The adaptive potential of clonality in aphid crop pests

蚜虫是世界上最具破坏性的昆虫害虫之一，每年对多种粮食和商品作物造成数十亿美元的产量损失。害虫蚜虫的控制主要依赖于化学杀虫剂的使用，然而，抗药性的进化对蚜虫的可持续控制构成了越来越大的威胁。蚜虫如此成功，部分原因是它们在有利条件下迅速增加数量的能力，事实上，据估计，如果没有捕食或疾病，一只蚜虫在一个季节内可以产生6000亿个后代。这种令人难以置信的生殖输出是通过无性生殖（孤雌生殖）实现的-成年雌性蚜虫在生长季节的大部分时间里生下的女儿都是自己的克隆。对于大多数蚜虫物种来说，这种繁殖模式与每年的有性繁殖周期交替，然而，在一些国家，如英国，某些物种，包括重要的害虫如桃蚜，完全通过单性生殖进行繁殖。因为蚜虫克隆谱系被认为是遗传上相同的，它们被称为“进化的死胡同”，几乎没有进化能力。然而，我们最近发现，来自单一雌性蚜虫的蚜虫克隆种群可以进化出对杀虫剂的遗传抗性。尽管这清楚地表明蚜虫克隆谱系具有适应潜力，但蚜虫克隆进化的机制完全未知。本项目的目的是了解蚜虫克隆谱系的适应潜力和支持蚜虫克隆进化的分子机制。我们将使用全球蚜虫害虫M。以桃为模式，利用基因组学、转录组学和表观遗传学的最新进展，填补关于这一主题的一系列关键知识空白。这些包括了解突变在蚜虫克隆谱系中积累的速度有多快，这是如何受到农药胁迫的影响，以及克隆如何在没有性别的情况下在表型和分子水平上适应。在该提案的第一个目标中，我们将计算M克隆中自发出现的突变的频率和谱。使用称为突变积累的实验方法（该方法克服了直接研究罕见突变如何产生的困难，通过允许它们在由单个后代繁殖的品系中在几代中积累）来研究桃。在这一目标中，我们还将通过比较暴露于杀虫剂的品系与未暴露于杀虫剂的品系中突变如何积累来检验亚致死杀虫剂暴露增加突变率的假设。在第二个目标中，我们将使用一种称为实验进化的方法（在实验室中使用暴露于特定条件下的实验种群来研究进化过程）来研究M的大型克隆种群的反应。对杀虫剂选择的影响。我们将联合收割机与三种不同的测序方法相结合，以探索支持进化抗性的分子机制，这将在目标3中使用功能方法进行验证。这些实验的数据将从根本上推进我们对昆虫在没有性别的情况下如何进化的理解。此外，所产生的知识将在可持续控制蚜虫害虫方面具有相当大的应用价值。例如，它将使我们能够预测蚜虫无性繁殖国家的抗性风险发展，并优化农药剂量策略，以避免加速可能导致抗性的突变的演变。最后，了解克隆害虫种群如何在分子水平上进化抗性，可能会提供机会，利用和对抗这一过程，制定战略，对所涉及的基础机制。

Aphids are among the world's most damaging group of insect pests, causing billions of US dollars of yield loss per annum to a wide range of food and commodity crops. The control of pest aphids has relied heavily on the use of chemical insecticides, however, the evolution of resistance poses a growing threat to their sustainable control.Aphids are in part so successful because of their remarkable capacity to rapidly increase in number under favourable conditions, indeed, it has been estimated that without predation or disease a single aphid could produce 600 billion descendants in just one season. This incredible reproductive output is achieved by asexual reproduction (parthenogenesis) - with adult female aphids giving birth to daughters that are clones of themselves for most of the growing season. For most aphid species this mode of reproduction alternates with a yearly cycle of sexual reproduction, however, in some countries such as the UK certain species, including important pests such as Myzus persicae, reproduce exclusively by parthenogenesis.Because aphid clonal lineages have been assumed to be genetically identical they have been referred to as 'evolutionary dead ends' with little or no capacity to evolve. However, we have recently shown that aphid clonal populations derived from a single female aphid can evolve heritable resistance to insecticides. Although this clearly demonstrates that aphid clonal lineages have adaptive potential the mechanisms by which aphid clones evolve are completely unknown. The aim of this project is to understand the adaptive potential of aphid clonal lineages and the molecular mechanisms underpinning clonal evolution in aphids. We will use the global aphid pest M. persicae as a model and exploit recent advances in genomics, transcriptomics and epigenetics to address a range of key knowledge gaps on this topic. These include understanding how quickly mutations accumulate in aphid clonal lineages, how this is affected by pesticide stress, and how clones adapt at the phenotypic and molecular level in the absence of sex. In the first objective of the proposal we will calculate the frequency and spectrum of mutations that spontaneously arise in clones of M. persicae using an experimental approach called mutation accumulation (which overcomes the difficulty of directly studying how rare mutations arise by allowing them to build up over several generations in lines propagated by single progeny descent). In this objective we will also test the hypothesis that sub-lethal insecticide exposure increases mutation rate by comparing how mutations accumulate in lines exposed to insecticide with insecticide unexposed lines. In the second objective we will use an approach called experimental evolution (the use of experimental populations exposed to specific conditions in the laboratory to study evolutionary processes) to examine the response of large clonal populations of M. persicae to insecticide selection. We will combine this approach with three different sequencing approaches to explore the molecular mechanisms underpinning evolved resistance, which will be validated in Objective 3 using functional approaches. The data from these experiments will fundamentally advance our understanding of how insects evolve in the absence of sex. Furthermore, the knowledge generated will be of considerable applied importance in relation to the sustainable control of aphid pests. For example, it will allow us to anticipate resistance risk development in countries where aphids reproduce asexually and optimise pesticide dosing strategies to avoid accelerating the evolution of mutations that might lead to resistance. Finally, understanding how clonal pest populations evolve resistance at the molecular level may provide opportunities to exploit and counter this process by developing strategies against the underpinning mechanisms involved.