Binding sites of Drosophila melanogaster sex peptide pheromones

Drosophila melanogaster sex peptide (SP) and Ductus ejaculatorius peptide (DUP99B) are male pheromones transferred in the seminal fluid to the female during copulation. Both reduce sexual receptivity and stimulate oviposition in females. The presence of high-affinity SP and DUP99B binding sites in the female were investigated by incubation of cryostat tissue sections with (125)I-iodinated peptides and subsequent autoradiography. We found that in adult females radiolabeled SP and DUP99B bind to peripheral nerves, the subesophageal ganglion, the cervical connective, to discrete parts of the thoracic ganglion, and to the genital tract. Weak and uniform labeling was detected in the neuropil of the brain and the thoracic ganglion. The labeling pattern in the nervous system suggests binding of the peptides to sensory afferents or glial cells. Scatchard analysis of the binding of (125)I-DUP99B to antennal nerves yielded a dissociation constant K(d) of 6.4 nM. Competition experiments with peptide fragments show that the peptides bind with their homologous C-terminal regions. Binding sites in the nervous system of females are established throughout sexual maturation. Prominent binding of the peptides to afferent nerves suggests modification of sensory input.     

Control of female pheromones in Drosophila melanogaster by homeotic genes

We have investigated the role of the Antennapedia and Bithorax complexes (ANT-C and BX-C) on the production of cuticular hydrocarbons in Drosophila melanogaster. In males, there is little, if any, influence of these complexes on the hydrocarbon pattern. In females, there are large and opposite effects of these complexes on diene production: two ANT-C mutations cause an increase in diene production and a reduction of monoenes, whereas most BX-C mutations result in a decrease in dienes and an increase in monoenes, although their sum remains constant. The effect is the highest in Mcp and iab6 females. It is suggested that a factor originating from the prothorax might activate the conversion of monoenes to dienes in females. The abdomen seems to have a crucial role in the production or control of pheromones: abdominal segments four to seven have the main effects, with a most dramatic effect for segments four and five.     

Associations between female remating behavior, oogenesis and oviposition in Drosophila melanogaster and Drosophila pseudoobscura

An association between female remating behavior, oogenesis and oviposition was examined in Drosophila melanogaster and Drosophila pseudoobscura to investigate mechanisms that elicit remating. Females receptive to remating oviposited more eggs in both species; however, the species differed in the association between remating behavior and the number and distribution of oocyte stages. We found no differences in the number of either developing eggs of different stages or mature eggs between female D. pseudoobscura that were either receptive or nonreceptive to remating. In contrast, D. melanogaster females that are receptive to remating had significantly more mature eggs in the ovaries than nonreceptive females. Nonremating females had a significantly greater number of immature, vitellogenic oocytes. These results suggest that factors associated with oogenesis are related to female remating behavior in D. melanogaster but not in D. pseudoobscura. We discuss these results in conjunction with other evidence on the role male ejaculatory components play in mediating female remating behavior.     

Feeding, fecundity and lifespan in female Drosophila melanogaster

Male seminal fluid proteins induce a profound remodelling of behavioural, physiological and gene signalling pathways in females of many taxa, and typically cause elevated egg production and decreased sexual receptivity. In Drosophila melanogaster, these effects can be mediated by an ejaculate 'sex peptide' (SP), which, in addition, contributes significantly to the cost of mating in females. Recent research has revealed that SP can stimulate female post-copulatory feeding, raising the possibility that the widespread female cost of mating could be due to over-feeding. In this study, we used D. melanogaster as a model to test this hypothesis. We first show that elevated post-mating feeding is dependent upon egg production and does not occur in sterile ovoD1 mutant females. This conclusion was also supported by the increase in feeding of virgin females whose egg production was experimentally elevated. We then demonstrated that sterile ovoD1 and fertile females experienced identical survival costs of mating, related to their frequency of mating and not to female feeding rate or to egg production. We conclude that female mating costs are not the result of over-feeding, but may be due to other, potentially more direct, effects of ejaculate molecules.     

Germ-line sex determination in Drosophila melanogaster

In Drosophila melanogaster, the mechanism of sex determination is substantially different in the germ line and in the soma. In the germ line, the process is not completely cell-autonomous, but requires some signals from the soma. Only some of the genes involved in somatic sex determination are also needed for germ cell development. Recent genetic studies have identified loci required for germ-line sex determination.     

Circadian modulation of light-induced locomotion responses in Drosophila melanogaster

The relationship between light and the circadian system has long been a matter of discussion. Many studies have focused on entrainment of light with the internal biological clock. Light also functions as an environmental stimulus that affects the physiology and behaviour of animals directly. In this study, we used light as an unexpected stimulus for flies at different circadian times. We found that wildtype flies showed circadian changes in light-induced locomotion responses. Elevation of locomotor activity by light occurred during the subjective night, and performance in response to light pulses declined to trough during the subjective day. Moreover, arrhythmic mutants lost the rhythm of locomotion responses to light, with promotion of activity by light in timeless(01)mutants and inhibition of activity by light in Clock(ar)mutants. However, neither ablation of central oscillators nor disturbance of the functional clock inside compound eyes was sufficient to disrupt the rhythm of light responses. We show that, compound eyes, which have been identified as the control point for normal masking (promotion of activity by light), are sufficient but not necessary for paradoxical masking (suppression of activity by light) under high light intensity. This, taken together with the clear difference of light responses in wildtype flies, suggests that two different masking mechanisms may underlie the circadian modulation of light-induced locomotion responses.     

Effects of female behavior on wing display and courtship of male Drosophila simulans and Drosophila melanogaster

Corrolations between female rejection behaviors and male wing display were calculated for both Drosophila simulans and Drosophila melanogaster intraspicific pair-matings. No significant correlations were found for D. melanogaster, but in D. simulans flicking by the female appeared to be associated with a shift in male wing display pattern resulting in higher levels of vibration. Flicking did not appear to discourage courtship by males in either species.     

Variation in the male pheromones and mating success of wild caught Drosophila melanogaster

Drosophila melanogaster males express two primary cuticular hydrocarbons (male-predominant hydrocarbons). These act as sex pheromones by influencing female receptivity to mating. The relative quantities of these hydrocarbons vary widely among natural populations and can contribute to variation in mating success. We tested four isofemale lines collected from a wild population to assess the effect of intrapopulation variation in male-predominant hydrocarbons on mating success. The receptivity of laboratory females to males of the four wild-caught lines varied significantly, but not consistently in the direction predicted by variation in male-predominant hydrocarbons. Receptivity of the wild-caught females to laboratory males also varied significantly, but females from lines with male-predominant hydrocarbon profiles closer to a more cosmopolitan one did not show a correspondingly strong mating bias toward a cosmopolitan male. Among wild-caught lines, the male-specific ejaculatory bulb lipid, cis-vaccenyl acetate, varied more than two-fold, but was not associated with variation in male mating success. We observed a strong inverse relationship between the receptivity of wild-caught females and the mating success of males from their own lines, when tested with laboratory flies of the opposite sex.     

A single mutation alters production and discrimination of Drosophila sex pheromones

The evolution of communication is a fundamental biological problem. The genetic control of the signal and its reception must be tightly coadapted, especially in inter-individual sexual communication. However, there is very little experimental evidence for tight genetic linkage connecting the emission of a signal and its reception. We found that a single genomic transposon inserted in the desatl gene of Drosophila melanogaster simultaneously affected the emission and the perception of sex-specific signals. This mutation greatly decreased the production of unsaturated hydrocarbons on the cuticle of mature flies of both sexes. These substances represent the sex pheromones necessary for mate discrimination: control males could not discriminate the sex of mutant desatl flies. Moreover, mutant males were unable to discriminate the sex pheromones of con-trol flies. Expression of desatl was found in the peripheral tissues that produce and detect sex pheromones.Excision of the transposon rescued both the production and discrimination phenotypes, but the two effects did not always coincide. This indicates that the emission and perception of pheromones are coded by differ-ent products of the same gene, reflecting the pleiotropic activity of desatl .     

Osmometric behavior of Drosophila melanogaster embryos

The osmometric behavior of Drosophila melanogaster embryos in permeabilized eggs was studied in a microscope diffusion chamber designed to impose a rapid change in osmotic environment at various temperatures. A numerical model of NaCl diffusion in the chamber predicted that radial variations in concentration arising from the presence of a thin film of solution at the top of the chamber were negligible. On the basis of transient electrical conductance measurements in the chamber, characteristic time constants for the change in concentration averaged over the chamber depth occupied by the eggs were 0.99, 0.77, and 0.60 min at 0, 10, and 20 degrees C, respectively. The chamber response was sufficiently rapid that the characteristic response of the embryo was not masked. Equilibrium volumetric behavior of the embryos indicated that they behaved as nearly ideal osmometers over the range of 0.256 to 2.000 osm, and followed the relation FVeq = 0.123C-1 + 0.541, where FVeq is equilibrium fractional volume and C is osmolality. Nonlinear regression of volumetric data during osmotic contraction yielded an average Lp of 0.722 micron/(min.atm) at 20 degrees C and an apparent activation energy delta E of 8.11 kcal/mol. The coefficients of variation in the Lp estimates among individual embryos were 38, 18, and 47% at 0, 10, and 20 degrees C, respectively. With the use of probability rules and a model for volumetric behavior during freezing, it was determined that the observed variability in Lp (assuming delta E is fixed) considerably broadens the transition range of cooling rates over which the predicted probability of intracellular ice formation goes from 0 to 1. However, experimental observations (21) show the actual transition range is even wider, indicating that there exist other important sources of variability which determine the event of ice formation in D. melanogaster embryos.     

Social effects for locomotion vary between environments in Drosophila melanogaster females

Despite strong purifying or directional selection, variation is ubiquitous in populations. One mechanism for the maintenance of variation is indirect genetic effects (IGEs), as the fitness of a given genotype will depend somewhat on the genes of its social partners. IGEs describe the effect of genes in social partners on the expression of the phenotype of a focal individual. Here, we ask what effect IGEs, and variation in IGEs between abiotic environments, has on locomotion in Drosophila. This trait is known to be subject to intralocus sexually antagonistic selection. We estimate the coefficient of interaction, Ψ, using six inbred lines of Drosophila. We found that Ψ varied between abiotic environments, and that it may vary across among male genotypes in an abiotic environment specific manner. We also found evidence that social effects of males alter the value of a sexually dimorphic trait in females, highlighting an interesting avenue for future research into sexual antagonism. We conclude that IGEs are an important component of social and sexual interactions and that they vary between individuals and abiotic environments in complex ways, with the potential to promote the maintenance of phenotypic variation.     

Male genotype affects female longevity in Drosophila melanogaster

Several recent studies suggest that interactions with conspecific males can reduce the longevity of female Drosophila melanogaster or support the idea that male and female fitness components are involved in antagonistic interactions. Here we report that males from third-chromosome isogenic lines demonstrated significant genetic variation in male reproductive performance and in the longevity of their mates. Increased male performance was marginally significantly associated with one measure of increased female survival rate. However, there was no indication of tradeoffs or negative correlations between male reproductive success and female survival. We discuss alternative hypotheses for the cause of the induced variation in female longevity.