Courtship song recognition in the Drosophila melanogaster complex: heterospecific songs make females receptive in D. melanogaster, but not in D. sechellia

Abstract. The courtship song emitted by male wing vibration has been regarded as one of the most important signals in sexual isolation in the species of the Drosophila melanogaster complex. Inter- and intraspecific crosses were observed using males whose wings were removed (mute) or females whose aristae were removed (deaf). Females of D. melanogaster, D. simulans , and D. mauritiana mated with heterospecific males in the song-present condition (cross between normal females and winged males) more often than in the no-song condition (cross between normal females and wingless males or between aristaless females and winged males) or they showed no preference between the two conditions. It is possible that in these females heterospecific courtship songs play a role as if they were conspecific. In contrast, the females of D. sechellia mated with D. melanogaster or D. simulans males in the no-song condition more often than in the song-present condition, suggesting that they reject males with heterospecific song. Female mate recognition depending on the courtship song in D. melanogaster, D. simulans , and D. mauritiana is considered to be relatively broader and that in D. sechellia narrower.     

Female mate recognition and sexual isolation depending on courtship song in Drosophila sechellia and its siblings

In Drosophila sechellia, females accept males that sing heterospecific songs less than those that do not sing, whereas in D. melanogaster and D. simulans, females accept males that sing heterospecific song more than those that do not sing. Here we studied the sexual isolation of D. sechellia and its siblings using interspecific hybrids to reveal the mechanisms underlying female mate recognition. The females of hybrids mated more with winged males of the parent species than with wingless ones, suggesting that the discrimination against heterospecific songs by D. sechellia females is recessive. Female preference for courtship songs seems to be inherited additively or semidominantly. In addition, we examined female receptivity without the stimuli of courtship songs by comparing the mating frequencies between the crosses using wingless males and found that it is also inherited additively or semidominantly.     

Identification of acoustic stimuli that mediate sexual behavior inDrosophila busckii (Diptera: Drosophilidae)

We have shown that D. busckiimales and females, unlike other drosophilids that have been analyzed in this regard, court and copulate as well in relatively dim red light as they do in bright white light. We have also shown that males and females of this species flutter their wings during courtship and that wing fluttering in both sexes is associated with acoustic stimuli. Wingless males perform vigorous courtship but are incapable of mating, suggesting that females must perceive male song to be receptive to copulation. When they are tested with normal males, wingless females stimulate vigorous courtship, but their copulation frequencies are significantly lower than winged females. This observation suggests that perception of the female's song by either or both sexes facilitates mating.     

Mate choice in Drosophila melanogaster and D. sechellia: criteria and their variation depending on courtship song

Courtship song is one of the most important male signals in Drosophila mating. A female D. melanogaster copulates more readily when given a conspecific type of courtship song. Female D. melanogaster accepted winged D. sechellia more than wingless ones in a no choice test. Copulation frequencies varied between strains and were significantly correlated with male mating propensity of D. sechellia. Females from three of five strains of D. sechellia accepted winged D. melanogaster less than wingless ones in no choice tests, suggesting that D. melanogaster songs reduce mating in D. sechellia females. Multiple choice tests showed that males prefer conspecifics. In female choice tests, D. melanogaster females copulated with winged heterospecific D. sechellia males more than with wingless conspecific D. melanogaster males in the confined condition, suggesting that song differences between D. melanogaster and D. sechellia affect D. melanogaster females less than the absence of courtship song. Copyright 2000 The Association for the Study of Animal Behaviour.     

Behavioral Sequence Leading to Sexual Isolation Between <Emphasis Type="Italic">Drosophila ananassae</Emphasis> and <Emphasis Type="Italic">D. pallidosa</Emphasis>

Drosophila ananassae and D. pallidosa are closely related, sympatric species that lack postmating isolation. Sexual isolation has been considered important in maintaining them as independent species. To clarify the behavioral processes leading to sexual isolation, we analyzed behavioral sequences and examined the effect of courtship song on mating success and on behaviors of both sexes by surgically removing male wings (song generators), female aristae (song receivers), or female wings (means of fluttering). We found that heterospecific courtship songs evoked female wing fluttering, whereas conspecific courtship song did not. Furthermore, female wing fluttering made courting males discontinue courtship. These findings suggest that strong sexual isolation is achieved through the following behavioral sequence: heterospecific song→female wing fluttering→courtship discontinuation.     

Information transmission during intra- and interspecific courtship inEphestia elutella andCadra figulilella

Using information theory, courtship posturing in the moths Ephestia elutella(Hübner) and Cadra figulilella(Gregson) was analyzed for information transmission, which was partitioned into autocovariability (intraindividual transmission) and cross-covariability (interindividual transmission). This two-factor analysis was sufficient to account for more than 60% of the behavioral variance in males of E. elutellaand in both sexes of C. figulilelladuring intraspecific courtships; however, there were large residual variances in the behavior of male and female C. figulilelladuring interspecific courtships and in E. elutellafemales during both inter- and intraspecific courtships. In E. elutella,significant levels of transmission were attributable to both inter- and intraindividual effects, whereas in C. figulilella,only autocovariability was high and no interindividual communication could be assigned to courtship postures. Although courtship in these two species was qualitatively very similar and males readily courted nonconspecific females, high levels of reproductive isolation resulted from courtship. Male C. figulilellahad 94% fewer copulations with E. elutellafemales than with conspecific females and E. elutellamales had 78% fewer copulations with C. figulilellafemales than with conspecifics. These reductions were due to a differential response in both females and males, causing inter-specific courtships to be terminated much earlier than intraspecific courtships. This discrimination indicates that interindividual communication was indeed occurring during courtship and was only partially measured by analysis of postures. Thus, communication took place largely in some other modality, most likely the chemical modality, where species specificity is suggested for both male and female pheromones.     

Interactions of the Males and Females of Three Sympatric Drosophila virilis-Group Species, D. montana, D. littoralis, and D. lummei, (Diptera: Drosophilidae) in Intra- and Interspecific Courtships in the Wild and in the Laboratory

Four species of the Drosophila virilis group, D. montana, D. littoralis, D. lummei, and D. ezoana, occur sympatrically in several locations in northern Europe. Courtship interactions between the flies of the three first-mentioned species were observed at malt baits in Kemi, northern Finland, to find out how the flies of different species recognize conspecific individuals and how interspecific courtships differ from intraspecific ones in the wild. Intraspecific courtships (including females of different reproductive stages) and interspecific courtships were also videotaped and analyzed in laboratory. In the wild the males courted both conspecific and allospecific females, even though the species varied in how much the males were attracted to females of different species. Interspecific courtships usually broke off when the male touched the female or when the male and/or the female vibrated his/her wings, producing acoustic cues. In the laboratory males courted conspecific females irrespective of the reproductive stage of the female, even though the courtships directed toward immature and fertilized females usually included only orienting and touching (no licking and singing). D. littoralis, and very rarely D. montana and D. lummei, males courted also allospecific females. In the few interspecific courtships between these three species, where the male proceeded to singing, females responded to male singing by vibrating their wings. This ended the courtship. It is suggested that both the chemical cues affecting female attractivity and the acoustic signals of males and females, which are produced by wing vibration, function in maintaining sexual isolation between these three species.     

Drosophila melanogaster males respond differently at the behavioural and genome‐wide levels to Drosophila melanogaster and Drosophila simulans females

Drosophila melanogaster are found in sympatry with Drosophila simulans, and matings between the species produce nonfertile hybrid offspring at low frequency. Evolutionary theory predicts that females choose mates, so males should alter their behaviour in response to female cues. We show that D. melanogaster males quickly decrease courtship towards D. simulans females. Courtship levels are reduced within 5 min of exposure to a heterospecific female, and overall courtship is significantly lower than courtship towards conspecific females. To understand changes at the molecular level during mate choice, we performed microarray analysis on D. melanogaster males that courted heterospecific D. simulans females and found nine genes have altered expression compared with controls. In contrast, males that court conspecific females alter expression of at least 35 loci. The changes elicited by conspecific courtship likely modulate nervous system function to reinforce positive conspecific signals and dampen the response to heterospecific signals.     

Courtship behavior and sexual isolation between Drosophila auraria and D. triauraria in darkness and light

Sexual isolation between two species of the Drosophila auraria complex, D. auraria and D. triauraria is different in darkness and light. In darkness there is complete isolation while in light it is only partial. The sensory bases of these differences were investigated by behavioral studies in darkness and light. In darkness there was no normal courtship sequence but males of both species displayed attempted copulation to homospecific and heterospecific females, as well as homospecific males. After a few hours together, homospecific copulations were observed after females displayed a characteristic posture: spreading the wings. Such an acceptance posture, also observed in other Drosophila species, was probably released by the wing vibration of a homospecific male. In light, visual signals alone are able to elicit male's orientation and following, whether flies are housed together or physically separated. Intense homosexual courtships were observed. All these data suggest that males have a low discrimination ability and females play the main role in sexual isolation.     

The significance of wing pattern diversity in the Lycaenidae: mate discrimination by two recently diverged species

Closely related species of lycaenid butterflies are determinable, in part, by subtle differences in wing pattern. We found that female wing patterns can act as an effective mate‐recognition signal in some populations of two recently diverged species. In field experiments, we observed that males from a Lycaeides idas population and an alpine population of L. melissa preferentially initiate courtship with conspecific females. A morphometric study indicated that at least two wing pattern elements were important for distinguishing the two species: hindwing spots and orange crescent‐shaped pattern elements called aurorae. We deceived male L. idas into initiating courtship with computer generated paper models of heterospecific females when these pattern elements were manipulated, indicating that the wing pattern elements that define the diversity of this group can be effective mate recognition signals.     

The role of auditory stimuli in the courtship of Drosophila melanogaster

Simulated courtship song of male Drosophila melanogaster was played to males or females of this species. Upon receiving the song males increase their locomotor activity and start courting each other, whereas females reduce their locomotor activity. In wingless males the locomotor activity difference between the silent control and the experimental sound situation is much larger than in winged males, due to the inactivity of wingless males in the control situation. Males which had been kept singly up to the time of the experiment exhibit higher locomotor and sexual activity than group housed males. A second component of the male courtship song ‘sine song’ is described, together with experiments which investigate the sensory basis of the effect male courtship song has on males.     

Reproductive interference by male Drosophila subobscura on female D. persimilis: A laboratory experiment

While females often reject courtship attempts by heterospecific males, reproductive interference by harassment from such males can nonetheless occur, potentially reducing female fitness. Such effects may be profound following a range expansion, when males from a new species may suddenly encounter (and perhaps even become abundant relative to) females of related native species. Drosophila subobscura recently invaded North America and may impact native species through reproductive interference and other processes. We test for the potential for reproductive interference by D. subobscura males on D. persimilis females in the laboratory. D. subobscura males aggressively copulated with D. persimilis females, including many females that exhibit rejection behaviors. Despite females attempting to dismount the males, the heterospecific copulations are on average longer than conspecific copulations, and females exhibit some reluctance to remate with conspecific males following this harassment. Females confined with both conspecific and heterospecific males produce fewer adult progeny than those with either conspecific males only or with conspecific males and distantly related D. simulans males that do not engage in female harassment. Overall, our results illustrate how reproductive interference by an invasive species can have negative effects on resident natural populations.     

Reproductive isolation inProkelisia planthoppers (Homoptera: Delphacidae): Acoustic differentiation and hybridization failure

Males and females of Prokelisia marginata (Van Duzee) and Prokelisia dolusWilson communicate through substrate-transmitted vibrations. The acoustic signals (attraction and courtship calls) of these planthoppers are effective in mate location, attraction, and mate choice. Attraction calls are structurally distinct for both species and differ in pulse type, pulse repetition rate, and pulse duration. Using playback of prerecorded calls, individuals discriminated between conspecific and heterospecific signals. Depending on the sex and species, response calls were produced three to eight times more frequently to conspecifics than to heterospecifics. However, acoustic signals alone did not explain reproductive isolation and hybridization failure in these two congeners. Some heterospecific pairs called, courted, and attempted to join genitalia, but no connections were successful and no progeny were produced. Thus, acoustic behavior is not a guaranteed premating isolating mechanism in no-choice situations. Other courtship behaviors and possibly morphological differences in genitalia also contributed to their isolation. Females displayed a variety of rejection behaviors to conspecific and heterospecific males, suggesting that sexual selection (female choice), in addition to species recognition, may be an important force in the evolution of the acoustic signals of planthoppers. Although signal structure was not dependent on wing form (planthoppers exhibit wing dimorphism), the age when females first began to call was related to wing form. Brachypterous (flightless) females of both species began calling early in adult life (day 2), whereas macropterous (migratory) females began calling later in adult life (day 6). This pattern is consistent with the oogenesis-flight syndrome, in which reproductive maturity is delayed until after migration occurs.     

INTRINSIC REPRODUCTIVE ISOLATION BETWEEN TWO SISTER SPECIES OF DROSOPHILA

Drosophila santomea and D. yakuba are sister species that live on the volcanic African island of São Tomé. Previous work has revealed several barriers to gene flow, including sexual isolation, hybrid sterility, and “extrinsic” ecological isolation based on differential adaptation to and preference for temperature. Here, we describe several new “intrinsic” barriers to gene flow—barriers that do not depend on the species’ ecology. These include reduced egg number, reduced egg hatchability, and faster depletion of sperm in interspecific compared to intraspecific matings. Further, hatching interval and egg‐to‐adult development time are significantly longer in interspecific than intraspecific crosses. If a female of either species is initially mated to a heterospecific male, she lays fewer and less‐fertile eggs than if she is first mated to a conspecific male, so that heterospecific matings permanently reduce female fertility. Finally, D. santomea females mated to D. yakuba males do not live as long as virgin or conspecifically mated females. The “poisoning” effects of heterospecific ejaculates may be byproducts of antagonistic sexual selection. Although these species diverged relatively recently, they are clearly separated by many isolating barriers that act both before and after mating.     

Acoustic Component and Social Context of the Wing Display of the Walnut Fly Rhagoletis juglandis

Courtship signaling via wing vibration, accompanied by sound production, has been reported in several species of tephritids. In this large family of flies, sound communication as well as complex courtship displays appears to be restricted to species with lekking mating systems (i.e., Mediterranean fruit fly, Anastrepha and Dacus species). In contrast, in tephritid species with resource-defense mating systems, such as species in the genus Rhagoletis, little or no courtship behavior, acoustical or otherwise, has been described. Wing displays in Rhagoletis species have been considered to play a visual role. This study describes a distinctive wing display performed by males of the walnut fly, Rhagoletis juglandis. Laboratory experiments and field observations demonstrate that the male wing display plays a role in courtship. We used sound and vibration detectors to record the signals produced by this wing display. Using a combination of techniques, we were able to record both the very low-frequency vibration and its accompanying airborne infrasound (12–22 Hz) produced by the males.     

The Importance of Acoustic Signals in Multimodal Courtship Behavior in Drosophila virilis,D. lummei and D. littoralis

The courtship rituals of Drosophila include an exchange of several signals with different modalities, chemical, visual, acoustic and tactile stimuli, between sexes. Using a video recording method, we studied the role of acoustic communication in courtship behavior in three species of the Drosophila virilis group, D. virilis, D. lummei and two populations of D. littoralis. Five series of experiments were performed: tests with intact flies (control), tests with mute flies (wingless males or females), and tests with deaf flies (aristaless males or females). We distinguished the two situations: either a female did not hear a male or vice versa, males did not hear females. When females did not hear males, the reduction in the copulation number was found in D. virilis and both populations of D. littoralis, but not in D. lummei. When males did not hear females, the reduction in the copulation number was only found in D. littoralis. The ablation of the male aristae in D. virilis and D. lummei even increased the mating success as compared to the control, which may be explained by the ‘sensory overload’ hypothesis. The changes in courtship temporal structure usually included the delayed onset of the main courtship elements (tapping, licking, and singing), and the variation in their duration and the total time of courtship. These effects were, however, more substantial in D. virilis and both populations of D. littoralis than in D. lummei. Thus, the effect of blocking the acoustic channel was different in the three species regardless of their phylogenetic relationship, and the role of acoustic communication in courtship behavior seemed to increase in the order D. lummei – D. virilis – D. littoralis.

     

Alary polymorphism in Triatoma spinolai and its possible relationship with demographic strategy

Among collections of Triatoma spinolai from various sites in northern Chile, adults from coastal populations are invariably wingless, whereas inland populations show balanced alary polymorphism between wingless females and males that are either winged or wingless. Laboratory crosses showed that male offspring from normal-winged parents were always winged (88% long-winged) and those from long-winged male parents were all long-winged. The male offspring from wingless males always included winged males: 11/33 = 33%, of which 8/11 = 73% were long-winged. An X-linked mutation is proposed to inhibit wing development. Field studies of population demography indicate that male alary polymorphism is advantageous in the desert environment of northern Chile.     

Courtship with two spoons—Anatomy and presumed function of the bizarre antennae of Cardiocondyla zoserka ant males

Mating in ants often occurs on the wing during nuptial flights or on the ground when scattered female sexuals attract males by pheromones. In both scenarios, there is little opportunity for males to engage in prolonged aggressive competition or elaborate courtship displays. Male morphology is therefore adapted to locating female sexuals and mating, and it lacks specific weapons or other traits associated with courtship. In contrast, sexuals of the ant genus Cardiocondyla typically mate in their natal nests. As a consequence, in many species winged males have been replaced by wingless fighter or territorial males, which kill or expel rival males with their strong mandibles and show complex mating behavior. However, no wingless males are known from Cardiocondyla zoserka from West Africa, and instead, winged males have evolved a bizarre secondary sexual trait: uniquely shaped antennae with spoon‐like tips that show heavily sculptured ventral surfaces with numerous invaginations. We here report on the courtship behavior of C. zoserka males and describe antennal glands with class 3 gland cells, which presumably secrete a close range sex pheromone. Antennal glands have not yet been found in males of other ant species, including a close relative of C. zoserka, suggesting that in ants with intranidal mating sexual selection can rapidly lead to highly divergent adaptations and the evolution of novel structures.     

Behavioral reproductive isolation inDrosophila silvestris,D. heteroneura,and their F1 hybrids (Diptera: Drosophilidae)

We investigated the role that courtship and aggressive interactions may have for the maintenance of reproductive isolation betweenDrosophila silvestris andD. heteroneura. We examined the behavioral bases of reproductive isolation between the parental species and we examined the courtship success of each sex of both reciprocal F₁ hybrids when paired with the parental species. We found reduced copulation success among heterotypic parental pairs compared to homotypic pairs, which was primarily due to the lack of courtship initiation betweenD. silvestris males andD. heteroneura females. When hybrid males from both reciprocal crosses were paired with parental females their copulation successes were not significantly different from that of parental males. In contrast, hybrid females from both crosses had reduced copulation success withD. silvestris males, which in turn was primarily due to a reduced success of reaching later stages of courtship. The time spent in copulation by hybrid males was intermediate between the two parental males. We studied aggression by observing the interactions of males of heterotypic pairs, both between the parental species and between the hybrids and parental males. A lack of aggressive interactions betweenD. silvestris males andD. heteroneura males in addition to the lack of courtship suggests thatD. silvestris males do not respond toD. heteroneura individuals of either sex. Hybrid males were equally successful in winning fights with bothD. silvestris andD. heteroneura males. These results indicate that the behavioral isolation betweenD. silvestris andD. heteroneura may be largely a consequence of the earliest stages of interactions. The two species may differ either in activity levels or in morphological or chemical traits that are important for species and mate recognition. The relatively high copulation and aggressive success of hybrids indicates that sexual selection against hybrids alone is unlikely to be a sufficient force to reduce gene flow and maintain species distinctions.     

Hammering,mauling, and kissing: stereotyped courtship behavior in <Emphasis Type="Italic">Cardiocondyla</Emphasis> ants

Sex appears to be a rather prosaic and casual event in the life of most social Hymenoptera. In contrast, mating in the ant genus Cardiocondyla is regularly preceded by a prolonged and stereotypic courtship display. Pummeling the head of the female with mandibles and / or antennae and vibrations of the gaster, presumably stridulation, are essential parts of male courtship. The overall structure of the mating pattern is conserved throughout species and between winged and wingless, “ergatoid” males, but exhibits species-specific idiosyncrasies. For example, C. elegans males regularly end the interaction with a female with a short mouth-to-mouth contact. Variation in the duration of the precopulatory phase and the copulation itself might reflect different degrees of inter- and intrasexual selection. More information on the dynamics of sperm transfer and the risk and intensity of sperm competition are needed to better understand the evolution of the complex mating behavior in this genus. Received 15 December 2006; revised 25 June 2007; accepted 11 September 2007.