Adh Frequencies Research Articles

LATITUDINAL CLINE INDROSOPHILA MELANOGASTERFOR KNOCKDOWN RESISTANCE TO ETHANOL FUMES AND FOR RATES OF RESPONSE TO SELECTION FOR FURTHER RESISTANCE

We have introduced a device for selecting Drosophila for increased resistance to very high concentrations of ethanol fumes. This device has enabled us to: 1) select quickly and easily over a thousand flies at a time, and 2) score the knockdown time of every fly in the distribution, while causing very little injury to the flies. A sample of nine west coast populations of Drosophila melanogaster showed a significant trend toward higher knockdown resistance in more northern populations. A population's level of knockdown resistance was virtually uncorrelated with its alcohol dehydrogenase (Adh) allele frequencies. Five of the above nine populations were then subjected to selection for further knockdown resistance. Each population was divided randomly into four groups of 256 flies: two lines to be selected, and two lines to remain unselected as control lines. In every generation each selected line was measured for knockdown resistance, and the last quartile of flies to be knocked down was saved to continue the selection cycle. Population sizes of the selected and unselected lines were all maintained at 256. Realized heritability, based on the responses to selection of the first four generations, was calculated for each selected line. The five populations were significantly heterogeneous for heritability estimates; the average heritability of the five populations pooled was 0.143 ± 0.019. Over the course of twelve generations, the ten selected lines increased their knockdown times by an average factor of 2.40. Before selection, the five populations were heterogeneous for knockdown resistance, and resistance was greatest among the most northern populations. The amount of change of knockdown resistance over the course of selection was also correlated with latitude: the most southern population increased its knockdown time by a factor of 2.23, and the most northern population increased it by a factor of 2.55. After ten generations of selection, the cline of knockdown resistance was about 4.5 times as steep as that before selection. Small phenotypic differences among populations before selection were thus exaggerated by the action of selection. The differences among populations in their rates of response to selection were attributed to genetic differences that existed before selection. The pattern of change of Adh frequencies over the course of selection was very inconsistent, both among and within populations. From this inconsistency of change of Adh alleles with selection, and the lack of correlation between Adh frequencies and knockdown resistance before selection, we concluded that Adh frequency changes could not have had much effect on the responses of the selected lines.

Selective effects of the genetic background and ethanol on the alcohol dehydrogenase polymorphism in Drosophila melanogaster.

Eight freshly caught Australasian mass collections ranging in Adh F frequency from 4 to 96 per cent were each divided into eight selection lines. Two selection lines from each base population were put on one of four types of medium-standard food supplemented with 0 per cent, 3 per cent, 6 per cent or 9 per cent ethanol. After 30 generations the tolerance of 6 per cent and 9 per cent selection lines on a test dose of 9 per cent ethanol was greater than that of the 0 per cent lines on this dose. The tolerance of the 3 per cent lines on this dose was less than that of the 0 per cent lines. There were no significant differences in the tolerance responses across the eight base populations but in only one did Adh frequencies diverge among the four ethanol selection environments: F frequencies in the Brisbane 9 per cent lines were higher than in the Brisbane 0 per cent, 3 per cent and 6 per cent lines. Although the selection affecting Adh did not generally differ among the four selection environments, it differed highly significantly among the eight base populations. The equilibrium F frequencies predicted from the maximum likelihood estimates of the selection coefficients were in close agreement with the frequencies observed in the original collections. The only aspect of the coefficients which was consistent across base populations was FS heterozygote superiority.

An attempt to measure selection coefficients affecting the alcohol dehydrogenase polymorphism in Drosophila melanogaster populations maintained on ethanol media

Eleven populations polymorphic for Adh F and S alleles were established from wild-caught D. melanogaster. Seven of the populations were founded from mass collections each of several hundred flies and the other four were isofemale lines. Subcultures from all eleven were maintained on one of four different types of medium—standard laboratory medium, standard media supplemented to 3% or 9% (v/v) ethanol, and simulated wine seepages. These subcultures were rescored for F and S gene frequencies after 10, 20 and 30 generations. Maximum-likelihood methods were then used to estimate selection coefficients among the Adh genotypes and analyses of deviance were carried out to test the coefficients against hypotheses of neutrality and various modes of selection. No significant selective changes in Adh frequencies were observed in the seven mass cultures on any of the four different media types. However, highly significant selective effects were detected in the four isofemale lines; these effects were homogeneous across the four lines and the four media types and the underlying fitness set was estimated as 1.00:1.04:1.09 for S/S:F/S:F/F.

Genetic variation at the alcohol dehydrogenase locus in Drosophila melanogaster in relation to environmental variation: Ethanol levels in breeding sites and allozyme frequencies

Ethanol levels in Drosophila breeding sites in seepages of unfortified wine inside wineries have been found to be similar to those in many decaying fruits and vegetables. Fortified wine seepages inside wineries have ethanol levels on average three times as high as other breeding sites. However there was no evidence that this variation in ethanol levels was associated with differences in Adh F frequencies in D. melanogaster at sites either within wineries or outside wineries. D. simulans was at lower frequencies at sites inside wineries compared to sites outside although this difference may not be related to ethanol levels. It is concluded that adaptation to natural levels of environmental ethanol by D. melanogaster does not necessarily modify Adh frequencies.

Seasonal variation in the frequencies of the alcohol dehydrogenase isoalleles of Drosophila: correlation with environmental factors

SUMMARYDrosophila melanogaster adults were collected throughout the summers of 1976 and 1977 in Hartford, Connecticut. The frequencies of the Adh isoalleles were determined and seasonal variation demonstrated. Correlation coefficients were calculated between Adh frequencies and the seasonal variations in temperature, precipitation, relative humidity and barometric pressure. Although five correlations were significant it was concluded that these were due to chance.

Ethanol tolerance and the Adh polymorphism in a natural population of Drosophila melanogaster

A DETAILED understanding of the balanced selective forces maintaining the alcohol dehydrogenase (Adh) polymorphism of Drosophila melanogaster will come about when the properties of the enzymatic products of the genotypes can be directly related to selective forces acting on the phenotypes. This approach has been discussed by Clarke1, but it was Gibson2 who first probed the Adh locus in this way when he successfully selected for a specific allele using high levels of ethanol. Enzyme activity of AdhF / AdhF, AdhF / Adhs and Adhs / Adhs genotypes on specific alcohol substrates can generally be related to differential survival and changes in gene frequency in population cages1–8. Briscoe, Robertson and Malpica3 showed a higher AdhF frequency in a Spanish wine cellar population than at a neighbouring site and explained this by the relative ethanol resistance of adult Adh phenotypes. In a study of an Australian winery population McKenzie and Parsons9 also observed differences in ethanol tolerance between the cellar and peripheral sections of the population but they found no correlation between tolerance and Adh frequencies. We now report a more intensive study of this population where samples have been taken from inside and outside the cellar during both vintage and non-vintage periods over two years. In this population a different adaptive system is operating. Unlike Briscoe et al., we found no relationship between the distributions of tolerance and of Adh phenotypes although tolerance can be directly related to the selective effect of alcohol in the adult environment.