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.     

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.     

Male Choice and Male-male Competition in Idotea baitica (Crustacea,Isopoda)

Sexual selection in mate-guarding Crustacea may involve several processes: male choice, male-male competition, and female choice. To evaluate the relative importance of the different processes in mate choice of the aquatic isopod I. baitica we studied 1) the mate-choice criteria of males, 2) effects of sex ratio on the outcome of the mating contest, and 3) the role of size in male-male interactions. When given a choice between a small and a large female, males most often chose the one that matured earlier for parturial ecdysis. Maturity was a more important choice criterion than female size, but these also correlated positively. Large males had a mating advantage in both male- and female-biased sex ratios; pairing was size-assortative only in the male-biased ratio where guarding was also longer. If an extra male was placed with a precopulatory pair, 30 % take-overs occurred, large males surpassing. Present and earlier work suggests that male size is an asset in both intra- and intersexual interactions. There is little or no direct phenotypic sexual selection on female size: sexual selection for large males presumably contributes to the evolution of sexual size dimorphism in I. baitica.     

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.     

First Quantification of Courtship Behavior in a Silver Fly,Leucopis palumbii (Diptera: Chamaemyiidae): Role of Visual,Olfactory and Tactile Cues

Research on the courtship and mating behavior of insects is the first step toward a full understanding of their behavioral ecology. Investigating mating behavioral sequences could help to unravel mate assessment and mate choice dynamics in entomophagous organisms, adding useful information to develop behavior-based control strategies. In this research, courtship and mating displays, magnitude of male-male sexual interactions and role of female-borne cues evoking male courtship were analyzed in Leucopis palumbii Rondani (Diptera: Chamaemyiidae), a larval predator of aphids. Courtship was initiated by the male and was characterized by three main steps: chasing of the female, wing fanning in her close proximity and tarsal tapping with forelegs on the female’s body. Copulation may follow lasting 765?±?211.25 s. Same-sex interactions among males (i.e. wing fanning followed by tarsal tapping) were also registered. Male fanning before a successful courtship differed from fanning performed prior to an unsuccessful approach in terms of mean frequency. Female-borne stimuli played a key role in eliciting courtship responses from males. The best male’s response was achieved when physical and chemical cues arising from the female body were contemporarily provided, allowing synergistic visual, olfactory and tactile perception. Results contribute to understanding the role of visual, olfactory and tactile channels among sensory modalities used by aphidophagous Chamaemyiidae during sexual communication.     

Path analysis and the relative importance of male-female conflict, female choice and male-male competition in water striders

Three major behavioural mechanisms underlying sexual selection in many systems are male-male competition, female choice and male-female conflict. We used path analysis to evaluate the relative importance of these mechanisms in generating sexual selection on a suite of male traits in the stream-dwelling water strider, Aquarius remigis. To gather data for the analysis, we quantified the morphology (total length, limb length, forefemur width, genital length), behaviour (activity), mating frequency, mean mating duration and overall mating success of 96 adult males over a 10-day period. Males varied considerably in mating success. Over the 10 days, individual males mated 0-14 times, spending 0-67% of their time in copula. Path analysis showed that male-male competition was important in favouring larger males with longer limbs that tended to be more active. Active males should encounter females more frequently. In water striders, almost all male-female encounters result in intense premating struggles pitting female resistance to mating against male insistence. This male-female conflict favoured larger males with longer genitalia. These traits help males overcome female resistance. Female choice was expressed via female-controlled variation in mate-guarding durations. Female choice favoured smaller males perhaps because they are lighter, less expensive ‘shields’ against harassment by other males. Male size thus affected mating success via all three behavioural mechanisms. Weak, overall sexual selection favouring larger males was the product of conflicting effects: male-female conflict strongly favouring larger males and male-male competition weakly favouring larger males, offset by female choice favouring smaller males. Separate analyses for warmer versus colder days showed that on colder days (daily high below 20 °C), male-male competition was the main mechanism generating variation in mating frequency, while on warmer days, both male-male competition and male-female conflict were important. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Male Courtship Behavior and Weapon Trait as Indicators of Indirect Benefit in the Bean Bug,Riptortus pedestris

Females prefer male traits that are associated with direct and/or indirect benefits to themselves. Male–male competition also drives evolution of male traits that represent competitive ability. Because female choice and male–male competition rarely act independently, exploring how these two mechanisms interact is necessary for integrative understanding of the evolution of sexually selected traits. Here, we focused on direct and indirect benefits to females from male attractiveness, courtship, and weapon characters in the armed bug Riptortus pedestris. The males use their hind legs to fight other males over territory and perform courtship displays for successful copulation. Females of R. pedestris receive no direct benefit from mating with attractive males. On the other hand, we found that male attractiveness, courtship rate, and weapon size were significantly heritable and that male attractiveness had positive genetic covariances with both courtship rate and weapon traits. Thus, females obtain indirect benefits from mating with attractive males by producing sons with high courtship success rates and high competitive ability. Moreover, it is evident that courtship rate and hind leg length act as evaluative cues of female choice. Therefore, female mate choice and male–male competition may facilitate each other in R. pedestris. This is consistent with current basic concepts of sexual selection.     

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 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.     

Does sexual experience affect the strength of male mate choice for high‐quality females in Drosophila melanogaster?

Although females are traditionally thought of as the choosy sex, there is increasing evidence in many species that males will preferentially court or mate with certain females over others when given a choice. In the fruit fly, Drosophila melanogaster, males discriminate between potential mating partners based on a number of female traits, including species, mating history, age, and condition. Interestingly, many of these male preferences are affected by the male''s previous sexual experiences, such that males increase courtship toward types of females that they have previously mated with and decrease courtship toward types of females that have previously rejected them. D. melanogaster males also show courtship and mating preferences for larger females over smaller females, likely because larger females have higher fecundity. It is unknown, however, whether this preference shows behavioral plasticity based on the male''s sexual history as we see for other male preferences. Here, we manipulate the sexual experience of D. melanogaster males and test whether this manipulation has any effect on the strength of male mate choice for large females. We find that sexually inexperienced males have a robust courtship preference for large females that is unaffected by previous experience mating with, or being rejected by, females of differing sizes. Given that female body size is one of the most common targets of male mate choice across insect species, our experiments with D. melanogaster may provide insight into how these preferences develop and evolve.     

Sexual behavior in brown capuchins (Cebus apella)

We observed sexual behavior patterns in two captive groups of Cebus apella.We obtained data on intersexual solicitations and intersexual competition. The length of proceptivity cycles by females averaged 18.8 ± 1.2 days; this corresponds with published reports of physiological measures of ovulatory cycles. Females initiated sexual interactions with males significantly more than males initiated interactions with females, and female solicitations increased in frequency over the duration of displayed periods of proceptivity. In contrast, male solicitations of females were infrequent and did not change significantly throughout female proceptive phases. Each female solicited the same male throughout a given proceptive phase. We observed no evidence of male-male or female-female competition. Males seem to respond to female sexual behavior directed toward them, rather than initiating sexual interactions themselves. Even so, male sexual interactions with females followed only a small proportion of solicitations.     

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 female precopulatory behavior is modulated by ecdysteroids

The effect of ecdysteroid signaling on Drosophila female precopulatory behavior was investigated using two types of mutants with either globally reduced ecdysteroid availability or reduced expression of ecdysone receptors in fruitless neurons, known to control sexual behavior. While being courted by males, mutant females performed significantly less full ovipositor extrusion behavior to reject male copulation attempts. Ecdysteroid depleted females (ecdysoneless(1)) performed male-like courtship behaviors, including unilateral wing extension and song production with patterns very similar to male courtship song. These results support the hypothesis that ecdysteroids modulate female sexual behavior, perhaps acting as a regulator of sexual motivation, and as a component affecting the performance of sex specific behavior patterns.     

Effect of Drosophila melanogaster Female Size on Male Mating Success

In this study, we examined the influence of female size on mating success in Drosophila melanogaster. The results that were obtained from experiments performed in mating chambers allowed us to confirm the results of previous studies, demonstrating higher mating success of larger D. melanogaster males, and to conclude that female size also affects mating success, either when considering a single male or two competing males. We observed that the advantage for larger males depends on their size relative to that of the female, demonstrating a previously unknown role for female size in mating behavior studies. This effect of female size on mating success depends on various factors: males take longer to initiate courtship toward larger females, large females receive more wing vibrations from males prior to mating, and large females tend to keep moving for longer periods during male courtship. The importance of this finding is discussed in the context of recent reports on sexual conflict in D. melanogaster, in which males were observed to depress fitness in females as a result of intercourse.     

Female receptivity and male mate-guarding in the jewel spiderGasteracantha minax thorell (Araneidae)

In field populations, several male jewel spidersGasteracantha minax Thorell (Araneidae) may be found at the periphery of the orb web of a female, indicating that males may compete for fertilisation success. Laboratory experiments revealed that virgin femaleG. minax readily remate shortly after their first mating. However, they appear to enter a refractory period between 1 and 24 h postmating and respond aggressively to courting males. Males that have mated with a female initially defend her from rival males but cease to do so after the onset of the refractory period. These data can be interpreted within the context of mate-guarding and sperm competition. There is marked size dimorphism in this species, which may be the result of selection for protandry. In contrast with other orb-weaving spiders, this selection pressure does not seem to be counterbalanced by selection for larger male size through either sexual cannibalism or male-male competition.     

Pheromonal inhibition of male courtship behaviour in the brown tree snake, Boiga irregularis: a mechanism for the rejection of potential mates

Pheromones play a central role in coordinating the events leading up to copulation in snakes. We report here a novel pheromone system in the brown tree snake in which females release a pheromone that inhibits male courtship behaviour. In a previous study, we made observations of female brown tree snakes releasing cloacal secretions (CS) during courtship that appeared to cause courting males to cease courtship. All snakes have glands that release CS through ducts located along the cloacal orifice. Although CS have been studied for many years, their function in the mediation of snake behaviour has not been experimentally well determined. We examined the role of CS in the reproductive behaviour of male and female brown tree snakes. We conducted four experiments to test the effect of both male and female CS on brown tree snake behaviour under two behavioural contexts, courtship and male-male ritualized combat. Within each experiment, we compared the effects of CS to a control. Female CS caused a decrease in the time that males spent courting females and a decrease in the intensity of courtship compared with the control treatment. Male CS did not, however, affect the time that males spent displaying courtship or the intensity of that courtship. Neither male nor female CS had significant effects on male ritualized combat behaviour, including time that males spent in combat or the intensity of combat behaviours displayed. Furthermore, neither female nor male CS had an effect on female courtship versus controls. The inhibition of brown tree snake reproductive behaviours is specific to female CS inhibiting male courtship behaviour. This pheromone acts in concert with the female sex pheromone to regulate the events leading to copulation.Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

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.     

Increased density and male-male interactions reduce male longevity in the medfly, Ceratitis capitata

We investigated the effect of adult density on male and female longevity and behavioural interactions in a mass-reared strain of the medfly. Male survival decreased significantly, and male-male behavioural interactions increased significantly, with increasing male density (males were kept at 1, 2, 6 and 10 flies per 285 cm²in pots of 5.5 cm in diameter and 12 cm high). No such effects were observed in females over the same density range. This suggests that male survival decreased in response to the deleterious effects of male-male behavioural interactions. At the highest density, courtship wing fanning directed towards other males decreased significantly over time. In addition, as either density or male-biased sex ratio increased, males were increasingly likely to be engaged in courtship wing fanning that was not directed towards females. These results suggest that high adult density may significantly reduce male reproductive success, by decreasing survival and mating success. The results highlight the potentially high survival costs of male-male interactions and indicate differences in the nature of reproductive costs in the two sexes.     

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.     

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.