Shared neural circuitry for female and male sexual behaviours in Drosophila

Abstract

Sexual reproduction in most species involves innate behaviours that are dramatically distinct in males and females. The different behaviours of males and females are generally thought to reflect the activation of sex-specific neural circuits; however, sex differences could also arise through the sex-specific modulation of circuits that are common to both sexes. Here, we present evidence that the sex-specific reproductive behaviours of females and males of the fruitfly Drosophila melanogaster indeed involve shared neural circuits.Male courtship behaviour is specified in Drosophila by the male-specific products of the fruitless (fru) gene, FruM[1xfruitless splicing specifies male courtship behavior in Drosophila. Demir, E. and Dickson, B.J. Cell. 2005; 121: 785–794Abstract | Full Text | Full Text PDF | PubMed | Scopus (209)See all References[1], which are expressed in approximately 2% of the neurons in the male nervous system [2xSpatial, temporal, and sexually dimorphic expression patterns of the fruitless gene in the Drosophila central nervous system. Lee, G., Foss, M., Goodwin, S.F., Carlo, T., Taylor, B.J., and Hall, J.C. J. Neurobiol. 2000; 43: 404–426Crossref | PubMed | Scopus (125)See all References, 3xNeural circuitry that governs Drosophila male courtship behavior. Stockinger, P., Kvitsiani, D., Rotkopf, S., Tirian, L., and Dickson, B.J. Cell. 2005; 121: 795–807Abstract | Full Text | Full Text PDF | PubMed | Scopus (268)See all References, 4xMale-specific fruitless specifies the neural substrates of Drosophila courtship behaviour. Manoli, D.S., Foss, M., Villella, A., Taylor, B.J., Hall, J.C., and Baker, B.S. Nature. 2005; 436: 395–400PubMedSee all References]. These neurons can be manipulated using fruGAL4, in which GAL4 coding sequences have been inserted into the fru locus [3xNeural circuitry that governs Drosophila male courtship behavior. Stockinger, P., Kvitsiani, D., Rotkopf, S., Tirian, L., and Dickson, B.J. Cell. 2005; 121: 795–807Abstract | Full Text | Full Text PDF | PubMed | Scopus (268)See all References, 4xMale-specific fruitless specifies the neural substrates of Drosophila courtship behaviour. Manoli, D.S., Foss, M., Villella, A., Taylor, B.J., Hall, J.C., and Baker, B.S. Nature. 2005; 436: 395–400PubMedSee all References]. In males, synaptic silencing of these fruGAL4 neurons, with a UAS-shits transgene, inhibits courtship behaviour [3xNeural circuitry that governs Drosophila male courtship behavior. Stockinger, P., Kvitsiani, D., Rotkopf, S., Tirian, L., and Dickson, B.J. Cell. 2005; 121: 795–807Abstract | Full Text | Full Text PDF | PubMed | Scopus (268)See all References, 4xMale-specific fruitless specifies the neural substrates of Drosophila courtship behaviour. Manoli, D.S., Foss, M., Villella, A., Taylor, B.J., Hall, J.C., and Baker, B.S. Nature. 2005; 436: 395–400PubMedSee all References] but leaves unrelated behaviours intact [3xNeural circuitry that governs Drosophila male courtship behavior. Stockinger, P., Kvitsiani, D., Rotkopf, S., Tirian, L., and Dickson, B.J. Cell. 2005; 121: 795–807Abstract | Full Text | Full Text PDF | PubMed | Scopus (268)See all References[3]. Corresponding neurons are present in females, and express fruGAL4 but not FruM. The functions of these neurons in females are unknown. We tested whether they might mediate female sexual behaviour.A virgin female responds to a male's courtship song by slowing down and opening her vaginal plates to allow copulation. Virgin females in which the fruGAL4 neurons are synaptically silenced with UAS-shits are largely unreceptive to courting males (Figure 1Figure 1A): fewer than 10% of fruGAL4UAS-shits virgin females copulated within a 20 minute observation period (experiment 3), whereas approximately 50% of various control females copulated in the same period (experiments 1, 4, 5 and 10). This was not due to a passive failure to accept the male, but rather an active rejection behaviour in which the female extends her ovipositor to prevent mating (Figure 1Figure 1B).Figure 1fruGAL4 neurons mediate female reproductive behaviours.(A) To assay receptivity, a female of the indicated genotype was paired with a wild type Canton S male in a 10 mm diameter mating chamber. The female was scored as receptive if copulation occurred within 20 minutes. (B) To assay rejection behaviour, 20-minute mating assays were videotaped at high magnification and scored for the number of ovipositor extrustions per minute. (C) To assay egg-laying, a single female was transferred to a new food vial and the eggs laid during the next 24 hours were manually counted. For all assays, flies were raised at 20°C. For assays performed at 30°C (lines 1–7), flies were shifted to 30°C about an hour before performing the assay (A and B), or for the entire 24 hour egg-collection period (C). 3–5 day old virgin females were used for all assays, except for those shown in lines 2 and 9, which were of the same age but mated to a wild-type male one day prior to performing the assay. Values in B and C are mean ± s.e.m. ∗P< 0.01, ∗∗P< 0.001, ∗∗∗P< 0.0001 compared to wild-type (+/+) virgins at the appropriate temperature (χ2 test for A, Kruskal-Wallis one-way ANOVA for B and C).View Large Image | View Hi-Res Image | Download PowerPoint SlideIn addition, we found that silencing the fruGAL4 neurons in virgin females induces them to lay their unfertilized eggs (Figure 1Figure 1C). These rejection and egg-laying behaviours are characteristic of mated females (Figure 1Figure 1, experiment 2). Thus, synaptic activity of the fruGAL4 neurons is required in virgin females to promote mating behaviour and to inhibit post-mating reproductive behaviours.We observed that, in females forced to express FruM (fruM females), male courtship behaviour is induced and certain virgin and mated female behaviours are suppressed (copulation and egg-laying, respectively; Figure 1Figure 1 experiments 6 and 13, and [1xfruitless splicing specifies male courtship behavior in Drosophila. Demir, E. and Dickson, B.J. Cell. 2005; 121: 785–794Abstract | Full Text | Full Text PDF | PubMed | Scopus (209)See all References[1]). Silencing the fruGAL4 neurons in fruM virgin females does not induce egg-laying, as it does in wild-type (fruF) females (Figure 1Figure 1C, experiment 7). Thus, FruM appears to reconfigure the circuit for male rather than female behaviour in a way that cannot be explained entirely by altered patterns of neuronal activity.We infer from these data that the distinct reproductive behaviours of males and females are mediated by a common fruGAL4 neural circuit (Figure 2Figure 2). Activation of this circuit is required for mating behaviour, which is manifested as male behaviour in fruM males and females, but as female behaviour in fruF females. In females, the transition from pre-mating to post-mating behaviour is triggered experimentally by silencing these neurons (Figure 1Figure 1), or naturally by the sex peptide transferred in the male's seminal fluid [5xThe sex peptide of Drosophila melanogaster: female post-mating responses analyzed by using RNA interference. Chapman, T., Bangham, J., Vinti, G., Seifried, B., Lung, O., Wolfner, M.F., Smith, H.K., and Partridge, L. Proc. Natl. Acad. Sci. USA. 2003; 100: 9923–9928Crossref | Scopus (233)See all References, 6xSex-peptide is the molecular basis of the sperm effect in Drosophila melanogaster. Liu, H. and Kubli, E. Proc. Natl. Acad. Sci. USA. 2003; 100: 9929–9933Crossref | PubMed | Scopus (225)See all References]. Sex peptide may therefore promote post-mating behaviours by modulating the activity of the fruGAL4 circuit in females.Figure 2Control of sexual behavior by fruGAL4 neurons.Model for the role of fruGAL4 neurons in Drosophila sexual behaviour, based on the results presented in Figure 1Figure 1 for female behaviours and in [1xfruitless splicing specifies male courtship behavior in Drosophila. Demir, E. and Dickson, B.J. Cell. 2005; 121: 785–794Abstract | Full Text | Full Text PDF | PubMed | Scopus (209)See all References[1] for male behaviours. Male mating behaviour is observed in both males and females, provided FruM is present. Virgin and mated female behaviours are only observed in females (they are not anatomically possible in males). Flies in which the FruM neurons are both silenced and masculinized perform neither male behaviour, virgin female behaviour, nor mated female behaviour, irrespective of their sex.View Large Image | View Hi-Res Image | Download PowerPoint SlideThe editors of Current Biology welcome correspondence on any article in the journal, but reserve the right to reduce the length of any letter to be published. All Correspondence containing data or scientific argument will be refereed. Queries about articles for consideration in this format should be sent by e-mail to cbiol@current-biology.com