or largely of a single family unique to that species. Several clones of each family were obtained and sequenced. Palindromes in each consensus sequence suggest the formation in vivo of hairpin structures that may play a role in the mode of heterochromatin condensation in these insects. The ancestral repeating motifs were determined from the consensus sequences. Plausible scenarios are presented for the evolution of the two satellite DNAs. The occurrence of only one family of satellite DNAs in both species may indicate that, in male haploids, such families have shorter persistence times than necessary for the origins of new duplicated sequences.

Animals↗
PubMed1989

Comparison of the regulation of P elements in M and M' strains of Drosophila melanogaster.

M and M' strains of Drosophila melanogaster in the P-M system of hybrid dysgenesis were compared in two series of tests, with the following results. (1) The singed-weak hypermutability regulation test showed that M' strains had lower P excision rates than M strains, suggesting that P-elements repression must occur in M' strains although it is not detectable by gonadal dysgenesis assays. (2) The evolution of mixed P+M and mixed P+M' populations was compared, using a strong P strain. The P+M cultures invariably evolved in a few generations into strong P cultures, while the P+M' cultures evolved into P-type cultures with reduced P-factor potentials. However, after 30 generations of culture, both these types of mixed cultures had similar P copy numbers, suggesting that regulation of copy number had occurred in them.

Animals↗
PubMed1989

Are Drosophila melanogaster populations under a stable geographical differentiation due to the presence of P elements?

In order to simulate the outcome of the P-M status of Eurasian populations of Drosophila melanogaster, the evolution of experimental mixed-strains was monitored for up to 50 generations. The results were compared with the evolution in natura of European populations sampled in 1981-83 and 1986-87 over a similar period of time. Different combinations of P and M' strains, Q and M' strains, M' and M' strains and M and M' strains were set up at 25 degrees C and duplicated at 13 degrees C night-21 degrees C day. The possibility of a change towards a P type only appeared with the introduction of the strong P strain Harwich into Eurasian strains. Strains with strength similar to that of Harwich are not currently found in wild populations. With the introduction of weak P and Q strains of the strength presently observed in western Europe, experimental populations evolved slowly towards a Q state or a weak M' state. M'-M' mixed populations resulted in strong M' strains, as was the case for M-M' populations. In these cases. P sequences were not eliminated. In wild populations both genetic and molecular analyses showed no significant differences, over a five year period, for GD sterility potentials, for total P copy number or for distribution of the full-sized and KP elements. Changes in Eurasian populations are probably taking place at a very low rate and may even have stopped, leading to a quasi-stable differentiation over the continent. During the different steps of progressive invasion of P transposable elements, several deleted elements developed and natural selection may have acted on them. The possibility of the selection of different types of regulatory mechanisms according to the presence of different kinds of derivative elements, leading to a world-wide differentiation between P-Q and M' strains is discussed.

Animals↗
PubMed1988

Molecular characteristics of diverse populations are consistent with the hypothesis of a recent invasion of Drosophila melanogaster by mobile P elements.

Approximately 100 strains derived from natural populations of Drosophila melanogaster were tested for the presence or absence of P-element sequences by using two molecular probes derived from internal regions of a full-sized P element. Strains that had been collected from several continents at varying times during the past 60 years were examined. The oldest available strains, representing most major geographical regions of the world, exhibited no detectable hybridization to the P-element probes. In contrast, all recently collected natural populations that were tested carried P-element sequences. The earliest appearance of P elements occurred in collections made during the 1950s and early 1960s in the Americas and during the late 1960s on other continents. The youngest strains that were completely devoid of P elements originated in populations sampled during the mid-1960s in America, but as late as 1974 in populations from the USSR. There are differences in the patterns of hybridization to the two P-element probes between populations from different geographical regions. These differences are consistent with the varying P-M phenotypic properties of these populations. Taken together with the results of phenotypic tests reported in earlier studies, the available evidence is consistent with the hypothesis of a worldwide P-element invasion of D. melanogaster during the past 30 years and suggests that the putative invasion of the Americas possibly preceded by approximately a decade that in Europe, Africa, and the rest of the world.

Animals↗