The evolution of parasitic sex ratio distortion

宿主-寄生虫相互作用在整个自然界中普遍存在，形成了植物和动物群落的重要组成部分。其中，扭曲宿主性别比例的寄生虫广泛存在于无脊椎动物中。性别比例扭曲的影响可能对生物多样性产生强大的影响;它们可能导致种群灭绝并改变社区中动物的组成。此外，由于它们可以影响有害和有益的宿主，因此目前对使用这种寄生虫进行生物防治有很大的兴趣。性别比例扭曲已经在不同的寄生虫（真核生物和细菌）中进化，并影响不同的宿主。为什么要扭曲性别比例？这些寄生虫通过卵从母亲传给后代，并且仅由雌性传播。这些寄生虫已经进化出许多策略来增加女性宿主的相对频率（从而增加寄生虫的传播）。雌性化是由细菌沃尔巴克氏体和微孢子虫（真核寄生虫）在甲壳纲中诱导的。相反，沃尔巴克氏体导致昆虫中的雄性死亡。发现雄性杀死和雌性化的机制是理解宿主-寄生虫共同进化的关键。我们认为，这些细胞内寄生虫最有可能通过分泌分子进入宿主细胞，然后影响宿主分子途径，它们可能会改变对外部激素信号的反应，甚至诱导细胞程序性死亡（凋亡）。这种变化可能会破坏性发育模式或导致性别特异性胚胎死亡。目标：我们将调查性比扭曲的进化在远亲寄生虫通过测试的假设，-类似的机制导致对比策略的性操纵沃尔巴克氏体（男性杀死昆虫宿主，女性化甲壳类动物的主机）-女性化的平行机制已经进化在远亲寄生虫（沃尔巴克氏体和微孢子虫）寄生虫I。我们将阐明沃尔巴克氏菌诱导雄性死亡和雌性化的分子基础。我们将使用最先进的技术（蛋白质组学）来识别分泌到宿主细胞质中导致雌性化或雄性杀死的分子，并跟踪它们在宿主中诱导的变化。我们将首先在果蝇/沃尔巴克氏体雄性杀伤系统中研究这一点。这两种生物的基因组是已知的，将有助于我们识别蛋白质及其功能。然后，我们将继续研究甲壳动物Armadillidium vulgare（木虱）中的雌性化Wolbachia。二.我们将通过对寄生宿主细胞死亡模式的操纵来检测沃尔巴克氏体和小孢子虫诱导雌性化的细胞基础寄生虫通过抑制雄激素腺（控制雄性性分化的腺）的发育来引起甲壳动物的雌性化。为了精确定位作用位点，我们将绘制女性化微孢子虫和沃尔巴克氏体在甲壳类宿主性别分化过程中的分布图。最近，我们观察到雄性杀死双带果蝇的沃尔巴克氏体和细胞凋亡（程序性细胞死亡）之间的关联。我们将测试女性化寄生虫是否也诱导雄激素腺的细胞凋亡，以使宿主女性化。

Host-parasite interactions are pervasive throughout the natural world, forming a critical component of plant and animal communities. Among them, parasites that distort host sex ratios are widespread in invertebrates. The effect of sex ratio distorters can have a powerful effect on biodiversity; they can cause populations to become extinct and change the composition of animals in the community. Additionally as they can affect harmful as well as beneficial hosts, there is currently a great deal of interest in the use of such parasites for biological control. Sex ratio distortion has evolved in diverse parasites (eukaryotes and bacteria) and affects diverse hosts. Why distort sex ratio? These parasites are passed from mother to offspring in the eggs and are only transmitted by females. These parasites have evolved a number of strategies to increase the relative frequency of female hosts (so increasing the spread of the parasite). Feminisation is induced by the bacterium Wolbachia and by microsporidia (eukaryotic parasites) in Crustacea. In contrast Wolbachia causes male killing in insects. Discovering the mechanisms of male killing and feminisation is key to understanding host-parasite coevolution. We propose that these intracellular parasites are most likely to act by secreting molecules into the host cell which will then influence host molecular pathways, they may modify the response to external hormonal signals or even induce programmed cell death (apoptosis). Such changes could disrupt patterns of sexual development or lead to sex-specific embryo mortality. AIMS: We will investigate the evolution of sex ratio distortion in distantly related parasites by testing the hypotheses that - Similar mechanisms lead to contrasting strategies of sexual manipulation by Wolbachia (male killing in insect hosts, feminisation in crustacean hosts) - Parallel mechanisms of feminisation have evolved in distantly related parasites (Wolbachia and microsporidia) OBJECTIVES I. WE WILL INVESTIGATE THE MOLECULAR BASIS OF WOLBACHIA INDUCED MALE KILLING AND FEMINISATION. We will use state of the art techniques (proteomics) to identify molecules secreted into the host cytoplasm that cause feminisation or male killing, and to follow the changes they induce in the host. We will study this initially in the Drosophila (fruit fly)/Wolbachia male killing system. The genome of both these organisms is known and will help us to identify proteins and their function. We will then go on to study feminising Wolbachia in the crustacean Armadillidium vulgare (woodlouse). II. WE WILL INVESTIGATE THE CELLULAR BASIS OF WOLBACHIA AND MICROSPORIDIA INDUCED FEMINISATION BY TESTING FOR MANIPULATION OF THE PATTERN OF CELL DEATH IN THE DEVELOPING HOST Parasites cause feminisation in Crustacea by inhibiting development of the androgenic gland (the gland that controls male sexual differentiation). To pinpoint the site of action, we will map the distribution of feminising microsporidia and Wolbachia during sexual differentiation of their crustacean hosts. We have recently observed an association between male killing in Drosophila bifasciata by Wolbachia and apoptosis (programmed cell death). We will test whether feminising parasites also induce apoptosis in the androgenic gland in order to feminise the host.