The relative quantities and catalytic activities of enzymes produced by alleles at the alcohol dehydrogenase locus in Drosophila melanogaster

Quantitative genetic variation of enzyme activities in natural populations of Drosophila melanogaster

The genetic component of variation of enzyme activity in natural populations of Drosophila melanogaster was investigated by using two sets of chromosome substitution lines. The constitution of a line of each type is: i(1)/i(1);+(2)/ +(2);i(3)/i(3) and i(1)/i(1);i(2)/ i(2);+(3)/+(3), where i refers to a chromosome from a highly inbred line and + refers to a chromosome from a natural population. The + but not the i chromosomes vary within a set of lines. By use of a randomized block design to test and estimate components of variance, 50 of the second- and 50 of the third- chromosome substitution lines have been screened for variation in the activity levels of seven enzymes. Six of the seven enzymes show a significant genetic component in at least one set of lines, and five of the seven enzymes show activity variations attributable to factors that are not linked to the structural gene. These unlinked activity modifiers identify possible regulatory elements. Analyses of covariance show that most of the genetic variation of enzyme activities cannot be accounted for by genetic variation of live weight or protein content. These results and the lack of strong correlations between the genetic effects on the activities of different enzymes indicate that the effects are mainly specific for individual enzymes.

Alloprocoptic selection: A mode of natural selection promoting polymorphism

The fitness effect of genetic variation at three loci coding for enzymes is studied in Drosophila melanogaster. The fertility of a female is determined by the female genotype as well as by the genotype of the male with which she mates. Significant interactions exist between female and male genotype, so that the fertility of a given mating combination cannot be predicted from the average fertility of the two genotypes involved. Multiple stable equilibria are possible when such interactions exist. At two loci, the fertility is greater than expected when the two mating individuals are homozygous for different alleles and smaller than expected when they are homozygous for the same allele. This mode of selection in which association of opposites increases their fitness is herein named alloprocoptic selection. It will contribute to maintaining genetic polymorphism in nature.

[A short history of evolutionary theory]

The history of the Theory of Evolution has been told a number of times by historians, philosophers, professors, writers, scientists and so on. However, many of these versions differ from or even contradict one another. In this article, the history of the Theory of Evolution is retold according to a dialectical-materialistic perspective. It analyzes the historical contradictions between Darwinian evolution theory and Mendel's model, the background that led to the synthetic theory of evolution, the debate carried out by classic schools and the result of synthesis, as well as the still current debate between Neutralism and Selectionism. Finally, it also discusses the interpretative model used ("an idiosyncratic dialectic materialism"), mainly in relation with Popper's and Kuhn's models.

Synergistic effect of Adh alleles in Drosophila melanogaster

In laboratory cultures of Drosophila melanogaster derived from an African population, the quantities of six out of seven enzymes (G6PD, IDH, GPDH, ME, MDH, PGM and ADH) were higher in Adh-FF homozygotes than they were in Adh-SS. In crosses between Adh-FF and Adh-SS flies, the differences segregated as co-dominant alleles of a single Mendelian gene closely linked, or identical, to the Adh locus. The generality of these associations was suggested by the study of a French population with a very different history and genetic background. The possibility that the associations were caused by artefacts of the immunodiffusion techniques, or to a linked inversion (In(2L)t), was excluded. Possible ways by which the Adh locus may affect the quantities of other enzymes are discussed.

Allozyme polymorphism at the alpha Gpdh and Adh loci and fitness in Drosophila melanogaster

We have studied in Drosophila melanogaster the effects of allozyme variation at the alpha Gpdh and Adh loci on the following fitness components: female fecundity, egg hatchability, egg-to-adult survival under near-optimal and competitive conditions, rate of development under near-optimal and competitive conditions, and mating capacity of males. Significant effects of the alpha Gpdh locus on rate of development under competitive conditions (SS greater than FS greater than SS), and of the Adh locus on egg hatchability (FF = SS greater than FS) and egg-to-adult survival under competitive conditions (FF greater than SS = FS) were revealed. Possible natural selection mechanisms involved in the maintenance of allozyme polymorphisms at the alpha Gpdh and Adh loci are described. These mechanisms and the fitness of In(2L)t may account for the persistence and clinal distribution of the two allozyme polymorphisms in nature.

Quantitative analysis of RNA produced by slow and fast alleles of Adh in Drosophila melanogaster

The alcohol dehydrogenase (ADH) locus (Adh) of Drosophila melanogaster in polymorphic on a world-wide basis for two allozymes, Fast and Slow. This study was undertaken to determine whether the well-established difference in ADH protein concentration between the allozymes is due to a difference in mRNA levels. RNA gel blot hybridization and an RNase protection assay were used to quantify ADH mRNA levels. Each method used an Adh null mutant as an internal standard. Several Slow and Fast allele pairs of different geographic origins were analyzed. The results provide strong evidence that the ADH protein concentration difference is not accounted for by RNA level.

Recent origin for a thermostable alcohol dehydrogenase allele of Drosophila melanogaster

The nucleotide sequence of the Fast-Chateau Douglas isolate of the thermostable alcohol dehydrogenase allele is compared with the sequences of the Slow and Fast alleles of Drosophila melanogaster. Conceptual translation of the FChD sequence indicates that the thermostable polypeptide has the diagnostic FAST amino acid replacement at residue 192 and an additional replacement of serine for proline at residue 214. This suggests a Fast origin for the thermostable Adh allele. However, some of the biochemical properties of the FCHD protein resemble those of the SLOW rather than the FAST polypeptides. The serine for proline replacement confers upon the thermostable polypeptide substrate specificities and some kinetic parameters similar to the SLOW protein. The same replacement substitution within the third coding exon also appears to alter the ADH protein concentration to a level similar to the SLOW polypeptide and the probable effect is at the level of mRNA concentration. The low level of nucleotide sequence variation, other than that leading to the amino acid substitution, suggests a recent origin for the thermostable allele. The time since divergence of the FChD sequence from Fast is estimated to be approximately 260,000-470,000 years.

The alcohol dehydrogenase alleloenzymes AdhS and AdhF from the fruitfly Drosophila melanogaster: an enzymatic rate assay to determine the active-site concentration

A rapid and reproducible enzymatic rate assay for the quantitative determination of the concentration of active sites is presented for the alleloenzymes AdhS and AdhF from Drosophila melanogaster. Using this procedure the turnover numbers as catalytic-center activities were found to be 12.2 sec-1 for AdhF and 3.4 sec-1 for AdhS with secondary alcohols. This showed a slower dissociation of the coenzyme from the binary enzyme-NADH complex with AdhS and hence a stronger binding of NADH to this alleloenzyme. With ethanol, the catalytic-center activity was 1.4 sec-1 for AdhS and 2.8 sec-1 for AdhF, and hence the single amino acid mutation distinguishing the two alleloenzymes also affected hydride transfer.

Alcohol dehydrogenase from Drosophila funebris and Drosophila immigrans: molecular and evolutionary aspects

Alcohol dehydrogenase from Drosophila funebris and D. immigrans is evident at all developmental stages. The highest activity level appears in third-instar larvae and declines to a lower level at all later stages of development. Both species are monomorphic. The enzyme is a dimer consisting of two identical subunits with molecular weight 27,600. The pI values are 8.6 for D. funebris and 9.02 for D. immigrans. The optimum pH is 8.6 and 8.7 for D. funebris and D. immigrans, respectively. The Km values for NAD+, propan-2-ol, and butan-2-ol are 0.15, 2.90, and 2.08 mM, respectively, for D. funebris and 0.16, 1.53, and 1.49 mM, respectively, for D. immigrans. The half-life for the purified enzyme is 45 days for D. funebris and 18 days for D. immigrans at 4 degrees C. Data on the amino acid composition of both enzymes and peptide maps of alcohol dehydrogenase of D. immigrans reveal that they have marked homologies between them and also with alcohol dehydrogenases of other species. D. funebris shows reduced levels of alcohol dehydrogenase synthesis but has the highest specific activity reported to date for a Drosophila species. D. immigrans synthesises six times more enzyme but the specific activity is comparable to that of other species of Drosophila. This evidence could explain their different alcohol tolerance. The molecular properties of these alcohol dehydrogenases together with other species of Drosophila suggest that the alcohol dehydrogenase of Drosophila has arisen by divergent evolution from a common ancestral gene.

Variation in the biochemical properties of the Drosophila alcohol dehydrogenase allozymes

Thirteen Drosophila Adh variants have been characterized with respect to gene expression, substrate preference, thermostability, and specific activity. The results suggest that the variants may be grouped into two biochemical classes, typified by the properties of the two most common enzyme forms, ADH-F and ADH-S. Membership of these classes cannot be predicted from electrophoretic mobility, nor is any simple classification possible with regard to the characteristics of level of gene expression (in terms of ADH activity or ADH protein) or thermostability of the gene product.

Alcohol dehydrogenase thermostability variants in Drosophila melanogaster: comparison of activity ratios and enzyme levels

Representatives of five allozymic classes of Drosophila alcohol dehydrogenase have been compared with respect to their activity levels on two alcohol substrates, quantities of ADH protein, and stability in crude extracts. Within each allozymic class, strains from widely diverse geographic locations differ in their enzyme activity levels but are identical for a measure known as "activity ratio," which is obtained by dividing the average activity reading on isopropanol by that obtained with ethanol. They are also similar in the rate at which ADH activity declines in crude extracts held at 25 degrees C. For several of the fast-resistant and fast-moderate strains, differences in ADH activity are associated with differences in the amount of enzyme present. The catalytic efficiencies of the fast-resistant forms are considerably lower than those of the fast-moderate allozymes. The origin and persistence of the rare but ubiquitous fast-resistant allozyme is discussed.

Genetic variation in the expression of ADH in Drosophila melanogaster

Several chromosomes derived from natural populations have been identified that affect the expression of alcohol dehydrogenase (ADH). Second chromosomes, which also carry the structural gene Adh, show a great deal of polymorphism of genetic elements that determine how much enzyme protein accumulates. The level of enzyme was measured in third instar larvae, 6-to-8-day-old males and in larval fat bodies and alimentary canals. In general, activities in the different organs and stages are highly correlated with one another. One line was found, however, in which the ADH level in the fat body is more than twice the level one would expect on the basis of the activity in alimentary canal. We have also found evidence of third-chromosome elements that affect the level of ADH.

Genetical variation for enzyme activity in a population of Drosophila melanogaster. VI. Molecular variation in the control of alcohol dehydrogenase (ADH) activity

Four characters, ADH activity at 25 degrees, immunologically determined ADH protein level, total protein and body weight were measured upon 72 hour old adult female and male Drosophila melanogaster from 16 highly inbred lines, derived from the laboratory population, "Texas" (established 1966). The highest levels of ADH activity and ADH protein level were observed in the 2 lined homozygous for the AdhF allele. Amongst the 14 AdhS/S lines variation for ADH protein level was associated with genetical variation for ADH activity (r = 0.6). The genetical association between ADH activity or ADH protein level and either body weight or total protein in the 16 inbred lines was not statistically significant. A study of ADH activity, ADH protein and total protein in 8 lines representing all homozygous combinations of chromosomes I, II and III and derived from two inbred AdhS/S lines, chosen for their respective high and low ADH activities, showed that ADH activity was considerably modified by a post-translational event controlled from chromosome III. Total protein was controlled by different chromosomal effects from those controlling ADH activity. Michaelis constants for crude fly extracts of the two AdhF/F and the above two AdhS/S lines showed clear differences in affinity for isopropanol.

The relative conformational stability of the alcohol dehydrogenase alleloenzymes of the fruitfly Drosophila melanogaster

The effect of temperature on four purified alleloenzymes of the alcohol dehydrogenase (Adhs, Adhf, AdhD and Adhn-5) of the fruitfly Drosophila melanogaster was investigated in detail. Initial-velocity studies showed that the naturally occurring Adhf and Adhs enzymes differed only in their temperature optima, and evidence of kinetic adaptation to high and low temperature was not apparent. All four alleloenzymes denatured irreversibly on heating purified enzyme solutions at pH 6.0. This technique revealed only small differences in thermostability between Adhf and Adhs, although the two mutant enzymes from AdhD and Adhn-5 were considerably more labile. Electrophoresis of the enzymes though a stable transverse temperature gradient proved to be a discriminating and reproducible technique. Enzymes of different net charge were compared on the same polyacrylamide gel. The Adhf enzyme was shown to be significantly less stable than the Adhs enzyme. Subunit interchange was observed at temperatures below the point at which the unfolding occurred. At pH 4.0, the Adhf/Adhs heterodimer was as stable as the Adhs homodimeric enzyme, and more stable than the Adhf homodimer. Adhn-5 and AdhD alleloenzymes were relatively thermolabile. The stability of the alleloenzymes towards urea denaturation was studied by urea-gradient electrophoresis. Only small differences in stability between the Adhf and Adhs enzymes were observed. The AdhD and Adhn-5 mutants were denatured at the same urea concentration, which was much lower than in the case of the wild-type enzymes. Except at pH 4.0, subunit dissociation could not be distinguished from the unfolding of the monomer.

Variation in activity and thermostability of alcohol dehydrogenase in Drosophila melanogaster

The activity and thermostability of alcohol dehydrogenase (ADH) from 247 strains ofDrosophila melanogasterwere studied by spectrophotometric assay. The strains, in which second chromosomes had been made homozygous in a standard genetic background, were derived from five natural populations from diverse geographical and ecological sites. Evidence is presented that the majority of variation in ADH activity is attributable to the presence, in all five populations, of two electromorphs of the enzyme. However, some variation does exist between strains carrying the same electromorph, to some extent associated with variation hi body weight. Two strains showed atypical ADH activities. Variation in ADH thermostability was almost wholly attributable to the presence of two electromorphs; only two strains had enzymes with thermostabilities atypical of their electromorph. In the four strains with abnormal ADH properties the locus (loci) responsible map in the region of theAdhlocus. Therelatively low level of heterogeneity within electrophoretic classes at this locus is discussed in view of recent findings at other enzyme loci inDrosophila.

Structural analysis of an electrophoretically cryptic alcohol dehydrogenase variant from an Australian population of Drosophila melanogaster

The existence of geographically widespread clines in genetic polymorphisms is persuasive evidence that the distribution of such genetic variance is determined by natural selection. However, when comparing clines it is important to be certain that identical structural genes are involved. We report a structural difference (proline-214 to serine) between the product of AdhF and an electrophoretically cryptic heat-stable variant isolated from an Australian natural population, ADH-FCh.D. ("fast" Chateau Douglas). The biochemical properties of this new variant must be taken into consideration when attempting to formulate a causal explanation of the maintenance of the three identified Adh alleles. Our data also show that the products of an AdhF and an AdhS allele in Drosophila melanogaster in an Australian population are identical over 70% of their amino acid sequences with their North American counterparts.

Selection associated with the alcohol dehydrogenase locus in Drosophila melanogaster: differential survival of adults maintained on low concentrations of ethanol

David and his collaborators have reported that adult Drosophila melanogaster survive longer on 2 per cent ethanol than on distilled water, but that the increased survival on ethanol does not occur in mutant flies lacking alcohol dehydrogenase activity. This has led us to enquire if the polymorphic alleles at the alcohol dehydrogenase locus (AdhF and AdhS), which code for enzymes with different activities, affect survival on low concentrations of ethanol. Flies were kept in sealed glass chambers containing either 2 per cent ethanol or distilled water. In four experiments, comprising a total of 126 replicates, the proportion of surviving FF flies, relative to SS, was greater on ethanol than on water. In two experiments the excess was highly significant. It appears that FF flies are better able than SS to use ethanol as food. Our results support the view that selection acts directly on the Adh polymorphism.

Effect of environmental alcohol on in vivo properties of Drosophila alcohol dehydrogenase

The effects of environmental 2-propanol on the in vivo properties of Drosophila alcohol dehydrogenase (E.C. 1..1.1.1.) are presented. Exposed flies were found to exhibit a significant decrease in ADH specific activity with a concomitant increase in the enzyme's relative in vivo stability and concentration. The possible adaptive significance of the observed responses is discussed.

Determination of some biochemical and structural features of alcohol dehydrogenases from Drosophila simulans and Drosophila virilis. Comparison of their properties with the Drosophila melanogaster Adhs enzyme

The biochemical properties of the enzyme alcohol dehydrogenase of two different Drosophila species, Drosophila simulans and Drosophila virilis, were studied and compared with those of Drosophila melanogaster Adhs enzyme. All of them consist of two identical subunits of molecular weight 27800 and share significant similarities in function. The substrate specificities of these enzymes were characterized and Km(app.) and Vmax.(app.) values were calculated. All these alcohol dehydrogenases show greater affinity for secondary rather than for primary alcohols. The amino acid compositions of the three enzymes were determined, and there is a close similarity between the D. simulans and the D. melanogaster enzymes, but there are significant differences from the alcohol dehydrogenase of D. virilis. The N-terminal amino acid is blocked and the C-terminal amino acid is the same for all three alcohol dehydrogenases. The enzymes from the three species were carboxymethylated and digested with trypsin. The peptide 'maps' reveal, as expected, more homologies between the enzymes of D. simulans and D. melanogaster than with the enzyme of D. virilis.

Evolutionary genetics of Metridium senile. I. Kinetic differences in phosphoglucose isomerase allozymes

Populations of the sea anemone Metridium senile from the northeast coast of the United States exhibit a one-locus, two-allele polymorphism for phosphoglucose isomerase. No additional "hidden" variation is exposed by changes in pH, gel pore size, or heat denaturation. The allozymes are similar in pH optimum, sensitivity of Km to pH, and sensitivity of Km and Vmax to temperature. In other respects they are functionally different, with the fast allozyme having a 3.5-fold higher specific activity and a slightly higher Km of fructose-6-phosphate than the slow form. In these respects, heterozygotes produce a mixture of enzymes that appears to function roughly as the sum of its component parts. Comparisons of Vmax/Km ratios reveal significant differences among genotypes, with the fast form having higher values at all temperatures than the slow form and heterozygotes falling intermediate. In addition, there is a significant difference among genotypes in sensitivity of this parameter to temperature, with the fast homozygote and heterozygote displaying greater sensitivity than the slow homozygote. Temperature is probably an important selective agent in maintaining this polymorphism.

Maintenance of an aminopeptidase allele frequency cline by natural selection

The product of the Lap locus in the marine bivalve Mytilus edulis is a neutral, membrane-associated aminopeptidase that is primarily localized on intestinal microvilli and in digestive cell lysosomes. Natural populations are genetically differentiated at the Lap locus between areas of differing salinity. A steep (0.55-0.15) allele frequency cline connects differentiated populations between the Atlantic Ocean and Long Island Sound. We demonstrate an annual gene flow/mortality cycle in cline populations whereby gene frequencies after mortality are correlated with salinity and enzyme activity. The cline is spatially and temporally unstable in immigrants, but stable in residents after mortality. Mortality is nonrandom with regard to the Lap locus; genotype-dependent properties of the aminopeptidase enzyme apparently led to a differential rate of the utilizaiton of nutrient reserves because selected genotypes exhibited an increased rate of tissue weight loss. Aminopeptidase genotypes are differentially adapted to different temperatures and salinities, which provides a mechanism for the relationship among biochemical, physiological, and population phenotypes.

Alcohol dehydrogenase polymorphism in the seaweed fly, Coelopa frigida

Seaweed flies (Coelopa frigida) inhabit piles of decaying seaweed on the seashore. All populations so far studied have been found to be polymorphic at the alcohol dehydrogenase locus (Adh). This article reports an attempt to identify some of the forces of natural selection that may be maintaining this polymorphism First, the genetic determination of the rather complex isozyme system is described. Several inbred lines homozygous at the Adh locus were derived and the biochemical properties of their allozymes compared. Significant differences in both specific activities and thermal stabilities were found between ADH allozymes. A simple experiment is reported in which individuals with different Adh genotypes were cultured in competition with each other in the presence of elevated levels of ethanol. Although the presence of ethanol resulted in greater mortality, there is no evidence that it was selective with respect to the Adh genotypes. The possible relevance of these results to the maintenance of the Adh polymorphism is discussed.

Analysis of genetic variation affecting the relative activities of fast and slow ADH dimers in Drosophila melanogaster heterozygotes

When AdhF/Adhs heterozygote homogenates are stained after electrophoresis, considerable variation is observed in the activity ration of the FF dimer to the SS dimer. Two AdhS strains showed a sharp, consistent difference when crossed to a common AdhF strain. Optical scanning and genetic analysis confirmed that this difference originates close to the Adh locus. Since the morphs varied concordantly in their activities on numerous alcohols, and since aging and heat treatment experiments failed to reveal a stability difference, it is proposed that the difference is regulatory in nature, affecting ADH synthesis and primarily cisacting. A survey of wild flies revealed additional variation in the FF/SS activity ratio. Further genetic analysis showed that the basis of this variation is not restricted to the second chromosome. Furthermore, modification of the activity ratio implies some degree of allelespecificity on the part of the modifiers.

Purification and enzyme stability of alcohol dehydrogenase from Drosophila simulans, Drosophila virilis and Drosophila melanogaster adhS

Three alcohol dehydrogenases from Drosophila simulans, Drosophila virillis and Drosophila melanogaster adhS (which possesses an alloenzyme with slow electrophoretic mobility) were purified essentially to homogeneity. The purification procedure involves a new step of affinity chromatography, which efficiently lowers the amount of contaminants in the final preparation, producing a very stable enzyme. The purification procedure developed consists of a salmine sulphate precipitation, two CM-Sepharose CL-6B colume-chromatography steps, an affinity-chromatography step and a Sephacryl gel filtration. A minimum of 30-fold purification is obtained and the yield is not less than 34%. The isoelectric points and molar absorption coefficients were determined.

Genetical variation for enzyme activity in a population of Drosophila melanogaster. V. The genetical architecture, as shown by diallel analysis, of alcohol dehydrogenase (ADH) activity

Fifteen highly inbred lines extracted by sib-mating from the laboratory cage population, "Texas", of Drosophila melanogaster were crossed in a half-diallel mating design. Female progeny were assayed individually for ADH activity at 25 degrees and 35 degrees C and for total protein. At 25 degrees C there was considerable additive genetical variation and the dominance variation was attributable to specific parents and to specific crosses at random in the diallel table. The character total protein also showed considerable additive variation but less dominance variation. Largely independent gene action was shown by the characters ADH activity and total protein. There were strong genotype-environment interactions for heat-stability. At 35 degrees C most of the genetical variation was additive and mainly due to modifier loci. It was concluded that at 25 degrees C dominance was ambidirectional and almost complete. This genetical architecture was compatible with a past history of stabilising selection for ADH activity in the "Texas" population.

Functional significance of amylase polymorphism in Drosophila melanogaster. III. Ontogeny of amylase and some alpha-glucosidases

Changes in amylase (E.C. 3.2.1.1), maltase (E.C. 3.2.1.20), sucrase, and PNPGase activities in relation to changes in wet weight and protein content were studied during the development of larvae and adult flies from two strains of Drosophila melanogaster, homozygous for different amylase alleles. All alpha-glucosidase activities increase exponentially during a large part of larval development, parallel to the increase in weight, and drop at the end of the third instar. Amylase activity of the Amy1 strain follows the same pattern. In contrast, amylase activity of the Amy4,6 strain continues its exponential increase longer. In the third larval instar amylase activity in the Amy4,6 strain becomes much higher than in the Amy1 strain. During the first hours of adult life amylase activity of the two strains does not differ. Then Amy4,6 activity starts to rise and becomes much higher (4-5 times) than Amy1 amylase activity, which remains approximately constant. All adult enzyme activities are much higher than in larvae. Comparison of enzyme activity of amylase and alpha-glucosidases in larvae and adults confirms that differences in amylase activities can become important only when starch is a limiting factor in the food.

X-ray-induced mutations affecting the level of the enzyme alcohol dehydrogenase in Drosophila melanogaster: frequency and genetic analysis of null-enzyme mutants

The frequency of X-ray-induced (null-enzyme) mutations at the alcohol dehydrogenase locus in Drosophila melanogaster was measured. The rate of recovery of chromosomes that fail to direct the synthesis of a functional Adh protein is 3 x 10(-8) per R for chromosomes that do not include large chromosome rearrangements. However, this analysis excludes a larger number of chromosomes that are "null-enzyme mutations" because thye are deleted for the region of the Adh locus. The dose of X-rays required to induce a frequency of non-deletion null-enzyme mutants equal to the spontaneous frequency is about 73 rad calculated from the data reported in this communication.

The alcohol dehydrogenase polymorphism in populations of Drosophila melanogaster. 3. Differences in developmental times

From the F2ratios of crosses betweenDrosophila melanogasterstrains homozygous for theAdhF(F) and theAdhs(S) allele it has been concluded that the developmental time ofFFhomozygotes is shorter than that ofSShomozygotes. This difference is found to be reinforced by increasing levels of crowding. A further analysis of developmental times has been performed by the transfer of larvae to agar medium after they have stayed for periods of variable length on regular food. From the percentage of emerging adults it can be concluded thatFFlarvae and, to a lesser extentFSlarvae, either reach their critical weights for pupation earlier thanSSlarvae or possess a lower critical weight. These differences in developmental time influence the course of allele frequencies. Between populations kept on a 2-week transfer schedule and on a 3-week schedule a divergence of allele frequencies is observed, in the former a decrease inSfrequency occurs. The relevance of the observed differences in developmental time for the maintenance of theAdhpolymorphism is discussed for laboratory populations kept on regular food and at varying densities.

Alcohol-oxidizing enzymes in 13 Drosophila species

Starch and polyacrylamide gel electrophoresis were used to ascertain the substrate specificities of alcohol-oxidizing enzymes in 13 Drosophila species. The substrates used were a variety of long- and short-chain aliphatic alcohols, one aromatic alcohol, and benzaldehyde. Only one enzyme (product of a single-gene locus) showed significant NAD+-dependent alcohol dehydrogenase activity with short-chain aliphatic alcohols. The 13 species, belonging to four different Drosophila groups, all showed a similar complement of alcohol-oxidizing enzymes, although differences in electrophoretic mobility and in levels of activity existed from species to species. These findings are relevant to the adaptation of Drosophila to alcohol environments.

Variation in amount of enzyme protein in natural populations

Among strains of Drosophila melanogaster each derived from a single fertilized female taken from natural populations, there is variation in both alcohol dehydrogenase (ADH) activity and the amount of ADH protein. The correlation between ADH activity and number of molecules over all strains examined is 0.87 or 0.96 in late third instar larvae depending on whether the substrate is 2-propanol or ethanol. With respect to the two common electrophoretic allozymic forms, F and S, segregating in these populations, the FF strains on the whole have higher ADH activities and numbers of ADH molecules than the SS strains. Over all strains examined, enzyme extracts from FF strains have a mean catalytic efficiency per enzyme molecule higher than that of enzyme extracts from SS strains when ethanol is the substrate, and much higher when 2-propanol is the substrate. One FF strain had an ADH activity/ADH protein ratio characteristic of SS strains.