Mutation of Drosophila dopamine receptor DopR leads to male-male courtship behavior

In Drosophila, dopamine plays important roles in many biological processes as a neuromodulator. Previous studies showed that dopamine level could affect fly courtship behaviors. Disturbed dopamine level leads to abnormal courtship behavior in two different ways. Dopamine up-regulation induces male-male courtship behavior, while down-regulation of dopamine level results in increased sexual attractiveness of males towards other male flies. Until now, the identity of the dopamine receptor involved in this abnormal male-male courtship behavior remains unknown. Here we used genetic approaches to investigate the role of dopamine receptors in fly courtship behavior. We found that a dopamine D1-like receptor, DopR, was involved in fly courtship behavior. DopR mutant male flies display male-male courtship behavior. This behavior is mainly due to the male's increased propensity to court other males. Expression of functional DopR successfully rescued this mutant phenotype. Knock-down of D2-like receptor D2R and another D1-like receptor, DAMB, did not induce male-male courtship behavior, indicating the receptor-type specificity of this phenomenon. Our findings provide insight into a possible link between dopamine level disturbance and the induced male-male courtship behavior.     

Drosophila male courtship behavior is modulated by ecdysteroids

Temperature-dependent induction of ecdysteroid deficiency in the ecdysoneless mutant ecd¹ adult Drosophilamelanogaster results in altered courtship behavior in males. Ecdysteroid deficiency brings about significantly elevated male-male courtship behavior including song production resembling that directed toward females. Supplementation with dietary 20-hydroxyecdysone reduces male-male attraction, but does not change motor activity, courtship patterns or attraction to females. These observations support the hypothesis that reduced levels of ecdysteroids increase the probability that male fruit flies will display courtship behaviors to male stimuli.     

Drosophila Pheromone-Sensing Neurons Expressing the ppk25 Ion Channel Subunit Stimulate Male Courtship and Female Receptivity

As in many species, gustatory pheromones regulate the mating behavior of Drosophila. Recently, several ppk genes, encoding ion channel subunits of the DEG/ENaC family, have been implicated in this process, leading to the identification of gustatory neurons that detect specific pheromones. In a subset of taste hairs on the legs of Drosophila, there are two ppk23-expressing, pheromone-sensing neurons with complementary response profiles; one neuron detects female pheromones that stimulate male courtship, the other detects male pheromones that inhibit male-male courtship. In contrast to ppk23, ppk25, is only expressed in a single gustatory neuron per taste hair, and males with impaired ppk25 function court females at reduced rates but do not display abnormal courtship of other males. These findings raised the possibility that ppk25 expression defines a subset of pheromone-sensing neurons. Here we show that ppk25 is expressed and functions in neurons that detect female-specific pheromones and mediates their stimulatory effect on male courtship. Furthermore, the role of ppk25 and ppk25-expressing neurons is not restricted to responses to female-specific pheromones. ppk25 is also required in the same subset of neurons for stimulation of male courtship by young males, males of the Tai2 strain, and by synthetic 7-pentacosene (7-P), a hydrocarbon normally found at low levels in both males and females. Finally, we unexpectedly find that, in females, ppk25 and ppk25-expressing cells regulate receptivity to mating. In the absence of the third antennal segment, which has both olfactory and auditory functions, mutations in ppk25 or silencing of ppk25-expressing neurons block female receptivity to males. Together these results indicate that ppk25 identifies a functionally specialized subset of pheromone-sensing neurons. While ppk25 neurons are required for the responses to multiple pheromones, in both males and females these neurons are specifically involved in stimulating courtship and mating.     

Influence of the White Locus on the Courtship Behavior of Drosophila Males

Since its discovery by Morgan, the Drosophila white gene has become one of the most intensely studied genes and has been widely used as a genetic marker. Earlier reports that over- and misexpression of White protein in Drosophila males leads to male-male courtship implicated white in courtship control. While previous studies suggested that it is the mislocalization of White protein within cells that causes the courtship phenotype, we demonstrate here that also the lack of extra-retinal White can cause very similar behavioral changes. Moreover, we provide evidence that the lack of White function increases the sexual arousal of males in general, of which the enhanced male-male courtship might be an indirect effect. We further show that white mutant flies are not only optomotor blind but also dazzled by the over-flow of light in daylight. Implications of these findings for the proper interpretation of behavioral studies with white mutant flies are discussed.     

Removal of both antennae influences the courtship and aggressive behaviors in male crickets

To test whether insect antennae are necessary for eliciting courtship and aggression toward appropriate partners, we antennectomized adult male crickets (Gryllus bimaculatus) and observed their behavior toward other antennectomized males and intact females. At 7 days after removal of both antennae, pairs of antennectomized males were placed together; 80% displayed courtship behavior, generating courtship song by rubbing their forewings together, toward other antennectomized males, and 20% displayed aggressive behavior. Only 45% courted intact females. No intact males courted antennectomized males, and 80% displayed aggressive behavior. All intact males courted females. The results for males with one antenna removed were essentially the same as for intact males. These findings indicate that a high proportion of male crickets with both antennae removed court other males and fail to display male-male aggression, demonstrating that removal of antennae from male crickets induces male-male courtship and that an antenna is necessary for the expression of male-male aggression. Moreover, brain serotonin (5-hydroxytryptamine; 5-HT) levels in male crickets were significantly reduced at 7 days after removal of antennae. The reduction of 5-HT was detected primarily in the central body of the brain. Thus, 5-HT in the central body of the male cricket brain may be involved in the behavioral changes.     

Visual and Olfactory Female-Borne Cues Evoke Male Courtship in the Aphid Parasitoid Aphidius colemani Viereck (Hymenoptera: Braconidae)

We investigated the courtship and mating behavior of the pan-tropical polyphagous endoparasitoid Aphidius colemani Viereck. The courtship and mating displays, the magnitude of male-male sexual approaches and the role of female-borne cues evoking male courtship behavior were quantified. The sequence of events leading to copulation in this parasitoid did not differ from that found for other braconids. Females refused to copulate more than once. Same-sex courtships were observed among males and their possible role in an adaptive context is discussed. Olfactory female-borne cues played a key role in eliciting the courtship responses of males. Males were attracted by freshly dead females, but not by dead females soaked in hexane, nor by visual cues from females alone. Intense male wing fanning behavior was elicited by crushed abdomens of virgin females, suggesting that the female abdomen is the source of a short-distance pheromone crucial in evoking male courtship. Further studies are required to clarify the exact nature of the chemicals involved.     

The mushroom body D1 dopamine receptor controls innate courtship drive

Mating is critical for species survival and is profoundly regulated by neuromodulators and neurohormones to accommodate internal states and external factors. To identify the underlying neuromodulatory mechanisms, we investigated the roles of dopamine receptors in various aspects of courtship behavior in Drosophila. Here, we report that the D1 dopamine receptor dDA1 regulates courtship drive in naïve males. The wild‐type naïve males actively courted females regardless their appearance or mating status. On the contrary, the dDA1 mutant (dumb) males exhibited substantially reduced courtship toward less appealing females including decapitated, leg‐less and mated females. The dumb male's reduced courtship activity was due to delay in courtship initiation and prolonged intervals between courtship bouts. The dampened courtship drive of dumb males was rescued by reinstated dDA1 expression in the mushroom body α/β and γ neurons but not α/β or γ neurons alone, which is distinct from the previously characterized dDA1 functions in experience‐dependent courtship or other learning and memory processes. We also found that the dopamine receptors dDA1, DAMB and dD2R are dispensable for associative memory formation and short‐term memory of conditioned courtship, thus courtship motivation and associative courtship learning and memory are regulated by distinct neuromodulatory mechanisms. Taken together, our study narrows the gap in the knowledge of the mechanism that dopamine regulates male courtship behavior.     

Endocrine modulation of primary chemosensory neurons regulates Drosophila courtship behavior

The decision to engage in courtship depends on external cues from potential mates and internal cues related to maturation, health, and experience. Hormones allow for coordinated conveyance of such information to peripheral tissues. Here, we show Ecdysis-Triggering Hormone (ETH) is critical for courtship inhibition after completion of copulation in Drosophila melanogaster. ETH deficiency relieves post-copulation courtship inhibition (PCCI) and increases male-male courtship. ETH appears to modulate perception and attractiveness of potential mates by direct action on primary chemosensory neurons. Knockdown of ETH receptor (ETHR) expression in GR32A-expressing neurons leads to reduced ligand sensitivity and elevated male-male courtship. We find OR67D also is critical for normal levels of PCCI after mating. ETHR knockdown in OR67D-expressing neurons or GR32A-expressing neurons relieves PCCI. Finally, ETHR silencing in the corpus allatum (CA), the sole source of juvenile hormone, also relieves PCCI; treatment with the juvenile hormone analog methoprene partially restores normal post-mating behavior. We find that ETH, a stress-sensitive reproductive hormone, appears to coordinate multiple sensory modalities to guide Drosophila male courtship behaviors, especially after mating.     

The Drosophila dopamine 2-like receptor D2R (Dop2R) is required in the blood brain barrier for male courtship

The blood brain barrier (BBB) has the essential function to protect the brain from potentially hazardous molecules while also enabling controlled selective uptake. How these processes and signaling inside BBB cells control neuronal function is an intense area of interest. Signaling in the adult Drosophila BBB is required for normal male courtship behavior and relies on male-specific molecules in the BBB. Here we show that the dopamine receptor D2R is expressed in the BBB and is required in mature males for normal mating behavior. Conditional adult male knockdown of D2R in BBB cells causes courtship defects. The courtship defects observed in genetic D2R mutants can be rescued by expression of normal D2R specifically in the BBB of adult males. Drosophila BBB cells are glial cells. Our findings thus identify a specific glial function for the DR2 receptor and dopamine signaling in the regulation of a complex behavior.     

What does the fruitless gene tell us about nature vs. nurture in the sex life of Drosophila?

The fruitless (fru) gene in Drosophila has been proposed to play a master regulator role in the formation of neural circuitries for male courtship behavior, which is typically considered to be an innate behavior composed of a fixed action pattern as generated by the central pattern generator. However, recent studies have shed light on experience-dependent changes and sensory-input-guided plasticity in courtship behavior. For example, enhanced male-male courtship, a fru mutant “hallmark,” disappears when fru-mutant males are raised in isolation. The fact that neural fru expression is induced by neural activities in the adult invites the supposition that Fru as a chromatin regulator mediates experience-dependent epigenetic modification, which underlies the neural and behavioral plasticity.     

An Essential Role of the Arginine Vasotocin System in Mate-Guarding Behaviors in Triadic Relationships of Medaka Fish (Oryzias latipes)

To increase individual male fitness, males of various species remain near a (potential) mating partner and repel their rivals (mate-guarding). Mate-guarding is assumed to be mediated by two different types of motivation: sexual motivation toward the opposite sex and competitive motivation toward the same sex. The genetic/molecular mechanisms underlying how mate presence affects male competitive motivation in a triadic relationship has remained largely unknown. Here we showed that male medaka fish prominently exhibit mate-guarding behavior. The presence of a female robustly triggers male-male competition for the female in a triadic relationship (2 males and 1 female). The male-male competition resulted in one male occupying a dominant position near the female while interfering with the other male''s approach of the female. Paternity testing revealed that the dominant male had a significantly higher mating success rate than the other male in a triadic relationship. We next generated medaka mutants of arginine-vasotocin (avt) and its receptors (V1a1, V1a2) and revealed that two genes, avt and V1a2, are required for normal mate-guarding behavior. In addition, behavioral analysis of courtship behaviors in a dyadic relationship and aggressive behaviors within a male group revealed that avt mutant males displayed decreased sexual motivation but showed normal aggression. In contrast, heterozygote V1a2 mutant males displayed decreased aggression, but normal mate-guarding and courtship behavior. Thus, impaired mate-guarding in avt and V1a2 homozygote mutants may be due to the loss of sexual motivation toward the opposite sex, and not to the loss of competitive motivation toward rival males. The different behavioral phenotypes between avt, V1a2 heterozygote, and V1a2 homozygote mutants suggest that there are redundant systems to activate V1a2 and that endogenous ligands activating the receptor may differ according to the social context.     

Male-male courtship behavior induced by ectopic expression of the Drosophila white gene: Role of sensory function and age

Male-male courtship behavior was recently reported to be induced in large populations of Drosophila (e.g., 600–1500 flies) by ectopic expression of the white (w) gene. Little is known about the basis of this behavior; in male-female courtship, sensory cues are believed to play an important role. Previous data are consistent with the possibility that misexpression of w causes abnormal reception or processing of sensory information. We show here that w-induced male-male courtship occurs in isolated pairs of flies. Thus the behavior does not depend on sensory cues found only among large populations of flies, or on cues produced only by a small subset of such populations. This finding enabled quantitative analysis of mechanisms that underlie the behavior. Specifically, male-male courtship does not depend on the reception of olfactory information, nor on the reception or generation of auditory cues, as determined by surgical ablation of antennae, maxillary palps, or wings. Although the rapid onset of the behavior following w induction suggested that its basis could lie in a modulation of sensory physiology, we found visual, olfactory, and gustatory function to be normal in physiological or behavioral tests. The only sensory deprivation to produce an effect on male-male courtship was testing under dim red light; the percentage of flies courting another male was reduced to one-fourth of control values. A striking age dependence of the behavior is also documented: courtship between paired male mini-w⁺ flies was not observed in tests of very young (1-day-old) flies, but occurs at high levels between the ages of 1 and 4 weeks. © 1996 John Wiley & Sons, Inc.     

Courtship Behavior of Zaprionus indianus (Gupta) (Diptera: Drosophilidae) from Populations Colonizing South America

We describe for the first time the sexual behavior and the courtship song of males of the African fly Zaprionus indianus (Gupta), a recent invader of South America. The male courtship song is formed by monocyclic pulses and the courtship behavior is simple when compared to that of species of Drosophila. Two interpulse interval (IPI) distributions were observed: pre-mounting and mounting. No significant difference was observed between the pre-mounting IPIs of males that descended from three geographical populations from South America. We also observed the songs produced by females and the homosexual behavior exhibited by males. A sequence of bursts is produced by females as a refusal signal against males, while males emit a characteristic song that identifies sex genus, which differs from the courtship song. The short courtship and mating latencies recorded reveal vigorous males and receptive females, respectively.     

Male Mating Success in the Presence of a Conspecific Opponent in a Madagascar Hissing Cockroach,Gromphadorhina portentosa (Dictyoptera: Blaberidae)

The influence of a conspecific competitor on male mating behavior was examined in a Madagascar hissing cockroach, Gromphadorhina portentosa. Previous studies have suggested that both male-male competition and female discrimination during courtship interactions may influence male mating success. Familiar pairs of males with a known social association were placed in an arena with a single virgin female and observed. As expected, subordinate males mated significantly less often than their dominant opponents. In pairs in which one male mated, dominant individuals limited the access of subordinates to females. Dominant males displayed an increased frequency and duration of interaction with the female. However, in pairs where both males remained unmated, the mating behavior of dominant and subordinate males did not differ significantly. As interactions progressed, as in the case of males that remained unmated, subordinate males gained increased access to the female. Mated males tended to be larger than their opponent although within a rank, males that mated were no larger than those that remained unmated. These results are discussed in light of the possible roles of male-male competition and female discrimination during courtship interactions.     

The effect of body size on male courtship success in a plethodontid salamander

Two different sets of courtship encounters between female Desmognathus ochrophaeus and males of large (X¯=58) and small (X¯=38 mm) body size were staged in the laboratory. In the first set, encounters were arranged between male-female pairs so that each of five females individually encountered each of 10 males. In these encouters, small and large males were equally likely to court with and inseminate females. In the second set, each encounter was staged for a trio fo one female and two males (one large and one small); each female had a courtship opportunity with five large-small pairs of males, and each pair of males encountered five different females. In the 25 trio encounters, the large male always chased away the small male before proceeding to court the female. Small males never deposited spermatophores if a large male was present. Male body size should have a significant effect on courtship success in natural populations of D. ochrophaeus if male-male competition affects access to females.     

Modification of Male Courtship Motivation by Olfactory Habituation via the GABAA Receptor in Drosophila melanogaster

A male-specific component, 11-cis-vaccenyl acetate (cVA) works as an anti-aphrodisiac pheromone in Drosophila melanogaster. The presence of cVA on a male suppresses the courtship motivation of other males and contributes to suppression of male-male homosexual courtship, while the absence of cVA on a female stimulates the sexual motivation of nearby males and enhances the male-female interaction. However, little is known how a male distinguishes the presence or absence of cVA on a target fly from either self-produced cVA or secondhand cVA from other males in the vicinity. In this study, we demonstrate that male flies have keen sensitivity to cVA; therefore, the presence of another male in the area reduces courtship toward a female. This reduced level of sexual motivation, however, could be overcome by pretest odor exposure via olfactory habituation to cVA. Real-time imaging of cVA-responsive sensory neurons using the neural activity sensor revealed that prolonged exposure to cVA decreased the levels of cVA responses in the primary olfactory center. Pharmacological and genetic screening revealed that signal transduction via GABA_A receptors contributed to this olfactory habituation. We also found that the habituation experience increased the copulation success of wild-type males in a group. In contrast, transgenic males, in which GABA input in a small subset of local neurons was blocked by RNAi, failed to acquire the sexual advantage conferred by habituation. Thus, we illustrate a novel phenomenon in which olfactory habituation positively affects sexual capability in a competitive environment.     

Sexual dimorphism and courtship behavior in Drosophila prolongata

Sexual dimorphism is often derived from sexual selection. In sexually dimorphic Drosophila species, exaggerated male structures are used for specific behaviors in male-to-male competition or courtship toward females. In Drosophila prolongata, a member of the melanogaster species group, males have enlarged forelegs whereas females do not. However, the adaptive role of the enlarged forelegs is unclear because little is known about the behavior of D. prolongata. In this study, the courtship behavior of D. prolongata was investigated in comparison with closely related species. Males of D. prolongata use their forelegs in a specific behavior, “leg vibration”, in which the male vigorously vibrates the female’s abdomen by extending his forelegs from in front of her. Leg vibration was observed immediately before “attempting copulation”, indicating that it has an adaptive role in the mating process. In contrast, leg vibration was not observed in closely related species. Because the large forelegs are necessary to accomplish leg vibration, it was suggested that the sexual dimorphism of D. prolongata forelegs is currently under the influence of sexual selection in courtship behavior.