Drosophila TRPA channel painless inhibits male-male courtship behavior through modulating olfactory sensation

The Drosophila melanogaster TRPA family member painless, expressed in a subset of multidendritic neurons embeding in the larval epidermis, is necessary for larval nociception of noxious heat or mechanical stimuli. However, the function of painless in adult flies remains largely unknown. Here we report that mutation of painless leads to a defect in male-male courtship behavior and alteration in olfaction sensitivity in adult flies. Specific downregulation of the expression of the Painless protein in the olfactory projection neurons (PNs) of the antennal lobes (ALs) resulted in a phenotype resembling that found in painless mutant flies, whereas overexpression of Painless in PNs of painless mutant males suppressed male-male courtship behavior. The downregulation of Painless exclusively during adulthood also resulted in male-male courtship behavior. In addition, mutation of the painless gene in flies caused changes in olfaction, suggesting a role for this gene in olfactory processing. These results indicate that functions of painless in the adult central nervous system of Drosophila include modulation of olfactory processing and inhibition of male-male courtship behavior.     

Taste,movement, and death: varying effects of new prospero mutants during Drosophila development

The PGal4 transposon inserted upstream of the pan-neural gene prospero (pros) causes several neural and behavioral defects in the Voila(1) strain. The precise excision of the transposon simultaneously rescued all these defects whereas its unprecise excision created new pros(V) alleles, including the null allele pros(V17). Here, we describe the relationship between the genetic structure of pros locus, larval locomotion, and larval gustatory response. These two behaviors showed varying degrees of variation depending upon the pros allele. We also found a good relation between behavioral alteration, the level of Pros protein in the embryo, and the degree of disorganization in the larval neuromuscular junction. These data suggest that the complete development of the nervous system requires a full complement of Pros, and that a gradual decrease in the levels of this protein can proportionally alter the development and the function of the nervous system.     

Density-Dependent Fertility Selection in Experimental Populations of DROSOPHILA MELANOGASTER

The effects of larval density on components of fertility fitness were investigated with two mutant lines of Drosophila melanogaster. The differences in adult body weight, wing length, larval survivorship and development time verified that flies reared at high density were resource limited. Experimental results indicate that: (1) relative fecundities of both sexes show density-dependent effects, (2) there is a strong density effect on male and female mating success, and (3) in general, there is a reduction in fecundity differences between genotypes at high density. These results imply that it may be important to consider fertility in models of density-dependent natural selection.     

Heterozygous Effects on Fitness of Ems-Treated Chromosomes in DROSOPHILA MELANOGASTER

The heterozygous effects on fitness of second chromosomes carrying mutants induced with different doses of EMS were ascertained by monitoring changes in chromosome frequencies over time. These changes were observed in populations in which the treated chromosomes, as well as untreated competitors, remained heterozygous in males generation after generation. This situation was achieved by using a translocation which links the second chromosome to the X chromosome; however, only untranslocated second chromosomes were mutagenized. Chromosomes were classified according to their effects on viability in homozygous condition. A preliminary homozygosis identified completely lethal chromosomes; secondary tests distinguished between drastic (viability index < 0.1) and nondrastic chromosomes. Chromosomes that were nondrastic after treatment were found to reduce the fitness of their heterozygous carriers by 3-5%. The data show that flies homozygous for these chromosomes were about 2.7% less viable per treatment with 1 mm EMS than flies homozygous for untreated chromosomes. By comparing the fitness-depressing effects of nondrastic EMS-induced mutants in heterozygous condition with the corresponding viability-depressing effects measured by Temin, it is apparent that the total fitness effects are several times larger than the viability effects alone. Completely lethal chromosomes derived from the most heavily treated material reduced fitness by 11% in heterozygous condition; approximately half of this reduction was due to the lethal mutations themselves.     

Circadian synchronization and rhythmicity in larval photoperception-defective mutants of Drosophila

A single light episode during the first larval stage can set the phase of adult Drosophila activity rhythms, showing that a light-sensitive circadian clock is functional in larvae and is capable of keeping time throughout development. These behavioral data are supported by the finding that neurons expressing clock proteins already exist in the larval brain and appear to be connected to the larval visual system. To define the photoreceptive pathways of the larval clock, the authors investigated circadian synchronization during larval stages in various visual systems and/or cryptochrome-defective strains. They show that adult activity rhythms cannot be entrained by light applied to larvae lacking both cryptochrome and the visual system, although such rhythms were entrained by larval stage-restricted temperature cycles. Larvae lacking either pathway alone were light entrainable, but the phase of the resulting adult rhythm was advanced relative to wild-type flies. Unexpectedly, adult behavioral rhythms of the glass60j and norpAP24 visual system mutants that were entrained in the same conditions were found to be severely impaired, in contrast to those of the wild type. Extension of the entrainment until the adult stage restored close to wild-type behavioral rhythms in the mutants. The results show that both cryptochrome and the larval visual system participate to circadian photoreception in larvae and that mutations affecting the visual system can impair behavioral rhythmicity.     

PGal4 excision reveals the pleiotropic effects of Voila, a Drosophila locus that affects development and courtship behaviour

In Drosophila melanogaster, the PGal4 transposon inserted at the chromosomal site 86E1-2 is associated with the Voila1 allele that causes multiple phenotypes. Homozygous Voila1/1 flies rarely reach adulthood and heterozygous Voila1/+ adult males display strong homosexual courtship behaviour. Both normal behavioural and developmental phenotypes were rescued by remobilizing the PGal4 element. Yet, the rescue of heterosexual courtship and of adult viability did not occur in the same strains, indicating that these defects have different genetic origins. Furthermore, many strains showed a partial rescue of both characters. Molecular analysis revealed that the PGal4 transposon is inserted upstream of the 5'UTR of the prospero gene. The excision strains with no detectable fragment of the PGal4 transposon remaining showed a rescued viability for homozygote adults. Moreover, the developmental period with the highest homozygote lethality was correlated with the size of PGal4 element that remained inserted at the Voila locus. This suggests a relationship between developmental viability and the amount of DNA inserted within the promoter of prospero.     

Experimental analysis of sensory nerve pathways inDrosophila

Summary The pathway of adult sensory nerves has been analysed in three experimental situations: (i) in flies with grossly abnormal thoracic morphology resulting from X-irradiation early during development, (ii) in flies which had been subjected to surgical operations late in the larval period, (iii) in homoeotic mutants. The results provide experimental support for a simple mechanism in which developing adult axons join the nearest larval nerve and are guided by it up to the central nervous system. In particular, experimental interference with normal development can result in nerves from different segments, or from dorsal and ventral appendages, joining each other and entering the central nervous system together.     

In this issue of Fly

Previous studies in Drosophila have demonstrated that whether flies fight like males or females can be switched by selectively manipulating genes of the sex determination hierarchy in male and female nervous systems. Here we extend these studies by demonstrating that changing the sex of cholinergic neurons in male fruit fly nervous systems via expression of the transformer gene increases the levels of aggression shown by the flies without altering the way the flies fight. transformer manipulation in this way does not change phototaxis, geotaxis, locomotion or odor avoidance of the mutant males compared to controls. Cholinergic neurons must be feminized via this route during the late larval/early pupal stages of development to show the enhanced aggression phenotype. Other investigators have shown that this is the same time period during which sexually dimorphic patterns of behavior are specified in flies. Neurons that co-express fruitless and choline acetyl transferase are found in varying numbers within different clusters of fruitless-expressing neurons: together they make up approximately 10% of the pool of fruitless-expressing neurons in the brain and nerve cord.     

Genetic effects of cosmic radiation in Drosophila melanogaster]

To examine possible effects of space radiation on living organism, we have analyzedtwo types of mutations, sex-linked recessive lethal mutations and somatic mutations, in fruit fly of the species Drosophila melanogaster. Drosophila strains used were wild type strains and a radiation-sensitive strain mei-41. Two different developmental stages of samples were sent into space; young adult males to analyze sex-linked recessive lethal mutations and about 30hr-old larvae to detect somatic mutations in wing epidermal cells. For wild type and mei-41 strains each, about 200 adult male flies and about 6,000 larvae were loaded on space shuttle Endeavour. The male flies returned from space were mated to virgin female flies of a tester strain, and the presence of the lethal mutations was analyzed at F2 generation. The frequencies of sex-linked recessive lethal mutations in flight groups were 2 and 3 times higher for wild type Canton-S and mei-4 1, respectively, than those in ground control groups. Most larvae sent to space emerged as adult flies within about 10 days after the landing. The presence of wing-hair somatic mutations, which give morphological change in hairs growing on the surface of wing epidermal cells, was analyzed under microscope. In wild type strain Muller-5, the frequency of wing hair mutant spots in flight group was about 1.5-fold higher than that in ground control, and in Canton-S-derived wild type strain the frequencies were similar between the two groups. By contrast, for mei-41 strain the mutation frequency was lower in flight group than in control group. The observed higher frequency of lethal mutations in the flight group might be due to a possibility that radiation effects on reproductive cells could be greatly enhanced under micro gravity. However, if this would be the case, we do not have appropriate explanation for the apparent absence of such synergistic effects on somatic wing-hair mutation system.     

Allee effect in larval resource exploitation in Drosophila: an interaction among density of adults, larvae, and micro-organisms

Abstract 1. Aggregation pheromones can evolve when individuals benefit from clustering. Such a situation can arise with an Allee effect, i.e. a positive relationship between individual fitness and density of conspecifics. Aggregation pheromone in Drosophila induces aggregated oviposition. The aim of the work reported here was to identify an Allee effect in the larval resource exploitation by Drosophila melanogaster, which could explain the evolution of aggregation pheromone in this species. 2. It is hypothesised that an Allee effect in D. melanogaster larvae arises from an increased efficiency of a group of larvae to temper fungal growth on their feeding substrate. To test this hypothesis, standard apple substrates were infested with specified numbers of larvae, and their survival and development were monitored. A potential beneficial effect of the presence of adult flies was also investigated by incubating a varying number of adults on the substrate before introducing the larvae. Adults inoculate substrates with yeast, on which the larvae feed. 3. Fungal growth was related negatively to larval survival and the size of the emerging flies. Although the fungal growth on the substrate was largely reduced at increased larval densities, the measurements of fitness components indicated no Allee effect between larval densities and larval fitness, but rather indicated larval competition. 4. In contrast, increased adult densities on the substrates prior to larval development yielded higher survival of the larvae, larger emerging flies, and also reduced fungal growth on the substrates. Hence, adults enhanced the quality of the larval substrate and significant benefits of aggregated oviposition in fruit flies were shown. Experiments with synthetic pheromone indicated that the aggregation pheromone itself did not contribute directly to the quality of the larval resource. 5. The interaction among adults, micro‐organisms, and larval growth is discussed in relation to the consequences for total fitness.     

Larval Competition, Adult Fitness, and Reproductive Strategies in the Acoustically Orienting Ormiine Homotrixa alleni (Diptera: Tachinidae)

Homotrixa alleni is a gregarious endoparasitoid fly that attacks adult male Sciarasaga quadrata (Orthoptera: Tettigoniidae) in southwestern Western Australia. Gravid female flies acoustically orient to their host's call and deposit live first-instar larvae upon or near their calling host. Up to 16 larvae may be found developing in the one host, and since only calling adult male S. quadrata are parasitized, host size and hence larval resources are essentially fixed at parasitism. This study examines parasitism by H. alleni in relation to intraspecific larval competition and adult fitness. The mean number of larvae emerging per host failed to increase significantly beyond a clutch size of four. Mean pupal weight and survival to the adult stage decreased linearly with increasing clutch size across the entire range of clutch sizes examined. Within a clutch, heavier pupae successfully completed pupal development significantly more often than lighter pupae. Pupal weight was directly related to adult size, with adult males being significantly larger than adult females at any given pupal weight. Female body size was positively correlated with fecundity. The size distribution of emerging females was normally distributed, while the distribution of searching gravid females collected at acoustic traps in the field was significantly skewed toward larger flies, suggesting yet another fitness benefit associated with large size. Using fecundity and survival to adulthood as our measure of fitness we calculated the optimal clutch size maximizing fitness per host to be seven, which exceeds the majority of observed clutch sizes in the field. Uncertainties associated with larvae successfully entering the host following larviposition are likely to reduce clutch sizes of H. alleni below this optimum in the field.     

EAST and Chromator control the destruction and remodeling of muscles during Drosophila metamorphosis

Metamorphosis involves the destruction of larval, the formation of adult and the transformation of larval into adult tissues. In this study, we demonstrate the role of the Drosophila nuclear proteins EAST and Chromator in tissue destruction and remodeling. To better understand the function of east, we performed a yeast two-hybrid screen and identified the euchromatin associated protein Chromator as a candidate interactor. To analyze the functional significance of our two-hybrid data, we generated a set of novel pupal lethal Chro alleles by P-element excision. The pupal lethal Chro mutants resemble lethal east alleles as homozygous mutants develop into pharates with normal looking body parts, but fail to eclose. The eclosion defect of the Chro alleles is rescued in an east heterozygous background, indicating antagonistic genetic interactions between the two genes. Live cell imaging was applied to study muscle development during metamorphosis. Consistent with the eclosion defects, mutant pharates of both genes show loss and abnormal differentiation of adult eclosion muscles. The two genes have opposite effects on the destruction of larval muscles in metamorphosis. While Chro mutants show incomplete histolysis, muscles degenerate prematurely in east mutants. Moreover east mutants affect the remodeling of abdominal larval muscles into adult eclosion muscles. During this process, loss of east interferes with the spatial coordination of thinning of the larval muscles. Overexpression of EAST-GFP can prevent the disintegration of polytene chromosomes during programmed cell death. We propose that Chro activates and east inhibits processes and genes involved in tissue destruction and remodeling.     

Larval competition within seeds: From the behaviour process to the ecological outcome in the seed beetle Callosobruchus maculatus

Abstract Environmental conditions experienced by organisms during development can have profound impacts on adult fitness and behaviour. Internally feeding larvae unable to leave the seed selected by their mother face limitations of resource suitability and competition. The host seed may guide the larval behaviour within the seed leading to differential intensity of competition and determining its process and outcome, which varies in strains of the legume seed beetle Callosobruchus maculatus (Coleoptera: Bruchidae). However, the intensity, process and outcome of larval competition in different hosts have yet to be simultaneously considered, the objective of the present study. Here we assessed the intensity, process and outcome of intrastrain larval competition as related to host type, and how they are interrelated. Larval competition was faced with two distinct strategies – scramble and contest competition depending on the insect strain and host seed species. The intensity of competition did not show any straight link with the process and outcome of competition. Only a single strain showed a contest competition process with likely interference between larvae, while the four other strains studied showed the process of scramble competition. The process of scramble competition, however, led to variable outcomes in mung beans based on larval competition curves. Such differences were not apparent on cowpea seeds and either the plateau or the peak expected on the larval fitness curves were not reached preventing the distinction of the competition outcome, a likely consequence of the egg laying behaviour of these strains limiting the maximum number of eggs laid per seed. Seed host species rather than seed size are the likely cause of the differences observed from the initial expectation. The strain showing the process of contest competition increased larval fitness with density of larvae emerged per seed regardless of the host species, an unexpected outcome based on theoretical models. In this case the egg laying behaviour of the adult female is probably the main fitness determinant of its progeny.     

Developmental expression of drop-dead is required for early adult survival and normal body mass in Drosophila melanogaster

In Drosophila melanogaster, mutations in the gene drop-dead (drd) result in early adult lethality, with flies dying within 2 weeks of eclosion. Additional phenotypes include neurodegeneration, tracheal defects, starvation, reduced body mass, and female sterility. The cause of early lethality and the function of the drd protein remain unknown. In the current study, the temporal profiles of drd expression required for adult survival and body mass regulation were investigated. Knockdown of drd expression by UAS-RNAi transgenes and rescue of drd expression on a drd mutant background by a UAS-drd transgene were controlled with the Heat Shock Protein 70 (Hsp70)-Gal4 driver. Flies were heat-shocked at different stages of their lifecycle, and the survival and body mass of the resulting adult flies were assayed. Surprisingly, the adult lethal phenotype did not depend upon drd expression in the adult. Rather, expression of drd during the second half of metamorphosis was both necessary and sufficient to prevent rapid adult mortality. In contrast, the attainment of normal adult body mass required a different temporal pattern of drd expression. In this case, manipulation of drd expression solely during larval development or metamorphosis had no effect on body mass, while knockdown or rescue of drd expression during all of pre-adult (embryonic, larval, and pupal) development did significantly alter body mass. Together, these results indicate that the adult-lethal gene drd is required only during development. Furthermore, the mutant phenotypes of body mass and lifespan are separable phenotypes arising from an absence of drd expression at different developmental stages.     

Effects of larval diet on development rates and reproductive maturation of male and female Mediterranean fruit flies

Abstract Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae) larvae are capable of developing in one of many hosts that may vary greatly in quality. We hypothesized that they will respond to the larval environment in a manner beneficial to their subsequent reproductive performance. Accordingly, we investigated the effects of various larval diets (varying in the amount of protein and sugar they contain) on the size, development time, nutritional status and reproductive maturation (ovarian development and onset of sexual behaviour) of females and males. We found that flies which undergo larval development in artificial host fruit that contain sugar and protein ('protein-fed') were larger, developed faster and emerged with more nutritional reserves than flies that were protein-deprived as larvae. Protein-fed males, regardless of their size, became sexually active before males that developed in hosts with no protein. Protein-fed females produced more mature eggs than protein-deprived ones. Moreover, protein-fed females tended to copulate sooner than females that developed in hosts with no protein. In addition, regardless of female larval diet, females with more mature eggs tended to copulate sooner than females with less mature eggs. In light of these results, the importance of the larval environment for adult reproductive success is discussed.     

LIFE-HISTORY CONSEQUENCES OF ADAPTATION TO LARVAL NUTRITIONAL STRESS IN DROSOPHILA

Many animal species face periods of chronic nutritional stress during which the individuals must continue to develop, grow, and/or reproduce despite low quantity or quality of food. Here, we use experimental evolution to study adaptation to such chronic nutritional stress in six replicate Drosophila melanogaster populations selected for the ability to survive and develop within a limited time on a very poor larval food. In unselected control populations, this poor food resulted in 20% lower egg‐to‐adult viability, 70% longer egg‐to‐adult development, and 50% lower adult body weight (compared to the standard food on which the flies were normally maintained). The evolutionary changes associated with adaptation to the poor food were assayed by comparing the selected and control lines in a common environment for different traits after 29–64 generations of selection. The selected populations evolved improved egg‐to‐adult viability and faster development on poor food. Even though the adult dry weight of selected flies when raised on the poor food was lower than that of controls, their average larval growth rate was higher. No differences in proportional pupal lipid content were observed. When raised on the standard food, the selected flies showed the same egg‐to‐adult viability and the same resistance to larval heat and cold shock as the controls and a slightly shorter developmental time. However, despite only 4% shorter development time, the adults of selected populations raised on the standard food were 13% smaller and showed 20% lower early‐life fecundity than the controls, with no differences in life span. The selected flies also turned out less tolerant to adult malnutrition. Thus, fruit flies have the genetic potential to adapt to poor larval food, with no detectable loss of larval performance on the standard food. However, adaptation to larval nutritional stress is associated with trade‐offs with adult fitness components, including adult tolerance to nutritional stress.     

Flies without centrioles

Centrioles and centrosomes have an important role in animal cell organization, but it is uncertain to what extent they are essential for animal development. The Drosophila protein DSas-4 is related to the human microcephaly protein CenpJ and the C. elegans centriolar protein Sas-4. We show that DSas-4 is essential for centriole replication in flies. DSas-4 mutants start to lose centrioles during embryonic development, and, by third-instar larval stages, no centrioles or centrosomes are detectable. Mitotic spindle assembly is slow in mutant cells, and approximately 30% of the asymmetric divisions of larval neuroblasts are abnormal. Nevertheless, mutant flies develop with near normal timing into morphologically normal adults. These flies, however, have no cilia or flagella and die shortly after birth because their sensory neurons lack cilia. Thus, centrioles are essential for the formation of centrosomes, cilia, and flagella, but, remarkably, they are not essential for most aspects of Drosophila development.     

Genetic variation for rate of development in natural populations of Drosophila melanogaster

We have sampled wild chromosomes from two natural populations of Drosophila melanogaster and obtained flies fully homozygous for the second chromosome, the third chromosome, or both, as well as flies heterozygous for one or both wild chromosomes and balancer chromosomes. Rate of embryogenesis (egg laying to larval hatching) and rate of development from egg to adult are measured, by classifying the individuals into fast, intermediate, and slow developmental classes. The experiments indicate that variation for rate of embryogenesis and for rate of egg-to-adult development is plentiful in the natural populations. Various hypotheses are enunciated to account for the small range of phenotypic variation observed in wild-type individuals with respect to the two parameters (embryogenesis and egg-to-adult development) and for the difficulty in changing the mean rates by artificial selection. Appropriate experiments may decide among the hypotheses, helping us to understand the genetic control of rate of ontogenesis, which is an important fitness component.     

The influence of host fruit and temperature on the body size of adult Ceratitis capitata (Diptera: Tephritidae) under laboratory and field conditions

The adult body size of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), varies in natural conditions. Body size is an important fitness indicator in the Mediterranean fruit fly; larger individuals are more competitive at mating and have a greater dispersion capacity and fertility. Both temperature during larval development and host fruit quality have been cited as possible causes for this variation. We studied the influence of host fruit and temperature during larval development on adult body size (wing area) in the laboratory, and determined body size variation in field populations of the Mediterannean fruit fly in eastern Spain. Field flies measured had two origins: 1) flies periodically collected throughout the year in field traps from 32 citrus groves, during the period 2003-2007; and 2) flies evolved from different fruit species collected between June and December in 2003 and 2004. In the lab, wing area of male and female adults varied significantly with temperature during larval development, being larger at the lowest temperature. Adult size also was significantly different depending on the host fruit in which larvae developed. The size of the flies captured at the field, either from traps or from fruits, varied seasonally showing a gradual pattern of change along the year. The largest individuals were obtained during winter and early spring and the smallest during late summer. In field conditions, the size of the adult Mediterannean fruit fly seems apparently more related with air temperature than with host fruit. The implications of this adult size pattern on the biology of C. capitata and on the application of the sterile insect technique are discussed.