Nucleotide and copy-number polymorphism at the odorant receptor genes Or22a and Or22b in Drosophila melanogaster

In Drosophila, odorant receptors are encoded by an old and moderatelysized multigene family. Or22a and Or22b are two tandemly arrangedgenes of this family that have proved to be the result of arather young duplication. Nucleotide variation in the regionspanning both duplicates was surveyed in four natural populations(two African and two non-African) of Drosophila melanogasterand also analyzed in species of the melanogaster subgroup. Theintraspecific survey revealed a particular copy-number polymorphismin some of the studied populations, with the two genes (Or22aand Or22b) present in the long variant and a single chimericgene (Or22ab) present in the short variant. Estimated nucleotidediversity was higher in the short than in the long variant,despite the ancestral character of the latter variant in D.melanogaster. The general skew toward low-frequency variantsdetected in the non-African long variant and its reduced levelof silent polymorphism relative to divergence is consistentwith the recent fixation of an advantageous mutation at, ornearby, the Or22 long variant region. The nonnegligible frequencyof the short variant and the presence of a highly divergenthaplotype in the East African sample would point to direct orindirect selection for its maintenance in the species. Therewas evidence for a generally more rapid evolution of the Or22bcopy at both synonymous and nonsynonymous sites. However, anexcess of nonsynonymous substitutions was only detected in theearly history of this copy.     

The olfactory circuit of the fruit fly Drosophila melanogaster

The olfactory circuit of the fruit fly Drosophila melanogaster has emerged in recent years as an excellent paradigm for studying the principles and mechanisms of information processing in neuronal circuits. We discuss here the organizational principles of the olfactory circuit that make it an attractive model for experimental manipulations, the lessons that have been learned, and future challenges.     

Cation-distribution in developing follicles of the fruit fly Drosophila melanogaster

Abstract. Cations were precipitated with potassium antimonate in ovarian follicles of Drosophila and the distribution of the formed precipitates was studied. The precipitates were analyzed with a laser microprobe mass analyzer (LAMMA) and found to contain a high concentration of calcium; potassium and sodium were also detected. On counting the antimon precipitates in stage 10B follicles with the electron microscope, few precipitates per unit area were found in anterior nurse cells, but more in posterior nurse cells; the highest precipitate density occurred consistently in the oocyte. When follicles of different stages were compared, the precipitate density was found to increase in the ooplasm and in the posterior nurse cells during vitellogenesis, whereas it remained nearly constant in the anterior nurse cells. Thus, the ratio of precipitates between the posterior and anterior end of the follicle increases during vitellogenesis. It begins to decrease at the time when the nurse cells collapse. These results suggest that the electrical polarity observed in polytrophic ovarioles may be based on differences in the cation distribution along the antero-posterior axis of the follicle.     

Generic insect repellent detector from the fruit fly Drosophila melanogaster

Background

Insect repellents are prophylactic tools against a number of vector-bornediseases. There is growing demand for repellents outperforming DEET in costand safety, but with the current technologies R&D of a new product takesalmost 10 years, with a prohibitive cost of $30 million dollar inpart due to the demand for large-scale synthesis of thousands of testcompounds of which only 1 may reach the market. R&D could be expeditedand cost dramatically reduced with a molecular/physiological target tostreamline putative repellents for final efficacy and toxicologicaltests.

Methodology

Using olfactory-based choice assay we show here that the fruit fly isrepelled by not only DEET, but also IR3535 and picaridin thus suggestingthey might have “generic repellent detector(s),” which may be ofpractical applications in new repellent screenings. We performed single unitrecordings from all olfactory sensilla in the antennae and maxillary palps.Although the ab3A neuron in the wild type flies responded to picaridin, itwas unresponsive to DEET and IR3535. By contrast, a neuron housed in thepalp basiconic sensilla pb1 responded to DEET, IR3535, and picaridin, withapparent sensitivity higher than that of the DEET detectors in themosquitoes Culex quinquefasciatus and Aedesaegypti. DmOr42a was transplanted from pb1 to the “emptyneuron” and showed to be sensitive to the three insect repellents.

Conclusions

For the first time we have demonstrated that the fruit fly avoids not onlyDEET but also IR3535 and picaridin, and identified an olfactory receptorneuron (ORN), which is sensitive to these three major insect repellents. Wehave also identified the insect repellent-sensitive receptor, DmOr42a. Thisgeneric detector fulfils the requirements for a simplified bioassay forearly screening of test insect repellents.     

Limitation of size by hypoxia in the fruit fly Drosophila melanogaster

The size of an organism is of fundamental importance in all biological processes. It dictates many of the critical interactions and physical factors that delimit the envelope within which an organism can grow. We investigated the effects of reduced oxygen on size and development in the fruit fly Drosophila melanogaster, and showed that limiting the oxygen in the environment limits both whole animal and cell size. When oxygen levels were reduced from 20% in nitrogen to 15%, 10% and 7.5%, there was a linear decrease in both male and female mass. Both cell size and cell number decreased in low oxygen, but changes in cell size accounted for a larger proportion of the overall change in fly size. Cell numbers decreased by a maximum of 11% between flies reared in 20% oxygen and those reared in 7.5% oxygen, whereas cell surface area decreased by 17%. Low oxygen levels increased development time and mortality, but reduced fecundity. Reducing the level of oxygen available significantly slowed development times, with flies reared in 10% oxygen emerging on average 1.5 days later than those in 20% oxygen. The effect of oxygen on size is reversible during embryonic and larval development up to the pupal stage, when final size is set.     

Ambient temperature affects free-flight performance in the fruit fly Drosophila melanogaster

To gain insight into how temperature affects locomotor performance in insects, the limits of flight performance have been estimated in freely flying fruit flies Drosophila melanogaster by determining the maximum load that a fly could carry following take-off. At a low ambient temperature of 15 °C, muscle mechanical power output matches the minimum power requirements for hovering flight. Aerodynamic force production rises with increasing temperature and eventually saturates at a flight force that is roughly equal to 2.1 times the body mass. Within the two-fold range of different body sizes, maximum flight force production during free flight does not decrease with decreasing body size as suggested by standard aerodynamic theories. Estimations of flight muscle mechanical power output yields a peak performance of 110 W kg⁻¹ muscle tissue for short-burst flight that was measured at an ambient temperature of 30 °C. With respect to the uncertainties in estimating muscle mechanical power during free flight, the estimated values are similar to those that were published for flight under tethered flight conditions. Accepted: 5 January 1999     

Spider odors induce stoichiometric changes in fruit fly Drosophila melanogaster

Animal senses and signals are amazingly diverse,and the major modalities by which animals acquire sensory input from their environments are sound,light,vibration,and chemical signals.Insects mainly rely on visual,nociceptive,and olfactory cues to discriminate between rewards and risks.It has been shown that the visual and olfactory cues of predators substantially affect the adult phenotype in Drosophila melanogaster(Krams et al.2016),a prominent animal model for biological research.     

Haltere-mediated equilibrium reflexes of the fruit fly, Drosophila melanogaster.

Flies display a sophisticated suite of aerial behaviours that require rapid sensory-motor processing. Like all insects, flight control in flies is mediated in part by motion-sensitive visual interneurons that project to steering motor circuitry within the thorax. Flies, however, possess a unique flight control equilibrium sense that is encoded by mechanoreceptors at the base of the halteres, small dumb-bell-shaped organs derived through evolutionary transformation of the hind wings. To study the input of the haltere system onto the flight control system, I constructed a mechanically oscillating flight arena consisting of a cylindrical array of light-emitting diodes that generated the moving image of a 30 degrees vertical stripe. The arena provided closed-loop visual feedback to elicit fixation behaviour, an orientation response in which flies maintain the position of the stripe in the front portion of their visual field by actively adjusting their wing kinematics. While flies orientate towards the stripe, the entire arena was swung back and forth while an optoelectronic device recorded the compensatory changes in wing stroke amplitude and frequency. In order to reduce the background changes in stroke kinematics resulting from the animal's closed-loop visual fixation behaviour, the responses to eight identical mechanical rotations were averaged in each trial. The results indicate that flies possess a robust equilibrium reflex in which angular rotations of the body elicit compensatory changes in both the amplitude and stroke frequency of the wings. The results of uni- and bilateral ablation experiments demonstrate that the halteres are required for these stability reflexes. The results also confirm that halteres encode angular velocity of the body by detecting the Coriolis forces that result from the linear motion of the haltere within the rotating frame of reference of the fly's thorax. By rotating the flight arena at different orientations, it was possible to construct a complete directional tuning map of the haltere-mediated reflexes. The directional tuning of the reflex is quite linear such that the kinematic responses vary as simple trigonometric functions of stimulus orientation. The reflexes function primarily to stabilize pitch and yaw within the horizontal plane.     

Evidence for adaptive male mate choice in the fruit fly Drosophila melanogaster

Theory predicts that males will benefit when they bias their mating effort towards females of higher reproductive potential, and that this discrimination will increase as males become more resource limited. We conducted a series of experiments to test these predictions in a laboratory population of the fruitfly, Drosophila melanogaster. In this species, courtship and copulation have significant costs to males, and females vary greatly in fecundity, which is positively associated with body size. When given a simultaneous choice between small and large virgin females, males preferentially mated with larger, more fecund, females. Moreover, after males had recently mated they showed a stronger preference for larger females. These results suggest that male D. melanogaster adaptively allocate their mating effort in response to variation in female quality and provide some of the first support for the theoretical prediction that male stringency in mate choice increases as resources become more limiting.     

Effects of gravity on positive phototaxis in fruit fly Drosophila melanogaster

Geotaxis and phototaxis are movements in response to gravity and light, respectively, and are commonly observed in nature. The interactions between these two types of movement have been shown to confer ecological advantages to many taxa. Although several studies have been conducted on phototaxis and geotaxis in various organisms, reports on the interactions between positive phototaxis and negative geotaxis are lacking. In the fruit fly, Drosophila melanogaster, any direct interactions that exist between positive phototaxis and negative geotaxis are yet to be determined and the ecological significance of such interactions remains unclear. In the present study, the effects of gravity on positive phototaxis in a Y‐maze were investigated using the Canton‐S wild type and gravity‐sensing‐deficient pyx³ mutant fruit flies. Gravity sensing was not necessary for horizontal positive phototaxis, but was required for vertical positive phototaxis. These results suggest that gravitoreception may selectively modulate positive phototaxis depending on the vertical and horizontal movements of the fruit flies.     

Circadian consequence of socio-sexual interactions in fruit flies Drosophila melanogaster

In fruit flies Drosophila melanogaster, courtship is an elaborate ritual comprising chasing, dancing and singing by males to lure females for mating. Courtship interactions peak in the night and heterosexual couples display enhanced nighttime activity. What we do not know is if such socio-sexual interactions (SSI) leave long-lasting after-effects on circadian clock(s). Here we report the results of our study aimed at examining the after-effects of SSI (as a result of co-habitation of males and females in groups) between males and females on their circadian locomotor activity rhythm. Males undergo reduction in the evening activity peak and lengthening of circadian period, while females show a decrease in overall activity. Such after-effects, at least in males, require functional circadian clocks during SSI as loss-of-function clock mutants and wild type flies interacting under continuous light (LL), do not display them. Interestingly, males with electrically silenced Pigment Dispersing Factor (PDF)-positive ventral lateral (LNv) clock neurons continue to show SSI mediated reduction in evening activity peak, suggesting that the LNv clock neurons are dispensable for SSI mediated after-effects on locomotor activity rhythm. Such after-effects in females may not be clock-dependent because clock manipulated females with prior exposure to males show decrease in overall activity, more or less similar to rhythmic wild type females. The expression of SSI mediated after-effects requires a functional olfactory system in males because males with compromised olfactory ability do not display them. These results suggest that SSI causes male-specific, long-lasting changes in the circadian clocks of Drosophila, which requires the presence of functional clocks and intact olfactory ability in males.     

Morphology and metamorphosis of the peptidergic Va neurons and the median nerve system of the fruit fly, Drosophila melanogaster

Metamorphosis is a fundamental developmental process and has been intensively studied for various neuron types of Drosophila melanogaster. However, detailed accounts of the fate of identified peptidergic neurons are rare. We have performed a detailed study of the larval morphology and pupal remodelling of identified peptidergic neurons, the CAPA-expressing Va neurons of D. melanogaster. In the larva, Va neurons innervate abdominal median and transverse nerves that are typically associated with perisympathetic organs (PSOs), major neurohaemal release sites in insects. Since median and transverse nerves are lacking in the adult, Va neurites have to undergo substantial remodelling during metamorphosis. We have examined the hitherto uncharacterised gross morphology of the thoracic PSOs and the abdominal median and transverse nerves by scanning electron microscopy and found that the complete reduction of these structures during metamorphosis starts around pupal stage P7 and is completed at P9. Concomitantly, neurite pruning of the Va neurons begins at P6 and is preceded by the high expression of the ecdysone receptor (EcR) subtype B1 in late L3 larvae and the first pupal stages. New neuritic outgrowth mainly occurs from P7-P9 and coincides with the expression of EcR-A, indicating that the remodelling of the Va neurons is under ecdysteroid control. Immunogold-labelling has located the CAPA peptides to large translucent vesicles, which are released from the transverse nerves, as suggested by fusion profiles. Hence, the transverse nerves may serve a neurohaemal function in D. melanogaster.This work was supported by the German Science Foundation (Deutsche Forschungsgemeinschaft, DFG), grant We 2652/2-1.     

Or47b-neurons promote male-mating success in Drosophila

Drosophila performs elaborate well-defined rituals of courtship, which involve several types of sensory inputs. Here, we report that Or47b-neurons promote male-mating success. Males with Or47b-neurons silenced/ablated exhibit reduced copulation frequency and increased copulation latency. Copulation latency of Or47b-manipulated flies increased proportionately with size of the assay arena, whereas in controls it remained unchanged. While competing for mates, Or47b-ablated males are outperformed by intact controls. These results suggest the role of Or47b-neurons in promoting male-mating success.     

Dissociation of photoreceptors from whole heads of the fruit fly,Drosophila melanogaster

Photoreceptor cells that were mostly free of extracellular material and suitable for most electrophysiological study procedures were dissociated from whole heads of the fruit fly, Drosophila melanogaster, by a simple smash technique employing gentle chopping by a razor blade through Parafilm sheets. A variety of commonly available proteolytic and glycolytic digestion enzymes were tested as additions to the basic dissociation procedure described. With the aid of Nomarski interference contrast optics, periodic acid-Schiff staining, and fluorescent labeling and microscopy methods, it was determined that proteolytic enzymatic digestion does little to enhance the dissociation procedure, and instead, often damages the cells that one is attempting to recover. Unexpectedly, certain glycolytic enzymes, when added to the basic procedure, appear to enhance the recovery of intact viable Drosophila photoreceptors that are stripped of most extracellular material. Based on these results, a hypothesis concerning the biochemical nature of the extracellular matrix of the Drosophila retina is proposed. Drosophila photoreceptors are an interesting model system for the study of invertebrate phototransduction and photoreceptor cell biology because of their many well-characterized mutant strains. The technique described here should produce clean viable photoreceptors or ommatidia that respond to light, and that are suitable for patch clamping or cell culture.     

Resource limitation and responses to rivals in males of the fruit fly Drosophila melanogaster

Diet has a profound direct and indirect effect on reproductive success in both sexes. Variation in diet quality and quantity can significantly alter the capacity of females to lay eggs and of males to deliver courtship. Here, we tested the effect of dietary resource limitation on the ability of male Drosophila melanogaster to respond adaptively to rivals by extending their mating duration. Previous work carried out under ad libitum diet conditions showed that males exposed to rivals prior to mating significantly extend mating duration, transfer more ejaculate proteins and achieve higher reproductive success. Such adaptive responses are predicted to occur because male ejaculate production may be limited. Hence, ejaculate resources require allocation across different reproductive bouts, to balance current vs. future reproductive success. However, when males suffer dietary limitation, and potentially have fewer reproductive resources to apportion, we expect adaptive allocation of responses to rivals to be minimized. We tested this prediction and found that males held on agar‐only diets for 5–7 days lost the ability to extend mating following exposure to rivals. Interestingly, extended mating was retained in males held on low yeast/sugar: no sugar/yeast diet treatments, but was mostly lost when males were maintained on ‘imbalanced’ diets in which there was high yeast: no sugar and vice versa. Overall, the results show that males exhibit adaptive responses to rivals according to the degree of dietary resource limitation and to the ratio of individual diet components.