Determining the genetic basis of sexual conflict in Drosophila melanogaster: the role of the sex peptide.

性冲突是一种革命性的方式来看待男性和女性之间在生殖决定方面发生的事情。两性在与谁交配、多久交配一次、生育多少后代以及给予多少父母照顾等问题上并不合作，相反，两性往往意见不一，并试图利用对方来达到自己的目的。这种“性冲突”的例子已经在许多不同的生物体中描述过，但在昆虫中的研究最为深入。在果蝇Drosophila melanogaster中，两性之间在交配频率上存在强烈的冲突。高频率的交配最适合雄性，因为它们不提供父母的照顾，因此每一次额外的交配都会导致它们生育更多的后代。雌性的利益最好是通过较低的交配频率来服务-它们有有限数量的卵来产卵，并且超过一定水平的再交配，它们不会进一步增加后代数量，此外，高频率的交配对雌性来说是昂贵的，缩短了它们的寿命并降低了它们的整体寿命繁殖。我们之前的研究表明，雌性的这些“交配成本”是由雄性精液中的分子作用引起的，这些分子在交配过程中转移到雌性身上。我们最近发现了一种被称为“性肽”的物质，这种物质负责雌性交配成本，而与缺乏这种肽的雄性交配对雌性来说是“免费的”。雄性从性肽的转移中受益，因为它的功能之一是使雌性暂时不愿意再次交配，因此转移它的雄性生育更多的后代。因此，性肽在伤害雌性的同时也对雄性有利，它是第一个被证明是任何物种中性冲突的基础的基因产物。我们的发现引发了许多问题：例如，SP如何伤害女性？女性在一生中是否对它同样敏感？性肽造成的损伤是永久性的吗我们在这里提出的工作中解决这些问题。我们有三大目标，即（1）量化性肽在性冲突中的作用程度，（2）揭示性肽如何对雌性产生伤害，（3）测量交配率和食物供应变化如何影响接受性肽的成本和收益。我们将在实验室里用健康的苍蝇做大规模的实验。这将使我们能够检测到细微的差异，并准确地估计“适应性”（生存和繁殖输出的组合）。为了控制雌性接受的性肽水平，我们将它们与正常雄性或缺乏性肽的雄性交配。研究结果将首次在基因层面上对性冲突的基础进行深入分析。这项研究的总体好处是，通过了解男性和女性之间冲突的性质和动态，加深我们对性冲突演变的理解。这将使我们更好地了解雄性和雌性的生殖策略是如何演变的。在害虫防治方面也有更广泛的潜在应用。例如，在世界上许多地方，真正的果蝇是害虫。雌性将卵产在成熟的果实中，随着幼虫的发育，果实被破坏。这些害虫通常使用“不育昆虫技术”（SIT）进行控制。在这种情况下，雄性在工厂中大规模饲养，绝育，然后释放到环境中与野生雌性交配。这种交配是不育的，因此减少了害虫种群的大小。如果雌性不再交配，SIT的效果最好，而性肽类因子似乎在其中起着至关重要的作用。因此，操纵性肽样因子的水平可以提供在昆虫进行SIT的害虫抑制的改善。

Sexual conflict is a revolutionary way of viewing what happens between males and females over reproductive decisions. Rather than co-operating over who to mate with, how often to mate, how many offspring to produce and how much parental care to give, the sexes instead often disagree, and try to exploit one another for their own ends. Examples of this 'sexual conflict' have been described in many different organisms, but have been most intensively studied in the insects. In the fruitfly Drosophila melanogaster, there is strong conflict between the sexes over how often to mate. A high frequency of mating best suits males, as they provide no parental care and thus each extra mating results in them fathering more offspring. The interests of females are best served by a lower frequency of mating - they have a limited number of eggs to lay and beyond a certain level of remating, they gain no further increases in offspring numbers, Furthermore, high frequencies of mating are costly to females, shortening their lifespans and lowering their overall lifetime reproduction. Our previous work has revealed that these 'mating costs' in females are caused by the actions of molecules in the male semen, which are transferred to females during mating. We have recently identified a substance known as the 'sex peptide' which is responsible for the female mating costs, and matings with males that lack this peptide are 'cost-free' for females. Males benefit from the transfer of the sex peptide because one of its functions is to render females temporarily unwilling to mate again, hence males who transfer it father more offspring. The sex peptide therefore simultaneously harms females and benefits males and is the first gene product shown to underlie sexual conflict in any species. Our discovery prompts many questions: e.g. how does the SP harm females?, are females equally sensitive to it throughout their lives? and is the damage caused by the sex peptide permanent? We address these questions in the work proposed here. We have three broad aims and these are (1) to quantify the extent to which the sex peptide underlies sexual conflict, (2) to reveal how sex peptide exerts harm on females and (3) to measure how the costs and benefits of receiving the sex peptide are affected by mating rate and by variations in food supply. We will do large-scale experiments in the laboratory, using healthy flies. This will allow us to detect subtle differences and to estimate accurately 'fitness' (a combination of survival and reproductive output). To manipulate the level of sex peptide that females receive we will mate them to normal males or those which lack the sex peptide. The results will provide an in depth analysis, for the first time, of the basis of sexual conflict at the genetic level. The general benefits of the research will be to deepen our understanding of the evolution of sexual conflict, by understanding the nature and dynamics of the conflicts between males and females. This will allow us to better understand how reproductive strategies evolve in males and females. There are also wider potential applications in insect pest control. For example, in many parts of the world the true' fruit flies are pests. The females lay their eggs in ripe fruit, which is spoiled as the larvae develop. These pests are often controlled using the 'sterile insect technique' (SIT). In this, males are reared on a large scale in factories, sterilised and then released into the environment to mate with the wild females. Such matings are sterile and the pest population size is thus reduced. SIT works best if females do not mate again, and sex-peptide-like factors appear to play a crucial role in this. Hence manipulating the level of sex peptide-like factors could provide improvements in pest suppression in insects subjected to SIT.