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.     

Vasotocin stimulates appetitive responses to the visual and pheromonal stimuli used by male roughskin newts during courtship

It is now well established that vasotocin (AVT) and its mammalian homologue vasopressin influence various social behaviors in vertebrates, but less is known about the mechanisms through which these peptides modulate behavior. In male roughskin newts, Taricha granulosa, AVT stimulates a courtship behavior, amplectic clasping. Three general explanations for how AVT affects male courtship behavior have been considered: by enhancing a central state of sexual motivation, by affecting sensorimotor integration mechanisms in individual sensory modalities, or by influencing a nonspecific state of attention, arousal, or anxiety. AVT administration enhanced appetitive responses to visual and olfactory sexual stimuli, as would be expected if AVT affects a state of sexual motivation that affects behavioral responses to sexual stimuli regardless of the sensory modality in which they are processed. However, AVT selectively enhanced responses to female olfactory stimuli (sex pheromones), but similarly enhanced responses to female and food-related visual stimuli (worms), thus questioning the utility of such a motivational mechanism, as responses to female stimuli were not selectively enhanced in all sensory modalities. We therefore propose that exogenous AVT independently influences olfactory processes associated with orientation/attraction toward a female sex pheromone and visual processes associated with orientation/attraction toward a visual feature common to females and worms. In further experiments AVT administration failed to stimulate feeding behavior but did decrease locomotor activity. Thus, AVT does not stimulate courtship behavior in this species by enhancing the animals' general state of attention or by decreasing general anxiety, as responses to nonsexual, attractive stimuli were not uniformly enhanced, nor by stimulating general arousal, as activity levels did not increase. Rather, the data support the conclusion that AVT affects courtship by influencing specific sensorimotor processes associated with behavioral responses to individual releasing stimuli, which suggests a mechanistic framework for understanding socially motivated behavior is this species.     

Female Choice or Male Sex Drive? The Advantages of Male Body Size during Mating in Drosophila Melanogaster

The mating success of larger male Drosophila melanogaster in the laboratory and the wild has been traditionally been explained by female choice, even though the reasons are generally hard to reconcile. Female choice can explain this success by virtue of females taking less time to mate with preferred males, but so can the more aggressive or persistent courtships efforts of large males. Since mating is a negotiation between the two sexes, the behaviors of both are likely to interact and influence mating outcomes. Using a series of assays, we explored these negotiations by testing for the relative influence of male behaviors and its effect on influencing female courtship arousal threshold, which is the time taken for females to accept copulation. Our results show that large males indeed have higher copulation success compared to smaller males. Competition between two males or an increasing number of males had no influence on female sexual arousal threshold;—females therefore may have a relatively fixed ‘arousal threshold’ that must be reached before they are ready to mate, and larger males appear to be able to manipulate this threshold sooner. On the other hand, the females’ physiological and behavioral state drastically influences mating; once females have crossed the courtship arousal threshold they take less time to mate and mate indiscriminately with large and small males. Mating quicker with larger males may be misconstrued to be due to female choice; our results suggest that the mating advantage of larger males may be more a result of heightened male activity and relatively less of female choice. Body size per se may not be a trait under selection by female choice, but size likely amplifies male activity and signal outputs in courtship, allowing them to influence female arousal threshold faster.     

A contextual definition of male sexual arousal

Sexual arousal is a construct without a widely shared definition. Historically, sexual arousal has usually referred to a central physiological state, but there has been much less agreement on its relation to motivation, emotion, and - for males - penile erection and ejaculation. Many behavioral and physiological measures have been used as operational definitions of sexual arousal, but the relation of the measure to arousal is often assumed rather than tested. For men, penile erection in the presence of erotic stimuli has been considered the most reliable and valid indicator of sexual arousal. The adoption of analogous criteria is recommended for research on other male mammals in order to establish a minimal basis for inferring that they are sexually aroused. That is, sexual arousal should be inferred only when penile erection is observed in a sexual context. A sexual context is provisionally defined as an environment that tends in most reproductively active males of the species to provoke further sexual stimulation, e.g., copulation or self-stimulation to ejaculation. Erection occurring outside of a sexual context, as during REM sleep or from injection of drugs, is not grounds for inferring arousal. Conversely, males engaging in behavior directed toward estrous females may be sexually motivated, but in the absence of erection, the males should not be assumed to be sexually aroused. Implications of other erection-context interactions are also considered. Adoption of these more conservative criteria for inferring sexual arousal may promote greater precision in identifying the physiological systems mediating this hypothetical construct.     

Interactions between behavior and plasma steroids within the scramble mating system of the promiscuous green turtle, Chelonia mydas.

We measured plasma androgen (combined testosterone and 5alpha-dihydrotestosterone) (A) and corticosterone (B) in the promiscuous green turtle (Chelonia mydas) during courtship in the southern Great Barrier Reef. This study examined if reproductive behaviors and intermale aggression induced behavioral androgen and adrenocortical responses in reproductively active male and female green turtles. Associations between reproductive behavior and plasma steroids were investigated in green turtles across the population and within individuals. Levels across a range of both asocial and social behaviors were compared including (a) free swimming behavior; (b) initial courtship interactions; (c) mounted behavior (male and female turtles involved in copulatory activities); (d) intermale aggression (rival males that physically competed with another male turtle or mounted males recipient to these aggressive interactions); and (e) extensive courtship damage (male turtles that had accumulated excessive courtship damage from rival males). Behavioral androgen responses were detected in male turtles, in that plasma A was observed to increase with both attendant and mounted behavior. Male turtles who had been subjected to intermale aggression or who had accumulated severe courtship damage exhibited significantly lower plasma A than their respective controls. No pronounced adrenocortical response was observed after either intermale aggression or accumulation of extensive courtship damage. Female turtles exhibited a significant increase in plasma B during swimming versus mounted behavior, but no change in plasma A. We discuss our results in terms of how scramble polygamy might influence behavioral androgen interactions differently from more typical combative and territorial forms of male polygamy.     

Increases in the circulating testosterone of maturing male guinea pigs appear neither necessary nor sufficient for heightened maternally directed sexual and social/courtship behavior

Periadolescent male guinea pigs housed continuously with their mother since birth exhibit little maternally directed sexual behavior. However, if rehoused apart from the mother for 24 h, they show elevations in circulating testosterone concentrations and display frequent sexual responses and increased social/courtship behavior upon reunion with her. We investigated the role of testosterone in the disinhibition of maternally directed sexual and social/courtship behavior. Subcutaneous implants of testosterone (Experiment 1) did not trigger maternally directed sexual behavior or an increase in social/courtship behavior among males housed continuously with their mothers. Further, neither blocking androgen receptors (Experiment 2) nor preventing the surge in testosterone (Experiment 3) prevented males housed without the mother from exhibiting increased maternally directed sexual and social/courtship behavior upon reunion. These findings indicate that the increase in testosterone that males exhibit when rehoused apart from the mother is neither sufficient nor necessary for the disinhibition of maternally directed sexual and social/courtship behavior observed when mother and son are reunited.     

The influence of environmental quality on sexual selection in Nauphoeta cinerea (Dictyoptera: Blaberidae)

We examined the impact of environmental conditions on the sexpheromone and mating behavior of the cockroach, Nauphoeta cinerea.Previous research on this species has shown that female behaviorduring courtship reflects female mate choice, male behaviorcorrelates with male social status, and the male sex pheromoneis the character used by females to assess males. In the presentstudy, males and females were allowed to develop from adultemergence to sexual maturity in either a high- or low-qualityenvironment. The environment affected the quantities of sexpheromone components. We found significantly less 3-hydroxy-2-butanoneand 4-ethyl-2-methoxyphenol, but not 2-methylthiazolidine, inthe pheromone glands of males from a poor environment. Pheromonequality was also affected; the ratios involving 2-methylthiazolidinewere altered, while the ratio 3-hydroxy-2-butanone to 4-ethyl-2-methoxyphenoldid not change. Development to sexual maturity under these environmentalconditions also influenced male and female sexual behavior.Male courtship activity reflected environmental influences;males from the low-quality environment took longer to initiatecourtship and spent more time copulating with females from allenvironments. Male quality, as assessed by females, was alsoaffected by their environment. Females were slower to respondto the courtship of males from the poor environment, regardlessof the females' own rearing environments. However, females fromthe low-quality environment also took longer to respond to thecourtship, and required more courtship, regardless of the males'rearing environments. Thus, poor environments also increasefemale choosiness. However, there was only one significant interactionterm, suggesting that the environmental effects are generaland that females do not show adaptive plasticity in mate choice.Studies of sexual selection that consider the effects of variableenvironments on behavior as well as the sexually selected morphologyin other systems are likely to provide new insights into thisevolutionary process     

Discrimination of conspecific individuals via cuticular pheromones by males of the cricket Gryllus bimaculatus

Cuticular substances on the body surface of crickets serve as pheromones that elicit a variety of different behaviors in male crickets. Antennal contact between males and females resulted in courtship behavior, and that between two males resulted in aggressive displays. As a first step in elucidating how crickets recognize and discriminate individuals, behavioral responses of male individuals to cuticular substances of conspecific males or females were investigated. The behavioral responses of males to antennal or palpal stimulation with an isolated antenna from a male or a female were recorded. To both antennal and palpal stimulation with female antennae, the majority of males responded with courtship behavior; to stimulation with male antennae, males responded with aggressive displays. To gain insight into the chemical nature of the behaviorally relevant components, isolated antennae were washed in either n-hexane, acetone or ethanol before behavior assays. Washed antennae no longer elicited courtship or aggressive responses in males. Next, polypropylene fibers were smeared with substances from the body surface of females and used for antennal stimulation. This experiment showed that the quality and quantity of cuticular substances appear to be highly age-dependent. Significantly more males responded with courtship behavior to cuticular substances from younger females. Isolated males generally showed higher levels of aggression than males reared in groups. Grouped males also were more likely to display courtship behavior towards antennae from younger females, and aggressive behavior towards antennae from older females. These results suggest that male discrimination of mating partners depends on the nature of female cuticular substances.     

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.     

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.     

Mate choice based on static versus dynamic secondary sexual traits in the dark-eyed junco

Some secondary sexual traits (SSTs) such as structural characteristicsare semi-permanent or static, while others, such as courtshipdisplay, are more labile or dynamic. In this paper we reportresults from two experiments designed to test the relative attractivenessto female dark-eyed juncos (Junco hyemalis, Passeriformes, Aves)of a relatively static plumage trait, the amount of white inthe tail, and a relatively dynamic behavioral trait, courtshipintensity. The experiments derived from a study showing that femalejuncos prefer males that court more vigorously. We asked whether femalesalso base their preferences on plumage traits and how they respond whenpresented with a choice between attractive traits that are eitherstatic (plumage) or dynamic (courtship) in nature. In the firstexperiment we presented males to females in paired mate-choicetrials and found that males enhanced with more white in theirtails were more attractive to females than controls with unenhancedtails. Females spent more time with enhanced males and directedmore sexual displays toward them. In the second experiment we testedwhether females preferred males with enhanced tails (a staticSST) or males with enhanced hormone-mediated courtship behavior(a dynamic SST). In this experiment females did not demonstratea consensus preference for either the static or the dynamictrait. Instead, some females preferred the male whose courtshipperformance was enhanced with testosterone, while others preferredthe male with an enhanced tail. We conclude that both kindsof traits are important in junco mate choice, but that somefemales apparently weigh static traits more heavily than dynamicones, while other females use opposite weightings.     

Dopaminergic modulation of arousal in Drosophila

BACKGROUND: Arousal levels in the brain set thresholds for behavior, from simple to complex. The mechanistic underpinnings of the various phenomena comprising arousal, however, are still poorly understood. Drosophila behaviors have been studied that span different levels of arousal, from sleep to visual perception to psychostimulant responses. RESULTS: We have investigated neurobiological mechanisms of arousal in the Drosophila brain by a combined behavioral, genetic, pharmacological, and electrophysiological approach. Administration of methamphetamine (METH) suppresses sleep and promotes active wakefulness, whereas an inhibitor of dopamine synthesis promotes sleep. METH affects courtship behavior by increasing sexual arousal while decreasing successful sexual performance. Electrophysiological recordings from the medial protocerebrum of wild-type flies showed that METH ingestion has rapid and detrimental effects on a brain response associated with perception of visual stimuli. Recordings in genetically manipulated animals show that dopaminergic transmission is required for these responses and that visual-processing deficits caused by attenuated dopaminergic transmission can be rescued by METH. CONCLUSIONS: We show that changes in dopamine levels differentially affect arousal for behaviors of varying complexity. Complex behaviors, such as visual perception, degenerate when dopamine levels are either too high or too low, in accordance with the inverted-U hypothesis of dopamine action in the mammalian brain. Simpler behaviors, such as sleep and locomotion, show graded responses that follow changes in dopamine level.     

Psychobiology of sexual behavior in a whiptail lizard, Cnemidophorus inornatus

This study investigated the effects of social environment on gonadal recrudescence and sexual behavior in male and female Little Striped Whiptail lizards (Cnemidophorus inornatus). The presence of sexually active males facilitates ovarian recrudescence in conspecific females. Similarly, the presence of reproductively active females facilitates testicular recrudescence in conspecific males. Males housed with females, however, had lower average circulating concentrations of testosterone and dihydrotestosterone, and higher average concentrations of corticosterone compared to intact males housed in isolation. In other studies, the presence of reproductively active females partially restored courtship behavior in castrated males compared to castrated males housed in isolation. Despite the stimulatory effects of females on castrates, exogenous androgens are required for complete restoration of all components of sexual behavior in male C. inornatus. Females are receptive to male courtship and copulatory behavior only during the vitellogenic stages; females in previtellogenic or postovulatory ovarian stages aggressively reject male courtship advances. These findings demonstrate reciprocal effects of sexual behaviors of males and females upon each other's reproductive behavior and physiology.     

Seasonal Changes in Courtship Song and the Medial Preoptic Area in Male European Starlings (Sturnus vulgaris)

In male starlings (Sturnus vulgaris) courtship song plays a critical role in mate attraction. During the breeding season courtship song occurs prior to copulation and appears to reflect male sexual arousal. Outside the breeding season starlings sing, but song appears unrelated to reproduction. The aromatization of testosterone (T), likely within the medial preoptic nucleus (POM), is critical for the expression of male sexual arousal. The present study was performed to determine whether seasonal changes in the POM might relate to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were examined both during and outside of the breeding season in male starlings. Song was also recorded at these times both with and without a female present. The POM was largest and contained dense aromatase immunostaining only during the spring breeding season, when T concentrations were highest and males responded to a female with an increase in courtship song. Outside the breeding season the volume of the POM was small, T concentrations were low, and males displayed no changes in song expression in response to female conspecifics. Song bout length was positively related to POM volume, and males sang longer songs in spring. Only males with nestboxes in spring responded to a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall, the findings suggest that T-dependent plasticity and aromatase activity within the POM might regulate courtship singing in a wild songbird.     

Differential roles of two major brain structures, mushroom bodies and central complex, for Drosophila male courtship behavior

Drosophila male courtship is a complex and robust behavior, the potential for which is genetically built into specific neural circuits in the central nervous system. Previous studies using male-female mosaics and the flies with defects in particular brain structures implicated the critical central regions involved in male courtship behavior. However, their acute physiological roles in courtship regulation still largely remain unknown. Using the temperature-sensitive Dynamin mutation, shibire(ts1), here we demonstrate the significance of two major brain structures, the mushroom bodies and the central complex, in experience-independent aspects of male courtship. We show that blocking of synaptic transmission in the mushroom body intrinsic neurons significantly delays courtship initiation and reduces the courtship activity by shortening the courtship bout length when virgin females are used as a sexual target. Interestingly, however, the same treatment affects neither initiation nor maintenance of courtship toward young males that release courtship-stimulating pheromones different from those of virgin females. In contrast, blocking of synaptic transmission in a central complex substructure, the fan-shaped body, slightly but significantly reduces courtship activity toward both virgin females and young males with little effect on courtship initiation. Taken together, our results indicate that the neuronal activity in the mushroom bodies plays an important role in responding to female-specific sex pheromones that stimulate initiation and maintenance of male courtship behavior, whereas the fan-shaped body neurons are involved in maintenance of male courtship regardless of the nature of courtship-stimulating cues.     

Seasonal changes in courtship song and the medial preoptic area in male European starlings (Sturnus vulgaris)

In male starlings (Sturnus vulgaris) courtship song plays a critical role in mate attraction. During the breeding season courtship song occurs prior to copulation and appears to reflect male sexual arousal. Outside the breeding season starlings sing, but song appears unrelated to reproduction. The aromatization of testosterone (T), likely within the medial preoptic nucleus (POM), is critical for the expression of male sexual arousal. The present study was performed to determine whether seasonal changes in the POM might relate to seasonal changes in courtship singing behavior in male starlings. T concentrations, the volume of the POM, and aromatase within the POM were examined both during and outside of the breeding season in male starlings. Song was also recorded at these times both with and without a female present. The POM was largest and contained dense aromatase immunostaining only during the spring breeding season, when T concentrations were highest and males responded to a female with an increase in courtship song. Outside the breeding season the volume of the POM was small, T concentrations were low, and males displayed no changes in song expression in response to female conspecifics. Song bout length was positively related to POM volume, and males sang longer songs in spring. Only males with nestboxes in spring responded to a female, and the POM tended to be larger in these males, suggesting that nestbox possession might influence neuroplasticity within the POM. Overall, the findings suggest that T-dependent plasticity and aromatase activity within the POM might regulate courtship singing in a wild songbird.     

Sex in flies: what 'body--mind' dichotomy?

Sexual behavior in Drosophila results from interactions of multiple neural and genetic pathways. Male-specific fruitless (fruM) is a major component inducing male behaviors, but recent work indicates key roles for other sex-specific and sex-non-specific components. Notably, male-like courtship by retained (retn) mutant females reveals an intrinsic pathway for male behavior independent of fruM, while behavioral differences between males and females with equal levels of fruM expression indicate involvement of another sex-specific component. Indeed, sex-specific products of doublesex (dsxF and dsxM), that control sexual differentiation of the body, also contribute to sexual behavior and neural development of both sexes. In addition, the single product of the dissatisfaction (dsf) gene is needed for appropriate behavior in both sexes, implying additional complexities and levels of control. The genetic mechanisms controlling sexual behavior are similar to those controlling body sexual development, suggesting biological advantages of modifying an intermediate intrinsic pathway in generation of two substantially different behavioral or morphological states.     

Effects of Acute or Chronic Ethanol Exposure during Adolescence on Behavioral Inhibition and Efficiency in a Modified Water Maze Task

Ethanol is well known to adversely affect frontal executive functioning, which continues to develop throughout adolescence and into young adulthood. This is also a developmental window in which ethanol is misused by a significant number of adolescents. We examined the effects of acute and chronic ethanol exposure during adolescence on behavioral inhibition and efficiency using a modified water maze task. During acquisition, rats were trained to find a stable visible platform onto which they could escape. During the test phase, the stable platform was converted to a visible floating platform (providing no escape) and a new hidden platform was added in the opposite quadrant. The hidden platform was the only means of escape during the test phase. In experiment 1, adolescent animals received ethanol (1.0g/kg) 30min before each session during the test phase. In experiment 2, adolescent animals received chronic intermittent ethanol (5.0g/kg) for 16 days (PND30 To PND46) prior to any training in the maze. At PND72, training was initiated in the same modified water maze task. Results from experiment 1 indicated that acute ethanol promoted behavioral disinhibition and inefficiency. Experiment 2 showed that chronic intermittent ethanol during adolescence appeared to have no lasting effect on behavioral disinhibition or new spatial learning during adulthood. However, chronic ethanol did promote behavioral inefficiency. In summary, results indicate that ethanol-induced promotion of perseverative behavior may contribute to the many adverse behavioral sequelae of alcohol intoxication in adolescents and young adults. Moreover, the long-term effect of adolescent chronic ethanol exposure on behavioral efficiency is similar to that observed after chronic exposure in humans.     

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.