Resolving the conflict: The ecology and evolution of horizontal versus vertical transmission strategies in a model insect-virus interaction

疾病感染整个自然界的植物和动物。它们可以通过直接接触或通过传染性颗粒的转移从受感染个体水平传播到易感个体。或者，这种疾病可以在成年生殖后垂直传播，即从父母转移到后代。这种传播可能会持续许多代，而受感染的动物似乎没有受到感染。这些被称为隐性疾病感染，因为病原体不会引起任何可见的症状。病原体环境中未感染宿主的丰度是影响其传播效率的关键因素。当未受感染的宿主密度很高时，致命病原体的水平传播频繁发生，因为个体之间可以频繁接触。相反，当宿主密度较低时，水平传播受到限制或根本不会发生。非致命隐性感染的垂直传播可能发生，因为这种形式的传播不依赖于感染者和未感染者之间的接触。由于致命疾病的水平传播会杀死宿主，因此它显然会阻碍非致命隐蔽感染的垂直传播，这些感染需要宿主生存和繁殖。解决传输模式之间的冲突是该提案的中心目标。我们将调查有利于不同传播模式的生态条件，并确定传播模式和病原体毒力之间的联系。杆状病毒是感染节肢动物，特别是蝴蝶和蛾的病原体，并且这些病原体在水平方向（和致命的）和垂直方向（非致命的）传播。致命病毒的爆发往往与森林害虫的高密度有关，但这些爆发通常是由多年的低宿主密度和没有明显的病原体存在所分隔的。此时发生的事情是病原体生命周期的重要组成部分，但人们对此知之甚少。我们的目的是测试的想法，主机密度是一个关键因素，影响水平或垂直传播途径的青睐。我们将通过监测长期实验室人群中致命性和隐蔽性感染的流行来做到这一点，这些人群在丰度模式上有显著差异。我们还将进行选择实验，确定不同的传播途径如何影响宿主的生活史特征，如发育和繁殖力，以及病原体的生活史特征，如致病性和病毒生产。垂直传播的感染对于那些稀有物种或密度变化很大的物种（例如害虫和入侵物种）可能尤其重要。确定有利于一种或另一种传播模式的条件及其对宿主和疾病生态的影响至关重要。

Diseases infect plants and animals throughout the natural world. They may be horizontally transmitted from an infected individual to a susceptible individual either by direct contact or through the transfer of an infectious particle. Alternatively, the disease can be vertically transmitted following adult reproduction, when it is transferred from the parent to its offspring. This kind of transmission may continue for many generations with the infected animal appearing to be uninfected. These are called covert disease infections because the pathogen does not cause any visible symptoms. The abundance of uninfected hosts in a pathogen's environment is a key factor affecting how efficiently it is transmitted. When uninfected host density is high, horizontal transmission of lethal pathogens occurs frequently because individuals can come into contact with each other frequently. Conversely, when host densities are low, horizontal transmission is limited or may not occur at all. Vertical transmission of non-lethal covert infections can occur as this form of transmission does not depend on contact between infected and uninfected individuals. Since horizontal transmission of a lethal disease kills the host, it will clearly impede the vertical transmission of non-lethal covert infections, which need their host to survive and reproduce. Resolving this conflict between transmission modes is the central aim of the proposal. We will investigate the ecological conditions that favour different transmission modes and determine the link between transmission mode and pathogen virulence. Baculoviruses are pathogens that infect arthropods, especially butterflies and moths, and these pathogens are transmitted both horizontally (and lethally) and vertically (non-lethally). Lethal virus outbreaks are often associated with high densities of forest insect pests, but these outbreaks are typically separated by years of low host density and no obvious presence of pathogens. What happens at these times is an important part of the pathogen life cycle that is very poorly understood. We aim to test the idea that host density is a key factor affecting whether horizontal or vertical transmission routes are favoured. We will do this by monitoring the prevalence of lethal and covert infections in long term laboratory populations that differ markedly in patterns of abundance. We will also carry out selection experiments where we determine how the different transmission routes affect the life history traits of the host, such as development and fecundity, and of the pathogen, such as pathogenicity and virus production. Vertically transmitted infections are likely to be especially important in those species that are rare, or those species that have highly variable densities, such as pests and invasive species. Identifying the conditions that favour one or other transmission mode and their impact on both host and disease ecology is crucial.