How do female insects get switched on to reproduction?

昆虫非常善于繁殖。许多昆虫的雌性会产下大量的卵，这意味着种群可以非常迅速地增加。这有助于解释昆虫如何成为包含最多物种的动物群体，以及为什么有些昆虫对人类如此有问题。由于它们非凡的繁殖能力，吃庄稼或携带人类疾病的害虫种类非常难以控制。为了避免产下未受精的卵，雌性只有在交配并从雄性那里获得足够的精子后才能转换为高产卵量。除了开始产卵，许多雌性昆虫也会避免再次与雄性交配，直到它们需要获得更多的精子，以便将精力集中在喂养和生育后代上。导致雌性行为转变的分子非常有趣，因为它们是昆虫繁殖成功的关键。如果我们知道负责的分子是什么，我们可能能够开发新的杀虫剂来破坏它们，并以非常有针对性的方式控制害虫物种。这些知识对于我们基本理解进化是如何运作的也很重要，因为我们预计，编码增加繁殖的分子的基因通常会在连续几代中变得更加普遍。目前，我们知道的基因和分子很少涉及女性的繁殖。果蝇（Drosophila melanogaster）是我们最了解的。这种物种的雄性会产生一种叫做“性肽”（SP）的蛋白质，并通过精液将其转移给雌性。交配后，SP激活雌性体内一种名为“性肽受体”（SPR）的蛋白质，这会导致雌性产卵增加，并拒绝雄性的进一步交配尝试。然而，我们不知道SP和SPR是否在其他昆虫物种中也有同样的作用。这是一个大问题，因为这意味着我们不知道SP和SPR是否在许多昆虫物种中开启了繁殖，或者是否在其他地方进化出了不同的基因和分子。如果我们知道答案，它将帮助我们了解昆虫如何进化到如此高效地繁殖，以及我们如何使用新的化学品或改进的生物控制方法来控制害虫物种。我们将通过测试SP和SPR如何在不同的昆虫物种中工作来解决这个问题，果蝇subobscura。这个物种也是一种苍蝇，它也有SP和SPR，但它是相当遥远的进化相关的果蝇黑腹。雌性果蝇在交配后也表现出非常强烈的行为转变：它们促进产卵，不再交配（因为一次交配提供了它们所需的所有精子）。这使得果蝇subobscura物种有用的候选人测试是否SP和SPR在相当广泛的物种服务相同的目的。我们将创建转基因果蝇subobscura缺乏SP和SPR。然后，我们将测试它们，看看去除这些分子是否会破坏正常的产卵和雄性排斥反应。这些结果将明确回答SP和SPR是否以与果蝇相同的方式控制果蝇的生殖开关，从而告诉我们这些分子发挥相同作用的普遍程度。因此，这些结果将使我们对昆虫生殖进化的理解发生重大变化，并为进一步研究更多物种（包括害虫物种）以及探索其他重要的生殖分子铺平道路。我们将产生的转基因苍蝇将成为我们自己未来研究的宝贵工具，并为其他研究人员提供免费的苍蝇。

Insects are highly adept at reproducing. The females of many insects lay huge numbers of eggs meaning that populations can increase very rapidly. This helps explain how insects have become the group of animals containing the most species, and also why some insects are so problematic for humans. Pest species that eat crops or carry human diseases can be extremely hard to control thanks to their phenomenal reproductive ability.But female insects don't typically lay eggs all the time. To avoid laying unfertilized eggs, females switch to high egg laying only after they've mated and received sufficient sperm from males. Alongside switching on egg laying, many female insects also avoid mating with males again until they need to obtain more sperm, in order to focus their energy on feeding and producing offspring.The molecules that cause these switches in behaviour in females are of great interest because they are key to insect reproductive success. If we know what the responsible molecules are we might be able to develop new pesticides that disrupt them, and control pest species in a very targeted way. Such knowledge is also important for our basic understanding of how evolution works, because we expect that genes that code for molecules that increase reproduction will typically become more common over successive generations.There are currently very few species for which we know the genes and molecules involved in switching on reproduction in females. The fruit fly, Drosophila melanogaster, is the best understood. Males in this species make a protein called 'Sex Peptide' (SP) which they transfer to females in the seminal fluid. After mating, SP activates a protein in the females called the 'Sex Peptide Receptor' (SPR) and this causes females to boost egg laying and reject further mating attempts from males. However, we don't know if SP and SPR do the same thing in other insect species. This is a big problem because it means we don't know whether SP and SPR switch on reproduction for lots of insect species, or whether different genes and molecules have evolved for this purpose elsewhere. If we knew the answer it would help us understand how insects evolve to reproduce so efficiently, and how we might control this in pest species using novel chemicals or improved biological control methods.We will address this problem by testing how SP and SPR work in a different insect species, Drosophila subobscura. This species is also a fly, it also has SP and SPR, but it is quite distantly evolutionarily related to Drosophila melanogaster. Drosophila subobscura females also show a very strong behavioural switch after mating: they boost egg laying and never mate again (because one mating provides all the sperm they ever need). This makes Drosophila subobscura species useful candidate for testing whether SP and SPR serve the same purpose over a fairly broad range of species.We will create genetically modified Drosophila subobscura that lack SP and SPR. We will then test them to see whether removing these molecules abolishes the normal boost to egg laying and rejection of males. The results will unequivocally answer the question of whether SP and SPR control the reproductive switch in Drosophila subobscura in the same way they do in Drosophila melanogaster, hence telling us how commonly these molecules play the same role. These results will thus create a step-change in our understanding of evolution of insect reproduction, and will pave the way for further studies across more species (including pest species), and for exploring other important reproductive molecules. The genetically modified flies we will generate will become an invaluable tool for our own future studies, and for other researchers with whom will share the flies freely.