Circuit and Behavioral Mechanisms of Sexual Rejection by Drosophila Females

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Male Courtship Song Frequency as an Indicator of Male Mating Success in Drosophila montana

Drosophila montana females have been found to prefer overwintered males with short and dense (high-frequency) sound pulses in the wild. In the present study males producing high-frequency song succeeded in their courtship more often than males producing low-frequency song in mate-choice experiments. Male mating success correlated with the carrier frequency of the male song recorded after, but not before, an artificial winter (flies kept 6 months at 4°C). The finding that female preference is based on a male song trait changing considerably during overwintering suggests that this trait may reflect the viability and condition of the males during the mating season of the flies in spring.     

From fruitless to sex: On the generation and diversification of an innate behavior

Male sexual behavior in Drosophila melanogaster, largely controlled by the fruitless (fru) gene encoding the male specific Fru^M protein, is among the best studied animal behaviors. Although substantial studies suggest that Fru^M specifies a neuronal circuitry governing all aspects of male sexual behaviors, recent findings show that Fru^M is not absolutely necessary for such behaviors. We propose that another regulatory gene doublesex encoding the male-specific Dsx^M protein builds a core neuronal circuitry that possesses the potential for courtship, which could be either induced through adult social experience or innately manifested during development by Fru^M expression in a broader neuronal circuitry. Fru^M expression levels and patterns determine the modes of courtship behavior from innate heterosexual, homosexual, bisexual, to learned courtship. We discuss how Fru^M expression is regulated by hormones and social experiences and tunes functional flexibility of the sex circuitry. We propose that regulatory genes hierarchically build the potential for innate and learned aspects of courtship behaviors, and expression changes of these regulatory genes among different individuals and species with different social experiences ultimately lead to behavioral diversification.     

Rapid evolution of courtship song pattern in Drosophila willistoni sibling species

Courtship behaviours may provide a more reliable means of identifying reproductively isolated taxa than traits such as morphology or many genetic markers. Here we describe the courtship songs of the Drosophila willistoni sibling species group, which consists of several species and subspecies. We find that song pattern is species-specific, despite significant differences among strains within species. D. paulistorum has the most variable song pattern, which reflects this species' traditional subdivision into semispecies. All the other species could be unambiguously identified by song. The major differences among these species was in the interpulse interval, as has been found in other studies of fly song. However, the interpulse intervals of the species studied here were often multimodal. This was partly due to the presence of multiple song types within the courtship repertoire, but it also reflected changes in interpulse interval within a song type by some males. Unusually, some species had distinctively patterned variation in interpulse interval. Song must have evolved rapidly within the species complex, probably due to sexual selection.     

The mechanism of sex-specific splicing at the doublesex gene is different between Drosophila melanogaster and Bombyx mori

We have previously reported that Bmdsx, a homologue of the sex-determining gene, doublesex (dsx), was found to be sex-specifically expressed in various tissues at larval, pupal, and adult stages in the silkworm, Bombyx mori, and was alternatively spliced to yield male- and female-specific mRNAs. To reveal sex-specific differences in splicing patterns of Bmdsx pre-mRNA, the genomic sequence was determined and compared with male- and female-specific Bmdsx cDNA sequences. The open reading frame (ORF) consisted of five exons. Exons 3 and 4 were specifically incorporated into the female type of Bmdsx mRNA. On the other hand, exon 2 was spliced to exon 5 to produce the male type mRNA of Bmdsx. As in the case of Drosophila dsx, the OD2 domain was separated by a female-specific intron into sex-independent and sex-dependent regions. Sex-specific splicing occurred in equivalent positions in the Drosophila dsx gene. However, unlike Drosophila dsx, the female-specific introns showed no weak 3′ splice sites, and the TRA/TRA-2 binding site related sequences were not found in the female-specific exon, nor even in any other regions of the Bmdsx gene. Moreover, an in vitro splicing reaction consisting of HeLa cell nuclear extracts showed that the female-type of Bmdsx mRNA represented the default splicing. These findings suggest that the structural features of the sex-specific splicing patterns of Bmdsx pre-mRNA are similar to those of Drosophila dsx but the regulation of sex-specific alternative splicing of Bmdsx pre-mRNA is different.     

果实蝇求偶行为与求偶歌

果实蝇Bactrocera是危害经济作物的一类重要农业害虫,研发有效的果实蝇防控技术是现代农业产业发展的迫切需求。雄性不育技术是防控果实蝇高效绿色的防控方法。深入研究果实蝇求偶行为是雄性不育技术顺利开展的前提,也能为开发新防控技术提供有效的生物学靶标。本文将以果蝇研究作为对照,对果实蝇求偶行为与求偶歌的研究相关进展进行总结。果实蝇求偶行为基本属于预交配求偶行为,但其求偶歌中是否具有物种特异性的特征参数还有待验证。这为下一步开展果实蝇求偶行为与求偶歌的研究工作提供了基本依据与方向性引导。     

Effects of Courtship Song in Interspecific Crosses Among the Species of the Drosophila auraria Complex (Diptera: Drosophilidae)

The courtship behavior and the effects of courtship song in inter- and intraspecific crosses were studied in the four sympatric species of the Drosophila auraria complex: D. auraria, D. biauraria, D. subauraria, and D. triauraria. Orientation, tapping, and vibration (the repertoires of male courtship) were observed in both inter- and intraspecific crosses, suggesting that signals from heterospecific females were enough to elicit such male behaviors. The crossability tests with wingless or winged heterospecific males (tests for wing effects) revealed that winged heterospecific males copulated less than wingless ones in all four species but not all the pairwise cases. Since the crossability tests with aristaless females (deaf) or normal females showed essentially the same results as the tests for wing effects, we concluded that the sound produced by wing vibration plays an important role and that the wing movement itself is less important. These findings suggest that courtship songs are of great importance in mate discrimination and the sexual isolation between the species of this complex.     

Sexual identity and sexual attractiveness of a gynandromorph of the lawn ground cricket,Polionemobius mikado (Orthoptera: Trigonidiidae)

A gynandromorph adult of the lawn ground cricket Polionemobius mikado (Shiraki, 1913) (Orthoptera: Trigonidiidae) was collected from a natural population. It had complete male forewings and a female ovipositor at the end of abdomen. A normal male that encountered the gynandromorph performed a courtship song and tried to transmit a spermatophore, whereas a normal female was indifferent to the gynandromorph. The gynandromorph showed aggressive behavior toward the normal male but not against the normal female. The gynandromorph raised its forewings immediately after the antenna touched the body of the normal male and female, but no sound was produced. Overall, the gynandromorph behaved as a male, but was courted by conspecific males. Thus, the sexual identity of the gynandromorph was masculine, but sexual attractiveness was feminine.     

Shared Song Detector Neurons in Drosophila Male and Female Brains Drive Sex-Specific Behaviors

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Co-evolving wing spots and mating displays are genetically separable traits in Drosophila

The evolution of sexual traits often involves correlated changes in morphology and behavior. For example, in Drosophila, divergent mating displays are often accompanied by divergent pigment patterns. To better understand how such traits co-evolve, we investigated the genetic basis of correlated divergence in wing pigmentation and mating display between the sibling species Drosophila elegans and Drosophila gunungcola. Drosophila elegans males have an area of black pigment on their wings known as a wing spot and appear to display this spot to females by extending their wings laterally during courtship. By contrast, D. gunungcola lost both of these traits. Using Multiplexed Shotgun Genotyping (MSG), we identified a ∼440 kb region on the X chromosome that behaves like a genetic switch controlling the presence or absence of male-specific wing spots. This region includes the candidate gene optomotor-blind (omb), which plays a critical role in patterning the Drosophila wing. The genetic basis of divergent wing display is more complex, with at least two loci on the X chromosome and two loci on autosomes contributing to its evolution. Introgressing the X-linked region affecting wing spot development from D. gunungcola into D. elegans reduced pigmentation in the wing spots but did not affect the wing display, indicating that these are genetically separable traits. Consistent with this observation, broader sampling of wild D. gunungcola populations confirmed that the wing spot and wing display are evolving independently: some D. gunungcola males performed wing displays similar to D. elegans despite lacking wing spots. These data suggest that correlated selection pressures rather than physical linkage or pleiotropy are responsible for the coevolution of these morphological and behavioral traits. They also suggest that the change in morphology evolved prior to the change in behavior.     

Behavioral modification in choice process of Drosophila

Because of its clear genetic and developmental background, diversity of behavioral paradigms and neuroanatomy of the brain, Drosophila has become an important animal model for studying genetic, molecular and cellular bases of learning and memory[1]. Extensive research has explored the visual operant conditioning of Drosophila and related molecular bases[2—8]; recently, researchers began to address cognition-like functions and involved neural substrates[9—11]. In these studies, behavioral ana…     

Male courtship song and female preference variation between phylogeographically distinct populations of Drosophila montana

Understanding the variation within and between populations in important male mating traits and female preferences is crucial to theories concerning the origin of sexual isolation by coevolution or other processes. There have been surprisingly few studies on the extent of variation and covariation within and between populations, especially where the evolutionary relationships between populations are understood. Here we examine variation in female preferences and a sexually selected male song trait, the carrier frequency of the song, within and between populations from different phylogeographic clusters of Drosophila montana. Song is obligatory for successful mating in this species, and both playback and field studies implicate song carrier frequency as the most important parameter in male song. Carrier frequency varied among three recently collected populations from Oulanka (Finland), Vancouver (Canada), and Colorado (central United States), which represent the main phylogeographic groups in D. montana. Males from Colorado had the most distinct song frequency, which did not follow patterns of genetic differentiation. There was considerable variation in preference functions within, and some variation between, populations. Surprisingly, females from three lines from Colorado seem to have preferences disfavoring the extreme male trait found in this population. We discuss sources of selection on male song and female preference.     

Role of cell death in the formation of sexual dimorphism in the Drosophila central nervous system

Currently, sex differences in behavior are believed to result from sexually dimorphic neural circuits in the central nervous system (CNS). Drosophila melanogaster is a common model organism for studying the relationship between brain structure, behavior, and genes. Recent studies of sex‐specific reproductive behaviors in D. melanogaster have addressed the contribution of sexual differences in the CNS to the control of sex‐specific behaviors and the development of sexual dimorphism. For example, sexually dimorphic regions of the CNS are involved in the initiation of male courtship behavior, the generation of the courtship song, and the induction of male‐specific muscles in D. melanogaster. In this review, I discuss recent findings about the contribution of cell death to the formation of sexually dimorphic neural circuitry and the regulation of sex‐specific cell death by two sex determination factors, Fruitless and Doublesex, in Drosophila.     

The effect of neurospecific knockdown of candidate genes for locomotor behavior and sound production in Drosophila melanogaster

Molecular mechanisms underlying the functioning of central pattern generators (CPGs) are poorly understood. Investigations using genetic approaches in the model organism Drosophila may help to identify unknown molecular players participating in the formation or control of motor patterns. Here we report Drosophila genes as candidates for involvement in the neural mechanisms responsible for motor functions, such as locomotion and courtship song. Twenty-two Drosophila lines, used for gene identification, were isolated from a previously created collection of 1064 lines, each carrying a P element insertion in one of the autosomes. The lines displayed extreme deviations in locomotor and/or courtship song parameters compared with the whole collection. The behavioral consequences of CNS-specific RNAi-mediated knockdowns for 10 identified genes were estimated. The most prominent changes in the courtship song interpulse interval (IPI) were seen in flies with Sps2 or CG15630 knockdown. Glia-specific knockdown of these genes produced no effect on the IPI. Estrogen-induced knockdown of CG15630 in adults reduced the IPI. The product of the CNS-specific gene, CG15630 (a predicted cell surface receptor), is likely to be directly involved in the functioning of the CPG generating the pulse song pattern. Future studies should ascertain its functional role in the neurons that constitute the song CPG. Other genes (Sps2, CG34460), whose CNS-specific knockdown resulted in IPI reduction, are also worthy of detailed examination.