Enzymatic variation at seven loci in nine natural populations of Drosophila melanogaster

Studies of esterase 6 inDrosophila melanogaster: XI. Modification of esterase 6 activity by unlinked genes

The often remarkable similarity in structural gene products among related species has led to the hypothesis that species differences may reside largely in changes at regulatory gene loci. This hypothesis assumes that groups capable of speciating have allelic variation at regulatory loci in their natural populations. We have undertaken an analysis of the mode of regulation of theesterase 6(Est 6) locus inDrosophila melanogasterto determine the nature and extent of regulatory gene variation in natural populations. Analyses of esterase 6 (EST 6) activity among strains carrying the same thermostability variants reveal that significant, specific-activity differences are present. Reciprocal crosses between lines having high and low EST 6 activity show that loci other than theEst 6structural gene influence EST 6 activity. Analyses of male hybrids from crosses betweenD. melanogasterandsimulansindicate that theXchromosome of these flies affects the expression of theEst 6locus, resulting in unequal levels of enzyme activity from the two alleles. The effect is sex and tissue specific. Female hybrids carrying theXchromosomes of both species exhibit equal expression of the twoEst 6alleles. We have determined whether natural populations are polymorphic forXchromosomes which affect EST 6 activity by extracting singleXchromosomes from wild-collected males and placing these chromosomes in identical genetic backgrounds. Stocks which are otherwise genetically identical but carry independently derivedXchromosomes show significant differences in the activity of EST 6. These data suggest that regulatory loci may be commonly polymorphic in natural populations.

Distribution of nonrandom associations between pairs of protein loci along the third chromosome of Drosophila melanogaster

The within-chromosome distribution of gametic disequilibrium (GD) between protein loci, and the underlying evolutionary factors of this distribution, are still largely unknown. Here, we report a detailed study of GD between a large number of protein loci (15) spanning 87% of the total length of the third chromosome of Drosophila melanogaster in a large sample of haplotypes (600) drawn from a single natural population. We used a sign-based GD estimation method recently developed for multiallelic systems, which considerably increases both the statistical power and the accuracy of estimation of the intensity of GD. We found that strong GD between pairs of protein loci was widespread throughout the chromosome. In total, 22% of both the pairs of alleles and pairs of loci were in significant GD, with mean intensities (as measured by D' coefficients) of 0.43 and 0.31, respectively. In addition, strong GD often occurs between loci that are far apart. By way of illustration, 32% of the allele pairs in significant GD occurred within pairs of loci separated by effective frequencies of recombination (EFRs) of 15-20 cM, the mean D' value being 0.49. These observations are in sharp contrast with previous studies showing that GD between protein loci is rarely found in natural populations of outcrossing species, even between very closely linked loci. Interestingly, we found that most instances of significant interallelic GD (68%) involved functionally related protein loci. Specifically, GD was markedly more frequent between protein loci related by the functions of hormonal control, molybdenum control, antioxidant defense system, and reproduction than between loci without known functional relationship, which is indicative of epistatic selection. Furthermore, long-distance GD between functionally related loci (mean EFR 9 cM) suggests that epistatic interactions must be very strong along the chromosome. This evidence is hardly compatible with the neutral theory and has far-reaching implications for understanding the multilocus architecture of the functional genome. Our findings also suggest that GD may be a useful tool for discovering networks of functionally interacting proteins.

Enzyme polymorphism in Drosophila melanogaster populations in Iraq

Electrophoretic studies of the degree and pattern of polymorphism at two third-chromosome loci, esterase-6 (Est-6) and phosphoglucomutase (PGM), were carried out in three Drosophila melanogaster populations collected from different localities in Iraq: Mosul, Tuwaitha, and Basrah. The results show that only the Tuwaitha population was polymorphic for both loci; the other two populations were polymorphic for Est-6 and monomorphic for PGM. The allele frequency changes at both loci were followed for 20 generations in an experimental cage derived from the Tuwaitha population; it was found that there is a deviation from Hardy-Weinberg equilibrium at both loci toward the homozygote.

The existence of LSP-1 beta S in Drosophila melanogaster natural populations in two northern states

LSP-1 beta S is present in Michigan and Massachusetts Drosophila melanogaster natural populations. Its frequency, 10%, is significantly higher in an East Jordan, Mich. (latitude, 45.10 degrees N), population than in East Lansing, Mich. (latitude 42.44 degrees N), or Hadley, Mass. (latitude, 42.21 degrees N), populations, where it averages 3% at each location. The average frequency of LSP-2S is more comparable, 6, 5, and 7% at East Jordan, East Lansing, and Hadley, respectively. LSP-1 gamma F variants are also present. A total of 342 single third-instar larvae was scored for LSP-1 autosomal variants, and 323 for LSP-2 variants. Each larva represented a newly established isofemale line from collections at East Jordan in 1981 and 1983, East Lansing in 1982, and Hadley in 1981, 1982, and 1983. Within localities, frequencies of hemolymph protein variants did not differ significantly between years. Proteins 9, 10, 11, and 15 correspond to the LSP-1 gamma, beta, and alpha triplet and LSP-2 polypeptide in D. melanogaster. Our results together with those of Singh and Coulthart [(1982). Genetics 102:437] indicate that D. melanogaster populations in north temperate climates maintain considerable genetic heterogeneity for the larval hemolymph proteins.

Studies of esterase 6 in Drosophila melanogaster. XIV. Variation of esterase 6 levels controlled by unlinked genes in natural populations

The esterase 6 (Est-6) locus inDrosophila melanogasteris located on the third chromosome and is the structural gene for a carboxylesterase (E.C.3.1.1.1) and is polymorphic for two major electromorphs (slow and fast). Isogenic lines containingXchromosomes extracted from natural populations and substituted into a common genetic background were used to detect unlinked factors that affect the activity of theEst-6locus. Twofold activity differences of esterase 6 (EST 6) were found among males from these derived lines, which differ only in theirXchromosome. These unlinked activity modifiers identify possible regulatory elements. Immunoelectrophoresis was used to estimate quantitatively the levels of specific cross-reacting material in the derived lines. The results show that the variation in activity is due to differences in the amount of EST 6 present. The data are consistent with the hypothesis that there is at least one locus on the X chromosome that regulates the synthesis of EST 6 and that this regulatory locus may be polymorphic in natural populations.

Latitudinal variation in octanol dehydrogenase and acid phosphatase allele frequencies in Drosophila melanogaster

The octanol dehydrogenase (Odh) and acid phosphatase (Acph) loci of Drosophila melanogaster are each polymorphic for two electrophoretically detectable alleles. The frequencies of the Odh and Acph alleles have been analysed in populations sampled from up to a 40 ° latitudinal range in each of Australasia, North America and Europe/Asia. Odh (S) frequency is found to be significantly negatively associated with distance from the equator in all three zones. The relationship of Acph (S) frequency to distance from the equator is significant and negative in Australasia but neither significant nor consistent in sign in North America and Europe/Asia.

Latitudinal variability of Drosophila melanogaster: allozyme frequencies divergence between European and Afrotropical populations

Allelic frequencies at five polymorphic loci were determined in seven European and six Afrotropical populations of Drosophila melanogaster. African populations, which may be considered as ancestral for the species, showed a greater genetic diversity as measured by the number of alleles found. Within each geographic group (Europe or tropical Africa) genetic distances between local populations were very small (D = 0.027). By contrast, the average distance between European and African populations (D = 0.389) was more than 12 times bigger. It was previously known that various morphological or physiological differences, which probably reflect genetic adaptations to different environments, exist between these temperate and tropical populations. Data presented here suggest that the divergence in allozyme frequencies also reflects some selective mechanisms.

Selection at the alpha-Gpdh locus in experimental populations of Drosophila melanogaster

Three sets of experiments have been conducted in order to evaluate the role of natural selection at the alpha-Gpdh locus in Drosophila melanogaster. (1) The evolution of the F-allele frequency has been followed for many generations in 13 experimental populations having different genetic backgrounds. (2) Egg-to-adult viability has been measured in synthetic populations derived from one locality (Brouilly) and the results have been compared with those of a previous experiment involving a different local population (Tostes). (3) The effects of sodium octanoate on egg-to-adult viability have been measured on the genotypes FF, FS, SF, and SS. The results demonstrate that selection operates on a small block of genes which includes the alpha-Gpdh locus.

Esterase 6 in Drosophila melanogaster: reproductive function of active and null males at low temperature

Esterase 6 is a polymorphic carboxylesterase (carboxylic-ester hydrolase, EC 3.1.1.1) localized to the reproductive tract of male Drosophila melanogaster and transferred to females at copulation. The reproductive fitness of males is strongly affected by temperature and the esterase 6 alleles (active versus null) that they carry. Low temperature (18 degrees C) dramatically changes the character of reproductive functions relative to optimal 25 degrees C. Males with active esterase 6 mate sooner, copulate for a shorter time, and produce more progeny per mating than do esterase 6 null males at 18 degrees C, in contrast to equal progeny production at 25 degrees C. A male esterase 6 effect on the remating speed of females at 25 degrees C is absent at 18 degrees C. Previous work suggests that male esterase 6 promotes ejaculate transfer, sperm storage, and use in females. The differences in reproductive fitness at 18 degrees C noted here may follow from the effects of esterase 6 on sperm transfer and utilization. The esterase 6 effect on productivity is consistent for different female types, even though the components of productivity that were affected, egg laying and egg fertility, changed with female type. These data lead to the hypothesis that the wide-spread polymorphism for esterase 6 may be adaptively significant.

Latitudinal relationships of esterase-6 and phosphoglucomutase gene frequencies in Drosophila melanogaster

Geographic variation in Esterase-6 (Est-6) and Phosphoglucomutase (Pgm) gene frequencies in Australasian populations of Drosophila melanogaster are compared with analogous data collated from 16 previous reports for North America and Europe/Asia. A large-scale latitudinal cline is found on all three zoogeographic zones for Est-6 and overall, Est-61.00 frequency increases from about 20 per cent around 20 degrees latitude to about 80 per cent approaching 50 degrees latitude. In contrast, there is no consistent evidence for the latitudinal cline in Pgm gene frequencies in any of the three zones with Pgm1.00 frequency generally about 85 per cent and Pgm1.20 and Pgm0.70 frequencies each between 5 per cent and 10 per cent. The consistent Est-6 clines are attributed to latitudinal selection gradients but not consistent correlations are found between Est-6 gene frequencies and maximum or minimum temperature or rainfall which might be associated with these gradients. The directions of the Est-6 clines in fact run counter to expectations based on the in vitro thermostabilities of the respective allozymes.

Studies of esterase 6 in Drosophila melanogaster. VII. Remating times of females inseminated by males having active or null alleles

Esterase 6 (EST 6) in Drosophila melanogaster is a male reproductive enzyme transferred to females as a component of the seminal fluid [Richmond, R. C., Gilbert, D. G., Sheehan, K. B., Gromko, M. H., and Butterworth, F. W. (1980). Science 207:1483-1485]. Here we report investigation into the relation between EST 6 and remating by females. EST 6 activity in a strain selected for decreased time to remating is increased over control levels. Inseminated females remated to males carrying null or active alleles show no differences in the timing of remating, However, females inseminated by EST 6-active males remate significantly sooner than females inseminated by null males. Interrupted copulation experiments demonstrate that the remating effect is not due to EST 6 alone but requires other components of the ejaculate. Other evidence suggests that sperm stored in the ventral receptacle respond to EST 6 levels and control remating time. As the first mate of a female who will remate, null-EST 6 males have, under laboratory conditions, a significantly higher fitness than males carrying active alleles. Thus the absence of null alleles of EST 6 in natural populations presents a dilemma suggesting that the remating effect of EST 6 may be balanced by other effects on reproduction.

Studies of esterase 6 in Drosophila melanogaster. VI. ejaculate competitive abilities of males having null or active alleles

Recent studies of the function of the polymorphic seminal fluid enzyme, esterase 6, of Drosophila melanogaster suggested that it may act in the process of sperm displacement (Gilbert, Richmond and Sheehan, 1981a). This report examines the competitive ability of ejaculates from males homozygous for null or active alleles of esterase 6 under three experimental conditions that model aspects of sexual selection affecting males. The results demonstrate no significant difference in ejaculate competition between esterase 6 null or active male types, but marker males used for paternity identification had poorly competitive ejaculates. The proportion of second-male progeny, P2, used as an index of competition is primarily influenced by second-male genotype and uninfluenced by female genotype, P2 can change with time from remating and be unaffected by different intensities of competition, which suggests a complex ejaculate competition mechanism.

Multiple matings, effective population size and sexual selection in Drosophila melanogaster

The distribution of sexually efficient males has been analysed in two populations made up of 5 times more females than males. When observation stops as soon as the number of inseminated females equals the number of males, 25 per cent of males in both strains had not mated, 50 per cent of the matings were performed by 50 per cent of the males who mated only once and the other 50 per cent of matings were performed by 25 per cent of the males who mated 2 or 3 times. Productivity of the successive matings falls drastically after the third mating. The relative role of sexual selection and multiple matings as components of fitness are discussed, as well as their implications for the effective population size.

Maintenance mechanism of polymorphism at the alpha-Gpdh locus in Drosophila melanogaster

Polymorphism at the alpha-Gpdh locus was studied in Drosophila melanogaster. Using two different lines, one marked by the F allele (FF line) another by the S allele (SS line), four populations were initiated, two in which the initial frequency of F was 0.1 and two in which it was 0.9. They have been observed for 34 generations. From the fifth generation on, the equilibrium frequency in the four cages was about 0.60. Viability has been measured during the evolution of te populations while F frequencies changed and recombinations between the FF and SS lines occurred. It has been evaluated in synthetic populations built with different frequencies: (1) from the original FF and SS lines and (2) from FF and SS lines extracted after 34 generations of joint evolution. In all three cases, the FF viability depended on the frequency of the F allele. The similarity of the three linear regressions implies that alpha-Gpdh locus or other closely linked loci is the target of the selection in the populations analyzed here.