Latitudinal Adh allozymic variation and ethanol tolerance in Indian populations of Drosophila melanogaster

Ten Indian geographical populations of D. melanogaster were assayed electrophoretically for Adh genic variation. The Indian geographical populations of D. melanogaster revealed significant clinal variation (3 % for 1 d? latitude) at Adh locus and Adh^F allelic frequency correlated significantly with increase in latitude. It was suggested that the abundance of secondary alcohols in the southern Indian tropical and humid environment might exert selective pressure favouring higher frequency of Adh^S allele. Patterns of ethanol utilization as well as ethanol tolerance were analyzed in larval and adult individuals of six geographical populations of D. melanogaster. Latitudinal variation in ethanol tolerance was observed in D. melanogaster populations from India. The parallel occurrence of latitudinal variation it Adh locus as well as ethanol tolerance in Indian geographical populations of D. melanogaster could be maintained by balancing natural selection varying spatially along the north-south axis of the Indian sub-continent.     

A biochemical genetic study of alcohol dehydrogenase isozymes of the medfly,Ceratitis capitata wied

A concerted effort is under way to analyze, at the genetic, biochemical, and molecular level, theAdh gene system in the medflyCeratitis capitata, an important agricultural pest. The isoelectric focusing (IEF) pattern of alcohol dehydrogenase (ADH) of the medfly demonstrates the presence of two well-differentiated, genetically independent dimeric proteins, called ADH-1 and ADH-2. These proteins do not exhibit interlocus heterodimeric isozymes, and the genes are not controlled coordinately during development,Adh ₁ andAdh ₂ being expressed mainly in muscle or in fat body and ovary, respectively. From the intensity of the IEF isozyme patterns, primary alcohols are judged to be better substrates than secondary alcohols, in contrast withDrosophila melanogaster ADH, and ethanol is probably the most efficient substrate for both sets of isozymes. The isoelectric points of ADH-1 (pI=5.4) and ADH-2 (pI=8.6) are different fromD. melanogaster ADH (pI=7.6), but the medfly ADH-1 has a native molecular weight (approx. 58 kD) close to that ofD. melanogaster. A population survey of samples both from laboratory strains and from wild geographically different populations showed that theAdh ₁ locus is more polymorphic thanAdh ₂. The most variable populations are from Africa, the supposed source area of the species. Further, a case of selection at theAdh ₁ locus under laboratory conditions is reported. The hypothesis ofAdh gene duplication and the degree of similarity between medfly andDrosophila ADH are also discussed. This research was supported mainly by National Research Council of Italy, Special Project RAISA, Sub-project No. 2, Paper No. 342. Grants from the International Atomic Energy Agency, Vienna, Austria, from European Communities Commission, Second R & D Programme, “Science and Technology for Development,” and from the Italian Ministry of University and Scientific Research and Technology (“Funds 40%”) also supported this work. This paper was written when the senior author was on leave of absence at the IMBB, Crete, Greece; he was financially supported by an ECC Senior Fellowship.     

Studies of esterase 6 in Drosophila melanogaster XII. Evidence for temperature selection of Est 6 and Adh alleles

Changes in allele frequencies at the esterase 6 (Est 6) and alcohol dehydrogenase (Adh) enzyme loci of Drosophila melanogaster and simulans are examined in natural populations and artificial populations maintained at two temperatures. Results from cage populations at 18 °C and 25 °C provide evidence for temperature selection at both loci. Seasonal population samples show no significant change in gene frequencies for either locus, a reasonable outcome given the small selection coefficients found in cage populations. The temperature effect for the Adh locus appears to be direct: natural selection of the fast allele in cool environs and of the slow allele in warm environs. The temperature effect for Est 6 is weaker and complicated by sex differences and deviations from Hardy-Weinberg expectation. This evidence and different Est 6 frequencies found for melanogaster and simulans, in conjunction with evidence of the male reproductive function of this enzyme, suggest that Est 6 polymorphisms are maintained in natural populations by a complex form of sexual selection.     

Adaptive significance of the action of the Drosophila melanogaster alcohol dehydrogenase locus through the heat shock protein system

Four Drosophila melanogaster strains, each homozygous for one of the two major ADH aliozymes, Fast and Slow (Adh ^F1, Adh ^S , Adh ^F2 and Adh ^S2) were used to study the interaction of the Adh locus with ethanol and temperature. The separate and especially the combined effects of these two parameters allow the conclusion that the Adh locus of D. melanogaster intervenes in the adaptation process through the heat shock protein system.     

Allozyme variation in Greek wild populations of Drosophila melanogaster and D. simulans along a North-South gradient

Allozyme frequency data from five Greek wild sympatric populations of Drosophila melanogaster and D. simulans along a North-South gradient were analyzed for genotype-environment relationships. The regression coefficient of genetic distance on geographic distance indicates that there is a significant relationship between these parameters for D. melanogaster only. Highly significant differences in specific alleles at certain loci were found between the various local populations studied. The changes in Gpdh ^F of D. melanogaster and Est-6 ^F of D. simulans exhibited clinal patterns in allele frequencies. In addition, analysis of D. melanogaster Gpdh ^Fand Adh ^F allele frequencies shows that the Greek data do not have regression coefficients (regressing allele frequency on degrees North of latitude) of the same sign as East-and West-Coast United-States populations. These contradictory data are discussed in relation to what is known about the maintenance of the Adh and Gpdh polymorphisms.     

Phenotypic expression of ADH regulatory genes inDrosophila melanogaster: a comparative study between a paleartic and a tropical population

In vitro ADH activity was studied inD. melanogaster males from two sets of third chromosome substitution lines, one from a paleartic population (Gigean, France), the other from a tropical population (Brazzaville, Congo). As a linear model with raw ADH activity dependent on fresh weight was significant in both sets of lines, the raw activity was adjusted by regression on weight. Two main results were found: (a) the well-known substantial intrapopulation variability; and (b) third chromosome geographical origin did not affect the mean ADH activity. Unlike the structuralAdh gene polymorphism which allows the two populations to be distinguished, the polymorphism of the third chromosome ADH regulatory genes (or more exactly their phenotypic expression) does not allow to discriminate between them. These results are discussed in the context of the adaptation ofD. melanogaster to the alcoholic substrates in light of a model proposed by Hedrick and McDonald (1980) in order to interpret variations in both structural and regulatory gene polymorphisms.     

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

Summary 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.     

Distinct electrophoretic polymorphism pattern at alcohol dehydrogenase (<Emphasis Type="Italic">Adh</Emphasis>) locus of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> natural populations from Turkey

Small number of Drosophila melanogaster populations from two distinct geographical regions of Turkey, Central Anatolia and Black Sea, were studied. Populations sampled were electrophoresed for a single locus, alcohol dehydrogenase (Adh) to assess population differentiation. Both the magnitude of genetic differentiation levels and the population structure based on hierarchical F-statistics allow populations to be grouped on two genetically divergent area, Central Anatolian and Black Sea. One ecological correlate, average yearly maximum rainfall, R _year, seems to track this Adh genetic variation pattern. The study also shows that a typical pattern of geographical Adh polymorphism can emerge with a handfull of populations sampled across a relatively small distance. The text was submitted by the author in English.     

Impact of body melanization on mating success in Drosophila melanogaster

Mating speed and copulation duration respond rapidly to laboratory selection in Drosophila melanogaster Meigen (Diptera: Drosophilidae), but there is a lack of data on the evolutionary response to natural selection in the wild. Further, it is not clear whether body melanization and mating behavior are correlated traits. Accordingly, we tested whether variation in body color impacts on mating latency, copulation duration, and fecundity in latitudinal populations of D. melanogaster. We observed geographical variation (cline) for mating propensity, i.e., mating speed as well as copulation duration increased along latitude. Phenotypic plastic responses for body melanization at 17 and 25 °C also showed significant correlations with mating latency and copulation duration. Within‐population analysis based on assorted dark and light flies of five geographical populations showed significant positive correlations of copulation duration and fecundity with body melanization. To assess the role of males and/or females on mating speed and copulation duration, we used atypical body color strains (i.e., dark and light males of D. melanogaster) for no‐choice mating tests. Our data showed a major influence of males for copulation duration and of females for mating speed. Furthermore, a difference in impact of body melanization on mating speed and copulation duration was demonstrated between species, i.e., low melanization in Drosophila ananassae Doleschall is correlated with lower mating speed and shorter copulation duration than in D. melanogaster. Geographical changes in mating propensity were significantly correlated with body melanization at three levels, i.e., within and between populations and between species. Thus, we have shown that a relationship exists between body melanization and mating success. Further, we found seasonal changes in temperature and humidity to confer selection pressures on mating‐related traits.     

Variation in alcohol dehydrogenase activity in vitro in flies from natural populations ofDrosophila melanogaster

Alcohol dehydrogenase (ADH) activity variation in male flies taken directly from seven natural populations ofDrosophila melanogaster is largely accounted for by segregation of alleles at theAdh structural gene locus. There was little overlap in the ADH activities ofAdh ^F andAdh ^s homozygotes. Body weights varied only slightly betweenAdh genotypes and contributed little to ADH variation. Between and within population variation in ADH activity and ADH protein in flies in the wild is mainly due to the relative frequencies ofAdh ^F andAdh ^s.     

A comparison of behavioural change in Drosophila during exposure to thermal stress

In order to understand how adaptive tolerance to stress has evolved, we compared related species and populations of Drosophila for a variety of fitness relevant traits while flies directly experienced the stress. Two main questions were addressed. First, how much variation exists in the frequency of both courtship and mating among D. melanogaster, D. simulans, and D. mojavensis when each are exposed to a range of temperatures? Second, how does variation in these same behaviours compare among four geographically isolated populations of D. mojavensis, a desert species with a well defined ecology? Our hierarchical study demonstrated that mating success under stress can vary as much between related species, such as D. melanogaster and D. simulans, as between the ecologically disparate pair, D. melanogaster and D. mojavensis. Strains of this latter desert species likewise varied in tolerance, with differences approaching the levels observed among species. The consequences of stress on male courtship differed markedly from those on female receptivity to courtship, as mating behaviours among species and among strains of D. mojavensis varied in subtle but significant ways. Finally, a comparison of variation in thermotolerance of F₁ hybrids between the two most extreme D. mojavensis populations confirmed that genetic variation underlying traits such as survival or the ability to fly after heat stress is completely different. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83 , 197–205.     

THE GENETIC BASIS OF SEXUAL ISOLATION BETWEEN DROSOPHILA MELANOGASTER AND D. SIMULANS

The genetic analysis of sexual isolation between the closely-related species Drosophila melanogaster and Drosophila simulans involved two experiments with no-choice tests. The efficiency of sexual isolation was measured by the frequency of courtship initiation and interspecific mating. We first surveyed the variation in sexual isolation between D. melanogaster strains and D. simulans strains of different geographic origin. Then, to investigate variation in sexual isolation within strains, we made F₁ diallel sets of reciprocal crosses within strains of D. melanogaster and D. simulans. The F₁ diallel progeny of one sex were paired with the opposite sex of the other species. The first experiment showed significant differences in the frequency of interspecific mating between geographic strains. There were more matings between D. simulans females and D. melanogaster males than between D. melanogaster females and D. simulans males. The second experiment uncovered that the male genotypes in the D. melanogaster diallel significantly differed in interspecific mating frequency, but not in courtship initiation frequency. The female genotypes in the D. simulans diallel were not significantly different in courtship initiation and interspecific mating frequency. Genetic analysis reveals that in D. melanogaster males sexual isolation was not affected by either maternal cytoplasmic effects, sex-linked effects, or epistatic interaction. The main genetic components were directional dominance and overdominance. The F₁ males achieved more matings with D. simulans females than the inbred males. The genetic architecture of sexual isolation in D. melanogaster males argues for a history of weak or no selection for lower interspecific mating propensity. The behavioral causes of variation in sexual isolation between the two species are discussed.     

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.This work was supported by a grant to T. H. D. from the Science Research Council.     

Isozyme variability in species of the genus Drosophila. VI. Frequency-property-environment relationships of allelic alcohol dehydrogenases in D. melanogaster

Adult Drosophila melanogaster from naturally occurring populations in the Eastern United States were examined by gel electrophoresis for their alcohol dehydrogenase (ADH) phenotype. The ADH enzymes were partially purified and characterized. Frequencies of the controlling alleles, Adh ⁴ and Adh ⁶, were discovered to vary in a clinal pattern. Adh ⁶ reaches a maximum frequency of about 0.90 in the South and minimum of about 0.50 in the North. Partially purified enzymes from the three Adh genotypes varied according to specific activity, substrate specificity, and heat stability. A differential influence of pH was indicated. There was little variation in K _m values for ethanol and DPN⁺ among the enzymes.This work was supported by AEC Contract No. AT-(40-1)-3980 and by PHS Research Grant No. GM 11546.Paper No. 3880 of the Journal Series of the North Carolina Experiment Station, Raleigh, North Carolina. This work incorporates, in part, the thesis research of C. L. Vigue to be submitted in partial fulfillment of the Ph.D. requirements in Genetics.     

The fate of several migrant genes in isolated populations of Drosophila melanogaster

Sepia-eyed flies carrying the slow electrophoretic variant of either Est-6 or Adh were introduced in low numbers and at infrequent intervals into populations of wildtype flies (+ ^se /+ ^se ) that were also homozygous for the fast moving variant of either Est-6 (50 populations) or Adh (50 populations). After 24 generations, the frequency of the sepia alleles was approximately 25%, although there was considerable variation from population to population. The fate of the Est-6 slow allele corresponded closely to that of sepia (which is located ten map units distant), although one population retained the slow allozyme variant but rejected sepia. The Adh slow allele was also retained by many populations. A number of them retained Adh-S but not sepia, and vice versa; these loci are on different chromosomes. The advantage of sepia heterozygotes was estimated to be about twice that of wildtype homozygotes. The data suggest that the selective advantage resides not with the sepia locus itself, but with a nearby chromosomal region.Financial support for work reported here was supplied under grant number GM24850, National Institutes of Health.     

Perturbation of gene frequencies in a natural population of Drosophila melanogaster: evidence for selection at the Adh locus

The cellar population of Drosophila melanogaster at the Chateau Tahbilk Winery (Victoria, Australia) was perturbed for alcohol dehydrogenase (Adh) gene frequencies. Phenol oxidase (Phox) frequencies were also perturbed and monitored as a control. Subsequent gene frequency changes, together with information on population structure, indicated that selection acted on the chromosome regions of both loci. Adh gene frequencies returned to preperturbation levels in a predictable manner. A model in which the relative fitness of Adh phenotypes was determined by temperature-dependent specific activities of enzymes of Adh genotypes adequately accounts for the rate of gene frequency change at this locus. Thus temperature behaves as a selective agent in modulating Adh gene frequencies in this cellar environment.     

Alcohol dehydrogenase polymorphism in populations of Drosophila melanogaster. II. Relation between ADH activity and adult mortality

Eight Drosophila melanogaster strains, seven homozygous for Adh ^F alleles and one for an Adh-null mutant, were compared for ADH activity in males and adult mortality on ethanol-supplemented food. The strains differed considerably in these qualities. A positive correlation was found between ADH activity and ld ₅₀. The relevance of this finding is discussed in relation to the differential selection acting on Adh genotypes kept on ethanol-supplemented food.     

Complexity in evolved regulatory variation for alcohol dehydrogenase genes in HawaiianDrosophila

Summary The alcohol dehydrogenase gene (Adh gene) ofDrosophila affinidisjuncta is expressed at a higher level in the larval midgut and Malpighian tubules than the homologous gene fromDrosophila hawaiiensis. This study analyzed thecis-acting sequences responsible for these regulatory differences in larval tissues ofDrosophila melanogaster transformants. A series of 10 chimeric and deletedAdh genes was introduced into the germ line ofD. melanogaster, and tissue-specific expression levels were quantified by gel electrophoresis of tissue extracts. Sequences in the upstream region of the two genes had the strongest influence on enzyme production in the midgut and Malpighian tubules. Other sequence elements also showed effects, some of which were tissue specific. Most gene fragments displayed context-dependent effects, thus supporting the proposed model of polygenic regulation ofAdh gene expression.     

A courtship behavior that makes monandrous females polyandrous

Females of many animal species mate several times with different males (polyandry), whereas females of some species mate with a single male (monandry) only once. Little is known about the mechanisms by which these different mating systems evolve. Females of Drosophila prolongata mate serially, unlike Drosophila melanogaster females that refuse to remate for several days after their first mating (remating suppression [RS]). Nevertheless, interestingly, nonvirgin D. prolongata females refuse to remate with males that are prohibited from performing their species-specific courtship behavior, leg vibration (LV), suggesting that LV overrides RS making it cryptic in D. prolongata. In this study, we examined how long this cryptic RS persists. Surprisingly, it was sustained for at least 2 weeks, showing that RS is substantially augmented in D. prolongata compared to that of D. melanogaster. The two most closely related species to D. prolongata, Drosophila rhopaloa and Drosophila carrolli, do not perform LV and showed augmented RS, supporting the idea that augmented RS could have evolved before LV was acquired. These results suggested that D. prolongata females are intrinsically monandrous, whereas the newly evolved courtship behavior makes them polyandrous. This is a rare case in which a proximate mechanism of polyandry evolution from monandry is demonstrated.     

Mimicry of isozyme adaptive advantage by gene association I. Relationship between Adh genotypes and body dimension in Drosophila cage populations: A multivariate analysis

Experiments are described that are to prove that the apparent selective responses at the Adh locus in Drosophila melanogaster are not independent from its genetic background and from the variation at the gene pool level brought about by the changes of selection pressure. The dynamics of allozyme frequencies were observed at the Adh locus, of five metric traits and of reproductive fitness in two synthetic populations of Drosophila melanogaster originated from the same cross between Canton and Oregon strains, homozygotes for different Adh alleles and reared at different temperature (25 °C and 28 °C), until all above mentioned characters showed no more variations. The results obtained by univariate and multivariate statistical analyses can be summarized as follows:

- Adh ^s allele frequency keeps high and reaches very similar values in spite of the different environmental temperatures, whose selective effects at the Adh locus are therefore unlikely;

- both populations evolve toward the stabilization of Adh frequencies and other characters with a process strictly dependent on the permanence of coadapted blocks of genes which were contributed to the F₂ generation by the parental Canton and which are identified phenotypically by the association of Adh ^s/s with short wing;

- at the stabilization point the flies classified on the basis of their Adh genotype exhibit different shapes, namely their metric phenotypes can be discriminated considering all the respective traits together by means of multivariate analyses.

Owing to the presence in the initial populations of heterosis and epistatic interactions between loci, the observed differences between Adh genotype groups should represent the outcome of selection upon coadapted blocks of genes rather than on individual loci. Therefore, these results are argued as further evidence that each Adh genotype can be associated to different gene arrangements and its adaptive value cannot be isolated from that of its genetic background.