Female-specific regulation of cuticular hydrocarbon biosynthesis by dopamine in Drosophila melanogaster

Melanin synthesis genes BgTH and BgDdc affect body color and cuticle permeability in Blattella germanica

Melanin is involved in cuticle pigmentation and sclerotization of insects, which is critical for maintaining structural integrity and functional completeness of insect cuticle. The 2 key enzymes of tyrosine hydroxylase (TH) and dopa decarboxylase (DDC) predicted in melanin biosynthesis are usually conserved in insects. However, it is unclear whether their function is related to epidermal permeability. In this study, we identified and cloned the gene sequences of BgTH and BgDdc from Blattella germanica, and revealed that they both showed a high expression at the molting, and BgTH was abundant in the head and integument while BgDdc was expressed highest in the fat body. Using RNA interference (RNAi), we found that knockdown of BgTH caused molting obstacles in some cockroaches, with the survivors showing pale color and softer integuments, while knockdown of BgDdc was viable and generated an abnormal light brown body color. Desiccation assay showed that the dsBgTH-injected adults died earlier than control groups under a dry atmosphere, but dsBgDdc-injected cockroaches did not. In contrast, when dsRNA-treated cockroaches were reared under a high humidity condition, almost no cockroaches died in all treatments. Furthermore, with eosin Y staining assay, we found that BgTH-RNAi resulted in a higher cuticular permeability, and BgDdc-RNAi also caused slight dye penetration. These results demonstrate that BgTH and BgDdc function in body pigmentation and affect the waterproofing ability of the cuticle, and the reduction of cuticular permeability may be achieved through cuticle melanization.

"Scent of a fruit fly": Cuticular chemoprofiles after mating in differently fed Drosophila melanogaster (Diptera: Drosophilidae) strains

In the world of complex smells in natural environment, feeding and mating represent two important olfactory-guided behaviors in Drosophila melanogaster (Diptera: Drosophilidae). Diet affects the chemoprofile composition of the individuals, which, indirectly, may significantly affect their mating success. In this study, chemoprofiles of recently mated flies belonging to four D. melanogaster strains, which were fed for many generations on different substrates (standard cornmeal-S strain; banana-B strain; carrot-C strain; tomato-T strain) were identified and quantified. In total, 67 chemical compounds were identified: 48 compounds were extracted from males maintained on banana and carrot, and 47 compounds from males maintained on cornmeal and tomato substrates, while total of 60 compounds were identified in females from all strains. The strains and the sexes significantly differed in qualitative nature of their chemoprofiles after mating. Significant differences in the relative amount of three major male pheromones (cis-vaccenyl acetate-cVA, (Z)-7-pentacosene, and (Z)-7-tricosene) and in female pheromone (Z,Z)-7,11-nonacosadiene among strains were also recorded. Furthermore, multivariate analysis of variance (MANOVA) pointed to significant differences between virgin and mated individuals of all strains and within both sexes. Differences in some of the well known sex pheromones were also identified when comparing their relative amount before and after mating. The presence of typical male pheromones in females, and vice versa may indicate their bidirectional transfer during copulation. Our results confirm significant effect of mating status on cuticular hydrocarbon (CHC) phenotypes in differently fed D. melanogaster flies.

Modulation of fatty acid elongation in cockroaches sustains sexually dimorphic hydrocarbons and female attractiveness

Insect cuticular hydrocarbons (CHCs) serve as important intersexual signaling chemicals and generally show variation between the sexes, but little is known about the generation of sexually dimorphic hydrocarbons (SDHCs) in insects. In this study, we report the molecular mechanism and biological significance that underlie the generation of SDHC in the German cockroach Blattella germanica. Sexually mature females possess more C29 CHCs, especially the contact sex pheromone precursor 3,11-DimeC29. RNA interference (RNAi) screen against the fatty acid elongase family members combined with heterologous expression of the genes in yeast revealed that both BgElo12 and BgElo24 were involved in hydrocarbon (HC) production, but BgElo24 is of wide catalytic activities and is able to provide substrates for BgElo12, and only the female-enriched BgElo12 is responsible for sustaining female-specific HC profile. Repressing BgElo12 masculinized the female CHC profile, decreased contact sex pheromone level, and consequently reduced the sexual attractiveness of female cockroaches. Moreover, the asymmetric expression of BgElo12 between the sexes is modulated by sex differentiation cascade. Specifically, male-specific BgDsx represses the transcription of BgElo12 in males, while BgTra is able to remove this effect in females. Our study reveals a novel molecular mechanism responsible for the formation of SDHCs and also provide evidences on shaping of the SDHCs by sexual selection, as females use them to generate high levels of contact sex pheromone.

Sexual dimorphism of body waxes is prevalent in insects; this study reveals that the sex-differentiation pathway regulates fatty acid elongation, ensuring production of the sexually dimorphic cuticular hydrocarbons needed for high levels of sex pheromone and sexual attractiveness in female cockroaches.

Pleiotropic Effects of ebony and tan on Pigmentation and Cuticular Hydrocarbon Composition in Drosophila melanogaster

Pleiotropic genes are genes that affect more than one trait. For example, many genes required for pigmentation in the fruit fly Drosophila melanogaster also affect traits such as circadian rhythms, vision, and mating behavior. Here, we present evidence that two pigmentation genes, ebony and tan, which encode enzymes catalyzing reciprocal reactions in the melanin biosynthesis pathway, also affect cuticular hydrocarbon (CHC) composition in D. melanogaster females. More specifically, we report that ebony loss-of-function mutants have a CHC profile that is biased toward long (>25C) chain CHCs, whereas tan loss-of-function mutants have a CHC profile that is biased toward short (<25C) chain CHCs. Moreover, pharmacological inhibition of dopamine synthesis, a key step in the melanin synthesis pathway, reversed the changes in CHC composition seen in ebony mutants, making the CHC profiles similar to those seen in tan mutants. These observations suggest that genetic variation affecting ebony and/or tan activity might cause correlated changes in pigmentation and CHC composition in natural populations. We tested this possibility using the Drosophila Genetic Reference Panel (DGRP) and found that CHC composition covaried with pigmentation as well as levels of ebony and tan expression in newly eclosed adults in a manner consistent with the ebony and tan mutant phenotypes. These data suggest that the pleiotropic effects of ebony and tan might contribute to covariation of pigmentation and CHC profiles in Drosophila.

Delegating Sex: Differential Gene Expression in Stolonizing Syllids Uncovers the Hormonal Control of Reproduction

Stolonization in syllid annelids is a unique mode of reproduction among animals. During the breeding season, a structure resembling the adult but containing only gametes, called stolon, is formed generally at the posterior end of the animal. When stolons mature, they detach from the adult and gametes are released into the water column. The process is synchronized within each species, and it has been reported to be under environmental and endogenous control, probably via endocrine regulation. To further understand reproduction in syllids and to elucidate the molecular toolkit underlying stolonization, we generated Illumina RNA-seq data from different tissues of reproductive and nonreproductive individuals of Syllis magdalena and characterized gene expression during the stolonization process. Several genes involved in gametogenesis (ovochymase, vitellogenin, testis-specific serine/threonine-kinase), immune response (complement receptor 2), neuronal development (tyrosine-protein kinase Src42A), cell proliferation (alpha-1D adrenergic receptor), and steroid metabolism (hydroxysteroid dehydrogenase 2) were found differentially expressed in the different tissues and conditions analyzed. In addition, our findings suggest that several neurohormones, such as methyl farnesoate, dopamine, and serotonin, might trigger stolon formation, the correct maturation of gametes and the detachment of stolons when gametogenesis ends. The process seems to be under circadian control, as indicated by the expression patterns of r-opsins. Overall, our results shed light into the genes that orchestrate the onset of gamete formation and improve our understanding of how some hormones, previously reported to be involved in reproduction and metamorphosis processes in other invertebrates, seem to also regulate reproduction via stolonization.

Control of pheromone production by ovaries in Drosophila

Drosophila pheromones are long chain hydrocarbons (CHCs) produced by specialized epidermal cells, the oenocytes. Here we were explored the role of ovaries in CHC regulation. We studied tudor, a grandchildless-like mutation, resulting in progeny without ovaries and three alleles of ovoD, resulting in ovarian defects depending on the strength of the allele. We show here that these mutant flies with no or abnormal ovaries have a decrease in C29 length CHC ratio, balanced by an increase in C23 and C25 length ratio; this effect is dependent on the strength of the mutation. An increase in the amount of CHCs also occurred but was not related to the strength of ovoD alleles. As ovaries are the main site of ecdysone production in females, we knocked down the receptor to ecdysone EcR in the oenocytes and obtained increased amounts of CHCs and inhibition of long chain CHC synthesis, showing that the lack of an ecdysone signal arriving into the oenocytes is responsible for these defects. We then investigated the role of follicular cells and oocyte on CHC regulation: we RNAi-knocked down the LPR receptors in the oocyte to hinder vitellogenesis without significantly modifying CHC profile. We then expressed apoptosis genes within the follicle cells or within the ovocytes and obtained less long chain and more short chain CHC levels in the former case and an enhanced CHC production in the latter case. Together, these results support the notion of an interaction between oocyte and follicular cells, which send an ecdysone signal to the oenocytes to regulate CHC synthesis.

Exposure to atrazine alters behaviour and disrupts the dopaminergic system in Drosophila melanogaster

Atrazine is an extensively used herbicide, and has become a common environmental contaminant. Effects on dopaminergic neurotransmission in mammals following exposure to atrazine have been previously demonstrated. Here, the effects of atrazine regarding behavioural and dopaminergic neurotransmission parameters were assessed in the fruit fly D. melanogaster, exposed during embryonic and larval development. Embryos (newly fertilized eggs) were exposed to two atrazine concentrations (10μM and 100μM) in the diet until the adult fly emerged. Negative geotaxis assay, as well as exploratory behaviour, immobility time and number of grooming episodes in an open field system were assessed. Tyrosine hydroxylase (TH) activity and gene expression of the dopaminergic system were also evaluated in newly emerged male and female flies. All analyzed parameters in male flies were not significantly affected by atrazine exposure. However female flies exposed to atrazine at 10μM presented an increase in immobility time and a reduction in exploratory activity in the open field test, which was offset by an increase in the number of grooming episodes. Also, female flies exposed to 100μM of atrazine presented an increase in immobility time. Gene expression of DOPA decarboxylase and dopamine (DA) receptors were also increased only in females. The behavioural effects of atrazine exposure observed in female flies were due to a disturbance in the dopaminergic system.

A dopamine receptor contributes to paraquat-induced neurotoxicity in Drosophila

Long-term exposure to environmental oxidative stressors, like the herbicide paraquat (PQ), has been linked to the development of Parkinson's disease (PD), the most frequent neurodegenerative movement disorder. Paraquat is thus frequently used in the fruit fly Drosophila melanogaster and other animal models to study PD and the degeneration of dopaminergic neurons (DNs) that characterizes this disease. Here, we show that a D1-like dopamine (DA) receptor, DAMB, actively contributes to the fast central nervous system (CNS) failure induced by PQ in the fly. First, we found that a long-term increase in neuronal DA synthesis reduced DAMB expression and protected against PQ neurotoxicity. Secondly, a striking age-related decrease in PQ resistance in young adult flies correlated with an augmentation of DAMB expression. This aging-associated increase in oxidative stress vulnerability was not observed in a DAMB-deficient mutant. Thirdly, targeted inactivation of this receptor in glutamatergic neurons (GNs) markedly enhanced the survival of Drosophila exposed to either PQ or neurotoxic levels of DA, whereas, conversely, DAMB overexpression in these cells made the flies more vulnerable to both compounds. Fourthly, a mutation in the Drosophila ryanodine receptor (RyR), which inhibits activity-induced increase in cytosolic Ca(2+), also strongly enhanced PQ resistance. Finally, we found that DAMB overexpression in specific neuronal populations arrested development of the fly and that in vivo stimulation of either DNs or GNs increased PQ susceptibility. This suggests a model for DA receptor-mediated potentiation of PQ-induced neurotoxicity. Further studies of DAMB signaling in Drosophila could have implications for better understanding DA-related neurodegenerative disorders in humans.

Pigmentation and behavior: potential association through pleiotropic genes in Drosophila

The molecular basis of pigmentation variation within and among Drosophila species is largely attributed to genes in melanin biosynthesis pathway, which involves dopamine metabolism. Most of the genetic changes underlying pigmentation variations reported to date are changes at the expression levels of the structural genes in the pathway. Within D. melanogaster, changes in cis-regulatory regions of a gene, ebony, are responsible for the naturally occurring variation of the body pigmentation intensity. This gene is also known to be expressed in glia, and many visual and behavioral abnormalities of its mutants have been reported. This implies that the gene has pleiotropic functions in the nervous systems. In this review, current knowledge on pigmentation variation and melanin biosynthesis pathway are summarized, with some focus on pleiotropic features of ebony and other genes in the pathway. A potential association between pigmentation and behavior through such pleiotropic genes is discussed in light of cis-regulatory structure and pleiotropic mutations.

Neurohormonal changes associated with ritualized combat and the formation of a reproductive hierarchy in the ant Harpegnathos saltator

Dominance rank in animal societies is correlated with changes in both reproductive physiology and behavior. In some social insects, dominance status is used to determine a reproductive division of labor, where a few colony members reproduce while most remain functionally sterile. Changes in reproduction and behavior in this context must be coordinated through crosstalk between the brain and the reproductive system. We investigated a role for biogenic amines in forming this connection in the ant Harpegnathos saltator. In this species, workers engage in an elaborate dominance tournament to establish a group of reproductive workers termed gamergates. We analyzed biogenic amine content in the brains of gamergates, inside-workers and foragers under stable colony conditions and found that gamergates had the highest levels of dopamine. Dopamine levels were also positively correlated with increased ovarian activity among gamergates. Next, we experimentally induced workers to compete in a reproductive tournament to determine how dopamine may be involved in the establishment of a new hierarchy. Dopamine levels rose in aggressive workers at the start of a tournament, while workers that were policed by their nestmates (a behavior that inhibits ovarian activity) showed a rapid decline in dopamine. In addition to dopamine, levels of serotonin and tyramine differed among castes, and these changes could contribute to differences in caste-specific behavioral patterns observed among non-reproductive workers. Overall, these results provide support that biogenic amines link changes in behavior and dominance with reproductive activity in H. saltator as well as drive differences in worker task performance.

Neurogenetics of female reproductive behaviors in Drosophila melanogaster

We follow an adult Drosophila melanogaster female through the major reproductive decisions she makes during her lifetime, including habitat selection, precopulatory mate choice, postcopulatory physiological changes, polyandry, and egg-laying site selection. In the process, we review the molecular and neuronal mechanisms allowing females to integrate signals from both environmental and social sources to produce those behavioral outputs. We pay attention to how an understanding of D. melanogaster female reproductive behaviors contributes to a wider understanding of evolutionary processes such as pre- and postcopulatory sexual selection as well as sexual conflict. Within each section, we attempt to connect the theories that pertain to the evolution of female reproductive behaviors with the molecular and neurobiological data that support these theories. We draw attention to the fact that the evolutionary and mechanistic basis of female reproductive behaviors, even in a species as extensively studied as D. melanogaster, remains poorly understood.

Grasshopper Lazarillo, a GPI-anchored Lipocalin, increases Drosophila longevity and stress resistance, and functionally replaces its secreted homolog NLaz

Lazarillo (Laz) is a glycosyl-phosphatidylinositol (GPI)-linked glycoprotein first characterized in the developing nervous system of the grasshopper Schistocerca americana. It belongs to the Lipocalins, a functionally diverse family of mostly secreted proteins. In this work we test whether the protective capacity known for Laz homologs in flies and vertebrates (NLaz, GLaz and ApoD) is evolutionarily conserved in grasshopper Laz, and can be exerted from the plasma membrane in a cell-autonomous manner. First we demonstrate that extracellular forms of Laz have autocrine and paracrine protecting effects for oxidative stress-challenged Drosophila S2 cells. Then we assay the effects of overexpressing GPI-linked Laz in adult Drosophila and whether it rescues both known and novel phenotypes of NLaz null mutants. Local effects of GPI-linked Laz inside and outside the nervous system promote survival upon different stress forms, and extend lifespan and healthspan of the flies in a cell-type dependent manner. Outside the nervous system, expression in fat body cells but not in hemocytes results in protection. Within the nervous system, glial cell expression is more effective than neuronal expression. Laz actions are sexually dimorphic in some expression domains. Fat storage promotion and not modifications in hydrocarbon profiles or quantities explain the starvation-desiccation resistance caused by Laz overexpression. This effect is exerted when Laz is expressed ubiquitously or in dopaminergic cells, but not in hemocytes. Grasshopper Laz functionally restores the loss of NLaz, rescuing stress-sensitivity as well as premature accumulation of aging-related damage, monitored by advanced glycation end products (AGEs). However Laz does not rescue NLaz courtship behavioral defects. Finally, the presence of two new Lipocalins with predicted GPI-anchors in mosquitoes shows that the functional advantages of GPI-linkage have been commonly exploited by Lipocalins in the arthropodan lineage.

The genetic basis of female mate preference and species isolation in Drosophila

The processes that underlie mate choice have long fascinated biologists. With the advent of increasingly refined genetic tools, we are now beginning to understand the genetic basis of how males and females discriminate among potential mates. One aspect of mate discrimination of particular interest is that which isolates one species from another. As behavioral isolation is thought to be the first step in speciation, and females are choosy more often than males in this regard, identifying the genetic variants that influence interspecies female mate choice can enhance our understanding of the process of speciation. Here, we review the literature on female mate choice in the most widely used model system for studies of species isolation Drosophila. Although females appear to use the same traits for both within- and between-species female mate choice, there seems to be a different genetic basis underlying these choices. Interestingly, most genomic regions that cause females to reject heterospecific males fall within areas of low recombination. Likely, candidate genes are those that act within the auditory or olfactory system, or within areas of the brain that process these systems.

Unsaturated cuticular hydrocarbons synergize responses to sex attractant pheromone in the yellow peach moth, Conogethes punctiferalis

Four trienyl hydrocarbons, (Z3, Z6, Z9)-tricosatriene (Z3, Z6, Z9-23:HC), (Z3, Z6, Z9)-pentacosatriene (Z3, Z6, Z9-25:HC), (Z3, Z6, Z9)-heptacosatriene (Z3, Z6, Z9-27:HC), and (Z3, Z6, Z9)-nonacosatriene (Z3, Z6, Z9-29:HC) were identified in a non-polar fraction of the body wax of male and female yellow peach moth, Conogethes punctiferalis. The relative amounts and ratios of these hydrocarbons differed between sexes. In females, the ratios in body wax and pheromone gland extracts were similar, with lesser amounts found in gland extracts. Synergistic effects of these hydrocarbons when added to the known aldehyde pheromone components were assessed in wind tunnel tests. A blend of (E)-10-hexadecenal (E10-16: Ald) and (Z)-10-hexadecenal (Z10-16: Ald) elicited upwind flight and orientation of males to the pheromone source, but arriving males did not remain close to source for very long. Among the hydrocarbons identified, only Z3, Z6, Z9-23:HC enhanced the activity of the aldehyde blend by increasing the time spent close to the source and the number of source contacts. Z3, Z6, Z9-23:HC and (Z9)-heptacosene (Z9-27:HC) also increased close-range responses to the aldehyde blend. The activity of the aldehyde blend plus these two hydrocarbons was similar to that of crude pheromone extract. Positive dose-response relationships between the aldehyde blend and two hydrocarbon mixtures were found. The lowest doses that elicited synergism were 10(-1) female equivalents (of body wax extracts) for the two hydrocarbons, and 10(-2) female equivalents for the total unsaturated hydrocarbon mixture.

Ontogeny of Drosophila melanogaster female sex-appeal and cuticular hydrocarbons

The chemical communication system in Drosophila melanogaster Meigen, 1830 plays a major role in courtship and consists of the male-specific cis-Vaccenyl acetate and sex-specific contact pheromones, cuticular hydrocarbons (CHC), which build up during ontogeny (first 4 days). They replace longer CHCs, common to both sexes and present only after the imaginal eclosion. A detailed quantitative description of the evolution of cuticular unsaturated hydrocarbons with age is presented here for males and females of different D. melanogaster strains, which have been bred in well controlled environments. Monoenes appear in both sexes at around 12 h, before female dienes. The present paper argues that this is likely linked to the switching on of a new set of genes. Ecdysone, which is more abundant in females than in males during this critical period, might control this switch. Parallel behavioral studies show that whereas female of all ages trigger early mature male courtship steps like wing vibration, only females older than 1 day trigger late courtship steps like attempted copulation. This supports the hypothesis that late male courtship steps might be triggered by the CHCs, which build up after this age, especially female-specific (Z,Z)-7,11 - and (Z,Z)-5,9-dienes.

Identification of a gene, Desiccate, contributing to desiccation resistance in Drosophila melanogaster

Suitable alterations in gene expression are believed to allow animals to survive drastic changes in environmental conditions. Drosophila melanogaster larvae cease eating and exit moist food to search for dry pupation sites after the foraging stage in what is known as the wandering stage. Although the behavioral change from foraging to wandering causes desiccation stress, the mechanism by which Drosophila larvae protect themselves from desiccation remains obscure. Here, we identified a gene, CG14686 (designated as Desiccate (Desi)), whose expression was elevated during the wandering stage. The Desi expression level was reversibly decreased by transferring wandering larvae to wet conditions and increased again by transferring them to dry conditions. Elevation of Desi expression was also observed in foraging larvae when they were placed in dry conditions. Desi encoded a 261-amino acid single-pass transmembrane protein with notable motifs, such as SH2 and PDZ domain-binding motifs and a cAMP-dependent protein kinase phosphorylation motif, in the cytoplasmic region, and its expression was observed mainly in the epidermal cells of the larval integuments. Overexpression of Desi slightly increased the larval resistance to desiccation stress during the second instar. Furthermore, Desi RNAi larvae lost more weight under dry conditions, and subsequently, their mortalities significantly increased compared with control larvae. Under dry conditions, consumption of carbohydrate was much higher in Desi RNAi larvae than control larvae. Based on these results, it is reasonable to conclude that Desi contributes to the resistance of Drosophila larvae to desiccation stress.

Contribution of oenocytes and pheromones to courtship behaviour in Drosophila

Background

In Drosophila, cuticular sex pheromones are long-chain unsaturated hydrocarbons synthesized from fatty acid precursors in epidermal cells called oenocytes. The species D. melanogaster shows sex pheromone dimorphism, with high levels of monoenes in males, and of dienes in females. Some biosynthesis enzymes are expressed both in fat body and oenocytes, rendering it difficult to estimate the exact role of oenocytes and of the transport of fatty acids from fat body to oenocytes in pheromone elaboration. To address this question, we RNAi silenced two main genes of the biosynthesis pathway, desat1 and desatF, in the oenocytes of D. melanogaster, without modifying their fat body expression.

Results

Inactivation of desat1 in oenocytes resulted in a 96% and 78% decrease in unsaturated hydrocarbons in males and females, respectively. Female pheromones (dienes) showed a decrease of 90%. Inactivation of desatF, which is female-specific and responsible for diene formation, resulted in a dramatic loss of pheromones (-98%) paralleled with a two-fold increase in monoenes. Courtship parameters (especially courtship latency) from wild-type males were more affected by desat1 knocked-down females (courtship latency increased by four fold) than by desatF knocked-down ones (+65% of courtship latency).

The number of transcripts in oenocytes was estimated at 0.32 and 0.49 attomole/μg for desat1 in males and females, respectively, about half of the total transcripts in a fly. There were only 0.06 attomole/μg desatF transcripts in females, all located in the oenocytes.

Conclusion

Knock-down results for desat1 suggest that there must be very little transport of unsaturated precursors from fat body to the oenocytes, so pheromone synthesis occurs almost entirely through the action of biosynthesis enzymes within the oenocytes. Courtship experiments allow us to discuss the behavioral role of diene pheromones, which, under special conditions, could be replaced by monoenes in D. melanogaster. A possible explanation is given of how pheromones could have evolved in species such as D. simulans, which only synthesize monoenes.

Reduction of dopamine level enhances the attractiveness of male Drosophila to other males

Dopamine is an important neuromodulator in animals and its roles in mammalian sexual behavior are extensively studied. Drosophila as a useful model system is widely used in many fields of biological studies. It has been reported that dopamine reduction can affect female receptivity in Drosophila and leave male-female courtship behavior unaffected. Here, we used genetic and pharmacological approaches to decrease the dopamine level in dopaminergic cells in Drosophila, and investigated the consequence of this manipulation on male homosexual courtship behavior. We find that reduction of dopamine level can induce Drosophila male-male courtship behavior, and that this behavior is mainly due to the increased male attractiveness or decreased aversiveness towards other males, but not to their enhanced propensity to court other males. Chemical signal input probably plays a crucial role in the male-male courtship induced by the courtees with reduction of dopamine. Our finding provides insight into the relationship between the dopamine reduction and male-male courtship behavior, and hints dopamine level is important for controlling Drosophila courtship behavior.

Spatial orientation in Drosophila

Spatial orientation is critical for many behaviors. Intrinsic to the oriented state is the knowledge of past, present, and future spatial location relative to one or more landmarks. How do animals so fluidly solve this problem? Determining mechanisms of orientation may benefit from investigation of relatively simple organisms. Two behaviors that presumably use path integration as a major input to orientation--place learning and persistent target selection--allow for the examination of cellular and neural circuit mechanisms in Drosophila. Although our understanding of these processes is still relatively immature, some recent findings provide insights into the mechanisms supporting orientation. First, place learning provides good access to the past, present, and future aspects of orientation, but currently is less open to understanding how a fly establishes a relationship to landmarks. The change in behavior after learning is orientation away from, and avoiding, a place predicted to punish a fly, incorporating all temporal aspects of orientation, and can last for minutes to hours. This conclusion is supported by several learning phenomena. Second, persistent target selection provides the best access to the processes determining relationships to landmarks. Using a disappearing visual-landmark paradigm, persistent target selection was shown to require parts of the central complex for a seconds-long "path integration memory." How the path integration memory, on this short time scale, is related to longer lasting place memories is, as yet, unknown. Nevertheless, studies of place learning and persistent target selection may provide insights into orientation mechanisms in a simple brain.

Interaction of dopamine, female pheromones, locomotion and sex behavior in Drosophila melanogaster

The regulation of female hydrocarbons and courtship behavior by dopamine and their relationship with locomotion, were investigated in Drosophila melanogaster. Ddc mutants and wild-type female flies treated with tyrosine hydroxylase inhibitors (alpha-methyltyrosine or 3-iodotyrosine) had fewer diene hydrocarbons (female pheromones) and there was a total (Ddc), partial (alpha-methyltyrosine) or no (3-iodotyrosine) rescue of hydrocarbon pattern after dopamine ingestion. There was a correlation between female pheromone level and male courtship intensity for these dopamine-depleted or rescued flies. Female locomotion was decreased in flies treated with tyrosine hydroxylase inhibitors and restored by dopamine, showing that decreased mobility of the female has little importance on male courtship. However, male courtship was inhibited by an increased mobility of dopamine-supplemented females. Tanning, which is altered in dopamine-deficient flies and in tan and ebony mutants, seemed to have no significant influence on female pheromones. Females with increased quantities of dopamine (by ingestion) exhibited larger quantities of pheromones. However, Catsup mutants did not, probably as a result of defects in the epidermis. The Dat mutation, which resulted in more dopamine being produced in the brain, showed no pheromone modification. Together, these data show a complex interaction between dopamine, female hydrocarbons, locomotion and male courtship behavior.

Serotonin is necessary for place memory in Drosophila

Biogenic amines, such as serotonin and dopamine, can be important in reinforcing associative learning. This function is evident as changes in memory performance with manipulation of either of these signals. In the insects, evidence begins to argue for a common role of dopamine in negatively reinforced memory. In contrast, the role of the serotonergic system in reinforcing insect associative learning is either unclear or controversial. We investigated the role of both of these signals in operant place learning in Drosophila. By genetically altering serotonin and dopamine levels, manipulating the neurons that make serotonin and dopamine, and pharmacological treatments we provide clear evidence that serotonin, but not dopamine, is necessary for place memory. Thus, serotonin can be critical for memory formation in an insect, and dopamine is not a universal negatively reinforcing signal.

Pheromonal communication involved in courtship behavior in Diptera

Sex pheromones are known for many dipteran species and play an important role in courtship behavior, together with visual, tactile, acoustic and other factors. Pheromones for a number of dipterans have been recently identified. This survey covers a number of species in all the families that have been studied. The review discusses diverse courtship behaviors in Diptera, with a special focus on the sex pheromones involved. In the Nematocera suborder, pheromones are volatile components, which act at a distance. They are derived from short-chain alkanes with acetoxy groups (Cecidomyidae) or terpenes (Psychodidae). In the Cyclorrhapha, pheromones may be volatile, derived from alkanes (Tephritidae) or terpenes (Agromyzidae), or non-volatile, unsaturated or methyl-branched hydrocarbons, which act by contact (the other subgenera). The behavioral roles and regulation of these pheromones are described, and their importance in species recognition is discussed.

Prospero mutants induce precocious sexual behavior in Drosophila males

Brain maturation, a developmental process influenced by both endogenous and environmental factors, can affect sexual behavior. In vertebrates and invertebrates, sexual maturation is under the influence of hormones and neuromodulators, but the role of developmental genes in this process is still poorly understood. We report that prospero (pros), a gene crucial for nervous system development, can change the age of onset of sexual behavior in Drosophila melanogaster males: adult males carrying a single copy of several pros mutations court females and mate at a younger age than control males. However, these pros mutations had no effect on female sexual receptivity and did not alter other male phenotypes related to mating behavior. The Pros protein was detected in several brain and sensory structures of immature adult males, some of which are normally involved in the regulation of male specific behaviors. Our data suggest that the altered pros expression affects the age of onset of male mating behavior.

Quantitative trait loci for cuticular hydrocarbons associated with sexual isolation between Drosophila simulans and D. sechellia

The identification of genes with large effects on sexual isolation and speciation is an important link between classic evolutionary genetics and molecular biology. Few genes that affect sexual isolation and speciation have been identified, perhaps because many traits influencing sexual isolation are complex behaviors. Cuticular hydrocarbons (CHs) of species of the Drosophila melanogaster group play a large role in sexual isolation by functioning as contact pheromones influencing mate recognition. Some of the genes that play key roles in determining species-specific CHs have been identified. We have performed separate quantitative trait locus (QTL) analyses of 7-tricosene (7-T) and 7,11-heptacosadiene (7,11-HD), the two major female CHs differing between D. simulans and D. sechellia. We find that approximately 40% of the phenotypic variance in each CH is associated with two to four chromosomal regions. A region on the right arm of chromosome 3 contains QTL that affect both traits, but other QTL are in distinct chromosomal regions. Epistatic interactions were detected between two pairs of QTL for 7,11-HD such that if either were homozygous for the D. simulans allele, the fly was similar to D. simulans in phenotype, with a low level of 7,11-HD. We discuss the location of these regions with regard to candidate genes for CH production, including those for desaturases.