Centrophobism inDrosophila melanogaster

Summary The term centrophobism is introduced to describe a newly discovered modification of search behavior in the walking fruitfly,Drosophila melanogaster: the avoidance of the center of an arena after diethylether narcosis. Evidence for the effect is obtained by comparison of the tracks of etherized and non-etherized flies under the influence of olfactory attractant around the center of the arena (Fig. 3). The tracks can be distinguished by their mean radial distance from the central district of the arena. Centrophobia denotes the relative difference of the distances of etherized flies and non-etherized controls (Fig. 4).Etherized flies avoid the center of the arena in spite of the attraction of olfactory, thermal or visual cues. The avoidance is significant even in the absence of conspicuous sensory cues for the discrimination of center and surround. The centrophobia obtained in the arena can be used to estimate the efficacy of attractants in the non-etherized control flies (Figs. 6, 7).The lowest possible dose of ether sufficient to elicit narcosis is sufficient to induce centrophobia. None of the other prevalent insect anaesthetics, CO₂, N₂ and cold, substitutes ether in the present experiments (Figs. 8, 9).Centrophobia arises immediately after ether narcosis. Once induced the effect lasts apparently undiminished for the life time of the flies (Fig. 9).Centrophobia has been found in either sex of the 9 strains tested so far (Fig. 5). Four strains including mutants deficient in wing formation (vestigial) or learning (dunce) show either temporal decline or partial suppression of centrophobia. The anomalous properties are actually due to enhanced spontaneous centrophobism in the non-etherized control groups of these strains (Fig. 10).     

Osmotropotaxis inDrosophila melanogaster

Summary Drosophila melanogaster is able to perform osmotropotaxis under open-loop conditions. With an optimal stimulus the average turning tendency to the side of higher concentration corresponds to a circular track with radiusr=0.8 cm. The response amplitude does not decrease within 1 or 2 h. Unilaterally antennectomized flies in an homogeneous odor field show a permanent turning tendency towards their intact side.The smallest concentration ratio to elicit osmotropotaxis in normal flies ranges between 610 and 910 at high and between 210 and 510 at an about 50 times lower odor intensity. No negative tropotaxis (i.e. turning to the side of lower concentration) is observed, even with strong repellents.     

Genetic characterization of dipeptidase activity modifiers inDrosophila melanogaster from natural populations

An examination of Drosophila melanogaster from natural populations revealed genetic variation for dipeptidase-A (DIP-A) and dipeptidase-B (DIP-B) activities within sets of lines that differed from one another only in the second or the third chromosome. Analyses of diallel crosses indicate that both activities are inherited additively, and coordinate control of expression is suggested by the significant positive correlation between the two activities. Electrophoresis and thermal denaturation studies failed to detect structural differences among lines with different levels of DIP-A activity. No characteristic level of activity could be associated with any DIP-A allozyme. Mapping experiments revealed the presence of activity modifiers that are in tight linkage with the structural gene, as well as those that manifest their effects from a distance. The maximum genetic distance between a high-activity effect on DIP-A and the structural gene was determined to be 0.029 map unit. These results are in accordance with the prevalence of activity modifiers for various enzymes in Drosophila melanogaster.     

Colour vision inDrosophila melanogaster

Summary Using a fully automatized procedure and a training scheme symmetrical with respect to the visual stimuli as well as to the aversive stimulus,Drosophila could be conditioned to blue and yellow lights. With constant test conditions and variation of the light intensities during the training procedure, it could be shown that the flies respond primarily to the colour of the light.We are grateful to Dr. W. Edrich and K.-F. Fischbach for exchange of ideas. Dr. J. Bammert gave advice for the statistical treatment.     

Wingless mutation inDrosophila melanogaster

A temperature sensitive lethal allele of thewingless locus ofDrosophila melanogaster together with previously studied lethal and viable alleles in this locus, has been used to study some properties of this locus. These studies show the existence of two lethal phases for thewingless lesion; one during embryogenesis and another during pupation. By growing embryos with temperature sensitivewingless lesion at the permissive temperature and letting the larvae develop at non-permissive temperature, a large-scale cell death and subsequent regeneration were seen to occur in the mutant wing discs. This cell death followed by regeneration alters the normal developmental potential of the wing disc. Disc transplantation experiments show that these discs are incapable of differentiating into wing blade structures.     

Enzyme polymorphism inDrosophila melanogaster populations collected in two different habitats in Hungary

The level of enzyme polymorphism was compared in tenDrosophila melanogaster populations collected in farmyards and distilleries in two regions of Hungary. The total genetic diversity was partitioned into between-and within-population components at each investigated locus using Wright's F-statistics. Population differentiation was studied in two different ways. Genetic distances between pairs of populations were calculated and a hierarchical analysis of gene diversity was performed. Based on the F values gene flow was estimated among the populations at different levels of the hierarchy. The results indicated that our farmyard populations collected within a region could be considered as parallel samples from a panmictic population rather than samples of distinct populations. In distilleries, the flies might be influenced by two different evolutionary forces: (i) selection due to the extremely high concentration of ethanol in the fermenting mash and (ii) genetic drift due to the combination of repeated founder effects and fluctuating population size. Our results suggested that distillery populations could not be regarded as real populations either. They could be considered as peculiar cases: founder individuals taken from the total population (region) established special populations which survived in the distilleries for many generations. Thus the dominating force acting on the distillery populations was genetic drift.     

Evidence for overdominance inDrosophila melanogaster

In artificial populations ofDrosophila melanogaster the mutantsvermilion (v) andcinnabar (cn), both interfering with eye pigment formation, appeared to be balanced against wild type, indicating that the heterozygotesv/+ andcn/+ have a selective advantage over the respective homozygotes. In a population homozygous forv, the mutantcn in competition with its wild type allele tended to be eliminated. Ifcn was homozygous,v showed a similar tendency. Thus in competion experiments it was found that the heterozygotes for one of the two recessive genes,v andcn, ceased to be heterotic when the other recessive is homozygous. These findings are considered to be evidence for the existence of overdominance.     

Evidence for myosin heterogeneity inDrosophila melanogaster

Summary Electrophoresis of myosin extracts from larvae and adult tissues ofDrosophila melanogaster under non-dissociating conditions indicate that two of the bands seen are myosins. They stain for Ca²⁺ ATPase activity and when cut and re-run under dissociating conditions are found to contain a myosin heavy chain that co-migrates with rabbit skeletal muscle myosin heavy chain. One of the forms of myosin seen is found primarily in extracts from the leg. The other is common to the adult fibrillar flight muscles and the larval body wall muscles.The electrophoretic evidence for two myosin types is strengthened by the histochemical demonstration of two myofibrillar ATPases on the basis of their lability to acid or alkali preincubation. The myofibrillar ATPase in the leg and the Tergal Depressor of the Trochanter (TDT) are shown to be relatively acid labile and alkali stable. The larval body wall muscles and the adult fibrillar flight muscles have an ATPase which is acid stable and alkali labile. This distribution of the two myofibrillar ATPase coincides with that predicted by electrophoresis of extracts from whole tissue and also locates the two myosins to specific muscle types.     

Development of thoracic curvature inDrosophila melanogaster

Summary The influence of muscle development on thorax morphogenesis has been investigated inDrosophila melanogaster. The development of an indirect flight muscle, the dorsal longitudinal muscle (DLM), has been thought to be responsible for the formation of the distinct thoracic curvature. Using aDrosophila mutant (sr/Df(3)sr) in which the DLM is completely missing, we have shown that a normally curved thorax still is produced. Such results indicate that an external structure (epidermis) is capable of developing wholly independent of an absent internal structure (muscle).     

Genomic imprinting of chromatin inDrosophila melanogaster

During gametogenesis, chromosomes may become imprinted with information which facilitates proper expression of the DNA in offspring. We have used a position effect variegation mutant as a reporter system to investigate the possibility of imprinting inDrosophila melanogaster. Genetic crosses were performed in which the variegating gene and a strong modifier of variegation were present either within the same parental genome or in opposite parental genomes in all possible combinations. Our results indicate that the presence of the variegating chromosome and a modifier chromosome in the same parental genome can alter the amount of variegation formed in progeny. The genomic imprinting we observed is not determined by the parental origin of the variegating chromosome but is instead determined by the genetic background the variegating chromosome is subjected to during gametogenesis.