Comparative analysis of MGE 412 patterns in 18 isogenic lines of Drosophila melanogaster

Comparative analysis of patterns of mobile genetic element 412 was conducted in 18 isogenic lines of Drosophila melanogaster isolated in three isogenic experiments in 1987 through 1999. Twelve "extra-hot" isogenization sites (in 15-18 lines) and 23 "hot" isogenization sites (> or = 10 lines) were found; of these, 19 occurred in the original heterogeneous line. These sites virtually do not overlap with hot induction sites of transposition. Sites of the latter group generally retain their positions during isogenization. It was shown that no more than 20% of the new sites were brought from the balancer by double recombination, while inbreeding and outbreeding caused 80% of them. Different factors were shown to have different hot isogenization sites. A similarity tree was constructed for the patterns of 18 isogenic lines. The maximum peak of the tree was very low (< 0.25), i.e., the isogenic lines are more similar to than different from one another. The tree was subdivided into subtrees. The division was in good agreement with the isogenization groups corresponding to individual isogenization experiments. Significant correlation was found between the total fragment length and the number of new sites per lines.     

Comparative Analysis of MGE 412 Patterns in 18 Isogenic Lines of Drosophila melanogaster

Comparative analysis of patterns of mobile genetic element 412 was conducted in 18 isogenic lines of Drosophila melanogaster isolated in three isogenic experiments in 1987 through 1999. Twelve extra-hot isogenization sites (in 15–18 lines) and 23 hot isogenization sites (10 lines) were found; of these, 19 occurred in the original heterogeneous line. These sites virtually do not overlap with hot induction sites of transposition. Sites of the latter group generally retain their positions during isogenization. It was shown that no more than 20% of the new sites were brought from the balancer by double recombination, while inbreeding and outbreeding caused 80% of them. Different factors were shown to have different hot isogenization sites. A similarity tree was constructed for the patterns of 18 isogenic lines. The maximum peak of the tree was very low (< 0.25), i.e., the isogenic lines are more similar to than different from one another. The tree was subdivided into subtrees. The division was in good agreement with the isogenization groups corresponding to individual isogenization experiments. Significant correlation was found between the total fragment length and the number of new sites per lines.     

Long-term selection for a quantitative character in large replicate populations of Drosophila melanogaster

Summary Six replicate lines of Drosophila melanogaster, which had been selected for increased abdominal bristle number for more than 85 generations, were assayed by hierarchical analysis of variance and offspring on parent regression immediately after selection ceased, and by single-generation realised heritability after more than 25 generations of subsequent relaxed selection.Half-sib estimates of heritability in 5 lines were as high as in the base population and much higher than observed genetic gains would suggest, excluding lack of sufficient additive genetic variance as a cause of ineffective selection in these lines. Also, there was considerable diversity among the six lines in composition of phenotypic variability: in addition to differences in the additive genetic component, one or more of the components due to dominance, epistasis, sex-linkage or genotype-environment interaction appeared to be important in different lines.Even after relaxed selection, single-generation realised heritabilities in four lines were as high as in the base population. As a large proportion of total genetic gain must have been made by fixation of favourable alleles, the compensatory increase of genetic variability has been sought in a genetic model involving genes at low initial frequencies, enhancement of gene effects during selection and/or new mutations.     

The response of the genomic pattern of transposable elements TE412 to quantitative trait selection in Drosophila melanogaster

The results of four selection-genetic experiments aimed at the genetic transformation of the quantitative trait controlled by the radius incompletus gene of Drosophila melanogaster are given. Directional (s+) and (s-)-selection was conducted. At the of end all the experiments, in (s+)-selection the radial vein of the wing was restored to the wild phenotype, in (s-)-selection complete elimination of the radial vein took place. In four variants of selection, different TE412 pattern was formed under (s+)-selection and (s-)-selection in final generations. Correlation coefficient between (s+)-selection and (s-)-selection is -0.576, p < 0.001. At the same time, correlation coefficient between two independent replications of (s+)-selection is 0.912, p < 0.001, and of (s-)-selection, 0.946, p < 0.001. Thus, the availability of associated response to the selection of a quantitative trait and to the TE412 pattern is experimentally proved. Three hypotheses of the possible TE behaviour under selection are discussed.     

Prolongation of MGE 412 transposition induction after gamma-irradiation in an isogenic line of Drosophila melanogaster]]

The dose dependence of the rate of gamma-induced transpositions and consequent dynamics of the MGE 412 pattern after gamma-irradiation were investigated in isogenic line 49 in generations F1, F12, F140, and F170. It was shown that the results on dose dependence of transpositions was very similar with the corresponding results of the classic works by Timofeeff-Ressovsky et al. (1935). It is suggested that the transcribed copies of retrotransposon 412 "cure" gamma-radiation-induced double-strand DNA breaks. The phenomenon of prolongation of MGE transposition induction during early generations after treatment was shown. In this period (F1-F12), the maximum transposition rate (lambda approximately equal to 2 x 10(-2) events per MGE copy, per haploid genome, per generation) and the maximum number of heterozygous MGE copies were achieved. In the late generations (F140 and F170), the reduced induction level (lambda approximately 10(-3) was established. In the population of effective size Ne = 2000 individuals, this corresponds to the state when lambda > 1/4Ne, i.e., when the transposition flow prevails over the MGE copy loss by genetic drift. These data together with some indirect evidence argue for the hypothesis that the spontaneous transposition rate is proportional to the average number of heterozygous MGE copies per diploid genome.     

Induction of MGE 412 Transposition in an Isogenic Strain of Drosophila melanogaster by Different Doses of Ethanol Fumes

The effect of treatment of males from an isogenic Drosophila melanogaster strain by limiting doses of ethanol fumes on transpositions of MGE412 was examined. Validity of the phenomenon of transposition induction was demonstrated. We estimated rates of induced transposition (10^–2 events per site, per sperm, per generation versus <10^–3 in control) and showed dose dependence of the rate on the exposure time of the males to ethanol fumes. Experiments with alcohol treatment at limiting doses must end either in death of the individuals or bursts of genetic variability in their progeny. In terms of genetics of an individual, this may mean loss of vital hereditary basis followed by mass degradation of the progeny of the hard drinkers. In terms of populations genetics, this mode of MGE transposition induction can rapidly create a burst of novel genetic variation, which, apart of great losses, may generate a number of advantageous individuals, i.e., be significant for population survival in new, stressful environments.     

Induction of MGE 412 transposition in an isogenic strain of Drosophila melanogaster by different doses of ethanol fumes

The effect of treatment of males from an isogenic Drosophila melanogaster strain by limiting doses of ethanol fumes on transpositions of MGE 412 was examined. Validity of the phenomenon of transposition induction was demonstrated. We estimated rates of induced transposition (approximately 10(-2) events per site, per sperm, per generation versus < 10(-3) in control) and showed dose dependence of the rate on the exposure time of the males to ethanol fumes. Experiments with alcohol treatment at limiting doses must end either in death of the individuals or bursts of genetic variability in their progeny. In terms of genetics of an individual, this may mean loss of vital hereditary basis followed by mass degradation of the progeny of the "hard drinkers." In terms of populations genetics, this mode of MGE transposition induction can rapidly create a burst of novel genetic variation, which, apart of great losses, may generate a number of advantageous individuals, i.e., be significant for population survival in new, stressful environments.     

Response of the MGE 412 pattern to truncation selection of a quantitative trait in an isogenic line of drosophila after severe heat shock (SHS)

Positive and negative selection on the total length of two fragments of an interrupted longitudinal wing vein in an isogenic line of Drosophila melanogaster was accompanied by changes in the genomic localization pattern of MGE 412. Strong truncation selection was conducted in the population of effective size Ne = 160 for 50 generations. Twenty-six out of 35 polymorphic HHS-induced segments of MGE localization behaved as independent copies and markers, whereas 9 segments proved to be selective. The second group included "hot" segments of HHS transposition induction (43B, 97E, etc.). Thus, final consensus patterns of induced MGE transpositions have a random and an adaptive component in generation 50 of positive and negative selection. Selective patterns probably include modifier MGEs, which generate induced genetic regulatory variation of polygenes controlling the selected quantitative trait in the isogenic line after HHS.     

Analysis of allozymic and quantitative variation produced by artificial selection in Drosophila melanogaster

In order to study a possible connection between allozymic and quantitative variation in D. melanogaster, three selection experiments were carried out, using founder strains of known genetic and chromosomal composition.The Adh and Gpdh-1 enzyme loci have been used as genetic markers and the maximum wing length has been the quantitative trait chosen. Two selected lines (high and low) were maintained and also one without selection (drift), to estimate the effect of random fluctuation on gene frequency variation. The allozymic variation was analysed by means of a polynomial regression, and a normal linear model allowed to make pairwise comparisons.The allelic combination ((F), A(-)) was favoured in the low lines of the selection experiments; the selection acted in favour of homozygotes, with a correlated loss of genetic homoeostasis. The similar behaviour of the drift and the control lines shows that random fluctuations in the gene frequencies in selected lines are negligible.     

Transposition induction of the mobile genetic element Dm412 in the Drosophila genome using heat shock]

Males of Drosophila melanogaster isogenic line with oligogene mutation radius incompletus (ri) were exposed to standard heat-shock (SHS: t = 37 degrees C, 90 min) and heavy heat-shock (SHS: three-fold transfer of males from t = 37 degrees C, 2h, t0t = 4 degrees C 1 h, and back). At F1 of the treated males with untreated females of the same isogenic line mass transpositions of MGE Dm412 were found. The new positions of MGE seem to be not random, and 5 "hot sites" of transpositions were detected. The probabilities of transpositions were estimated after SHS and HHS and in control sample. They were, correspondingly, 3.4 x 10(-2), 8.7 x 10(-2) and less than 4.1 x 10(-4) transpositions per genome, per site occupied, per generation. Therefore, as a result of HS treatment, the probabilities of transpositions were two orders of magnitude increased as compared to control, directly at next generation after induction. Comparison of these results with those obtained after step-wise temperature treatment shows that induction is dependent rather of "stressor effect" of temperature treatment than of treatment way used.     

Prolonged negative selection of Drosophila melanogaster for a character of adaptive significance disturbs stress reactivity.

The metabolism of juvenile hormone by JH-esterase and JH-epoxide hydrolase, and octopamine by tyrosine decarboxylase were studied under normal and stress conditions in flies of two related lines of D. melanogaster. One was selected for high (HA line) and another for low (LA line) male sexual activity for more than 700 generations. It was demonstrated that prolonged selection for low male sexual activity results in considerable changes in both systems. Tyrosine decarboxylase activity in males and females of the LA line was sharply reduced as compared with those of the HA and control Canton-S lines; JH-esterase and JH-epoxide hydrolase activities were decreased in females, and not in males, of the LA line. It was demonstrated that the response of both metabolic systems to heat stress is impaired in individuals of the LA line: the system of juvenile hormone metabolism does not respond to stress, and that of octopamine metabolism is decelerated. The role of juvenile hormone metabolism in male reproductive function is discussed.     

Dynamics of quantitative traits of Drosophila during long-term selection

The results of long-term mass selection for the number of abdominal bristles and thorax length in Drosophila population during over 60 generations in opposite directions are given. It is shown that effectiveness of selection depends upon additive genetic component of phenotypic variability of characters in the initial population.     

Analysis of lethals in selected lines of Drosophila melanogaster

Summary Five lines of Drosophila melanogaster that reached an extreme phenotype after long-term selection for increased dorsocentral bristle number, were analysed for the presence of lethals. Seven chromosome II and three chromosome III lethal types were detected in four of the lines, at frequencies ranging from between 6% and 36%. No lethal had any demonstrable effect over the selected trait. In one line, where almost every chromosome II was a lethal carrier, it was shown that the main lethal (at a frequency of 36%) was associated with the transmission ratio distortion in males. The processes which could lead to the accumulation of this lethal and others linked in disequilibrium to it is discussed. Some results suggest similar mechanisms for the accumulation of lethals in the other lines. These findings show that causes other than the direct effect of artificial selection must be taken into account when trying to explain the accumulation of lethals in selected lines.