Allelic variation at the frizzled locus of Drosophila

The epidermis of Drosophila has a tissue polarity that is manifested by a parallel array of polarized structures (primarily hairs and bristles). The production of normal tissue polarity requires the function of the frizzled (fz) locus. We have isolated a large number of alleles at this locus and have phenotypically characterized more than 25 of them. We have found extensive allelic variation that a previous study failed to detect. Most of the alleles fall into a hypomorphic to amorphic series. Two alleles, however, have unusual properties. These alleles, which in general are moderately strong alleles, fail to produce a rough eye phenotype that is characteristic of all the other moderate or strong fz alleles. Thus, these two alleles are tissue specific in effect. Furthermore, these two alleles also have a neomorphic or antimorphic effect on hair polarity in one region of the wing.     

Choline acetyltransferase-like immunoreactivity in the brain of Drosophila melanogaster

Summary Using a monoclonal antibody selective for the acetylcholine (ACh)-synthesizing enzyme choline acetyltransferase (ChAT) of Drosophila melanogaster we find ChAT-like immunoreactivity in specific synaptic regions throughout the brain of Drosophila melanogaster apart from the lobes and the peduncle of the mushroom body and most of the first visual neuropile (lamina). Several anatomically well-defined central brain structures exhibit particularly strong binding. Characteristic differential staining patterns are observed for each of the four neuromeres of the optic lobes. Cell bodies appear not to bind this antibody. The prominent features of the distribution of ChAT-like immunoreactivity are paralleled by the distribution of acetylcholine hydrolyzing enzymatic activity as revealed by histochemical staining for acetylcholine esterase (AChE). These results are discussed in comparison with published data on enzyme distribution, choline uptake and ACh receptor binding in the nervous system of Drosophila melanogaster.     

Determination of the shape of the operculum by the bithorax complex in Drosophila melanogaster

Summary We have studied the course of the operculum line in the larval hypoderm of several bithorax complex mutants of Drosophila melanogaster. The bifurcation of the line, a characteristic of the first abdominal segment in wild-type (A₁), can also appear in the metathoracic (T₃) and other abdominal segments (A₂, A₃) depending on mutations within the bithorax complex. Therefore, we concluded that the course of the operculum line and thus the shape of the operculum is not determined by a suprasegmental gradient of positional information but by the functional state of the genes of the bithorax complex in each metamere. The dorsal and ventral branches of the operculum line react differently, the dorsal branch being more sensitive to the effect of loss of function mutations (bxd, iab-2 ^k), the ventral branch more affected by gain of function mutations (Hab). In some cases the effects of the mutations on the operculum line differed from those in the adult, suggesting a difference in sensitivity of larval hypodermal cells and histoblast cells to the functional gene products of the bithorax complex.     

Temperature-related divergence in experimental populations of Drosophila melanogaster. II. Correlation between fitness and body dimensions

From a laboratory stock of Drosophila melanogaster (Oregon), reared for more than 20 years at 18° C, a new population was derived and maintained at 28° C for 8 years. The chromosomal and cytoplasmic contribution to genetic divergence between the two populations was estimated. Six body traits and reproductive fitness were taken into account. The third chromosome is responsible for the adaptive difference for temperature between the two lines. Temperature-selected genes which control body size are located on the second and third chromosomes, although the contribution of each chromosome depends on the environment in which the flies develop. The correlation between the chromosomal and cytoplasmic contributions to different traits and fitness, changes with temperature. At 28° C the correlation between fitness and each body trait is proportional to the response to selection exhibited by each of them, but this is not true at 18° C. Body size has, therefore, an adaptive significance in relation to temperature, which is expressed only in the environment where selection occurs. Cytoplasmic genes affect almost all characters to an extent similar to that of chromosomal genes. Inter-chromosomal and nucleo-cytoplasmic interactions are present and also change with temperature. In general, genes selected in a given environment produce greater phenotypic changes in that environment than in another. The population that experienced both temperatures is fitter in both environments, suggesting that the capacity to adapt to warm temperatures depends on genes other than those which are involved in the adaptation to cold.     

Allozyme divergence between different gene arrangements in Drosophila subobscura

Allozyme and chromosomal polymorphism were analysed simultaneously in three population samples of Drosophila subobscura from Scotland, Germany and Italy. The study revealed significant genic divergence between the various chromosomal gene arrangements for the loci Acph, Lap and Pep, which are located inside inversions. No difference was found with the loci Me and Odh, which are both on the same chromosome but proximal to the structurally polymorphic region. Samples of a given gene arrangement taken from the different localities are genetically uniform. The data indicate that the observed non-random associations between enzyme genes and chromosomal inversions are the result of inhibited recombination in heterokaryotypes and gradual differentiation of the separated gene pools, rather than selection and coadaptation.     

Detection and localization onDrosophila melanogaster polytene chromosomes of sequences homologous to oncogeneyes

Sequences homologous to oncogeneyes (Y73/Esh/sarcoma viral oncogene cDNA) in theDrosophila melanogaster Oregon genome were detected byin situ hybridization on salivary gland chromosomes. Three separate sites, 8D/X, 57BC/2R and 95CD/3R, were identified. Presence of sequences highly homologous toyes in the genomic DNA was confirmed by dot blot hybridization under high stringency conditions.     

SUBOPTIMAL VIRULENCE OF AN INSECT-PARASITIC NEMATODE

Recent considerations of parasite virulence have focused on the adverse effects that parasites can have on the survival of their hosts. Many parasites, however, reduce host fitness by an equally deleterious but different means, by causing partial or complete sterility of their hosts. A model of optimal parasite virulence is developed in which a quantity of host resources can be allocated to either host or parasite reproduction. Increases in parasite reproduction thus cause reductions in host fertility. The model shows that under a wide variety of ecological conditions, such parasites should completely sterilize their hosts. Only when opportunities for horizontal transmission are very limited should the parasites appropriate less than all of a host's reproductive resources. Field and laboratory evidence shows that the nematode parasite Howardula aoronymphium is relatively avirulent to one of its principal host species, Drosophila falleni, whereas it is much more virulent to D. putrida and D. neotestacea, suggesting that there may be substantial vertical transmission in D. falleni. However, epidemiological studies in the field and laboratory assays of host specificity strongly suggest that the three host species share a single parasite pool in natural populations, indicating that parasites in all three host species experience high levels of horizontal transmission. Thus, the low virulence of H. aoronymphium to D. falleni is not consistent with the model of optimal parasite virulence. It is proposed that this suboptimal virulence in D. falleni is a consequence of populations of H. aoronymphium being selected to exploit simultaneously several different host species. As a result, virulence may not be optimal in any one host. One must, therefore, consider the full range of host species in assessing a parasite's virulence.     

EFFECTS ON FITNESS COMPONENTS OF P-ELEMENT INSERTS IN DROSOPHILA MELANOGASTER: ANALYSIS OF TRADE-OFFS

We analyzed the trade-offs between fitness components detected in four experiments in which traits were manipulated by inserting small (control) and large (treatment) P-elements into the Drosophila melanogaster genome. Treatment effects and the interactions of treatment with temperature, experiment, and line were caused by the greater length and different positions of the treatment insert. In inbred flies, the treatment decreased early and total fecundity. Whether it increased the lifespan of mated females depended upon adult density. Analysis of line-by-treatment-by-temperature interactions revealed hidden trade-offs that would have been missed by other methods. They included a significant trade-off between lifespan and early fecundity. At 25°C high early fecundity was associated with decreased reproductive rates and increased mortality rates 10–15 days later and persisting throughout life, but not at 29.5°C. Correlations with Gompertz coefficients suggested that flies that were heavier at eclosion also aged more slowly and that flies that aged more slowly had higher fecundity late in life at 25°C. The results support the view that lifespan trades off with fecundity and that late fecundity trades off with rate of aging in fruitflies. Genetic engineering is an independent method for the analysis of trade-offs that complements selection experiments.     

Analysis of inbreeding in a colonizing population of Drosophila subobscura

An analysis of the effects of inbreeding on the genetic structure of a colonizing population of Drosophila subobscura has been carried out. Species of Drosophila, particularly D. subobscura, may have lethal alleles associated with chromosomal inversions and our aim was to assess the extent to which the genome is balanced in this way. The frequencies of chromosomal inversions were compared between a large population and a set of 72 lines that were maintained by brother-sister mating for 10 generations. Fisher's matrix method was used to calculate the expected homozygosity in these inbred lines for 5 allozyme loci (Aph, Hk-1, Lap, Odh, and Pept-1) used as markers of large chromosomal segments. Furthermore, the expected rates of fixation corresponding to these allozyme loci were also calculated. The results show that the amount of homozygosis observed did not differ significantly from expectations (with the corresponding loss of lines as a consequence of the reduction in viability). However, two deviations from strict neutrality were observed: there was a heterozygote excess at the Lap locus, and the frequency of the O ₅ inversion (always associated with a lethal gene in colonizing populations) was higher than expected.